No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effects of mycorrhizal colonization on biomass production and nitrogen fixation of black locust (Robinia pseudoacacia) seedlings grown under elevated atmospheric carbon dioxide
New Phytologist
Abstract
Interactive effects of elevated atmospheric CO2 and arbuscular mycorrhizal (AM) fungi on biomass production and N2 fixation were investigated using black locust (Robinia pseudoacacia). Seedlings were grown in growth chambers maintained at either 350 μmol mol−1 or 710 μmol mol−1 CO2. Seedlings were inoculated with Rhizobium spp. and were grown with or without AM fungi. The 15N isotope dilution method was used to determine N source partitioning between N2 fixation and inorganic fertilizer uptake. Elevated atmospheric CO2 significantly increased the percentage of fine roots that were colonized by AM fungi. Mycorrhizal seedlings grown under elevated CO2 had the greatest overall plant biomass production, nodulation, N and P content, and root N absorption. Additionally, elevated CO2 levels enhanced nodule and root mass production, as well as N2 fixation rates, of non- mycorrhizal seedlings. However, the relative response of biomass production to CO2 enrichment was greater in non-mycorrhizal seedlings than in mycorrhizal seedlings. This study provides strong evidence that arbuscular mycorrhizal fungi play an important role in the extent to which plant nutrition of symbiotic N2-fixing tree species is affected by enriched atmospheric CO2.
... water holding capacity, organic matter, extractable K, organic carbon, total nitrogen, and nitrate content [11][12][13][14][15][16][17][18]. Nitrogen fixation is a considerable characteristic of black locust, which has great importance to forestry and nature conservation as well. ...
... Plants 2023,12, 3253 ...
... Plants 2023, 12, 3253 ...
The black locust (Robinia pseudoacacia L.) is the second-most abundant deciduous tree in forest plantations, and one of the most important invasive woody species worldwide. The species has a strong transformer capacity, especially expressed by its nitrogen enrichment effect caused by nitrogen-fixing bacteria living in its root-nodules. The aim of this study was to explore the mutually interacting factors of nitrogen-fixing root-nodules, site characteristics, and herb-layer composition of 28 North Hungarian black locust stands. In the herb-layers of the study sites, a total of 121 plant species were identified, representing a relatively low species richness. The studied black locust stands showed high variability both in their herb-layer compositions and root-nodule formation, but no clear relationship could be demonstrated between these characteristics. The PCA component with which the species richness and Shannon-Wiener diversity index were strongly correlated was negatively associated with all root-nodule parameters (number, surface area, and weight), supporting the biodiversity-reducing effect of black locust by its nitrogen-fixing bacteria. All of the root-nodule parameters were negatively correlated with the PCA factor predominantly determined by stand age, confirming that the root-nodule biomass decreases as time progresses.
... It is widely accepted that the strongest ecological impact of Black Locust on native plant communities is mediated by changes in soil nutrient availability as a consequence of its association with N 2 -fixing rhizobia and the formation of root nodules (Ferrari and Wall, 2007;Macedo et al., 2008;Vítkov� a and Kolbek, 2010). Indeed, the Black Locust-rhizobia interaction is one of the most effective symbiotic N 2 -fixation systems studied to date (Olesniewicz and Thomas, 1999). In some locations, nitrogen (N) inputs from stands of Black Locust are greater than any other sources, including deposition from the atmosphere (Liu and Deng, 1991;Tian et al., 2003;Williard et al., 2005). ...
... Thus, knowledge of mycorrhiza specificity and preferences are crucial for understanding plant community dynamics, particularly for plant succession and migration as well as fungal compatibility in response to climate change (Molina and Horton, 2015). In general, arbuscular mycorrhizal (AM) associations have been considered to lack absolute specificity because AM fungi are able to colonize virtually any potential host plants and a given host can be colonized by several different fungal species (Hayman, 1982;€ Opik et al., 2006). It has been argued that the lack of specificity displayed by plants and fungi alike are an advantage not only because it increases the chance that plant roots are colonized by appropriate fungi, but also because association with fungal species with different physiological attributes may provide access to a broader range of nutrient pools (Molina et al., 1992). ...
... Both, arbuscular mycorrhizas and ectomycorrhizas have repeatedly been reported to colonize the roots of Black Locust, both in pot culture or in field studies, albeit in areas where this species has invaded (Bratek et al., 1996;Tian et al., 2003;Ferrari and Wall, 2008;Smith and Read, 2008). Non-mycorrhizal individuals have also been found in the field (Olesniewicz and Thomas, 1999;Hempel et al., 2013). Whether the successful establishment of ECM occurs in Black Locust still remains controversial as colonization by potential ECM fungi has been observed (Bratek et al., 1996), but the structures do not resemble typical ECM anatomy (Kov� acs et al., 2003) and the effect might also be attributed to saprophytic rather than symbiotic activities of the fungi (Cierjacks et al., 2013). ...
Black Locust (Robinia pseudoacacia L.) is a woody legume with a worldwide distribution. Its ecological and economical importance is largely due to fast growth and dinitrogen (N2)-fixation ability with rhizobia. These features make Black Locust suitable as a model species for other woody legumes as well. However, its symbiotic association with mycorrhizal fungi has not gained much attention. The small body of literature published indicates that this mycorrhizal association interacts with symbiotic N2-fixation, greatly enhancing the ecological and physiological performance of Black Locust by improving its rate of growth, nutrition status and resistance to stress conditions, such as drought and salt and heavy metal accumulation. Here we summarize the current knowledge on the benefits of the association of Black Locust with arbuscular mycorrhizal fungi with the aim of providing future research directions on how this symbiotic partnership is involved in a tripartite symbiotic association including rhizobia. This association is of particular importance considering both the invasive nature of Black Locust, its economic and cultural importance and its use in restoration of degraded or contaminated landscapes.
... They enhance the growth and the photosynthetic ability of the host plants by improving nutrient uptake and CO 2 assimilation (Smith and Read 2008, Sheng et al. 2008, Kaschuk et al. 2009). Many studies have confirmed that AMF can form a symbiotic relationship with black locust and significantly improve its growth (Olesniewicz andThomas 1999, Tian et al. 2003). However, there is little information about the effects of AMF on the photosynthesis, carbon content, and calorific value of black locust. ...
... Numerous papers have reported that mycorrhizal symbiosis can increase the growth and production of host plants (Requena et al. 1997, Olesniewicz andThomas 1999). In our study, AMF mycorrhization of black locust enhanced significantly the growth, biomass yield, photosynthetic ability, and carbon content of the seedlings. ...
... The AM plants grew faster than NM plants because of their larger root systems and enhanced nutrient uptake facilitated by the mycorrhizal hyphae (Olesniewicz andThomas 1999, Gong et al. 2013). In our study, AM plants had a significantly greater biomass than NM seedlings, and a significantly greater leaf biomass and LA, which is beneficial for carbon assimilation and solar energy absorption. ...
Arbuscular mycorrhizal fungi (AMF) form symbioses with many plants. Black locust (Robinia pseudoacacia L.) is an important energy tree species that can associate with AMF. We investigated the effects of AMF (Rhizophagus irregularis and Glomus versiforme) on the growth, gas exchange, chlorophyll (Chl) fluorescence, carbon content, and calorific value of black locust seedlings in the greenhouse. The total biomass of the arbuscular mycorrhizal (AM) seedlings was 4 times greater than that of the nonmycorrhizal (NM) seedlings. AMF greatly promoted the photosynthesis of black locust seedlings. AM seedlings had a significantly greater leaf area, higher carboxylation efficiency, Chl content, and net photosynthetic rate (P N) than NM seedlings. AMF also significantly increased the effective photochemical efficiency of PSII and significantly enhanced the carbon content and calorific value of black locust seedlings. Seedlings inoculated with G. versiforme had the largest leaf area and highest biomass, Chl content, P N , and calorific value.
... They enhance the growth and the photosynthetic ability of the host plants by improving nutrient uptake and CO 2 assimilation (Smith and Read 2008, Sheng et al. 2008, Kaschuk et al. 2009). Many studies have confirmed that AMF can form a symbiotic relationship with black locust and significantly improve its growth (Olesniewicz andThomas 1999, Tian et al. 2003). However, there is little information about the effects of AMF on the photosynthesis, carbon content, and calorific value of black locust. ...
... Numerous papers have reported that mycorrhizal symbiosis can increase the growth and production of host plants (Requena et al. 1997, Olesniewicz andThomas 1999). In our study, AMF mycorrhization of black locust enhanced significantly the growth, biomass yield, photosynthetic ability, and carbon content of the seedlings. ...
... The AM plants grew faster than NM plants because of their larger root systems and enhanced nutrient uptake facilitated by the mycorrhizal hyphae (Olesniewicz andThomas 1999, Gong et al. 2013). In our study, AM plants had a significantly greater biomass than NM seedlings, and a significantly greater leaf biomass and LA, which is beneficial for carbon assimilation and solar energy absorption. ...
Arbuscular mycorrhizal fungi (AMF) form symbioses with many plants. Black locust (Robinia pseudoacacia L.) is an important energy tree species that can associate with AMF. We investigated the effects of AMF (Rhizophagus irregularis and Glomus versiforme) on the growth, gas exchange, chlorophyll (Chl) fluorescence, carbon content, and calorific value of black locust seedlings in the greenhouse. The total biomass of the arbuscular mycorrhizal (AM) seedlings was 4 times greater than that of the nonmycorrhizal (NM) seedlings. AMF greatly promoted the photosynthesis of black locust seedlings. AM seedlings had a significantly greater leaf area, higher carboxylation efficiency, Chl content, and net photosynthetic rate (P
N) than NM seedlings. AMF also significantly increased the effective photochemical efficiency of PSII and significantly enhanced the carbon content and calorific value of black locust seedlings. Seedlings inoculated with G. versiforme had the largest leaf area and highest biomass, Chl content, P
N, and calorific value.
... Global change ecology of the interaction between plants and AM fungi could increase (Olesniewicz & Thomas, 1999;Rillig et al., 1999;Sanders et al., 1998;Syvertsen & Graham, 1999). ...
... Because AM fungal growth should be more limited at colder temperature and negatively affected by carbon limitation, we predicted that subambient temperature and CO 2 would inhibit AM fungal colonization of roots relative to ambient conditions, whereas the opposite would be observed for plants grown at superambient versus ambient temperature and CO 2 (Liu et al., 2004;Olesniewicz & Thomas, 1999;Rillig et al., 1999;Ruotsalainen & Kytöviita, 2004;Sanders et al., 1998;Syvertsen & Graham, 1999). These predictions were not supported; AM fungal colonization of roots did not differ between temperature (Figure 3a,b) or CO 2 treatments (Figure 3c,d). ...
Climate change and other anthropogenic activities have the potential to alter the dynamics of resource exchange in the mutualistic symbiosis between plants and mycorrhizal fungi, potentially altering its stability. Arbuscular mycorrhizal (AM) fungi, which interact with most plant species, are less cold‐tolerant than other groups of fungi; warming might therefore lead to increased fungal‐mediated nutrient transfers to plants, which could strengthen the mutualism. By stimulating photosynthesis, rising CO2 could reduce the carbon cost of supporting AM fungi, which may also strengthen the mutualism. Furthermore, rising temperature and CO2 could have stronger effects on the mutualism in wild plants than in domesticated plants because the process of domestication can reduce the dependence of plants on mycorrhizal fungi. We conducted a multi‐level random effects meta‐analysis of experiments that quantified the strength of the mutualism as plant growth response to AM fungal inoculation (i.e., mycorrhizal growth response) under contrasting temperature and CO2 treatments that spanned the Last Glacial Maximum (LGM) to those expected with future climate change. We tested predictions using a three‐level mixed effects meta‐regression model with temperature or CO2, domestication status and their interaction as moderators. Increases from subambient to ambient temperature stimulated mycorrhizal growth response only for wild, but not for domesticated plant species. An increase from ambient to superambient temperature stimulated mycorrhizal growth response in both wild and domesticated plants, but the overall temperature effect was not statistically significant. By contrast, increased CO2 concentration, either from subambient to ambient or ambient to super ambient levels, did not affect mycorrhizal growth response in wild or domesticated plants. These results suggest the mutualism between wild plants and AM fungi was likely strengthened as temperature rose from the past to the present and that forecasted warming due to climate change may have modest positive effects on the mutualistic responses of plants to AM fungi. Mutualistic benefits obtained by plants from AM fungi may not have been altered by atmospheric CO2 increases from the past to the present, nor are they likely to be affected by a forecasted CO2 increase. This meta‐analysis also identified gaps in the literature. In particular, (i) a large majority of studies that examined temperature effects on the mutualism focus on domesticated species (>80% of all trials) and (ii) very few studies examine how rising temperature and CO2, or other anthropogenic effects, interact to influence the mutualism. Therefore, to predict the stability of the mycorrhizal mutualism in the Anthropocene, future work should prioritize wild plant species as study subjects and focus on identifying how climate change factors and other human activities interact to affect plant responses to AM fungi. We conducted a meta‐analysis of experiments that quantified plant growth response to AM fungal inoculation under contrasting temperature and CO2 treatments. We found that the mycorrhizal mutualism was likely strengthened by past warming due to climate change. However, mycorrhizal growth response may not have been altered by increases in atmospheric CO2 from the past to the present, nor will it likely to be affected by increases in CO2 forecasted for the future.
... However, a lower plant N, P, or K under eCO 2 could be ameliorated by AM symbioses. For instance, compared to 50% decrease in non-AM plants, total plant P under 710 ppm eCO 2 was only decreased by 22% in 56-d-old AM Robinia pseudoacacia [28]. Positive AMF effects on lettuce's K concentration were greater under 700 ppm eCO 2 than under ACO 2 [29]. ...
... The higher biomass production and consequently greater nutrients demand of AMF plants under CO 2 might partly explain their increased nutrient accumulations. Similarly, Olesniewicz and Thomas [28] observed a significant increase of plant N and P in mycorrhizal Robinia pseudoacacia under 710 ppm eCO 2 . In a study with two citrus spp., Rhizophagus intraradices colonization under 700 ppm eCO 2 stimulated plant growth and P acquisition of sour orange (Citrus aurantium), but not of sweet orange (C. ...
Effects of arbuscular mycorrhizal fungi (AMF), elevated carbon dioxide (eCO2), and their interaction on nutrient accumulation of leguminous plants and soil fertility is unknown. Plant growth, concentrations of tissue nitrogen (N), phosphorus (P), and potassium (K) in 12-week-old nodulated faba bean (Vicia faba, inoculated with Rhizobium leguminosarum bv. NM353), and nutrient use efficiency were thus assessed under ambient CO2 (410/460 ppm, daytime, 07:00 a.m.–19:00 p.m./nighttime, 19:00 p.m.–07:00 a.m.) and eCO2 (550/610 ppm) for 12 weeks with or without AM fungus of Funneliformis mosseae inoculation. eCO2 favored AMF root colonization and nodule biomass production. eCO2 significantly decreased shoot N, P and K concentrations, but generally increased tissue N, P and K accumulation and their use efficiency with an increased biomass production. Meanwhile, eCO2 enhanced C allocation into soil but showed no effects on soil available N, P, and K, while AM symbiosis increased accumulation of C, N, P, and K in both plant and soil though increased soil nutrient uptake under eCO2. Moreover, plant acquisition of soil NO3−–N and NH4+–N respond differently to AMF and eCO2 treatments. As a result, the interaction between AM symbiosis and eCO2 did improve plant C accumulation and soil N, P, and K uptake, and an alternative fertilization for legume plantation should be therefore taken under upcoming atmosphere CO2 rising. Future eCO2 studies should employ multiple AMF species, with other beneficial fungal or bacterial species, to test their interactive effects on plant performance and soil nutrient availability in the field, under other global change events including warming and drought.
... Various studies suggest that total N 2 fixation and total plant N increase in several N 2 -fixing trees grown at CO 2 concentrations greater than the ambient value (Vogel et al. 1997;Atkin et al. 1999;Feng et al. 2004;Sanz-Sáez et al. 2010). Of these, Robinia pseudoacacia L. is the best known (Olesniewicz and Thomas 1999;Schortemeyer et al. 2002;Feng et al. 2004). R. pseudoacacia is native to North America and is now planted worldwide as a pioneer during the early stage of succession because of its adaptability to environmental stresses, high photosynthetic rate and rapid growth (Kurokochi et al. 2010). ...
... Several studies have found that N 2 -fixing trees (e.g. Alnus glutinosa, A. hirsute, Elaeagnus angustifolia, R. pseudoacacia) grown at elevated [CO 2 ] increase the nitrogenase activity of N 2 -fixing micro-organisms, or fixed more N, and made their leaf N concentration smaller (Norby 1987;Luo et al. 1994;Koike et al. 1997;Vogel et al. 1997;Olesniewicz and Thomas 1999;Tobita et al. 2005;Millett et al. 2012). Plants grown at elevated [CO 2 ] commonly accumulate carbohydrate in leaves and other tissues as starch, soluble sugars and structural compounds. ...
The black locust (Robinia pseudoacacia L.) is an invasive woody legume within Japan. This prolific species has a high photosynthetic rate and growth rate, and under- goes symbiosis with N2-fixing micro-organisms. To deter- mine the effect of elevated CO2 concentration [CO2] on its photosynthetic characteristics, we studied the chlorophyll (Chl) and leaf nitrogen (N) content, and the leaf structure and N allocation patterns in the leaves and acetylene reduction activity after four growing seasons, in R. pseudoacacia. Our specimens were grown at ambient [CO2] (370 lmol mol-1) and at elevated [CO2] (500 lmol mol-1), using a free air CO2 enrichment (FACE) system. Net photosynthetic rate at growth [CO2](Agrowth) and acetylene reduction activity were significantly higher, but maximum carboxylation rate of RuBisCo (Vcmax), maximum rate of electron transport driv- ing RUBP regeneration (Jmax), net photosynthetic rate under enhanced CO2 concentration and light saturation (Amax), the Nconcentration in leaf, and in leaf mass per unit area (LMA) and ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCo) content were significantly lower grown at ele- vated [CO2] than at ambient [CO2]. We also found that RuBisCo/N were less at elevated [CO2], whereas Chl/N increased significantly. Allocation characteristics from N in leaves to photosynthetic proteins, NL (Light-harvesting complex:LHC,photosystem I and II: PSI and PSII) and other proteins also changed. When R. pseudoacacia was grown at elevated [CO2], theNallocation to RuBisCo (NR) decreased to a greater extent butNL andNremaining increased relative to specimens grown at ambient [CO2]. We suggest that N remobilization from RuBisCo is more efficient than from proteins of electron transport (NE), and from NL. These physiological responses of the black locust are significant as being an adaptation strategy to global environmental changes.
http://link.springer.com/article/10.1007/s11738-017-2366-0
... This group of plants usually forms tripartite nutritional symbioses with bacteria, collectively referred to as rhizobia, and AME In this super-symbiotic system, the nodule symbiosis provides biologically fixed N, whereas AMF enhance mainly the acquisition of poorly available P. In exchange, the legume hosts supply their bacterial and fungal root symbionts with photosynthates. Therefore, under nutrientpoor soil conditions, a true reciprocal exchange of limiting resources results in mutual benefit for all three symbiotic partners (Olesniewicz & Thomas, 1999;Schulze, 2004). ...
... Synergism between the arbuscular mycorrhizal and nodule symbioses (e.g. Olesniewicz & Thomas, 1999) and the contribution of AMF to plant N nutrition (Tobar et al., 1994;Hawkins et al., 2000;Azcon et al., 2001) have been previously observed. Recently, Bago et al. (2004) reported on the ability of an G. intraradices isolate to take up nitrate efficiently through a change in extraradical hyphal growth under in vitro conditions. ...
• Altered environmental conditions may change populations of arbuscular mycorrhizal fungi and thereby affect mycorrhizal functioning. We investigated whether 8 yr of free-air CO2 enrichment has selected fungi that differently influence the nutrition and growth of host plants.
• In a controlled pot experiment, two sets of seven randomly picked single spore isolates, originating from field plots of elevated (60 Pa) or ambient CO2 partial pressure (pCO2), were inoculated on nodulated Trifolium repens (white clover) plants. Fungal isolates belonged to the Glomus claroideum or Glomus intraradices species complex, and host plants were clonal micropropagates derived from nine genets.
• Total nitrogen (N) concentration was increased in leaves of plants inoculated with fungal isolates from elevated-pCO2 plots. These isolates took up nearly twice as much N from the soil as isolates from ambient-pCO2 plots and showed much greater stimulation of biological N2 fixation. The morpho-species identity of isolates had a more pronounced effect on N2 fixation and on root length colonized than isolate identity.
• We conclude that rising atmospheric pCO2 may select for fungal strains that will help their host plants to meet increased N demands.
... Robinia is characterized by a high vitality, N 2 -fixing capability, fast growth and high ability of vegetation restoration in degraded land systems. The positive performance of Robinia is partially attributed to its root symbiosis with atmospheric N 2 -fixing rhizobia, one of the most effective symbiotic N 2 -fixation systems of plants (Olesniewicz and Thomas 1999). In this context, N 2 -fixing woody legume species, such as Robinia can provide more than half of the plant N demand thereby supporting biomass accumulation for forest restoration (Batterman et al. 2013). ...
Aims
The interaction between nitrogen (N) availability in the soil, rhizobia nodule formation and leaf physiological traits of Robinia pseudoacacia L. was explored at initial nodule development.
Methods
We selected two Robinia provenances, one from Northwest (GS) and one from Northeast China (DB), and cultivated seedlings in the greenhouse with and without rhizobia inoculation at normal and high N supply in the soil. After ca. 2.5 months growth, nodule formation, plant biomass, CO2 and H2O gas exchange of the leaves, and foliar N contents and partitioning were analyzed.
Results
Rhizobia inoculation strongly promoted the formation of root nodules independent of N availability in the soil, but this effect was more pronounced in the DB than for GS provenance. It reduced biomass accumulation of the GS provenance, but not for DB provenance at both, normal and high soil N availability. High N supply did not affect biomass accumulation independent of rhizobia inoculation. Leaf photosynthesis of both Robinia origins was enhanced by high N supply, but this effect was counteracted by rhizobia inoculation only in leaves of DB plants. In GS but not in DB plants, high N supply reduced not only nodule formation, but also stomatal conductance, but still enhanced transpiration without modifying the foliar water content. In addition, high N supply plus inoculation enhanced the organic N content in GS plants rather than DB plants.
Conclusion
These results indicate that excess N availability in the soil interacts with the performance of Robinia provenances, as previously reported for drought and phosphorus (P) depletion.
... In our mixed stands, higher stand density may constrain tree growth due to limited soil nutrients or water, in which case competitive strategies may benefit fine root growth in the shallow soil layer (Aerts and Chapin, 1999;Liao et al., 2019;Shipley and Meziane, 2002). Secondly, R. pseudoacacia in mixed forests improved soil nutrient conditions to promote fine root growth of P. tomentosa (Boring and Swank, 1984;Forrester, 2014;Marquard et al., 2009;Olesniewicz and Thomas, 1999;Vitkova et al., 2017). ...
Severe soil desiccation in mature forests has been discovered in many water-stressed regions around the world, threatening sustainable forest development. Only by understanding fine root distributions and root water uptake patterns of different forest stands can we timely deal with the severe water stress in tree growth. During the 2019 growing season, we repeated isotopic and soil water content sampling for four Populus tomentosa stands in the North China Plain (two young stands with lower- or higher-competition structure, and two mature stands with lower- or higher-competition structure), and fine root sampling was performed at the end of the growing season. The hydrogen-oxygen stable isotope method and the Bayesian mixture model were used to determine root water uptake patterns. The findings revealed that stand age had no effect on fine root distributions in the 0–2 m profile. However, P. tomentosa became more reliant on the deeper soil water with stand development. The stand structure did not affect fine root distributions of young stands but significantly affected that of mature stands. Regardless of developmental stage, the higher-competition structure would increase trees’ relative water uptake from the middle layers. However, this increase was at the expense of a decrease in the relative water uptake from shallow layers during the young stage and from deep layers during the mature stage. Furthermore, we discovered that the groundwater level in this area may have dropped to an extent that groundwater cannot provide sufficient water supply for P. tomentosa. This study clearly shows that fine root distribution patterns cannot be used to replace root water uptake patterns. In addition, the findings of this article will serve as a theoretical foundation for sus- tainable forest management in fast-growing plantations in other water-stressed areas around the world.
... Because of these features, Robinia also constituted one of the pioneer tree species for reforestation programs of degraded Loess Plateau area in North-west China (Yuan et al., 2022;Xu et al., 2020;Hu et al., 2017aHu et al., , 2017b. This positive performance isat least partially attributed to Robinia root symbiosis with atmospheric N 2 fixing rhizobia, one of the most effective symbiotic N 2 -fixation systems for plants (Olesniewicz and Thomas, 1999). N 2 -fixing tree species such as Robinia can provide more than half of the plant N thereby supporting biomass accumulation for the restoration of forest (Batterman et al., 2013). ...
In terrestrial ecosystems, the mechanisms that allow plants to adapted to low P availability are largely not understood, particularly for woody legume woody. Here, we investigated the responses of rhizobia inoculation and low phosphorus (P) availability on black locust (Robinia pseudoacacia L.) from different geographic origins of China. For this purpose, black locust seedlings from two provenances with distinct climatic and soil background, i.e., the Gansu Province (GS) of Northwest China and the Dongbei region (DB) of Northeast China, were exposed to sufficient (0.5 mM) and low P availability (0.5 µM) with and without rhizobia inoculation in a greenhouse for two months. The rhizobia strain used for inoculation was obtained from a black locust forest stand of 50-years-old in the Shandong Province of East China. CO2 and H2O gas exchange parameters as well as foliar physiological traits were measured. Our results indicated significantly different provenance-specific responses to inoculation and low P availability. Compared to sufficient P supply, inoculated DB Robinia showed a 57.6% decrease in whole plant biomass and a 49.2% decrease in the number of nodules at low P supply. However, low P availability had no effects on biomass accumulation of GS Robinia and increased its nodule formation by 240%. Still, gas exchange parameters and foliar physiological traits of GS Robinia plants were more responsive to low P supply than in DB plants. When inoculated with rhizobia at low P treatment, Robinia plants seem to use P preferentially for nodule production, thus weakening photosynthesis (86%) and reducing total biomass (58%) compared to non-inoculated plants. From these results it is concluded that GS Robinia may constitute a feasible candidate provenance for future afforestation programs of vulnerable terrestrial ecosystems. However, long-term systemic studies are needed in future to elucidate the physiological mechanisms of its adaption to low P availability.
... If the decline in nodule biomass between 1981 and 2017 years is real, we consider potential reasons for this change. Over these 37 years, atmospheric CO 2 has increased by 65 ppm and soil temperature by 1°C (Dlugokencky & Tans, n.d.;Knoepp et al., 2018), both of which may increase fixation potential by black locust (Houlton et al., 2008;Norby, 1987;Olesniewicz & Thomas, 1999). Yet at our study site, a total of 200 kg N/ha was deposited from the atmosphere over that time (National Atmospheric Deposition Program, 2019), and fire has been excluded since the turn of the 20th century; both of these, in contrast, have the potential to decrease fixation potential through increasing soil N pools (Carpenter et al., 2021;Veerman et al., 2020). ...
Carbon uptake by the terrestrial biosphere depends on supplies of new nitrogen (N) from symbiotic N fixation, but we lack a framework for scaling fixation accurately and for predicting its response to global change.
We scaled symbiotic N fixation from individual N fixers (i.e. plants that host N‐fixing bacteria), by quantifying three key parameters—the abundance of N fixers, whether they are fixing N and their N fixation rates. We apply this framework to black locust, a widespread N‐fixing tree in temperate forests of the eastern United States, and harness long‐term data from southern Appalachian forests to scale fixation from trees to the landscape and over succession.
Symbiotic N fixation at the landscape scale peaked in the first decade following forest disturbance, and then declined. This pattern was due to the declining density and declining fixation rates of individual black locust trees over succession. Independent of forest succession, and coincident with chronic atmospheric N deposition, we have evidence suggesting that nodule biomass produced by black locust trees has declined by 83% over the last three decades. This difference in nodule biomass translates to a maximum fixation rate of 11 kg N ha⁻¹ year⁻¹ and a landscape average of 1.5 kg N ha⁻¹ year⁻¹ in contemporary forests.
Synthesis. We find key controls on symbiotic N fixation by black locust over space and time, suggesting lower fixation rates in eastern deciduous forests than previous estimates. Our scaling framework can be applied to other N fixers to aid predictions of symbiotic N fixation and ecosystem response to global change.
... Short rotation forestry, therefore, requires reasonable nutrient management but Hungarian literature on the topic is scarce, especially under nursery conditions. Black locust fixes 75-150 kg/ha atmospheric nitrogen in a year (Boring et al. 1981), being one of the most effective tree species (Olesniewicz and Thomas 1999). Consequently, black locust can enhance the growing of poplars (Populus sp.) or oriental arborvitae (Platycladus orientalis) when planted in mixed forests (Shen et al. 1998;Chen et al. 2018). ...
Currently, black locust is the most important tree species in Hungary with significant economic value. Intensification of its cultivation and the improvement of the timber quality should include the use of highly productive clones and reasonable fertilization. Nutrition management should be based on reliable data from exact experiments. In our trial, nutrition intake of Turbo Obelisk OBE01 clone saplings was examined during a four-month period. Osmocote Pro (18:9:10 + 2Mg) was used as fertilizer at a dose of 2.5 and 5 kg m-3 mixed to a peat-based substrate. At the end of the growing period, saplings reached a height of 260-280 cm and a stem diameter of 16-18 mm. Nutrient intake order was found to be the following: Ca (3.3-4.2 g) > N (3.1-3.6 g) > K (2.1-2.9 g) > Mg (0.35-0.5 g) = P (0.3-0.5 g). Based on our results, a lower N:P and N:K rate fertilizer is recommended, especially if a non-peat based substrate and longer growing period is planned with a higher rate of nitrogen fixation. Considering nitrogen resource, a dose of 5 kg m-3 was proved to be less effective than a concentration of 2.5 kg m-3. However, the higher concentration of phosphorous, potassium and magnesium were well-utilized by the plants.
... Rhizobia inoculation improved the resistance of plants to environmental stresses in arid areas [25]. Under an elevated CO 2 level, similar to that expected with climate change, symbiotic microbes persisted and increased plant growth and photosynthesis [26], as well as enhanced nodule development, plant nutrition, and N 2 fixation rates [27]. ...
Adding biochar to soil can change soil properties and subsequently affect plant growth, but this effect can vary because of different feedstocks and methods (e.g., pyrolysis or gasification) used to create the biochar. Growth and biological nitrogen fixation (BNF) of leguminous plants can be improved with rhizobia inoculation that fosters nodule development. Thus, this factorial greenhouse study examined the effects of two types of biochar (i.e., pyrolysis and gasification) added at a rate of 5% (v:v) to a peat-based growth substrate and rhizobia inoculation (yes or no) on Robinia pseudoacacia (black locust) seedlings supplied with 15NH415NO3. Seedling and nodule growth, nitrogen (N) content, and δ15N × 1000 were evaluated after 3 months. While addition of biochar without inoculation had no effect on seedling growth, inoculation with rhizobia increased seedling growth, BNF, and N status. Inoculated seedlings had reduced δ15N, indicating that N provided via fertilization was being diluted by N additions through BNF. Biochar type and inoculation interacted to affect seedling growth. Combining inoculation with either biochar type increased seedling leaf, stem, and total biomass, whereas gasifier biochar and inoculation improved all seedling growth variables and nodule biomass.
... AMF inoculated plants exhibit rapid root expansion (Martin et al., 2012), therefore contributing to key growth promoting aspects like access to minerals and water which is facilitated by the mycorrhizal hyphae (Gong et al., 2013;Olesniewicz and Thomas, 1999). Simialr to present study, previous findings also demonstrate that inoculations of AMF along with supplementation of P better enhances the growth and mitigate drought stress efficiently. ...
... This implies that their presence might also prevent photosynthetic acclimation and enhance biomass production under e[CO 2 ] in leguminous species. However, results have been highly variable to date (e.g., Baslam, Erice, & Goicoechea, 2012;Gavito et al., 2000;Goicoechea et al., 2014;Jakobsen et al., 2016;Olesniewicz & Thomas, 1999), which may derive from differences in experimental conditions, including genotype/species assessed, level of CO 2 to which the plants were subjected, and rooting volume. ...
Why this research Matters
Legumes provide an important source of food and feed due to their high protein levels and many health benefits, and also impart environmental and agronomic advantages as a consequence of their ability to fix nitrogen through their symbiotic relationship with rhizobia. As a result of our growing population, the demand for products derived from legumes will likely expand considerably in coming years. Since there is little scope for increasing production area, improving the productivity of such crops in the face of climate change will be essential. While a growing number of studies have assessed the effects of climate change on legume yield, there is a paucity of information regarding the direct impact of elevated CO2 concentration (e[CO2]) itself, which is a main driver of climate change and has a substantial physiological effect on plants. In this review, we discuss current knowledge regarding the influence of e[CO2] on the photosynthetic process, as well as biomass production, seed yield, quality, and stress tolerance in legumes, and examine how these responses differ from those observed in non‐nodulating plants. Although these relationships are proving to be extremely complex, mounting evidence suggests that under limiting conditions, overall declines in many of these parameters could ensue. While further research will be required to unravel precise mechanisms underlying e[CO2] responses of legumes, it is clear that integrating such knowledge into legume breeding programs will be indispensable for achieving yield gains by harnessing the potential positive effects, and minimizing the detrimental impacts, of CO2 in the future.
... 1) The tree has allelopathic characteristics that negatively affect other plant species in the same habitat (Takahashi & Kameyama 1987;Morooka et al. 2000;Nose 2003;Iqbal et al. 2004;Fujii et al. 2009). 2) The rhizobia of R. pseudoacacia fix nitrogen (Elliott et al. 1999;Olesniewicz & Thomas 1999;Tian et al. 2003) and elevate the trophic status of surrounding soils (Tanno & Maeda 2007). Species that depend on oligotrophic soils, such as those occurring along riversides, may be displaced (Maekawa & Nakagoshi 1997b;Rice et al. 2004). ...
We investigated the invasion of Robinia pseudoacacia and subsequently affected riparian vegetation of the Saigawa and Azusagawa Rivers, which are upper tributaries of the Shinano River, the longest river in Japan. Habitats that had been affected by river water disturbance in recent years were located at a height relatively near the river surface and were composed of coarse gravel with numerous annual plants. We found subtrees and shrubs of R. pseudoacacia under willow canopies, but small willow individuals did not occur under the R. pseudoacacia canopies. Furthermore, forest floors in willow communities hosted more wetland and riverside species, including herb species, than those beneath R. pseudoacacia canopies. Mature R. pseudoacacia stands reduced the distribution of wetland and riverside species. Furthermore, the species composition at these sites was not riparian, instead consisting of various forest species. The resulting forest landscape is unlike the natural riparian zone in this area.
... La température influence le taux de germination des graines et sa cinétique (Giuliani et al., 2015), un déterminant important de l'invasion par le robinier (Masaka & Yamada, 2009). Les changements climatiques sont également susceptibles de modifier le potentiel envahissant du robinier (Kleinbauer et al., 2010) ainsi que sa biomasse, production ,primaire, nodulation et teneur en azote et phosphate (Olesniewicz & Thomas, 1999). Les différences de climat actuelles sont également susceptibles d'influencer la densité du robinier (Kleinbauer et al., 2010), et sa phénologie (Walkovszky, 1998) avec des répercussions probables sur le fonctionnement de l'écosystème (Pereira et al., 2011; Cette faible teneur en carbone organique, malgré l'augmentation de la teneur en carbone total, explique probablement la diminution importante de la biomasse microbienne et fongique avec la latitude. ...
Les espèces exotiques envahissantes végétales sont des plantes introduites et naturalisées hors de leur aire de répartition native et capables de maintenir et d’accroitre leur population. Certaines sont considérées comme transformatrices de par leur effet sur les écosystèmes : leur structure, leur fonctionnement ainsi que leur communauté végétale et animale. Ces transformations peuvent rendre certaines de ces espèces nuisibles de par leurs impacts écologiques et économiques important. Les travaux réalisés dans le cadre de cette thèse et présentés ici ont pour objectif d’approfondir les connaissances sur l’impact des invasions biologiques. La faune du sol, la végétation native et leur substrat ainsi que son fonctionnement ont été étudiés à différentes échelles spatiales. Deux espèces exotiques, envahissantes en Europe, ont été considérées comme modèles pour ces travaux : le robinier faux-acacia (Robinia pseudoacacia) et la renouée du japon (Reynoutria japonica). Premièrement, une méta-analyse globale a permis de démontrer l’effet positif des invasions biologiques végétales sur l’abondance de certains groupes de la faune du sol, notamment les consommateurs primaires, en fonction de la structure de l’habitat (ouvert ou fermé). Ensuite, une étude à large échelle sur le robinier faux-acacia a permis d’illustrer les différences qui peuvent exister dans la réponse des écosystèmes forestiers aux invasions le long d’un gradient latitudinal. Ce gradient, composé de quatre régions distinctes en Europe de l’Ouest présente des différences de climat et de végétation dominante, ces différences modifiant l’impact du robinier faux-acacia. Une étude approfondie sur le robinier faux-acacia en Normandie a permis de mieux comprendre l’effet du robinier faux-acacia sur les communautés animales et végétales ainsi que sur le fonctionnement des écosystèmes par comparaison avec deux essences natives dominantes. Finalement, une manipulation expérimentale en laboratoire a démontré l’impact des composés allélopathiques de la renouée du Japon sur une partie de la faune du sol. Cette étude a montré que certaines espèces exotiques envahissantes sont susceptibles d’influencer la faune, et les réseaux trophiques, du sol par leur métabolisme secondaire. Ces travaux illustrent l’intérêt, dans le contexte des invasions biologiques végétales, de l’étude simultanée des compartiments aériens et souterrains à différentes échelles spatiales.
... Black locust plantations are widely used for revegetation and soil stabilization in natural saline areas of northern China (Zhang, 2014). It was shown that AM fungi can improve black locust establishment and growth (Olesniewicz and Thomas, 1999;Chen et al., 2017), and therefore, evaluating the community dynamics of AM fungi associated with black locust grown in naturally saline areas will help us investigate cultivation practices for mycorrhizal black locust. Hence, we conducted a metagenomic analysis of the AM fungal communities in black locust roots and rhizosphere soils, obtained from four main saline sites in northern of China, via high-throughput sequencing of the 18S rRNA gene. ...
... The results revealed also an increase of N content in inoculated plants was concurred with Olesniewicz and Thomas, (1999), who's reported that VAM fungi enhanced N 2 -fixation by increasing root biomass, root-N absorption rates and finally the plant N contents. It seemed that the foliar N and P contents of inoculated maize plants reaffirms the key role of VAM fungi sustaining the plant cover in nutrient under heavy metals stress (Carrasco et al., 2011). ...
HE STUDY evaluated the physiological responses of maize ……..plant inoculated with vesicular arbuscular mycorrhiza (VAM) isolated from polluted site and growing in heavy metal (Cd or Pb) polluted soil. Chlorophyll, soluble carbohydrate, soluble protein, nutrient elements (P and N) content and phosphatase activity were analyzed. The phosphatase activity in inoculated plants was significantly increased in comparison to the non-inoculated ones. In addition, the contents of N, P, chlorophyll, total soluble carbohydrates and protein were significantly increased in plants inoculated with mycorrhiza grown in heavy metal (Cd or Pb) contaminated soil in comparing with the non-inoculated ones. Therefore, it can be concluded that the VAM inoculation is capable to alleviate the damage caused by heavy metal (Cd or Pb) on maize plants that maintain the growth and this could be related to nutrient status offered by VAM. Isolation of heavy metal tolerant VAM fungi can be a potential biotechnical tool for inoculation of plant to enhance its heavy metal tolerance.
... It is generally accepted that N-fixing species can improve soil N pools and thus benefit adjacent non-nitrogen-fixing species (Boring & Swank, 1984;Olesniewicz & Thomas, 1999;Rice et al., 2004;Rothe & Binkley, 2001;Tateno et al., 2007). In this study, we too found that the ions between the platelets of silicate clays (Duan, Huang, & Zhang, 2016;Kang et al., 2001;Wang, Liu, & Xue, 2012;Zhang et al., 2003). ...
To identify why tree growth differs by afforestation type is a matter of prime concern in forestry. A study was conducted to determine why oriental arborvitae (Platycladus orientalis) grows better in the presence of black locust (Robinia pseudoacacia) than in monoculture. Different types of stands (i.e., monocultures and mixture of black locust and oriental arborvitae, and native grassland as a control) were selected in the Loess Plateau, China. The height and diameter at breast height of each tree species were measured, and soil, shoot, and root samples were sampled. The arbuscular mycorrhizal (AM) attributes, shoot and root nutrient status, height and diameter of black locust were not influenced by the presence of oriental arborvitae. For oriental arborvitae, however, growing in mixture increased height and diameter and reduced shoot Mn, Ca, and Mg contents, AM fungal spore density, and colonization rate. Major changes in soil properties also occurred, primarily in soil water, NO3-N, and available K levels and in soil enzyme activity. The increase in soil water, N, and K availability in the presence of black locust stimulated oriental arborvitae growth, and black locust in the mixed stand seems to suppress the development of AM symbiosis in oriental arborvitae roots, especially the production of AM fungal spores and vesicles, through improving soil water and N levels, thus freeing up carbon to fuel plant growth. Overall, the presence of black locust favored oriental arborvitae growth directly by improving soil water and fertility and indirectly by repressing AM symbiosis in oriental arborvitae roots.
... N natural abundance (NA) Plants are grown in or watered with a solution containing N with 15 N close to natural abundance (e.g. Olesniewicz and Thomas 1999) and P atm is estimated according to Eq. 13. ...
Quantitative estimates of BNF are needed to improve our understanding of the ecology of N in the environment and aid efforts to improve agricultural N management. Static models based on the principle of ¹⁵N isotope dilution have been proposed to estimate the proportion of N in a N2-fixing species that is derived from the atmosphere via biological N2 fixation. Furthermore, equations have been developed to quantify the movement of biologically fixed N between neighboring species or from legumes to cereals in crop rotations. The present paper is structured to provide a comprehensive overview of these methods in a logical and systematic manner. While the relevant literature is vast, some aspects have fortunately been covered by recent in-depth reviews which will be identified and briefly summarized. The overview will emphasize the more practical indirect methodologies based either on artificial ¹⁵N enrichment or ¹⁵N depletion, or alternatively on ¹⁵N natural abundance. In considering methods used to estimate symbiotic dependence, the major structural division is whether or not a non-N2-fixing reference plant is employed, and approaches taken to remove this source of error are described. Four examples are provided to illustrate the contemporary success of ¹⁵N-based methods, one in basic research involving endophytic BNF, and three in applied research involving legume breeding for enhanced BNF, the response of legumes to climate change and biotic and abiotic factors affecting legume symbiotic performance.
... Here we demonstrate a positive correlation between the extensiveness of the root system and the accumulation of biomass. The plants provided with AMF (GM treatment) grew more rapidly than CK-treated plants with a more extensive root system, which facilitates nutrient uptake from the soil (Koske and Gemma, 1989;Olesniewicz and Thomas, 1999). ...
The poor quality and low productivity of cultivated liquorice (Glycyrrhiza uralensis) continues to put pressure on wild plant populations. As arbuscular mycorrhizal fungi are known to support plant growth and in some cases even to enhance the accumulation of valuable molecules in the plant, the effect of Glomus mosseae on the growth and active ingredient contents was evaluated in liquorice plants grown under nutrient deficiency. We created a nutrient-deficient environment by mixing paddy soil, washed river sand, and pumice at a ratio of 1:5:1. Our results showed that the inoculation of pot-grown liquorice plants with G. mosseae significantly increased the shoot and root biomass (by 25- and 17-folds, respectively) and the contents of glycyrrhizic acid, liquiritin, isoliquiritin, and isoliquiritigenin in the main root (by 1.6-, 4.8-, 6.5-, and 4.4-folds, respectively). Both isoliquiritin and isoliquiritigenin were detectable in the lateral roots of the plants inoculated with G. mosseae, but not in plants without G. mosseae inoculation. G. mosseae inoculation improved the features of the root system and increased photosynthetic efficiency of liquorice. The uptake of P and K by liquorice increased when G. mosseae was inoculated, leading to the depletion of these macronutrients in the soil; G. mosseae also improved the availability of Mg, Cu, Zn, and Mn. Based on these results, we concluded that the inoculation of liquorice plants with G. mosseae is beneficial, particularly for those grown in nutrient-deficient soil, and such positive effect is related to the improvement of the root system and an increased photosynthetic efficiency.
... Short-term exposure studies (56-71 d) have been conducted at NA on the effect of e[CO 2 ] on the symbiotic dependence of the woody legumes Gliricidia sepium (Thomas et al., 1991) and Robinia pseudoacacia (Olesniewicz and Thomas, 1999) grown in sand culture (Table 1). In both cases there was a significant increase in P atm at e[CO 2 ] in the presence of 1-7 mM N, which was consistent with the result obtained for Gliricidia by Thomas et al. (2000) at 10 mM N. In the case of black locust both the absolute values of P atm and the increase in the absolute values (18-22%) were similar, whether the exposure time was short (56 d, NA) or long (112 d, E), respectively (Table 1). ...
Methodologies based on (15)N enrichment (E) and (15)N natural abundance (NA) have been used to obtain quantitative estimates of the response of biological N2 fixation (BNF) of legumes (woody, grain and forage) and actinorhizal plants grown in artificial media or in soil exposed to elevated atmospheric concentrations of carbon dioxide e[CO2] for extended periods of time, in growth rooms, greenhouses, open top chambers or free-air CO2 enrichment (FACE) facilities. (15)N2 has also been used to quantify the response of endophytic and free-living diazotrophs to e[CO2]. The primary criterion of response was the proportional dependence of the N2-fixing system on the atmosphere as a source of N. i.e. the symbiotic dependence (Patm). The unique feature of (15)N-based methods is their ability to provide time-integrated and yield-independent estimates of Patm. In studies conducted in artificial media or in soil using the E methodology there was either no response or a positive response of Patm to e[CO2]. The interpretation of results obtained in artificial media or with (15)N2 is straight forward, not being subject to the assumptions on which the E and NA soil-cultured methods are based. A variety of methods have been used to estimate isotopic fractionation attendant on the NA technique, the so-called 'B value', which attaches a degree of uncertainty to the results obtained. Using the NA technique, a suite of responses of Patm to e[CO2] has been published, from positive to neutral to sometimes negative effects. Several factors which interact with the response of N2-fixing species to e[CO2] were identified.
... In the process of revegetation, Robinia pseudoacacia L. (black locust) was widely planted on Loess Plateau for revegetation to control soil erosion since 1950s [3,4]. R. pseudoacacia was used as a pioneer tree species due to its fast growth and strong capacity in improving soil nitrogen content and availability, available phosphorus pool, organic carbon sequestration as well as soil chemical and microbiological properties [2,[5][6][7][8][9]. Also, the choice of R. pseudoacacia in soil erosion control on Loess Plateau was because of its important economic value: it produces durable and rot-resistant wood as well as honey [10]; it can be used in coppice system and as fodder in silvopastoral system [11]; it has the potential for biooil production and fuel ethanol derived from biomass [12][13][14]. ...
Robinia pseudoacacia L. (black locust) is a widely planted tree species on Loess Plateau for revegetation. Due to its symbiosis forming capability with arbuscular mycorrhizal (AM) fungi, we explored the influence of arbuscular mycorrhizal fungi on plant biomass, root morphology, root tensile strength and soil aggregate stability in a pot experiment. We inoculated R. pseudoacacia with/without AM fungus (Rhizophagus irregularis or Glomus versiforme), and measured root colonization, plant growth, root morphological characters, root tensile force and tensile strength, and parameters for soil aggregate stability at twelve weeks after inoculation. AM fungi colonized more than 70% plant root, significantly improved plant growth. Meanwhile, AM fungi elevated root morphological parameters, root tensile force, root tensile strength, Glomalin-related soil protein (GRSP) content in soil, and parameters for soil aggregate stability such as water stable aggregate (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD). Root length was highly correlated with WSA, MWD and GMD, while hyphae length was highly correlated with GRSP content. The improved R. pseudoacacia growth, root tensile strength and soil aggregate stability indicated that AM fungi could accelerate soil fixation and stabilization with R. pseudoacacia, and its function in revegetation on Loess Plateau deserves more attention.
... This project is implemented through the CENTRAL EUROPE Programme co-financed by the ERDF important role in the extent to which plant nutrition by symbiotic N2-fixing tree species is affected by enriched atmospheric CO2 (Olesniewicz & Thomas, 1999). ...
The detailed information about the distribution and spreading of invasive species, the monitoring techniques and measures for removal and control of invasive plant species highlight one specific and increasingly important task of the protected area management under climate change. The spreading of invasive species is one of the most obvious and threatening impacts of climate change and is a major challenge for protected area management. It is expected that an increasing number of
protected areas will have to deal with an increasing number and density of invasive plant species that affect the biodiversity within the area negatively. Strategies and concepts have to be developed to respond to this new challenge in nature conservation.
... In many species CO 2 enrichment enhances root development of cuttings and their subsequent growth [Davis and Potter 1983]. At elevated CO 2 concentration increase in percentage of fine roots colonized by AM fungi was frequently observed [Olesniewicz and Thomas 1999]. In some studies no responses or even decreases in percent infection of AMF with high CO 2 have been reported [Staddon and Fitter 1999]. ...
Propagation conditions of bedding plants can eliminate or reduce the possibility of AMF inoculation of the root system during greenhouse production. Due to the ability of AMF to increase plant growth the effects of AMF and CO2 enrichment on rooting and some physiological traits of geranium and osteospermum cuttings were investigated. AMF and CO2 enrichment increased leaf number and fresh and dry weights of osteospermum shoots. Mycorrhization also significantly increased the length and fresh and dry weights of osteospermum roots formed in CO2 enriched atmosphere but it did not affect root system developed in ambient atmosphere. AMF increased the length and fresh weight of geranium roots, irrespectively of CO2 concentration, and dry weight of roots in CO2 enriched atmosphere. Transpiration and stomatal conductance values were higher in inoculated osteospermum at higher CO2 concentration. Mycorrhization and CO2 enrichment increased photosynthetic activity of garden geranium leaves and this effect was connected with the increased ratio of variable to maximum chlorophyll fluorescence (Fv/Fm).
... En effet, l'augmentation du métabolisme de la plante entraîne des besoins plus importants en nutriments ce qui explique qu'elle investit davantage d'énergie pour favoriser la colonisation microbienne répondant à ses besoins. Cet effet a été constaté pour les champignons(Olesniewicz & Thomas 1999) comme pour les bactéries avec une augmentation du nombre de nodules(Temperton et al 2003). En revanche, l'effet inverse peut être constaté comme c'est le cas dans les agroécosystèmes utilisant des fertilisants. ...
Understanding the interactions that bind plants and soil microorganisms is an essential step for the sustainable management of ecosystems, especially in agriculture. The ecosystem services resulting from such interactions include plant productivity which responds, in part, to the food requirements of the world's population and the regulation of biogeochemical cycles. These ecosystem services depend on trophic links between the two partners in the interaction and can be represented by a tradeoff between the costs and benefits for each partner. Plants, being autotrophic organisms or primary producers, are key organisms which introduce carbon into the ecosystem, through photosynthesis. Part of this carbon is released as more or less complex molecules at the roots level, thanks to the rhizodeposition process. These compounds act as signal molecules and nutrients for soil microorganisms, which are mainly heterotrophic, in the so-called rhizosphere effect. This process is costly for the plant but beneficial to the microorganisms. In return, microorganisms contribute to plant nutrition and health, which is costly but provides them with a beneficial source of nutrients. These trophic exchanges, however, are based on a balance which depends on the biotic and abiotic conditions that affect each partner. Microbial biodiversity, through the multitude of interactions occurring within microbial communities, is a significant biotic factor. Among the abiotic factors, the current environmental context, subject to global change, is tending to destabilize these interactions. The objective of this work was to understand how environmental changes affect the costs and benefits for each partner by applying changes to one or the other, the aim being to determine whether these changes would affect the benefits for plants and microorganisms that provide ecosystem services. To achieve this objective, a simplified framework for plants-microbes interaction was first chosen. Destabilization at the plant level was carried out by increasing the atmospheric CO2 and studying the interaction between Medicago truncatula and Pseudomonas fluorescens. The interactions were then made more complex by using a whole microbial community but this time the change was applied to the microbial compartment by subjecting it to diversity dilution. The effect of the resulting microbial diversity gradient was measured on the growth and reproduction of three model plant species (Medicago truncatula, Brachypodium distachyon and Arabidopsis thaliana). Finally, the microbial community was subjected to a DNA SIP analysis, with the isotope 13C, to identify the active portion, i.e., those microorganisms which really interacted with the plant and used compounds released by it. The main result, when the change affected one or other partner, was a destabilization of the costs and benefits. The first study showed a transient variation in the interactions in favour of the plant under increased CO2 conditions. In the case of a dilution of microbial diversity, the costs for the plant are conditioned by the natural dependency of plants on symbiotic microorganisms that interact with the rest of the community. This was confirmed by the last experiment that highlighted the between-microbes interactions which determined the composition of the microbial community that interacted with the plant. This work has helped to clarify the functioning of relationships between plants and soil microbes and the factors that contribute to their maintenance which is essential to the functioning of ecosystems. These studies also provide ways for predicting the impacts of global change on ecosystems. The conservation or restoration of ecosystem services is essential for human well-being
... The plant mainly used for the recultivation of these marginal sites is black locust (Robinia pseudoacacia L.), since it has the ability to grow on the nutrient poor sandy substrate with low water holding capacity [5,6]. Besides, as a N 2 fixing tree, it can also improve soil fertility through increase in soil OM input and thereby greatly improve and increase nutrient content and availability [7][8][9][10][11][12][13]. The cultivation of R. pseudoacacia is considered as a good method for land reclamation [6,11,[14][15][16]. ...
The objectives of the work were to study phosphorus (P) dynamics in postmining soils under short rotation coppices at different stages of Robinia pseudoacacia L. growth (2, 3, 4, and 14 years old). From the results obtained, the amount of total P, total organic P, plant available P, and P stock increased with increasing age of R. pseudoacacia. However, values were very low compared to that recommended for optimum plant growth, reflecting a general deficit in P. Additionally, the P sorption and desorption processes were investigated. The total P sorption capacity obtained from the laboratory experiments was on average, 2.5 times greater for soils under the oldest R. pseudoacacia than values measured at the younger sites. Values of P saturation factor (α) were comparatively lower compared to that reported in the literature. This may be attributed primarily to the less P saturation of the postmining soils, coupled with rather small contents of oxalate iron and aluminium (sum of 47 mmol kg−1). Results demonstrate significant difference between 2 and 14 years old R. pseudoacacia; thus establishing of short rotation coppice (SRC) on degraded marginal sites may be a valuable method of soil reclamations.
... Root growth may also be stimulated by increasing CO 2 , especially in early development with observed increases in length, diameter and cortex (Rogers et al., 1992). Changes in root production, in turn, may also be associated with increases in fine root colonisation of arbuscular mycorrhizal fungi (Olesniewicz and Thomas, 1999), and increased nodule formation in leguminous plants such as soybean (Temperton et al., 2003;Prevost et al., 2010). Sexual reproduction can also be influenced by elevated CO 2 with observed increases in floral number and pollen production (e.g. ...
Carbon dioxide (CO2) has two unique properties: physically it absorbs in the infra-red (heat) portion of the spectrum, and plays a role in maintaining global surface temperatures; secondly, it is the source of carbon for plant photosynthesis and growth. Recent, rapid anthropogenic increases in CO2 have been well-characterised with respect to climatic change; less recognised is that increase inCO2 will also impacthowplants supply food, energy and carbon to all living things. At present, numerous experiments
have documented the response of single leaves or whole plants to elevated CO2; however, it is difficult to
scale up or integrate these observations to plant biology in toto. To that end, a greater emphasis on multiple factor experiments for managed and unmanaged systems, in combination with simulative vegetative modelling, could increase our predictive capabilities regarding the impact of elevated CO2 on plant communities (e.g. agriculture, forestry) of human interest.
... It can significantly improve soil properties; especially increase soil nitrogen level since the tree is a nitrogen fixing plant. It has been estimated that Robinia pseudoacasia can add up to 75 kg N/(hm 2 • a) (Boring and Swank, 1984;Liu and Deng, 1991;Olesniewicz and Thomas, 1999). Wei et al. (2009) indicated that a twenty-one year's growth of black locust increased soil organic matter and nitrogen stocks by 24.65 t/hm 2 and 0.66 t/hm 2 respectively and reduced soil phosphorus stock by 2.41 t/hm 2 at 0-80 cm soil layer. ...
The role of the leaves of Robinia pseudoacacia L., which is widely distributed in the arid lands, on improving soil physical and chemical properties was analyzed at various incubation periods. The incu-bated soils added with 0, 25, 50 and 75 g Robinia pseudoacacia leaves were tested after consecutive in-cubation intervals of 6, 8 and 10 months and the different soil parameters were measured. The results showed the increases in organic matter (OM), extractable K, cation exchange capacity (CEC), aggregate stability and water holding capacity, but the decreases in pH value and bulk density after 6 months' incuba-tion. The gradual decrease in change rates of soil properties indicated less microbial population and or-ganic residual mineralization under acidic conditions, which were resulted from fast decomposition of leaves after the first 6 months incubation. The increases in soil organic matter content, extractable K, CEC, aggregate stability and water holding capacity and the decreases in soil pH and bulk density provide fa-vorable conditions for crop's growth.
... Its tolerance of low fertility sites, high genetic variability, and resistance to drought stress, air pollutants, temperature extremes, and most fungal decay (Hanover 1990) may be predictors of its prevalence in the future. R. pseudoacacia has also been shown to exhibit increased growth under elevated CO 2 (Olesniewicz and Thomas 1999). Possible implications of this study could be that, as atmospheric CO 2 concentrations continue to rise, R. pseudoacacia invasion could become more serious, particularly in areas without appropriate mycorrhizae such as newly reclaimed and restored sites. ...
... present. In the same experiment, nitrogen fixation increased 212 and 90 % in non-mycorrhizal and mycorrhizal seedlings, respectively (Olesniewicz and Thomas 1999). In a study with Plantago lanceolata and the AMF species Glomus mosseae, CO 2 enrichment increased net photosynthesis and root biomass, and this effect was greater in mycorrhizal plants (Staddon et al. 1999b). ...
Mycorrhizae, due to their key position at the plant-soil interface, are important to consider in the study of ecosystem impacts of global changes. Human-induced changes in the earth’s environment are clearly multi-factorial. Examples of important factors are: elevated concentrations of atmospheric gases (for example carbon dioxide or ozone), increased input of nutrients into ecosystems by atmospheric deposition (for example nitrogen), climate change (including altered precipitation and temperature regimes), invasive species, and increased UV-radiation. All of these components of future or present global changes can have positive or negative impacts on mycorrhizal associations. However, a more fundamental distinction has to be made between these factors, paying tribute to the fact that in the mycorrhizal symbiosis we are dealing with two classes of organisms with partially independent biology. There are those factors that directly affect only the host plant (e.g., carbon fixation), and that only have indirect effects on mycorrhizal fungi (mycobionts) via altered carbon allocation from the host. Examples include atmospheric changes, against which soil serves largely as a buffer. Other factors can (in addition) directly affect the mycobionts, for example warming or altered precipitation. This distinction is crucial for a mechanistic understanding of the impact of global change factors, and for experimental approaches. Global change factors rarely occur in isolation. The complexity of regional combinations of global change factors further highlights the need for mechanistic studies, since direct experimental exploration of a large number of scenarios would be virtually impossible. Finally, processes and patterns at larger temporal and spatial scales have to be considered in an assessment of global change impacts on mycorrhiza. Most experiments only allow access to short-term responses, while longer-term responses are really relevant. Possible approaches include the use of natural experiments, for example, CO2 springs. Large-scale processes such as shifts in the global distribution of plant communities (or their regional extinction) due to climate change would affect mycorrhiza, for example, alter the current distribution of mycorrhizal types on the globe. With potential impacts on host biodiversity, mycobiont species diversity may also be impacted at regional scales. In addition, changes in the mycorrhizal fungal community that are independent of changes in the plant community may be one of the least-understood, but potentially most important, mycorrhizal responses to global change.
... The effects of elevated CO 2 on mycorrhizal colonization of N 2 -fixing plants is also important in the consideration of how P limitations affect the responses on symbiotic N 2 fixation to climate change because mycorrhizal fungi typically stimulate the uptake of phosphorus. For example, it has been shown that the infection of Robinia pseudoacacia roots by mycorrhizal fungi was increased under elevated CO 2 , concurrent with increases in nodule mass and total plant N and P content (Olesniewicz and Thomas, 1999). ...
... Numerous pot-based experiments have clearly indicated that AM symbiosis can greatly assist nodulation and N 2 fixation of legumes [32,33]. We observed significant increases in Ndfa (as both percentage of total N content and amount of N fixed on an area basis) only under WS conditions. ...
Several studies, performed mainly in pots, have shown that arbuscular mycorrhizal symbiosis can mitigate the negative effects of water stress on plant growth. No information is available about the effects of arbuscular mycorrhizal symbiosis on berseem clover growth and nitrogen (N) fixation under conditions of water shortage. A field experiment was conducted in a hilly area of inner Sicily, Italy, to determine whether symbiosis with AM fungi can mitigate the detrimental effects of drought stress (which in the Mediterranean often occurs during the late period of the growing season) on forage yield and symbiotic N2 fixation of berseem clover. Soil was either left under water stress (i.e., rain-fed conditions) or the crop was well-watered. Mycorrhization treatments consisted of inoculation of berseem clover seeds with arbuscular mycorrhizal spores or suppression of arbuscular mycorrhizal symbiosis by means of fungicide treatments. Nitrogen biological fixation was assessed using the 15N-isotope dilution technique. Arbuscular mycorrhizal symbiosis was able to mitigate the negative effect of water stress on berseem clover grown in a typical semiarid Mediterranean environment. In fact, under water stress conditions, arbuscular mycorrhizal symbiosis resulted in increases in total biomass, N content, and N fixation, whereas no effect of crop mycorrhization was observed in the well-watered treatment.
... This difference is economically relevant if the wood is used for bioenergy generation and storage or transport capacity is a limiting factor. In addition to the high biomass productivity on marginal sites, several studies also highlight the potential of R. pseudoacacia to enhance soil properties in terms of cation exchange capacity, biomass and organic carbon (C) accumulation [14,15], nitrogen (N) accumulation and nitrification [16][17][18][19], soil phosphate [20], as well as the potential to improve soil structure, soil stability, and to support revitalization of degraded land [21,22]. The ability to fix atmospheric N reduces the plants requirement for N fertilization compared to other energy species and, in combination with the general high biomass productivity, supports the restoration of a high and sustainable soil productivity on reclamation sites [23]. ...
In the lignite mining region of Lower Lusatia (NE-Germany), Robinia pseudoacacia L. is an increasingly popular tree for the biomass production with short rotation coppices (SRCs) on reclamation sites. In order to evaluate biomass production, C and N allocation patterns in R. pseudoacacia stands between shoot, stump, coarse, and fine roots samples were collected from seedlings and three adjacent plantations and plants that were one, two and twelve years old. Results indicated that the summarized average dry matter production (DM) of the woody plant parts increased with plant age up to 7.45 t DM ha−1 yr−1 with a corresponding shoot increment of up to 4.77 t DM ha−1 yr−1 in the twelve-year-old stands. The shoot to root ratio changed from 0.2 for the one-year-old trees to 2.0 in the twelve-year-old plantation, whereby an average amount of 3.4 t C ha−1 yr−1 and 0.1 t N ha−1 yr−1 was annually bound in the living woody plant parts over the period of twelve years. Summing up, the results suggest a high potential for C and N storage of R. pseudoacacia what is also beneficial for land reclamation due to positive implications on soil humus and general site fertility.
... *P \ 0.05, **P \ 0.01, ***P \ 0.001, ****P \ 0.0001, ns not significant atmospheric N fixation since it is a legume species. This species is estimated to have fixation as much as 75 kg N hm -2 y -1 (Olesniewicz and Thomas 1999). Consistently, SOC and soil N stocks have been enhanced by ca. ...
To investigate influences of forest plantations on soil nutrient properties, biomass accumulation, major nutrient elements (NPK) and their stoichiometric couplings in different tissues and aged plants, and correlations between major nutrient contents in soils and in foliage of plants, 5-, 10-, 15- and 20-year-old plantations of black locust (Robinia pseudoacacia L.) and farmland were selected. Black locust plantations increased soil organic carbon (SOC) and N stocks by 23–327 and 23–119 %, respectively, in the 0–10 cm top soil layer compared to those in farmland. Soil C:N, C:P, C:K, N:P, N:K and P:K ratios were 10.1, 22.9, 0.7, 2.2, 0.7 and 0.03, respectively. These ratios were higher in the 0–10 cm soil layer than those in the 10–20 cm soil layer and increased under older plantations. Higher C contents in stem, N contents in leaf, the largest C pools in stem and N pools in root in 20-year-old plantation were observed. Correspondingly, the highest C:N, C:P and C:K and the lowest N:P and N:K ratios in stem, decreased C:N and C:P ratios in older trees were found. No strong correlations were observed between element contents in soils and in leaves of black locust trees. These results suggest that black locust plantations can increase soil nutrient concentrations, SOC and N stocks resulting in changes in element stoichiometric relations. CNPK contents and their stoichiometries vary with tissues and tree ages of black locust. No strong coupling relations exist between major nutrient element contents in the top soil and in foliage of black locust.
The remediation of land sites that have been declared as polluted/contaminated or unfit for agricultural activities is a major global issue. Traditional technologies are successfully employed to clear the contaminated sites, but cost effectiveness is a primary challenge. The restoration of contaminated sites through phytoremediation, especially by planting woody fiber crops, is progressively employed nowadays to achieve environmental, economic, and social sustainability. The phytoremediation potential of various woody fiber crops has been identified in the last two decades and many hybrid varieties have also been developed for the promising removal of contamination. Populus, Salix, Firmiana simplex, Ailanthus altissima, Eucalyptus camaldulensis, Robinia pseudoacacia, Acer saccharinum, and Morus nigra are examples of some woody trees that have been identified as tolerating and remediating inorganic and organic contaminants. Regardless of these intensive research studies, very few field trials of this approach have been followed by various environment protection agencies of different countries. In this chapter, an effort is made to present all relevant research studies reported for the phytoremediation of a variety of contaminants by woody fiber crops.
Generalised dose–response curves are essential to understand how plants acclimate to atmospheric CO2. We carried out a meta‐analysis of 630 experiments in which C3 plants were experimentally grown at different [CO2] under relatively benign conditions, and derived dose–response curves for 85 phenotypic traits. These curves were characterised by form, plasticity, consistency and reliability. Considered over a range of 200–1200 µmol mol⁻¹ CO2, some traits more than doubled (e.g. area‐based photosynthesis; intrinsic water‐use efficiency), whereas others more than halved (area‐based transpiration). At current atmospheric [CO2], 64% of the total stimulation in biomass over the 200–1200 µmol mol⁻¹ range has already been realised. We also mapped the trait responses of plants to [CO2] against those we have quantified before for light intensity. For most traits, CO2 and light responses were of similar direction. However, some traits (such as reproductive effort) only responded to light, others (such as plant height) only to [CO2], and some traits (such as area‐based transpiration) responded in opposite directions. This synthesis provides a comprehensive picture of plant responses to [CO2] at different integration levels and offers the quantitative dose–response curves that can be used to improve global change simulation models.
Atmospheric CO2 levels are steadily rising, which are predicted to affect plant and ecosystem functioning. Importantly, rising CO2 is a key driver of climate change thus impacting global food security. Elevated CO2 levels improve plant biomass due to stimulation of photosynthetic reactions resulting in enhanced sugar synthesis. However, many studies also report decline in protein and mineral contents essential for human nutrition. This overall suggests that rising CO2 will trigger plant nutritional imbalance, eventually leading to the generation of hidden hunger in human populations. Here we discuss the effects of rising atmospheric CO2 levels on the nutritional parameters including protein, mineral, and vitamin contents of crops. Emphasis is given to highlight the alteration caused in the nutritional status of plants belonging to different functional groups such as C3 versus C4 and grasses versus legumes. This will help to draw attention to breeding plants with decreased sensitivity to atmospheric CO2 concentration that could partly address emerging challenges of nutritional food security.
Black locust (Robinia pseudoacacia L.) was among the first North-American tree species imported in Europe. In Romania, black locust has established itself as a forest tree appreciated for multiple uses. The objective of the hereby study was to identify a quality planting material at black locust using seeds from trees with superior traits from five stands geographically close, located in North-western of Romania. An empirical selection was done, thus trees with the most favourable traits were selected as plus trees. Among the averages of the main traits (tree height, diameter at breast height, basal area, self pruning trunk length, crown diameter) of the plus trees from the five stands, there were registered significant differences, and two stands stood out with a high biomass growth. Even if the stands had different ages (between 20-35 year), the age did not influence significantly the growth traits of the trees. The seeds of the plus trees (open-pollinated) from all the stands had large size (mean seed weight of 0.057 g/seed). The seedling emergence rate was high, especially in the solarium condition (between 52.7-73.7% compared with 33.0-41.3% in the field). Coefficient of genetic correlation and heritability calculated for the seedlings belongings to half-sib families highlighted that black locust breeding can be extremely effective by a proper selection.
Auf wechselnde Umweltbedingungen an ihren Wuchsstandorten müssen Bäume mit ihrer ökophysiologischen und morphologischen Anpassungsfähigkeit reagieren, die sich auf deren genetische Ausstattung gründet. Sowohl die Bodeneigenschaften als auch das Klima beeinflussen die physiologischen Prozesse von der Blatt- bis zur Baumebene. Grundlage für das schnelle Wachstum und die hohe Biomasseproduktivität der Agrargehölze ist die Photosynthese und die hohe Anpassungsfähigkeit an sich ändernde Umweltbedingungen. Dabei ist zu bedenken, dass die Photosynthese die Voraussetzung für das Wachstum ist, aber diese nicht das Wachstum antreibt. Interaktionen zwischen dem Bedarf an Assimilation für die Wachstumsprozesse („sinks“) und dem Angebot („source“) steuern den Kohlenstoffhaushalt der Pflanzen. Zudem ist das Angebot von Ressourcen (Wasser, Nährstoffe, Licht) eine unverzichtbare Voraussetzung für die Wachstumsprozesse. Das Kapitel gibt einen Überblick über die ökophysiologischen Anpassungen der Photosynthese, des Wasserhaushaltes und der Pflanzenernährung der schnellwachsenden Baumarten und deren Bedeutung für das Wachstum und die Kohlenstoffallokation. Zudem werden die Grundlagen für die Modellierung der Biomasseproduktion und des Kohlenstoffhaushaltes vom Blatt bis zum Bestand vorgestellt.
Living organisms maintain a balance of chemical elements for optimal growth and reproduction, which plays an important role in global biogeochemical cycles1, 2, 3, 4, 5. Human domination of Earth’s ecosystems has led to drastic global changes6, 7, 8, but it is unclear how these affect the stoichiometric coupling of nutrients in terrestrial plants, the most important food source on Earth. Here we use meta-analyses of 1,418 published studies to show that the ratio of terrestrial plant nitrogen (N) to phosphorus (P) decreases with elevated concentrations of CO2, increasing rainfall, and P fertilization, but increases with warming, drought, and N fertilization. Our analyses also reveal that multiple global change treatments generally result in overall additive effects of single-factor treatments and that the responses of plant nutrients and their stoichiometry are similar in direction, but often greater in controlled than in natural environments. Our results suggest a decoupling of the P biogeochemical cycle from N in terrestrial plants under global changes6, 7, 8, which in turn may diminish the provision of ecosystem services1, 5, 9.
The optimum developmental stage of explant for somatic embryogenesis in Robinia pseudoacacia L. was achieved using immature zygotic embryos from 10 open-pollinated plus trees as explants for three consecutive years (2010-2012). The trend of explant age on callus induction rate was parabolic and the highest frequency (95%) of callus induction was obtained in 55-day-old explants incubated on Murashige and Skoog medium supplemented with 5.0 mg·L -1 2,4-Dichlorophenoxyacetic acid and 0.5mg·L-1 6-Benzyladenine. Controlled crosses were conducted with five plus trees in 2012 to study the parent genotype influence on somatic embryogenesis capacity of explants. The variation in callus induction rate between families was 73-97% and the maternal effect was significant at this stage. The frequency of direct and indirect somatic embryogenesis varied among families on optimum medium and only maternal genotypes were statistically significant. The mean number of somatic embryos per family and embryo maturation rate was affected by the mother×father interaction. More than 98% of somatic embryos were converted into complete plants after mature culture and more than 95% of regenerating plants were successfully transferred to soil.
Soil is a dynamic and complex system consisting of living organisms interacting with inorganic mineral particles and organic matter. A wide range of functions is performed by soil that directly or indirectly sustains the world’s human population. Soil plays a vital role in food production, as a reservoir for water and filter for pollutants. Soils store almost twice as much carbon as the atmosphere does and are important links in the natural cycle that determines atmospheric carbon dioxide level (O’Donnell and Görres 1999). Soils sustain an immense diversity of microbes, which exceeds that of eukaryotic organisms (Torsvik and Øvreås 2002). Microorganisms exist in every conceivable place on earth, even in extreme environments. One gram of soil may harbor up to 10 billion microorganisms of possibly thousands of different species.
It is widely accepted that the extent of microbial diversity has not been adequately explored. Some bacteriologists believe that about 100,000 to 1 billion bacterial species actually exist in the earth environment and only about 4000 species have been described (Staley 1997).Mycologists estimate that there are more than 1.5 million species of fungi of which only 72,000 species have been isolated or described (Hawksworth 1997). Microorganisms can exist either in an active or in a dormant yet persistent form. The ratio of viable counts to direct counts reflects the ratio between the numbers of the active (dividing) cells and the quiescent cells, and most bacteria in soil are in the latter form (Hattori et al. 1997). The tropics are considered to be richer in microbial diversity than boreal or temperate environments (Hunter-Cevera 1998). Some microbiologists believe that there is an equal amount of microbial diversity in the deserts.Actinomycetes with motile spores appear to be widely distributed in littoral zones and arid environments.
Short rotation woody bioenergy crops (SRWC)
could contribute a substantial portion of the biomass required
to meet federal mandates and offset carbon emissions. One
SRWC with strong bioenergy potential is black locust
(Robinia pseudoacacia L.), planted extensively for wood
and energy applications globally, but under-studied in its native
US. This member of the Fabaceae family can fix nitrogen,
tolerate stress, and sequester carbon while generating biomass
yields up to 14 Mg ha-1 yr-1. This article offers a comprehensive
state-of-the-art review of production practices, biomass
and energy yield estimates, environmental risks and benefits,
and economic considerations for this promising feedstock.
Mycorrhizal association increases the tolerance of plants to various nutritional and environmental stresses. The mycorrhizal plants get adapted to survive in unsuitable conditions. VA mycorrhizal plants become resistant to soil-borne pathogens. There is improved growth and survival of micropropagated plantlets upon association with VAM fungi. Different simple and modern techniques to study this aspect has been described.
Inoculated and uninoculated Alnus rubra Bong, seedlings were grown for 47 days in atmospheres containing ambient (350 μ1 CO2 1−1) and elevated (650 μl CO2 1−1) levels of CO2, with and without combined nitrogen (20 mg 1−1) supplied as ammonium nitrate. Five plants from each treatment were harvested 15, 30, and 47 days after exposure to CO2 treatments began. Evidence for the presence of a positive feedback loop between nitrogen fixation and photosynthesis was observed in nodulated plants growing at elevated CO2. These plants had greater whole-plant photosynthesis and nitrogenase activity, leaf area and nitrogen content, as well as nodule and plant dry mass, relative to nodulated plants grown at ambient CO2 and non-nodulated plants grown at both CO2 levels. This feedback may be an important way in which the potential carbon drain of nitrogen fixation on the host plant could be compensated; increased nitrogen availability resulting in stimulated leaf area growth and whole-plant photosynthesis. The relative amount of dry mass allocated below ground decreased for all seedlings over time, and the amount allocated above ground increased. This shift in allocation occurred slowly and at a constant rate in non-nodulated plants and more rapidly and abruptly when plants were nodulated. The proportion of dry mass allocated below ground was consistently greater in non-nodulated plants. Dry mass allocation to the stem was increased when combined nitrogen was applied and was greatest in nodulated plants grown at high CO2. Dry mass partitioning among other organs was not directly affected by nodulation, CO2 enrichment, or other treatment interactions.
Cucumis sativus L. cv. Aminex (F1 hybrid) was grown alone or in symbiosis with Glomus intraradices Schenck and Smith in containers with two hyphal compartments (HCA and HCB) on either side of a root compartment (RC) separated by fine nylon mesh. Plants received a total of either 100, 200 or 400 mg N which were applied gradually to the RC during the experiment. 15N was supplied to HCA 42 d after plating, at 50 mg 15NH4
+-N kg–1 soil. Lateral movement of the applied 15N towards the roots was minimized by using a nitrification inhibitor and a hyphal buffer compartment.Non-mycorrhizal controls contained only traces of 15N after a 27 d labelling period irrespective of the amount of N supplied to the RC. In contrast, 49, 48 and 27% of the applied 15N was recovered in mycorrhizal plants supplied with 100, 200 and 400 mg N, respectively. The plant dry weight was increased by mycorrhizal colonization at all three levels of N supply, but this effect was strongest in plants of low N status. The results indicated that this increase was due partly to the improved inflow of N via the external hyphae. Root colonization by G. intraradices was unaffected by the amount of N supplied to the RC, while hyphal length increased in HCA compared to HCB. Although a considerable 15N content was detected in mycorrhizal roots adjacent to HCB, only insignificant amounts of 15N were found in the external hyphae in HCB. The external hyphae depleted the soil of inorganic N in both HCA and HCB, while the concentration of soil mineral N was still high in non-mycorrhizal containers at harvest. An exception was plants supplied with 400 mg N, where some inorganic N was present at 5 cm distance from the RC in HCA. The possibility of a regulation mechanism for hyphal transport of N is discussed.
Short-term studies of tree growth at elevated CO2 suggest that forest productivity may increase as atmospheric CO2 concentrations rise, although low soil N availability may limit the magnitude of this response. There have been few studies of growth and N2 fixation by symbiotic N2-fixing woody species under elevated CO2 and the N inputs these plants could provide to forest ecosystems in the future. We investigated the effect of twice ambient CO2 on growth, tissue N accretion, and N2 fixation of nodulated Alnus glutinosa (L.) Gaertn. grown under low soil N conditions for 160 d. Root, nodule, stem, and leaf dry weight (DW) and N accretion increased significantly in response to elevated CO2. Whole-plant biomass and N accretion increased 54% and 40%, respectively. Delta-15N analysis of leaf tissue indicated that plants from both treatments derived similar proportions of their total N from symbiotic fixation suggesting that elevated CO2 grown plants fixed approximately 40% more N than did ambient CO2 grown plants. Leaves from both CO2 treatments showed similar relative declines in leaf N content prior to autumnal leaf abscission, but total N in leaf litter increased 24% in elevated compared to ambient CO2 grown plants. These results suggest that with rising atmospheric CO2 N2-fixing woody species will accumulate greater amounts of biomass N through N2 fixation and may enhance soil N levels by increased litter N inputs.
Seeds of Gliricidia
sepium, a fast-growing woody legume native to seasonal tropical forests of Central America, were inoculated with N2-fixing Rhizobium bacteria and grown in environmentally controlled glasshouses for 67–71 days under ambient CO2 (35 Pa) and elevated CO2 (70 Pa) conditions. Seedlings were watered with an N-free, but otherwise complete, nutrient solution such that bacterial N2 fixation was the only source of N available to the plant. The primary objective of our study was to quantify the effect of
CO2 enrichment on the kinetics of photosynthate transport to nodules and determine its subsequent effect on N2 fixation. Photosynthetic rates and carbon storage in leaves were higher in elevated CO2 plants indicating that more carbon was available for transport to nodules. A 14CO2 pulse-chase experiment demonstrated that photosynthetically fixed carbon was supplied by leaves to nodules at a faster rate
when plants were grown in elevated CO2. Greater rates of carbon supply to nodules did not affect nodule mass per plant, but did increase specific nitrogenase activity
(SNA) and total nitrogenase activity (TNA) resulting in greater N2 fixation. In fact, a 23% increase in the rate of carbon supplied to nodules coincided with a 23% increase in SNA for plants
grown in elevated CO2, suggesting a direct correlation between carbon supply and nitrogenase activity. The improvement in plant N status produced
much larger plants when grown in elevated CO2. These results suggest that Gliricidia, and possibly other N2-fixing trees, may show an early and positive growth response to elevated CO2, even in severely N-deficient soils, due to increased nitrogenase activity.
The interactive effects of phosphorus supply and combined nitrogen (nitrate) on dry matter and nitrogen accumulation by nodulated soybean (Glycine max L. Merr.) plants, and the relative effects of phosphorus supply on nodule number, mass, and function in comparison to host plant growth were used to investigate the role of phosphorus in symbiotic dinitrogen fixation. Mixed positive and negative phosphorus by nitrogen source interactions indicated that severe phosphorus deficiency markedly impaired both host plant growth and symbiotic dinitrogen fixation and that symbiotic dinitrogen fixation has a higher phosphorus requirement for optimal functioning than either host plant growth or nitrate assimilation. In the whole plant phosphorus concentration range of 0.8 to 1.5 grams per kilogram dry weight, plants supplied with 20 millimolar nitrate accumulated significantly more dry matter and nitrogen than symbiotic plants without nitrate. This suggested that the higher phosphorus requirement for symbiotic dinitrogen fixation is internal rather than being associated with differences in the ability of roots in the two nitrogen regimes to absorb phosphorus from the external solution. Increasing the phosphorus concentration in plants solely dependent on dinitrogen fixation resulted in highly significant (P = 0.0001) increases in whole plant nitrogen concentration as well as highly significant increases (P = 0.0001) in whole plant dry matter and nitrogen accumulation. This indicated a greater responsiveness of symbiotic dinitrogen fixation than of host plant growth to improvement in phosphorus nutrition. The large increases in whole plant nitrogen concentration were associated with about 3.5-fold increases in the ratio of nodule mass to whole plant mass and about 2-fold increases in specific acetylene reduction (nitrogenase) activity of the nodules. The large increase in nodule mass (>30-fold) between the 0 and 2.0 millimolar phosphorus levels resulted from 11- and 3-fold increases in nodule number per plant and average mass of individual nodules, respectively. Root mass per plant over the same concentration range increased 3.5-fold. These results indicate that phosphorus has specific roles in nodule initiation, growth, and functioning in addition to its involvement in host plant growth processes.
Interactions in the tripartite symbioses of pea (Pisum sativum L.), Glomus mosseae and Rhizobium leguminosarum were investigated. Plants were grown for 35 d under high light (390 µmol m−2 s−1) and low light conditions (190 µmol m−2 s−1) in a growth cabinet at moderate nitrogen fertilization but non-limiting phosphorus supply. Under high light, shoot dry mass was increased and root dry mass decreased by Rhizobium infection whereas VAM fungus infection had little influence on spoot growth but reduced root growth, although to a lesser extent. These growth reactions indicate changes in the carbohydrate allocation in the plant. In Rhizobium infected roots, P and K uptake per unit root length was more than doubled compared to non-nodulated plants and highest in double infected plants, especially under low light. Compared to the VAM plants in the tripartite system VAM infection rate was reduced to less than one half. VAM infection failed to influence nodule number but significantly depressed nitrogenase activity per plant (acetylene reduction). A reduction in total plant dry matter (about 50 %) was induced by low light conditions with only small differences within inoculation treatments. Love light also caused a depression in VAM infection which was even more pronounced in Rhizobium infected plants. Under low light nodule number decreased, acetylene reduction and consequently the amount of N2 fixed were very low. The results suggest that in tripartite symbiosis in P. sativum grown with non-limiting P supply photosynthesis may become the limiting factor for symbiotic activity and plant growth.
Inoculation of rhizobia onto host plants increased N2 fixation by 50-82 mg N per plant. Incidence of nodulation was also increased by R. phaseoli inoculation. Addition of VAM to the soils increased bean dry matter production by 9-54% over plants, and increased the N2 fixed by rhizobially-inoculated plants by 4-27 mg N per plant. VAM addition resulted in greater uptake of soil N by plants. Inoculation of captan-treated field beans with inoculum derived from a captan-tolerant strain of R. phaseoli did not result in improved N2 fixation rates compared with inoculation with the nontolerant parent strain. Seed-applied captan reduced the proportion of nodules formed by both strains of added rhizobia, but did not result in decreased amounts of N2 fixed by the root systems. Captan did not reduce the effectiveness of VAM. -from Authors
The limiting factor concept has often been used to describe plant growth responses to altered availability of resources. However, even preliminary experiments, where atmospheric CO2 concentrations and solution mineral concentrations were varied, demonstrated that a more complex concept was required to interpret the potential effects of climate change and mineral availability on plant growth. It is proposed that these resources for plant growth may be better viewed as simultaneously limiting. Further, in considering the limitation in plant growth to mineral nutrition it is important to consider both the solution concentration and the total amount of the individual minerals available to the plant. Sustaining a positive response to increased CO2 concentration, for example, requires an increase in plant uptake of the total amount of minerals. Consequently, it is very difficult to predict the plant growth response to climate change because of the large uncertainty about mineral availability. On the one hand, increased CO2 concentrations should stimulate nitrogen fixation by both free-living organisms and symbiotic systems, and improve soil properties for mineral availability as a result of increased organic matter deposition in the soil. On the other hand, increased temperature and altered rainfall patterns may result in increased losses of soil minerals. Even the direction in the net change in available soil minerals is unclear. Realistic evaluations of the effects of climate change on plant growth will be challenged to contend with the large uncertainty and complexities in understanding mineral availability and plant mineral nutrition.
Soybean plants [Glycine max (L.) Merr.] were grown in pots and inoculated with Rhizobium japonicum and/or Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, either at planting or 20 days later. Nitrogen was supplied in the nutrient solution to plants without nitrogen‐fixing bacteria, and P was added to those without the mycorrhizal fungus. At harvest, 50 days after planting, all plants had leaves of similar dry mass. Each root symbiont grew best in the absence of the other. Growth of Glomus reflected the duration of its growing time and the presence and duration of competition from Rhizobium. Nodule weight in the tripartite associations, on the other hand, was inhibited only by the earlier introduction of Glomus.Dipartite associations and the plants inoculated with both root symbionts at planting had the highest concentration of leaf N, and the lowest was in those inoculated with both organisms at d 20. Leaf P was highest in plants inoculated only with Rhizobium, and lowest in those tripartite associations involving any inoculation at day 20. The low values were presumably a result of the short duration of endophyte‐mediated P uptake before the plants were harvested.Although there was almost no difference in leaf sugar concentrations, starch concentrations reflected the duration of Glomus growth, and were greatest in those plants that had supported it for the least time. Uninoculated plants contained the least starch, but produced a greater fresh mass of leaf tissue than any of the tripartite symbionts.
Trifolium repens L. cv. aran was grown for 58 d at ambient (350 μol mol−1) and elevated (700 μol mol−1) atmospheric CO2, wish and without the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe cv. YV. Plant biomass, mycorrhizal infection, non-structural carbohydrates, C, N and P content were examined. Elevated CO2 (a) significantly increased above- and below-ground biomass, (b) decreased specific leaf area and specific root length, (c) decreased tissue %N and increased the C:N ratio, and (d) significantly increased total non-structural carbohydrates. Inoculating T. ripens with Glomus mosseae (a) significantly increased above- and below-ground biomass. (b) increased the total root length and total leaf area, and (c) significantly decreased tissue of Evidence of an increased influence of mycorrhiza on the P nutrition of T. repens at elevated CO2 was found in the 22%, increase in leaf total P (P < 005) of mycorrhizal plants grown at elevated CO2 compared with non-mycorrhizal plants. No significant interactions were found between CO2 and mycorrhiza treatments.
The proportion of T. repens root length colonized by Glomus mosseae was not affected by CO2 concentration. The percentage mycorrhizal infection was 29% at ambient CO2 and 35%, et al elevated CO2. However, exposure to elevated CO2 significantly increased the total mycorrhizal foot length from 3.4 to 6.1 m per plant.
The results show little evidence that the role of arbuscular mycorrhiza in the growth and nutrition of T. repens would increase if atmospheric CO2 were to increase as predicted.
Cucumber (Cucumis sativus L.) plants grown in PVC tubes with a partially sterilized soil-sand mixture were inoculated with the vesicular-arbuscular mycorrhizal fungus Glomus fasciculatum (Thaxter) Gerdemann & Trappe emend. Walker & Koske or left uninoculated. The soil column of each PVC tube was divided into a root and a hyphal compartment by a mesh bag (60 μm), which retained the roots but allowed external hyphae to pass. Inoculated plants rapidly became infected and an extensive mycelium developed. Three weeks after seedling emergence plants were labelled with 14CO2 for 16 h. The distribution of 14C within the plants and the 14C flow into external hyphae and soil were measured during an 80 h chase period. Below-ground respiration in mycorrhizal plants accounted for 27% of the photo assimilated 14C. Organic 14C in the soil represented 3˙1 % of the fixed 14C, and 26 % of this was located in external hyphae.
Based on conservative assumptions concerning dry weight of internal mycorrhizal infection and growth yield of the fungus, it was estimated that mycorrhizal events consumed 20 % of photoassimilated 14C. The specific incorporation of C by the external mycelium in the hyphal compartment was 41 μg C mg−1 dry wt. d−1.
The importance of external VA mycorrhizal hyphae for the distribution of plant-derived C in the soil volume and as a substrate source for the soil biota is discussed.
Activities of glutamate dehydrogenase and glutamine synthetase were determined using crude extracts of roots and shoots of mycorrhizal and non-mycorrhizal plants of Trifolium subterraneum L. and Allium cepa L., grown at different levels of fertilizer phosphate.
Glutamate dehydrogenase activity was low in all tissues [0.1 to 1.6 μmol NAD(P)H oxidized min−1 gFW−1 tissue] and there was no consistent effect of mycorrhizal infection or phosphate nutrition on this activity.
Glutamine synthetase (GS) activity (assayed by the transferase method) was in the range 1 to 40/iimol γ-glutamyl hydroxamate produced min−1 gFW−1. In general, activity of this enzyme was low in phosphate-deficient plants and was increased both by mycorrhizal infection and by improved phosphate supply. In T. subterraneum routine assays of GS were done on roots only. The effects of mycorrhizal infection in increasing enzyme activity in roots were similar whether natural soil inoculum (containing a mixture of several mycorrhizal fungi) or inoculum of Glomus mosseae Nichol. & Gerd. was used. Both increased phosphate supply and mycorrhizal infection increased nodulation of clover plants as well as GS activity, so that it was difficult to relate changes in GS activity to the interacting effects of mycorrhizal infection and phosphate nutrition.
Onions had low GS activity in uninfected roots, compared with shoots. Again improved phosphate supply resulted in increased enzyme activity in both roots and shoots. However, the patterns of interaction between phosphate supply, P concentration in tissues, mycorrhizal infection and enzyme activity were different in the two tissues. In shoots, as expected, the effects were consistent with an indirect effect of mycorrhizal infection on enzyme activity, via improved P nutrition. In roots there appeared to be a ‘fungal effect’ superimposed on the phosphate effect. This was investigated by manipulating the amount of fungal tissue in mycorrhizal roots via differences in propagule density of G. mosseae in soil. Results were again consistent with the hypothesis that the mycorrhizal fungi contributed GS activity to the symbiotic root system. Fungal structures were separated from roots following digestion in cellulase and pectinase. GS activity was high in fungal tissue from young roots (29 to 31 d), but low in older infections (55 d). The high activity could not have been caused by contamination of fungal tissue by root cells. The digestion technique reduced GS activity in uninfected and infected root segments, so that results obtained with separated fungi are not quantitatively comparable with those obtained from extracts of fresh tissues.
We conclude that vesicular-arbuscular mycorrhizal fungi are able to assimilate ammonium via GS. This ability would be important in increased uptake of nitrogen which is an inevitable prerequisite for increased growth following relief of phosphate stress. It is also consistent with the recent findings by others that hyphae of G. mosseae can absorb and translocate 15NH+4
The objective of this study was to examine the ability of arbuscular mycorrhizal (AM) fungi to take up nitrogen from soil and transport it to the host plant. Maize ( Zea mays L.) associated with Glomus intraradices Schenck and Smith or left uninoculated was grown in containers which were divided by a nylon net into a root compartment and a hyphal compartment. A 40 μm pore size nylon net was used to exclude plant roots while allowing fungal hyphae to grow into soil confined by the net. ¹⁵ N tracer was supplied either as inorganic N or as organic N to the hyphal compartment at a distance of 5 cm from the net.
Inoculation with the AM fungus increased the ¹⁵ N content of maize compared to the non‐mycorrhizal controls when N was applied as ( ¹⁵ NH 4 ) 2 SO 4 . However, there was no conclusive evidence that AM hyphae could derive N from organic ¹⁵ N sources. Most of the increased N uptake of mycorrhizal plants occurred by hyphal translocation from the hyphal compartment to the root compartment. Higher N uptake by mycorrhizal plants with access to the hyphal compartment was indicated by depletion of total ¹⁵ N in the soil of that compartment. Cutting the extraradical hyphae in the hyphal compartment in order to sever their connection with the host roots decreased the ¹⁵ N uptake of the maize plants. A time‐course study with inorganic ¹⁵ N over 26 d showed that G. intraradices transported most of the ¹⁵ N between 10 and 15 d after ¹⁵ N application, whereas the non‐mycorrhizal control plants had a consistently low concentration of ¹⁵ N throughout the period of sampling.
Nitrogen transport by external hyphae of three AM fungi, G. intraradices, Acaulospora laevis Gerdemann and Trappe and Gigaspora margarita Becker and Hall associated with maize, was further investigated. The results indicated that different isolates of AM fungi differ in the efficiency of hyphal N transport as a consequence of the different patterns of hyphal spread in the soil or of the different capacity for uptake by unit length of hyphae.
A technique using 15N-labelled inorganic fertilizer was applied to estimate N2 fixation by the forage legume Hedysarum coronarium L. and to ascertain the role of vesicular-arbuscular (VA) mycorrhizas in plant N nutrition throughout a growing season under field conditions. The absence of the specific Rhizobium for the forage legume in the test soil allowed us the use of 15N methodology with the same legume as reference ‘non-fixing’ crop.
At the first harvest, mycorrhizal inoculation behaved similarly to the phosphate addition in improving the percentage (70 %) and the total amount of N derived from fixation. But thereafter, mycorrhizal inoculation not only enhanced dry matter yield, N concentration and total N yield but also the amount of N derived from soil and from fixation, as compared with either phosphate-added or control plants. This indicated that mycorrhizas acted both by a P-mediated mechanism to improve N2 fixation and by enhancing N uptake from soil. The latter agrees with recent findings by others that VA mycorrhizal hyphae can translocate and assimilate ammonium, a fact of physiological and ecological interest.
Celery (Apium graveolens L.) plants were grown in pots in which the root system was separated from the soil in a side chamber by a fine mesh screen. The side chamber was treated with either an organic (ground plant tissue) or inorganic [(NH4)2SO4] source of 15N. Mycorrhizal (Glomus mosseae) and control (non-mycorrhizal) plants were exposed to 15N over a period of 30 days (inorganic-15N) or 88 days (organic-16N). Mycorrhizal and control plants did not differ in shoot dry weight or shoot P content. Dry weight of root was reduced in the mycorrhiza treatments. Mycorrhizal plants derived significantly (P= 0.01) more 16N, from both N sources, than did control plants. In the inorganic-N treatment, 15N in mycorrhizal plants was significantly (P= 0.001) and positively correlated with percent mycorrhizal fungal colonization (r= 0.58), number of hyphal crossings (±10 μ diameter) through the mesh into the area of 15N placement (r= 0.76), total length of hyphae per gram of soil (r= 0.74), and length of hyphae of 5 μ diameter in the soil (r= 0.77). No correlations were found between the 16N content of mycorrhizal plants and any parameter in the organic-N treatment. The 16N content of control plants was not correlated with hyphal length in the outer chamber and there were no hyphal crossings of the size ( 10 μ diameter) which was counted for the mycorrhiza treatments. The presence of the organic matter (ground plant tissue) increased the total length of saprophytic hyphae per gram of soil but decreased the number of vesicular-arbuscular mycorrhizal fungal hyphae crossing into the area of 16N placement. The mean flux of N through the hyphae of G. mosseae was 7.42 × 10−8 mol N cm−2 s−1 for the inorganic-N treatment over a 30-day period, and 1.74 × 10−8 mol N cm−2 s−1 for the organic-N treatment over an 88-day period.
This paper examines the extent to which atmospheric CO2 enrichment may influence growth of plant roots and function in terms of uptake of water and nutrients, and carbon allocation towards symbionts. It is concluded that changes in dry matter allocation greatly depend on the experimental conditions during the experiment, the growth phase of the plant, and its morphological characteristics. Under non-limiting conditions of water and nutrients for growth, dry matter partitioning to the root is not changed by CO2 enrichment. The increase in root/shoot ratio, frequently observed under limiting conditions of water and/or nutrients, enables the plant to explore a greater soil volume, and hence acquire more water and nutrients. However, more data on changes in dry matter allocation within the root due to atmospheric CO2 are needed. It is concluded that nitrogen fixation is favored by CO2 enrichment since nodule mass is increased, concomitant with an increase in root length. The papers available so far on the influence of CO2 enrichment on mycorrhizal functioning suggest that carbon allocation to the roots might be increased, but also here more experiments are needed.
S ummary
Assessment of infection is an essential part of many studies involving VA mycorrhiza. A summary is given of the range of techniques that have been used. We calculated the standard error of four methods of assessment based on observations of stained root samples either randomly arranged in a petri dish or mounted on microscope slides. The methods are based on presence or absence of infection at root/grid intersect points, on a visual estimate of percentage cortex occupied by fungus or on estimates of length, or presence or absence of infection in root pieces mounted on slides. The number of replicate observations required for a given standard error % infection can be read from the curves provided. The advantages of the different methods of assessment are discussed and reasons given why they all probably overestimate the true values.
Forest tree biomass is hypothesized to increase in a CO2-enriched atmosphere if mechanisms exist to ensure acquisition of limiting nutrients in forest soils. Investment of additional photosynthate produced at elevated CO2 into mycorrhizal proliferation and root growth may provide one such mechanism. To test this hypothesis, mycorrhizal density and seedling biomass were measured in shortleaf pine (Pinusechinata Mill.) and white oak (Quercusalba L.) grown in unfertilized forest soil in controlled-environment chambers at 360 μL L−1 and 700 μL L−1 CO2. Mycorrhizal density was greater at elevated CO2 in both species after 6 weeks of exposure; in white oak, the increased density persisted for 24 weeks. Root dry weight was increased 76% in P. echinata and 91% in Q. alba at 700 μL L−1 CO2; total seedling dry weight was increased by 66 and 56%, respectively. It is hypothesized that increased photosynthesis at elevated CO2 offsets the carbon requirement for mycorrhizal establishment on shortleaf pine. Greater mycorrhizal density and enhanced 1st-year root growth in both species may facilitate future nutrient acquisition, supporting further biomass increases in an enriched CO2 atmosphere.
The aim of the present study was to investigate with the 15N natural abundance method if inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi affects the N2 fixation of legume trees grown under Ethiopian nursery conditions. A further aim was to test if VAM fungi influence the δ15N values of non-fixing plants.
Five different VAM inocula and/or phosphorus fertilizer were applied to the standard, non-sterile nursery soil in which seedlings
of four different Acacia species and Eucalyptus globulus were grown. After 3–5 months the acacia shoot dry weights and the fraction of the fine roots which were colonized by VAM
fungi was increased by four of the VAM inocula. However, inoculation did not influence the δ15N values of non-nodulated A. nilotica or E. globulus; i.e., roots with low and high VAM colonization did not differ in discrimination against 15N. With E. globulus used as a reference species grown under the same conditions and in the same time period as A. abyssinica, the N2 fixation of A. abyssinica accounted for 5.1 to 46.7% of the seedling N content, dependent on the soil treatment. Deep shade reduced the N2 fixation of A. abyssinica from 36.2 to 5.1%.
The lower δ15N values of most VAM inoculated, nodulated acacias indicate that N2 fixation was increased by those VAM fungi which also promoted shoot dry weight. However, VAM inoculation generally did not
affect shoot N concentrations or nodule dry weights, and the δ15N values were not correlated with shoot N concentrations. N2 fixation may not be important for the N nutrition and growth of seedlings in nutrient-rich nursery soils, but it is an important
seedling property after outplanting in N deficient field soils.
It has been suggested the increase in atmospheric COâ produced by the burning of fossil fuels will be to some extent counteracted by an increase in carbon fixation by photosynthesis. This hypothesis is based on the assumption that the rate of photosynthesis is limited chiefly by COâ concentration. The effects on photosynthesis and dry matter production by increased levels of COâ are examined here. (ACR)
Hyphal transport of nitrogen from a 15N-labelled ammonium source by a VA-mycorrhizal fungus was studied under controlled experimental conditions. Cucumis sativus L. cv. Aminex (F1 hybrid) was grown alone or together with Glomus intraradices Schenck and Smith in containers with a hyphal compartment separated from the rooting medium by a fine nylon mesh. Lateral movement of the applied 15N towards the roots was minimized by using a nitrification inhibitor (N-serve) and a hyphal buffer compartment. Recovery of 15N by mycorrhizal and non-mycorrhizal plants was 6 and 0%, respectively, after a labelling period of 23 days. The corresponding figures, without N-serve added, were 4 and 7%. A prolongation of the labelling period by 8 days (N-serve applied) resulted in an increase in the 15N recovery by mycorrhizal plants to 30% of the applied 15N. Non-mycorrhizal plants contained only traces of 15N. The external hyphae depleted the soil in the hyphal compartment efficiently for inorganic N. In contrast, hyphal compartments of control containers still contained considerable amounts of inorganic N. The 15N assimilated by the external hyphae in one hyphal compartment was not translocated in significant amounts to the external hyphae in another hyphal compartment. The possible implication of this for inter-plant N transfer by VA hyphal connections is discussed.
Seeds of Gliricidia sepium (Jacq.) Walp., a tree native to seasonal tropical forests of Central America, were inoculated with N-fixing Rhizobium bacteria and grown in growth chambers for 71 days to investigate interactive effects of atmospheric CO2 and plant N status on early seedling growth, nodulation, and N accretion. Seedlings were grown with CO2 partial pressures of 350 and 650 bar (current ambient and a predicted partial pressure of the mid-21st century) and with plus N or minus N nutrient solutions to control soil N status. Of particular interest was seedling response to CO2 when grown without available soil N, a condition in which seedlings initially experienced severe N deficiency because bacterial N-fixation was the sole source of N. Biomass of leaves, stems, and roots increased significantly with CO2 enrichment (by 32%, 15% and 26%, respectively) provided seedlings were supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO2 enrichment but there was little indication that photosynthate translocation from leaves to roots or that plant N (fixed by Rhizobium) was altered by elevated CO2. In seedlings supplied with soil N, elevated CO2 increased average nodule weight, total nodule weight per plant, and the amount of leaf nitrogen provided by N-fixation (as indicated by leaf 15N). While CO2 enrichment reduced the N concentration of some plant tissues, whole plant N accretion increased. Results support the contention that increasing atmospheric CO2 partial pressures will enhance productivity and N-fixing activity of N-fixing tree seedlings, but that the magnitude of early seedling response to CO2 will depend greatly on plant and soil nutrient status.
In order to better elucidate fixed-C partitioning, nutrient acquisition and water relations of prairie grasses under elevated
[CO2], we grew the C4 grass Bouteloua gracilis (H.B.K.) lag ex Steud. from seed in soil-packed, column-lysimeters in two growth chambers maintained at current ambient [CO2] (350 μL L−1) and twice enriched [CO2] (700 μL L−1). Once established, plants were deficit irrigated; growth chamber conditions were maintained at day/night temperatures of
25/16°C, relative humidities of 35%/90% and a 14-hour photoperiod to simulate summer conditions on the shortgrass steppe in
eastern Colorado. After 11 weeks of growth, plants grown under CO2 enrichment had produced 35% and 65% greater total and root biomass, respectively, and had twice the level of vesicular-arbuscular
mycorrhizal (VAM) infection (19.8% versus 10.8%) as plants grown under current ambient [CO2]. The CO2-enriched plants also exhibited greater leaf water potentials and higher plant water use efficiencies. Plant N uptake was
reduced by CO2 enrichment, while P uptake appeared little influenced by CO2 regime. Under the conditions of the experiment, CO2 enrichment increased root biomass and VAM infection via stimulated growth and adjustments in C partitioning below-ground.
Interactive effects of elevated atmospheric CO2 and phosphorus supply on mycorrhizal colonization rates were investigated using loblolly pine (Pinus taeda L.) seedlings from Florida and coastal North Carolina. Seedlings from both populations were grown in greenhouses maintained
at either 35.5 Pa or 71.0 Pa CO2. In both CO2 treatments, seedlings were grown in a full factorial experiment with or without mycorrhizal inoculum and with an adequate
or a limiting supply of phosphorus. Seedlings were harvested 60, 90 and 120 days after emergence and at each harvest root
subsamples were examined to determine the percent of fine roots that were mycorrhizal. Additionally, root carbohydrate and
nutrient levels were measured at each harvest. Root starch, sugar and total non-structural carbohydrate (TNC) concentrations
were increased by growth in elevated CO2 and decreased by mycorrhizal colonization. Phosphorus stress decreased root starch concentrations, increased root sugar concentrations
and did not significantly affect TNC concentrations. However, despite significant effects on root carbohydrate levels, there
were generally no significant treatment effects on mycorrhizal colonization. Additionally, at all harvests, root starch and
sugar concentrations were not correlated with percent of fine roots that were mycorrhizal. These results suggest that although
elevated CO2 may significantly increase root carbohydrate levels, the increases may not affect the percent of fine roots that are mycorrhizal.
Increasing concentrations of atmospheric CO2 could have dramatic effects upon terrestrial ecosystems including changes in ecosystem structure, nutrient cycling rates, net primary production, C source-sink relationships and successional patterns. All of these potential changes will be constrained to some degree by below ground processes and mediated by responses of soil biota to indirect effects of CO2 enrichment. A review of our current state of knowledge regarding responses of soil biota is presented, covering responses of mycorrhizae, N-fixing bacteria and actinomycetes, soil microbiota, plant pathogens, and soil fauna. Emphasis will be placed on consequences to biota of increasing C input through the rhizosphere and resulting feedbacks to above ground systems. Rising CO2 may also result in altered nutrient concentrations of plant litter, potentially changing decomposition rates through indirect effects upon decomposer communities. Thus, this review will also cover current information on decomposition of litter produced at elevated CO2.
Soil N availability may play an important role in regulating the long-term responses of plants to rising atmospheric CO2 partial pressure. To further examine the linkage between above- and belowground C and N cycles at elevated CO2, we grew clonally propagated cuttings of Populus grandidentata in the field at ambient and twice ambient CO2 in open bottom root boxes filled with organic matter poor native soil. Nitrogen was added to all root boxes at a rate equivalent
to net N mineralization in local dry oak forests. Nitrogen added during August was enriched with 15N to trace the flux of N within the plant-soil system. Above-and belowground growth, CO2 assimilation, and leaf N content were measured non-destructively over 142 d. After final destructive harvest, roots, stems,
and leaves were analyzed for total N and 15N.
There was no CO2 treatment effect on leaf area, root length, or net assimilation prior to the completion of N addition. Following the N addition,
leaf N content increased in both CO2 treatments, but net assimilation showed a sustained increase only in elevated CO2 grown plants. Root relative extension rate was greater at elevated CO2, both before and after the N addition. Although final root biomass was greater at elevated CO2, there was no CO2 effect on plant N uptake or allocation. While low soil N availability severely inhibited CO2 responses, high CO2 grown plants were more responsive to N. This differential behavior must be considered in light of the temporal and spatial
heterogeneity of soil resources, particularly N which often limits plant growth in temperate forests.
Large intact soil cores of nearly pure stands of Pascopyrum smithii (western wheatgrass, C3) and Bouteloua gracilis (blue grama, C4) were extracted from the Central Plains Experimental Range in northeastern Colorado, USA and transferred to controlled environment
chambers. Cores were exposed to a variety of water, temperature and CO2 regimes for a total of four annual growth cycles. Root subsamples were harvested after the completion of the second and fourth
growth cycles at a time corresponding to late winter, and were examined microscopically for the presence of mycorrhizae. After
two growth cycles in the growth chambers, 54% of the root length was colonized in P. smithii, compared to 35% in blue grama. Field control plants had significantly lower colonization. Elevation of CO2 increased mycorrhizal colonization in B. gracilis by 46% but had no effect in P. smithii. Temperatures 4° C higher than normal decreased colonization in P. smithii by 15%. Increased annual precipitation decreased colonization in both species. Simulated climate change conditions of elevated
CO2, elevated temperature and lowered precipitation decreased colonization in P. smithii but had less effect on B. gracilis. After four growth cycles in P. smithii, trends of treatments remained similar, but overall colonization rate decreased.
The legume Medicago sativa (alfalfa)(+Rhizobium meliloti) and Lolium perenne (ryegrass) were grown, in a greenhouse, either alone or together in a soil and supplied with increasing amounts of soluble phosphate (P) with or without a vesicular-arbuscular inoculum (VAM). A small amount of 15N-labelled ammonium sulphate was added to each pot to distinguish the sources of N in the plants.The more mycotrophic legume enhance VAM formation by the grass in the mixture at all rates of P additions. Regardless of the cropping system and the P concentration in soil VAM improved, in most cases, dry matter production and the competitive ability of the legume. In spite of that competition from ryegrass reduced alfalfa development with increasing P concentration in the soil. In general VAM increased nodulation and the concentrations of N and P in alfalfa. The 15N enrichment of plant shoots indicated that VAM improved N2-fixation in alfalfa at all rates of P. In mixed cropping, alfalfa derived almost all its N from fixation, but the total amount fixed was decreased by competition from ryegrass in the same pot. The apparent soil N pool size (A-value) for the grass growing alone was significantly higher in mycorrhizal pots and VAM actually increased the total amount of N that the grass derived from soil, supporting a role of VAM in N-uptake. In mixed cropping the various interactions acting on N nutrition of the grass probably mask observations of the actual mechanisms involved, but there was clear isotopic evidence of N-transfer from the legume to the grass in non-mycorrhizal, P-supplemented plants. Apparently VAM enhanced N-transfer in one out of four cases.
The effects of elevated CO2 and N fertilization on fine root growth of Pinus ponderosa Dougl. ex P. Laws. C. Laws., grown in native soil in open-top field-exposure chambers at Placerville, CA, were monitored for a 2-year period using minirhizotrons. The experimental design was a replicated 3 × 3 factorial with a treatment missing; plants were exposed to ambient (≈ 365 μmol mol−1) air or ambient air plus either 175 or 350 μmol mol−1 CO2 and three levels of N addition (0, 100 and 200 kg ha−1 year−1). By the second year, elevated CO2 increased fine root occurrence and root length while N fertilization had no effect. The CO2 × N interactions were not significant. Neither elevated CO2 nor N fertilization altered fine root diameter. Fine root mortality was increased by increasing soil N but was reduced in elevated CO2. Highest fine root mortality occurred during summer and was lowest during winter. Elevated CO2 increased mycorrhizal and fungal occurrence earlier than N fertilization.
Net CO2-uptake of sets of clover plants (Trifolium subterraneum L.) was measured over 3 weeks in ambient air and in a highly CO2-enriched atmosphere (400 Pa CO2). Phosphate (P) in the nutrient solution was varied between 0·05 mol m−3 P (reduced P) and 2·0 mol m−3 P (high P). In ambient air, the daily increments of the daily rate of net CO2-uptake (DICU; a parameter related to relative growth) were higher at reduced P than at high P. Stimulation by high CO2 of net CO2-uptake in the first day was less at reduced P than at high P. In the following days, high CO2 markedly inhibited DICU at reduced P, and thus growthstimulation by high CO2 ceased after between 4 and 12 d. By contrast, at high P, DICU increased more than 2-fold upon CO2-enrichment, and thus growth stimulation by high CO2 was maintained. Intermediate results were obtained with half-strength Hoagland's solution (0·5 mol m−3 P).
Leaf pools of inorganic ortho P, soluble esterified P, and total P declined markedly in high CO2 when P-nutrition had been reduced. Considerable decline also occurred in high CO2 when P-nutrition had been increased suggesting that P-uptake was not well tuned with net CO2-uptake (growth).
It is proposed that high CO2 can perturb the P-metabolism of clover, the impairment being less at high levels of P-nutrition. With regard to high CO2 as a growth stimulus, these results demonstrate that increasing P-nutrition to a level supraoptimal in ambient air can considerably
improve the growth of a C3-plant in high CO2.
The objective of this study was to determine whether the supply of current photosynthate was limiting root nodule activity. Both short-term (36 hours) and long-term (16 days) periods of CO(2) enrichment were imposed on vegetative, growth chamber-grown soybean plants (Glycine max. [L.] Merr. cv. ;Clay') to increase the supply of current photosynthate and to observe the effects on photosynthate partitioning in the plants, plant growth, and root nodule activity.Neither total nor specific nodule activities were increased during exposure to short-term (36 hours) CO(2) enrichment. Dry weight of the leaves increased after 12, 24, and 36 hours of CO(2) enrichment and dry weight of the stems plus petioles increased after 36 hours of CO(2) enrichment. Dry weights of the roots and nodules were not altered by short-term CO(2) enrichment. Short-term CO(2) enrichment increased the total nonstructural carbohydrates in the leaves and stems plus petioles, but not in the roots and nodules. Analyses of the separate pools of carbohydrate reserves indicated that the majority of the additional carbohydrate provided by short-term CO(2) enrichment was stored as leaf starch with relatively little being partitioned to the roots and nodules.Long-term CO(2) enrichment (16 days) did not enhance specific nodule activity. Shoot, root, and nodule dry weights were increased 109, 34%, and 56% respectively. Total nodule activity per plant was significantly enhanced only after 16 days of treatment and was related to increased nodule mass. These results indicate that the increased total nodule activity in response to CO(2) enrichment is a consequence of a general growth response of the plant.Results of both studies indicate that nodule activity was not directly limited by current photosynthesis but rather by the partitioning and utilization of photosynthate in the plant.
Soybean (Glycine max [L.] Merr.) plants grown in pot cultures were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe and Rhizobium japonicum strain 61A118 at planting (G(1)R(1)) or at 20 days (G(20)R(20)), or with one of the endophytes after the other has colonized the host root (G(1)R(20), G(20)R(1)). Nodulated (PR(1)) and VAM (G(1)N) dipartite associations, or nonsymbiotic plants (PN) using nutrient solutions with N, P, or N + P concentrations providing endophyte-equivalent nutrient inputs were used as controls. The delayed tripartite associations received the appropriate N, P, or N + P amendment while one or both endophytes were absent during the first 20 days of growth. Prior inoculation with one endophyte significantly inhibited development of the other. Root hexose sugar concentrations were negatively correlated with VAM colonization (r = -0.89), nodule activity (r = -0.91), and root P content (r = -0.93). Nodule (r = 0.97) and root (r = 0.96) P content correlated positively with VAM colonization. Nodule weight or VAM-fungal biomass were significantly greater in associations grown with only one endophyte. Dry weights of the PN, G(1)N, PR(1), and G(20)R(20) plants were significantly greater than those of tripartite plants inoculated at planting with either or both endophytes. Interendophyte inhibition is attributed to competition for root carbohydrates, and this effect apparently also affects overall plant productivity. The objective of the study was to determine if the timing of endophyte introduction and establishment affected the development of the other symbiotic partners.
Soybean (Glycine max [L.] Merr. cv Hobbit) plants were grown in a growth chamber for 56 days in a phosphorus- and nitrogen-deficient soil and were colonized by the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd) Gerd. and Trappe and Rhizobium japonicum strain USDA 136, or by either organism alone, or by neither. Non-VAM plants received supplemental phosphorus and nonnodulated plants supplemental nitrogen to achieve the same rate of growth in all treatments. Plants of all four treatments had the same (P > 0.05) dry weights at harvest, but VAM plants had higher rates of CO(2) exchange (CER, P < 0.05) and lower leaf P concentrations (P < 0.01). Leaf nitrogen concentrations were lower in nodulated than in nitrogen-supplemented plants (P < 0.01) while starch concentrations were higher (P < 0.01). There was a significant negative relationship between nitrogen and starch (r = -0.989). Statistical evaluation of the data showed that some parameters (CER, leaf area and phosphorus content) were associated with phosphorus nutrition (or the presence of the VAM fungus), others (leaf fresh weight and root dry weight) with nitrogen nutrition (or the presence of Rhizobium), and some (leaf nitrogen and starch content) by both factors. The development of microsymbiont structures and nodule activity were significantly lower in the tripartite association than in plants colonized by one endophyte only. The findings suggest that endophyte effects go beyond those of simple nutrition and associated source-sink relationships.