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Arbuscular mycorrhizal fungi influence growth, osmotic adjustment and photosynthesis of citrus under well-watered and water stress conditions
Abstract
The influence of arbuscular mycorrhizal (AM) fungus Glomus versiforme on plant growth, osmotic adjustment and photosynthesis of tangerine (Citrus tangerine) were studied in potted culture under well-watered and water stress conditions. Seven-day-old seedlings of tangerine were transferred to pots containing Glomus versiforme or non-AMF. After 97 days, half of the seedlings were subject to water stress and the rest were well-watered for 80 days. AM colonization significantly stimulated plant growth and biomass regardless of water status. The soluble sugar of leaves and roots, the soluble starch of leaves, the total non-structural carbohydrates (NSC) of leaves and roots, and the Mg(2+) of leaves were higher in AM seedlings than those in corresponding non-AM seedlings. The levels of K(+) and Ca(2+) in leaves and roots were higher in AM seedlings than those in non-AM seedlings, but differences were only significant under water stress conditions. Moreover, AM colonization increased the distributed proportions of soluble sugar and NSC to roots. However, the proline was lower in AM seedlings compared with that in non-AM seedlings. AM seedlings had higher leaf water potential (Psi), transpiration rates (E), photosynthetic rates (Pn), stomatal conductance (g(s)), relative water content (RWC), and lower leaf temperature (Lt) than corresponding non-AM seedlings. This research also suggested that AM colonization improved the osmotic adjustment originating not from proline but from NSC, K(+), Ca(2+) and Mg(2+), resulting in the enhancement of drought tolerance.
... Mycorrhizae can be categorized into four types based on their morphology and the fungal and plant groups involved: ectomycorrhizae (ECM) and vesicular-arbuscular mycorrhizae (VAM), which are found in a wide diversity of plant taxa, and ericoid and orchid mycorrhizae, which are limited to members of Ericaceae and Orchidaceae, respectively [14,15]. Mycorrhizal associations provide multiple benefits to plants, including enhanced uptake of water and nutrients [10,16], and protection against both abiotic and biotic stresses, such as heavy metals [17][18][19], salinity [20,21], and soil pathogens [22,23]. They can also improve soil structure by contributing to the formation of long-lasting soil aggregates [10], and even increase plant root longevity [22]. ...
... Our third hypothesis, that there would be a significant correlation between mycorrhizal colonization percentage and plant growth rate, was based on the well-known benefits of mycorrhizae for plant growth in both containerized and natural settings [10,16,25,57]. However, there was no evidence to support this hypothesis over the six months of this study. ...
... Specifically, when the P level is sufficient, the contribution by mycorrhizal fungi gathering P for plants is insignificant, and growth responses to mycorrhizae are consequently more frequently reported under lower nutrients levels. For example, Wu and Xia [16] reported a significant positive effect of mycorrhizal colonization on plant growth and nutrient concentration in plant tissues in containerized citrus, with no fertilizer addition, while Sylvia et al. [61] reported no effect of mycorrhizal colonization on plant growth in 26 tree species when fertilizer was added, and Corkidi et al. [62] reported the same result in corn. Positive plant physiological and growth responses to mycorrhizal colonization are also more often reported under water deficit than well-watered conditions [63]. ...
Compost tea is a liquid organic amendment that has been reported to benefit plant growth and performance through positive effects on microbial communities and plant nutrition. However, few studies have demonstrated this for containerized plants produced in tree nurseries. Five common urban tree species (Acer negundo, Corymbia maculata, Ficus platypoda, Hymenosporum flavum, Jacaranda mimosifolia) were grown in a containerized experiment to investigate the effects of compost tea application on tree growth and root mycorrhizal colonization over six months. The microbial composition of compost tea was also determined with 16S (bacteria) and ITS1 (fungi) metabarcoding. No significant positive effect of compost tea on plant growth or root mycorrhizal colonization was observed. Roots of all tree species were colonized by one type of mycorrhizal fungi, ectomycorrhizae (ECM), or vesicular–arbuscular mycorrhizae (VAM). However, no relationship between the mycorrhizal colonization percentage and plant growth was detected. Thus, there was no evidence that a once-off application of compost tea had benefits for mycorrhizal colonization and growth of containerized trees in a nursery setting. Further research is needed to investigate whether any benefit from compost tea is evident once containerized trees are planted into urban landscapes where growth conditions may be more challenging.
... Most of the drought-resistant plants have shown deeper root penetration, heavier roots, and numerous primary and secondary roots, which indicate a greater rhizosphere volume that can hold a higher microbial population enduring drought tolerance. The ratio of root/shoot increases under drought conditions as roots are less vulnerable to water deficiency than shoots (Wu & Xia, 2006). Extracellular polys accha rides -prod ucing microbes can be exploited to increase the drought tolerance capacity of plants by increasing their population density in the rhizospheric zone of plants. ...
... Higher soil acid phosphatase activities in the mycorrhizosphere were also observed to be positively correlated to soil water content. Thus, an increase in soil acid phosphatase activity due to mycorrhiza partially alleviates plant drought stress in plants (Wu et al., 2006). Arbuscular mycorrhiza symbiosis increases the units of photosynthesis, increasing the rates of photosynthetic storage and export in the plants. ...
Drought and water stress are the major abiotic stresses that limit plant growth. Plant growth-promoting rhizobacteria, well known for their growth-promoting attributes, produce extracellular polysaccharides that form rhizosheath around the roots, thereby protecting them from desiccation for a longer duration. Arbuscular mycorrhizae, one of the key determinants of soil quality, secrete glomalin protein, which shows soil aggregation properties and helps in increasing water stability, thereby overcoming drought conditions. Increasing extracellular polys accharide-producing plant growth-promoting rhizobacteria and mycorrhizal fungi density in the rhizospheric soil can be a means to improve the survival of plants during water stress periods. The present review highlights the role of microbes producing extracellular polysaccharides in the maintenance of soil health and plant growth under drought.
... Research has shown that arbuscular mycorrhizal fungi (AMF) are ubiquitous soil microorganisms capable of forming symbiotic relationships with approximately 80% of terrestrial plant species, facilitating nutrient transport to plants (Smith and Read 2008). In addition, AMF can improve the plant-water relationship (Augé 2001) by enhancing plant nutrition, bolstering resistance to drought stress (Wu and Xia 2006), enhancing osmotic regulation in host plants (Zulfiqar et al. 2020), regulating root hydraulic conductivity to aid water absorption (Sánchez-Romera et al. 2016;Bitterlich et al. 2018a, b), and improving soil structure, aggregate stability, and water retention (Wu et al. 2008;Querejeta 2017;Marcacci et al. 2022;Pauwels et al. 2023). In addition, arbuscular mycorrhizal fungi can enhance plant water use efficiency (WUE i ) and transpiration accumulation (Querejeta et al. 2006, as well as redistribute water through common mycorrhizal networks connecting neighboring plant root systems (Egerton-Warburton et al. 2007. ...
... The remaining portion of the AM plant's daily additional transpiration is likely provided by AMF through various indirect mechanisms. These mechanisms include enhancing the development of plant roots, improving the osmotic regulation capability of the host plant, and regulating the water conductivity of the host plant roots to aid in water absorption by the roots (Wu and Xia 2006;Zulfiqar et al. 2020;Sánchez-Romera et al. 2016). It is important to note that the relative contributions of these direct and indirect mechanisms to the total plant transpiration may vary depending factors, such as the plant species in symbiosis with AM, environmental conditions, and the specific AMF species involved (Kakouridis et al. 2022). ...
Aims
Arbuscular mycorrhizal fungi (AMF) play a crucial role in enhancing plant resistance to drought stress by improving the plant-water relationship. However, the precise mechanism of AMF-mediated water transport to host plant roots remains elusive.
Methods
In a compartmentalized experiment comprising both plant and non-plant compartments, we employed heavy-oxygen water (¹⁸O-labeled) to directly trace and quantify the transport of water by AMF hyphae to alfalfa under the condition of high soil moisture (70% of the maximum field water holding capacity) and low soil moisture (40% of the maximum field water holding capacity).
Results
Our findings revealed that irrespective of soil moisture levels, hyphae entering the ¹⁸O-labeled compartment (AM treatment) significantly enriched ¹⁸O in alfalfa transpiration water compared to no hyphae entering the ¹⁸O-labeled compartment (NM treatment). We calculated the direct water transport by AMF using a standard isotope mixing model, demonstrating that in high and low- moisture soil substrates, AM fungi contributed 12.32% and 17.03% of the total transpiration water, respectively.
Conclusions
These results highlight that the direct transport of water from AMF hyphae to horticulture plants should not be underestimated in comparison to plant transpiration demand. Moreover, the water contribution of AM fungal hyphae to host plants is more significant in arid soil, especially in dry soil substrate. This underscores the critical role of mycelial water transport in supporting plant survival under water-limiting conditions.
... As AMF are the completely symbiotic fungi, and their growth and development depend on the photosynthetic products of the host plant [57], higher chlorophyll concentrations in +AM plants would help the host to enhance photosynthesis. The results of this study showed that, at the end of the experiment, chlorophyll a, chlorophyll b, and total chlorophyll concentrations were significantly higher in +AM than in non-AM seedlings, irrespective of AM species (Figure 6), which is consistent with previous results found for citrus plants [41,58]. However, although plant growth of the seedlings was greater with Ri (Table 2), no differences between Fm and Ri were found, and both fungi presented similar chlorophyll a, chlorophyll b, and total chlorophyll concentrations. ...
... Several studies have shown that mycorrhizal citrus seedlings present higher root hydraulic conductivity, stomatal conductance, and transpiration rates than non-mycorrhizal seedlings [45,48,58]. Due to their greater stomatal openness, and, therefore, due to their higher transpiration rates, mycorrhizal plants show higher levels of water uptake through their roots and are able to lower the water potential of the soil in pots more than nonmycorrhizal plants [48]. ...
In addressing the agricultural challenges posed by climate change, the use of biofertilizers, derived from living organisms, promotes environmentally friendly crop cultivation, and represents an adaptive strategy for sustainable agriculture in the face of climate uncertainty. Careful selection of the arbuscular mycorrhizal fungus (AMF) would represent a crucial step in mycorrhizal inoculation, considering the varying levels of compatibility between the AMF and the host plant. This study aimed to assess the impact of two AMF species that are prevalent in citrus soils of south-eastern Spain (Rhizophagus irregularis and Funneliformis mosseae) on the Citrus aurantium seedlings’ behavior. Sour-orange plants showed a high mycorrhizal dependence regardless of the specific AMF species. Both R. irregularis and F. mosseae fungi exhibited high colonization percentages, with R. irregularis outperforming F. mosseae in root colonization. Inoculation with both AMF yielded notable growth improvements, but R. irregularis exhibited higher positive effects in the long term. The heightened P nutrition and increased chlorophyll concentration significantly enhanced the performance of AMF-inoculated plants. With F. mosseae, plants showed more pronounced improvements in P nutrition and a stronger correlation of their dry mass with P concentration; however, in general, inoculation with R. irregularis produced a higher sour-orange-plant performance. Both R. irregularis and F. mosseae fungi produced strong positive effects in sour-orange growth, which positioned them as viable biofertilizer options. These results can contribute to enhancing understanding for the development of an improved design of biofertilizers used in regions that are vulnerable to climate change, such as south-eastern Spain. This promotes a shift towards more sustainable and environmentally friendly agricultural practices by reducing dependence on chemical fertilizers.
... It was due to AMF's important role in plant growth, which allowed for more efficient water and nutrient absorption through the hyphal network (Shi et al. 2016;Guo et al. 2020). Wu and Xia 2006;Fidelibus et al. 2001;Dell' Amico et al. 2002;Wu et al. 2008;Asrar and Elhindi 2011;Shi et al. 2016) all confirmed the findings of this study. Furthermore, as Shi et al. (2016) reported that increased biomass by mycorrhization could greatly increase the absorption surface and thus nutrient uptake capacity under FW conditions. ...
... Drought stress [FW] increased leaf temperature in AMF− plants significantly, whereas the same attribute decreased with AMF inoculation in all species except T. arjuna under WW conditions, which could be due to high leaf water potential FW conditions due to AM symbiosis, as [36], have suggested. External hyphal extraction of soil water, stomatal regulation through hormonal signals (Aroca et al. 2008), more significant osmotic adjustment (Wu and Xia 2006), and higher hydraulic conductivity (Caitlyn et al. 2023) may all contribute to mycorrhizal plants' better water status. Furthermore, (Campo et al. 2020) demonstrated that plants accumulate a high concentration of low molecular mass organic solutes such as soluble sugars, proline, and other amino acids to regulate cell osmotic potential, aiming to improve water absorption under drought stress by maintaining a favorable gradient for water entry into the roots (Abbaspour et al. 2012). ...
Background
Entisol is a very poor, compact, and low-water-holding capacity soil. They are obstacles to the plant's root system's penetration and the availability of water, particularly in dry months. However, Arbuscular mycorrhizae fungi (AMF) is used for seedling growth and reduces water stress in the plant.
Results
In this experiment, the growth parameters and the physiological activities of the plant were changed for the well watering (WW), fractionated watering (FW), and stopped/no watering conditions of the T. arjuna seedling. This experiment demonstrated higher mycorrhizal dependency (24.90%) under the FW condition than that of the WW condition (18.58%). Also the root colonization was higher (67%) under FW plants compared to WW plants (53%) associated with AMF+ in T. arjuna seedling. Photosynthesis was found 24.27% more with FW than the WW condition. Experiment' shows posivitivecorrelation between the photosynthesis and interval of no watering for AMF− plants (r2 = 0.873 for AMF− (control) and comparatively very weak for plants with AMF+ (r2 = 0.259 for AMF+ plants).
Conclusions
The findings confirms the use of AMF in entisol soil to improve plant growth and biomass by reducing edaphic stress.
... Furthermore, there are indications that the increased water-use efficiency in plants during their symbiotic interaction with fungi could offer a distinct approach to impart drought tolerance (Rodriguez et al., 2008). This is achieved through processes like osmotic adjustment and regulation of stomatal function (Wu et al., 2006). ...
An investigation was conducted into how the beneficial fungal root endophyte Piriformosopra indica impacts the growth and physio-biochemical attributes of two watermelon varieties, Sugarbaby and Thar Manak under varying water conditions: well-watered (75% field capacity) and water-stressed (35% field capacity). Piriformosopra indica has stimulated vegetative growth in both varieties of watermelon irrespective of the water treatments. A significantly higher root length of 31.33 cm was observed in P. indica colonized Thar Manak at 35% field capacity. Piriformosopra indica colonization helped in mitigating the increase in leaf temperature and decline in leaf gas exchange parameters, leaf pigment concentration, and relative water content induced by water stress. During water stress, the highest proline content was observed in colonized seedlings of Sugarbaby (119.46 μg g−1 fresh weight) and lowest in non-colonized Sugarbaby seedlings (60.44 μg g−1 fresh weight). Diphenyl picrylhydrazyl free radical scavenging activity and catalase activity were enhanced due to pre-treatment with P. indica. The highest free radical scavenging activity of 60.30% was observed in P. indica colonized Thar Manak at 35% field capacity and the lowest in non-colonized Thar Manak at 75% field capacity (21.79%). Accumulation of harmful reactive oxygen species like H2O2 was lower in P. indica colonized seedlings when compared with the non-colonized ones during water stress. Although both varieties benefited due to colonization, the influence of P. indica was more pronounced in the susceptible variety, Sugarbaby.
... Klironomos et al. (2001),Wu and Xia (2006),Kennedy and Peay (2007),Erlandson et al. (2021),Lenoir et al. (2016),Huang et al. (2011, andGholamhoseini et al. (2013) SalinityDecrease spore germination and production, hyphae elongation, AMF colonization, and diversityJahromi et al. (2008), Wilde et al. (2009), and Estrada et al. (2013) Chilling Inhibit the arbuscular mycorrhizal colonization Baon et al. (1994), Klironomos et al. (2001), Liu et al. (2004), Abdel Latef and Chaoxing (2011), and Pasbani et al. (2020) Heat Decrease hyphal elongation, spores, and colonization Zhu et al. (2011), Lenoir et al. (2016), and Mathur et al. (2021) Nitrogen High soil N reduces spore density, AMF richness, diversity, and AM fungal community composition Averill et al. (2018), Jiang et al. (2018), Han et al. (2020), and Lu et al. (2021) Phosphorus High P soils reduce the spores production and colonization, and alter AMF diversity Qin et al. (2020), Trejo et al. (2020), and El-Sherbeny et al. al. (2010), Karimi et al. (2011), and Lenoir et al. (2016) Water logging Inhibit mycorrhizal colonization Wang et al. (2011, 2016), Wu et al. (2013), Zhouying et al. (2016), and Solís-Rodríguez et al.(2020)AM, Arbuscular mycorrhizal; AMF, arbuscular mycorrhizal fungi. ...
Mycorrhizal symbioses assist plants in responding to environmental stimuli, typically boosting the symbiotic system's ability to tolerate environmental stresses. However, the continuous signal exchange between the two symbionts is necessary for the development of mycorrhizal association because it causes coordinated differentiation in both partners and permits their contact within the root cells. In addition to controlling mycorrhizal symbioses, phytohormones are key regulators of plant immunity and development, and play a key role in coordinating plants' reactions to their ever-changing environment. Conversely, phytohormones and environmental signals are known to play a crucial role in regulating this symbiosis. The crosstalk between phytohormones and environmental signals is complex and can vary depending on the specific plant-fungus interaction. Similarly, the effects of environmental signals on mycorrhizal symbiosis can vary depending on the plant species, the type of mycorrhizal fungus, and other factors. Furthermore, promising developments in the regulation of phytohormone signaling at the molecular level are revealing the mechanistic details about how plants respond to environmental ques and mycorrhizal activity. In this chapter, we discussed how these mechanisms allow the symbiosis to be adjusted to the continuously changing environment.
... Arbuscular mycorrhizal fungi (AMF) within both the rhizosphere and the mycorhizosphere influence crop physiology in several ways to promote the absorption and utilization of soil water by crops (Hart et al., 2003), including processes associated with the uptake of nutrients and water (Begum et al., 2019) and tolerance towards environmental stress (Chandrasekaran, 2022;Rillig and Steinberg, 2002;Wu and Xia, 2006). AMF inoculation could significantly enhance the WUE of plants under drought stress (Hoang et al., 2022;Wu et al., 2021), and improve the drought resistance and post-drought recovery ability of AMF plants (Li et al., 2023). ...
In a rainfed agroecosystem with limited water resources, the symbiotic interactions between crop-arbuscular mycorrhizal fungi may have a significant impact on field productivity and water absorption and utilization. However, the interaction between AMF characteristics of root endophyte and rhizosphere soil and water use patterns of summer maize has not been studied under ridge-furrow with film mulching planting patterns (RFPM) in dry farmland. Based on a field experiment, we aimed to reveal the effects of different RFPM planting patterns (i.e., ridge/furrow ratio of 40:70 cm (RF40:70), ridge/furrow ratio of 55:55 cm (RF55:55), and ridge/furrow ratio of 70:40 cm (RF70:40)) on the root water use patterns of summer maize, the distribution characteristics of AMF in root endophyte and rhizosphere soil, and their interaction relationship by using the water isotope (δD and δ 18 O) tracer technique, the high-throughput sequencing technology, MixSIAR model, and the structural equation models. As a result, compared to flat planting without mulching (FP), RF40:70, RF55:55, and RF70:40 significantly increased grain yield by 29.74%, 35.24%, and 45.53%, and water use efficiency by 23.13%, 35.99%, and 50.25%, across the two growing seasons, respectively (P < 0.05). The root characteristic parameters of summer maize decreased with the increase in soil depth, and were mainly distributed in the shallow layer (0-20 cm) and middle layer (20-60 cm). Compared with FP, the distribution ratio of root surface area density, root length density, and root dry weight density in shallow soil layer was significantly increased by 5.03%, 7.46%, and 9.70% averaging the different RFPM treatments, respectively (P<0.05). Besides, compared to FP, the AMF abundance and diversity in rhizosphere soil and root endogenous averaged RFPM treatments increased by 32.32% and 29.66% and 5.88% and 28.43% respectively, in which the abundance and diversity gradually increased with the increase of the ratio of ridge-furrow. The PLS-PM results found that the larger ridge-furrow ratio could significantly increase the yield and WUE of summer maize mainly by increasing the root surface area density, root length density, and the abundance and diversity of AMF in the root endophyte and rhizosphere soil, which increased the water use of the middle and deep layer soils. In summary, the large ridge-furrow ratio can significantly increase the yield and WUE of summer maize by extending the hyphal network of maize root symbiotic AMF, which increases the water uptake of middle and deep layer soil.
... Mycorrhizal symbiosis may improve plant nutrition, and AMF can enhance the uptake of mineral nutrients by the host through their extensive extraradical mycelium network, especially for N and P (Ortiz et al. 2015;Zhao et al. 2015). Therefore, they can increase Gs, Pn, leaf chlorophyll content and photosynthetic efficiency, which has been generally regarded as an important mechanism of salt tolerance (Auge et al. 2007;Wu and Xia 2006). AMF facilitates biological nitrogen fixation through symbiosis with diazotrophs and boosts the bioavailability of micronutrients, including phosphorus (Hodge and Storer 2015;Yu et al. 2021). ...
Arbuscular mycorrhizal fungi (AMF) enhance plant tolerance to abiotic stresses like salinity and improve crop yield. However, their effects are variable, and the underlying cause of such variation remains largely unknown. This study aimed to assess how drought modified the effect of AMF on plant resistance to high calcium-saline stress. A pot experiment was performed to examine how AMF inoculation affects the growth, photosynthetic activity, nutrient uptake and carbon (C), nitrogen (N) and phosphorus (P) stoichiometric ratio (C:N:P) of maize under high calcium stress and contrasting water conditions. The results showed that high calcium stress significantly reduced mycorrhizal colonization, biomass accumulation, C assimilation rate and C:N stoichiometric ratio in plant tissues. Besides, the adverse effects of calcium stress on photosynthesis were exacerbated under drought. AMF inoculation profoundly alleviated such reductions under drought and saline stress. However, it barely affected maize performance when subjected to calcium stress under well-watered conditions. Moreover, watering changed AMF impact on nutrient allocation in plant tissues. Under well-watered conditions, AMF stimulated P accumulation in roots and plant growth, but did not induce leaf P accumulation proportional to C and N, resulting in increased leaf C:P and N:P ratios under high calcium stress. In contrast, AMF decreased N content and the N:P ratio in leaves under drought. Overall, AMF inoculation improved maize resistance to calcium-salt stress through enhanced photosynthesis and modulation of nutrient stoichiometry, particularly under water deficit conditions. These results highlighted the regulatory role of AMF in carbon assimilation and nutrient homeostasis under compound stresses, and provide significant guidance on the improvement of crop yield in saline and arid regions.
... These compounds are valued from the human health perspective as well as provide tolerance to the plants against various biotic and abiotic stresses [20]. Moreover, the PGPF also play a significant role in enhancing the production of several enzymes [21], stimulating the photosynthesis process [22], and improving the fertility of the soil [23]. According to Streletskii et al. [24], fungi produce plant hormones, and these hormones regulate the development of plants by activating signaling pathways throughout the biotic and/or abiotic stresses. ...
... Root symbionts have the potential to alter fPAR, aRUE and tRUE, but there is only indirect evidence of their effect on fPAR through changes in the canopy's structural variables that define the leaf area index (LAI). Nil and positive effects of both AMF and rhizobia have been reported on plant density, number of leaves per plant, and leaf area (Seneviratne et al. 2000;Estrada-Luna and Davies 2003;Elnesairy et al. 2005;Wu and Xia 2006;Zhang et al. 2012;Askari et al. 2016;Mathur et al. 2018;Ibiang and Sakamoto 2018). In particular, increases in specific leaf area (cm 2 leaf/g leaf) have been reported (Pereira et al. 2019), which allow an increase in LAI with a lower carbon (C) investment. ...
Context Root symbionts affect forage production by influencing host plant growth, but their specific effects on canopy intercepted photosynthetically active radiation (IPAR) and its conversion to plant biomass have not been investigated. Aims We evaluated the extent to which changes in plant biomass resulting from arbuscular mycorrhizal fungi (AMF) and rhizobia can be explained by alterations in IPAR and aboveground and total radiation-use efficiency (RUE: the ratio between shoot or total biomass and IPAR). Methods Under controlled greenhouse conditions, we evaluated single and dual inoculation effects of AMF and rhizobia on the forage legume white clover (Trifolium repens L.). Experimental units comprised canopies created in trays (50 cm by 34 cm by 13 cm deep). Key results On average, AMF inoculation increased IPAR by 43%, owing to greater leaf area and density, and decreased total RUE by 30%. Aboveground RUE was lower in AMF-inoculated plants without rhizobial inoculation, despite their higher leaf phosphorus status and greenness during the vegetative and reproductive stages, respectively. Rhizobial inoculation reduced the negative effect of AMF inoculation on aboveground RUE. Conclusions Both AMF and rhizobia alter white clover structure and function at canopy level. These variations may not be detected if the analysis considers only the impact of root symbionts on plant biomass. Implications These findings offer valuable insights into the intricate interactions between root symbionts and canopy-level processes, providing a basis for further research at agricultural scale.
... Cam quýt khá nhạy cảm với tình trạng thiếu nước (Aparicio-Durán et al., 2021). Ở những vùng khô hạn và bán khô hạn, "stress" về nước đã hạn chế năng suất cây trồng, thiếu nước ở cam quýt làm giảm sinh trưởng và năng suất, làm giảm kích thước trái đôi khi là chất lượng trái dẫn đến thiệt hại kinh tế (Wu & Xia, 2006;Manner et al., 2006;Rodríguez-Gamir et al., 2010).Vì vậy, đã có một số nghiên cứu về giống cam quýt chịu hạn: theo García-Sánchez et al. (2007) đã chứng minh rằng Cleopatra (Citrus resnhi Hort. ex Tanaka chịu hạn cao hơn Carrizo citrange (Citrus sinensis (L.) Osb. ...
Nghiên cứu được thực hiện nhằm xác định khả năng chống chịu hạn của cam đường. Thực hiện từ 10/2022-12/2022 trong nhà màng với nhiệt độ và ẩm độ không khí trung bình tương ứng là 33,8oC và 64,9%. Thí nghiệm bố trí hoàn toàn ngẫu nhiên, thừa số 2 nhân tố là môi trường (không và có xử lý hạn) và giống cam (đường, ba lá và mật), thí nghiệm có 30 lặp lại, 1 lặp lại là 1 cây/chậu. Kết quả cho thấy: cây cam đường duy trì màu sắc lá (ΔE*ab) sau 25 ngày xử lý hạn. Điều kiện hạn có ảnh hưởng ít đến chỉ số diệp lục tố của cam đường. Hàm lượng proline trong lá cũng như khả năng tích lũy proline trong điều kiện hạn của cây cam đường rất thấp, cho thấy cam đường ít nhạy cảm với hạn. Cây cam đường có biểu hiện héo sau 23,8 ngày xử lý hạn và tỷ lệ cây chết (thân lá khô) sau 30 ngày xử lý hạn thấp (30%) khi ẩm độ cát còn 1,53%. Cây cam đường có sự sinh trưởng tương đương với điều kiện không xử lý hạn và có bộ rễ phát triển tốt. Sinh khối của cây cam đường cao hơn so với các giống trong cùng điều kiện hạn. Do đó, cây cam đường có khả năng chống chịu tốt với điều kiện hạn.
... This is because M. sinensis can tolerate a wide range of environmental stresses due to the trait of C 4 photosynthesis, leading to high productivity and a low nutrient requirement (Stewart et al., 2009). Apart from Miscanthus traits that adapt to the volcanic soil, the root-associated fungal communities are widely reported to benefit the growth of host plants and promote their adaptation to stress, such as aridity (Wu and Xia, 2006), salinity (Porcel et al., 2012), and oligotrophic conditions (Jeewani et al., 2021). A better understanding of plant-microbe interactions, therefore, can help improve our understanding of vegetation recovery and plant growth promotion including in agricultural application scenarios. ...
Growth of the pioneer grass Miscanthus condensatus, one of the first vegetation types to be established on volcanic deposits, is promoted by root-associated fungi, particularly dark septate endophytes (DSEs). Fungal taxa within DSEs colonize the root of Miscanthus condensatus in oligotrophic Andosol, and their function in plant growth promotion remains largely unknown. We, therefore, comprehensively assessed the composition of the DSE community associated with Miscanthus condensatus root in volcanic ecosystems using the approaches of both metabarcoding (next-generation sequencing) and isolation (culturing). Also, the promotion effects of DSEs on plant growth (rice as a proxy) were evaluated by inoculation of core isolates to rice roots. Here, we found the following: (i) 70 % of culturable fungi that colonized Miscanthus condensatus phylogenetically belonged to DSEs; (ii) seven orders were identified by both sequencing and culturing methods; and (iii) inoculation of DSE isolates (Phialocephala fortinii, P. helvetica, and Phialocephala sp.) validated their effects on rice growth, particularly under an extremely low pH condition (compared to the control without inoculation, rice biomass was enhanced 7.6-fold after inoculation of P. fortinii). This study helps improve our understanding of the community of Miscanthus condensatus-associated DSE fungi and their functions in promoting plant growth.
... Seedlings of date palm roots that AMF had colonized have been shown to have a higher ability to tolerate salt stress [96,97]. When water stress is applied to the host plant, the mycorrhizal symbiosis decreases [98][99][100]. This is also true for date palms, where the percentage of AMF colonization in roots was higher under optimal irrigation than when plants were subjected to water drought [101]. ...
... The root system was strongly stimulated, which resulted in a remarkable balance between the root system and the vegetative parts, as the Mycorrhizal fungus G.mosseae increased the readiness of nutrients and the absorption of water and nutrients necessary for growth due to its release of Siderophores compounds, which are produced in iron deficiency conditions by the Mycorrhizal fungus. It works to improve the growth of the plant through its ability to search for iron in the environment in which the roots of the plant grow, as well as its work on the readiness of the elements in the area near the root cells 17,53 , which was positively reflected in improving growth and increasing biomass production sweet-scented geranium plant and its leaf content of nutrients 28 , in addition to the fact that plants treated with mycorrhizal fungal inoculum recorded an increase in the rate of photosynthesis 65 . This was reflected in the increase in the number of leaves in this study (Table 4), which was at the expense of the average area of one leaf in the plant whose roots were not treated with the Mycorrhizal vaccine M1 ( Table 5). ...
The experiment was carried out in one of the fields of Research Station B in the College of Agricultural Engineering Sciences / University of Baghdad - Al-Jadiriya on the fragrant plant for the spring season 2021 in order to study the effect of harvest date, mycorrhiza, bio-stimulants and the interaction among them on some characteristics of vegetative growth and the essential oil yield of sweet-scented geranium plants. The experiment used a randomized complete block design (RCBD) with a split-plot design with three replications. The experiment included three factors, as the factor of harvest dates represents the main panels with two harvest dates, which are 60 and 90 after planting and symbolized by H1 and H2. In contrast, the secondary panels include the treatment of the mycorrhizal fungal vaccine by two treatments, namely, not adding the mycorrhizal fungal vaccine to the root system and adding it with symbols M1 and M2 As for the sub-secondary panels, the treatments include four stimulating factors: the measurement treatment and the spraying of the vegetative mass with the amino acid phenylalanine at a concentration of 300 mg l ̄¹. The treatment of spraying the foliage with moringa leaf extract at a concentration of 10 gm L ̄¹ and the treatment of spraying the foliage with licorice root powder extract at a concentration of 10gm L ̄¹symbolized by B1, B2, B3, and B4 respectively. The results showed the superiority of the H2 treatment in most indicators of vegetative growth, as well as the increase in the percentages of each of the nutrients and volatile oil in the dried leaves and the volatile oil yield in the dried leaves. Treatment M2 significantly increased all vegetative growth characteristics as well as the percentages of nutrients and volatile oil in dried leaves and volatile oil yield in dried leaves. In contrast, treatment B3 showed an increase in the number of main branches, total number of leaves, total leaf area, fresh and dry weight of leaf yield in the plant and the content of The dried leaves of total chlorophyll as well as the percentages of nutrients and volatile oil in the dried leaves of the plant and the yield of volatile oil in the dried leaves. In contrast, treatment B2 had a significant effect in increasing the plant height rate, the number of main branches and the fresh weight of the leaves. It is one of the most prominent triple interaction treatments recorded. The largest increase in all the traits studied above is the triple interaction H2M2B3 treatment, which was characterized by an Bionatura http://dx.doi.org/10.21931/RB/CSS/2023.08.04.69 2 increase in most vegetative growth characteristics, especially the wet and dry weight of leaves and the percentages of nutrients as well as the percentage of volatile oil and volatile oil yield in the leaves. The triple interaction treatment H2M2B4 was also characterized by its recording of Remarkable superiority in both plant height and leaf content of Total chlorophyll and potassium percentage. Keywords: Sweet-scented geranium plant, Harvest date, Mycorrhizae, Biostimulants, vegetative growth, volatile oil.
... Various mechanisms can be responsible for such an effect. AMF can increase osmotic adjustment in plants exposed to drought [67,68]. Through opposite effects on plant Ψ and turgor, osmotic adjustment can prolong water uptake and photosynthesis as the soil dries out [69]. ...
The establishment of Artemisia tridentata, a keystone species of the sagebrush steppe, is often limited by summer drought. Symbioses with arbuscular mycorrhizal fungi (AMF) can help plants to cope with drought. We investigated this possible effect on A. tridentata seedlings inoculated with native AMF and exposed to drought in greenhouse and field settings. In greenhouse experiments, AMF colonization increased intrinsic water use efficiency under water stress and delayed the decrease in photosynthesis caused by drought, or this decrease occurred at a lower soil water content. In the field, we evaluated the effect of AMF inoculation on colonization, leaf water potential, survival, and inflorescence development. Inoculation increased AMF colonization, and the seedlings experienced water stress, as evidenced by water potentials between −2 and −4 MPa and reduced stomatal conductance. However, survival remained high, and no differences in water potentials or survival occurred between treatments. Only the percentage of plants with inflorescence was higher in inoculated than non-inoculated seedlings. Overall, the greenhouse results support that AMF colonization enhances drought tolerance in A. tridentata seedlings. Yet, the significance of these results in increasing survival in nature remains to be tested under more severe drought than the plants experienced in our field experiment.
... These soil microorganisms form symbiotic associations with approximately 72% of land plant species (Brundrett and Tedersoo, 2018) and have shown promise in mitigating drought effects in plants through various mechanisms (Boomsma and Vyn, 2008). AMF have been found to improve cell turgor in shoots by facilitating osmotic adjustment (Wu and Xia, 2006) and counteract the damaging effects of reactive oxygen species by synthesizing enzymes like superoxide dismutase (Ruiz-Lozano et al., 1996). Additionally, they enable plants to access soil pores that are usually inaccessible to roots or root hairs (Smith and Read, 2008) and transport water through extraradical mycelium to root cells (Sánchez-Díaz and Honrubia, 1994;Ahmad Khan et al., 2003). ...
... Similarly, B and Ni amounts of irrigated Gemlik leaves were higher than those of rainfed samples during collection period. Regarding to the effect of irrigation on P, K, Mg, Ca contents of olive leaves, a similar increase was informed due to higher mobility in soils and enhance transportion of these elements to the leaves with irrigation process (Bie et al., 2004;Koyro, 2006;Wu and Xia, 2006;Cetinkaya et al., 2016). Moreover, the water stress conditions decrease in leaf area because of leaf shrinkage and also cause reduction in some elements such as N, P, K, Ca, Na, Cl in olive leaves (Shaheen et al., 2011). ...
The objective of this study was to evaluate the effect of factors such as irrigation, variety and collection time on mineral contents of olive leaves. The highest Ca (31115.73 mg/kg), K (8398.34 mg/kg) and S (1679.05 mg/kg) contents were determined in leaves of Gemlik variety collected in irrigated orchard. Olive leaves of Ayvalık variety grown in irrigated orchard contained the maximum levels of Mg (3394.94 mg/kg) and P (949.13 mg/kg). The P, K and Mg amounts of olive leaves, in general, showed an increase with irrigation treatment. Generally, a regular increase or decrease did not observe in levels of macro elements of olive leaves based on collection time. Concerning the micro element contents of leaves, the highest Na contents were found in Ayvalık (241.11 mg/kg) and Yağlık (237.65 mg/kg) varieties. An increase was obtained in Fe contents of Yağlık olive leaves with irrigation during collection period. The concentrations of both macro and micro elements showed differences depending on the collection time, irrigation process and variety of olive leaves.
... However, of the plants subjected to a water deficit, only plants inoculated with AMF significantly improved water absorption [49][50][51]. Furthermore, stable RWC values under drought stress have been found for Cupressus atlantica, Casuarina equisetifolia, and Citrus tangerine [52][53][54]. This is because mycorrhizae can: (a) improve water absorption through the network of hyphae, which extends beyond the root itself; (b) generate morphological changes in plant roots [55]; and (c) stimulate the synthesis of abscisic acid [56]. ...
In its natural distribution, Araucaria araucana is a plant species usually exposed to extreme environmental constraints such as wind, volcanism, fires, and low rainfall. This plant is subjected to long periods of drought, accentuated by the current climate emergency, causing plant death, especially in its early growth stages. Understanding the benefits that both arbuscular mycorrhizal fungi (AMF) and endophytic fungi (EF) could provide plants under different water regimes would generate inputs to address the above-mentioned issues. Here, the effect of AMF and EF inoculation (individually and combined) on the morphophysiological variables of A. araucana seedlings subjected to different water regimes was evaluated. Both the AMF and EF inocula were obtained from A. araucana roots growing in natural conditions. The inoculated seedlings were kept for 5 months under standard greenhouse conditions and subsequently subjected to three different irrigation levels for 2 months: 100, 75, and 25% of field capacity (FC). Morphophysiological variables were evaluated over time. Applying AMF and EF + AMF yielded a noticeable survival rate in the most extreme drought conditions (25% FC). Moreover, both the AMF and the EF + AMF treatments promoted an increase in height growth between 6.1 and 16.1%, in the production of aerial biomass between 54.3 and 62.6%, and in root biomass between 42.5 and 65.4%. These treatments also kept the maximum quantum efficiency of PSII (Fv/Fm 0.71 for AMF and 0.64 for EF + AMF) stable, as well as high foliar water content (>60%) and stable CO2 assimilation under drought stress. In addition, the EF + AMF treatment at 25% FC increased the total chlorophyll content. In conclusion, using indigenous strains of AMF, alone or in combination with EF, is a beneficial strategy to produce A. araucana seedlings with an enhanced ability to tolerate prolonged drought periods, which could be of great relevance for the survival of these native species under the current climate change.
... In fact, inoculated plants under stressed conditions showed higher total dry biomass with high WUE suggesting the importance of dual inoculation in alleviating the stress effects. AM fungal symbiosis has been reported to positively mediate photosynthetic rate [60] , leaf stomatal regulation and transpiration rate [61] as compared to non-mycorrhizal plants. ...
Background
Drought stress is currently the primary abiotic stress factor for crop loss worldwide. Although drought stress reduces the crop yield significantly, species and genotypes differ in their stress response; some tolerate the stress effect while others not. In several systems, it has been shown that, some of the beneficial soil microbes ameliorate the stress effect and thereby, minimizing yield losses under stress conditions. Realizing the importance of beneficial soil microbes, a field experiment was conducted to study the effect of selected microbial inoculants namely, N-fixing bacteria, Bradyrhizobium liaoningense and P-supplying arbuscular mycorrhizal fungus, Ambispora leptoticha on growth and performance of a drought susceptible and high yielding soybean cultivar, MAUS 2 under drought condition.
Results
Drought stress imposed during flowering and pod filling stages showed that, dual inoculation consisting of B. liaoningense and A. leptoticha improved the physiological and biometric characteristics including nutrient uptake and yield under drought conditions. Inoculated plants showed an increased number of pods and pod weight per plant by 19% and 34% respectively, while the number of seeds and seed weight per plant increased by 17% and 32% respectively over un-inoculated plants under drought stress condition. Further, the inoculated plants showed higher chlorophyll and osmolyte content, higher detoxifying enzyme activity, and higher cell viability because of less membrane damage compared to un-inoculated plants under stress condition. In addition, they also showed higher water use efficiency coupled with more nutrients accumulation besides exhibiting higher load of beneficial microbes.
Conclusion
Dual inoculation of soybean plants with beneficial microbes would alleviate the drought stress effects, thereby allowing normal plants’ growth under stress condition. The study therefore, infers that AM fungal and rhizobia inoculation seems to be necessary when soybean is to be cultivated under drought or water limiting conditions.
... A sudden rise in the ambient temperature leads to excessive heating of the soil that can modify the rhizospheric microbiome structure developed post-interaction with plants (Okubo et al. 2014). Due to the increased temperature, heat stress has become one of the detrimental factors causing increased evaporation of soil moisture and reducing the establishment of extra mycorrhizal mycelium (Wu and Xia 2006). Researchers have also confirmed that extensive heat dryness of the soil causes loss of photosynthates in the plants formed during photosynthesis (Figueiredo et al. 2008). ...
Out of all the abiotic stress, heat stress is considered one of the detrimental factors that limit crop yield worldwide. Temperature modulates the normal physiology, morphology, genetic behavior, and a series of biochemical events in plants. Researchers are endlessly putting their efforts into solving this global problem through biological means. The use of beneficial microorganisms for the elevation of heat stress in plants is an emerging horizon of today’s research. Interaction of plants with soil microbes such as plant growth-promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF), and bacterial or fungal endophytes helps in the mitigation of heat or chilling stress and promotes plant growth. These microorganisms in interaction with plants stimulate the production of essential phytohormones, secondary metabolites, organic acids, and amino acids that helps the plant to overcome heat stress. This chapter mainly focuses on the amelioration of temperature stress through the use of beneficial soil microbes.KeywordsArbuscular mycorrhizal fungiEndophytesHeat shock proteinPlant growth-promoting rhizobacteriaRhizosphere
... In this paper, effects of AMF on grapevine photosynthesis in simultaneous coinfection with virus have been investigated. So far, the negative effects of grapevine viruses, particularly GLRaV-3 [3,10,11,34] and the positive effects of AMF on grapevine photosynthesis and photosynthesis-related parameters have been reported [35][36][37]. However, there is a gap in research of their interactive effects in perennial plants and up to now no investigation on virus-AMF interactions with grapevine physiology was reported. ...
The negative effects of viruses and the positive effects of arbuscular mycorrhizal fungi (AMF) on grapevine performance are well reported, in contrast to the knowledge about their interactive effects in perennial plants, e.g., in grapevine. To elucidate the physiological consequences of grapevine-AMF-virus interactions, two different AMF inoculum (Rhizophagus irregularis and 'Mix AMF') were used on grapevine infected with grapevine rupestris stem pitting virus, grapevine leafroll associated virus 3 and/or grapevine pinot gris virus. Net photosynthesis rate (A N), leaf transpiration (E), intercellular CO 2 concentration (C i) and conductance to H 2 O (g s) were measured at three time points during one growing season. Furthermore, quantum efficiency in light (Φ PSII) and electron transport rate (ETR) were surveyed in leaves of different maturity, old (basal), mature (middle) and young (apical) leaf. Lastly, pigment concentration and growth parameters were analysed. Virus induced changes in grapevine were minimal in this early infection stage. However, the AMF induced changes of grapevine facing biotic stress were most evident in higher net photosynthesis rate, conduc-tance to H 2 O, chlorophyll a concentration, total carotenoid concentration and dry matter content. The AMF presence in the grapevine roots seem to prevail over virus infection, with Rhizophagus irregularis inducing greater photosynthesis changes in solitary form rather than mixture. This study shows that AMF can be beneficial for grapevine facing viral infection, in the context of functional physiology.
... Previous studies have shown that mycorrhizal colonization prolonged the longevity of roots from forest tree plantations, thus reducing fine root turnover (Guo et al., 2008;King et al., 2002;Lambais et al., 2017). This is probably due to the symbiosis which increases plant water and nutrient absorption capacity and consequently, enhances plant tolerance to drought and poor soil nutrient availability (Lambais et al., 2017;Wu and Xia, 2006). However, we believe that this was not the case for our ICLF system. ...
Integrated crop-livestock-forestry (ICLF) systems explore synergistic interactions between soil, plant, and animals, maximizing land-use efficiency and sustainability. However, belowground dynamics under ICLF have not been investigated deeply, particularly the role of incorporating dead root material, a forefront strategy for releasing nutrients and storing carbon. To better understand belowground interactions, we conducted a 21-
month assessment of fine-root growth and decomposition in an ICLF system, starting when Eucalyptus urograndis trees were three years old. Eucalyptus rows were spaced 15 m apart and integrated with annual crops and pasture. Distances of 1.9, 4.3, and 7.5 m from the trees were evaluated under two successional periods: (i) annual crop, when corn was interspaced with palisade grass (Urochloa brizantha); and (ii) pasture, when palisade grass
was grazed. We used the minirhizotron technique to track fine-root production and decomposition down to a depth of 70 cm, capturing 2400 images. Root longevity was estimated per root diameter class (0-0.5-, 0.5–1.0-, and 1.0–2.0-mm) and phenotypical groups (e.g., grasses [corn + palisade grass] and Eucalyptus). Our data showed that root decomposition rate and necromass inputs into the soil were reduced at the closest distance from the Eucalyptus rows (i.e., 1.9 m). The incorporation of decomposed roots was higher in the topsoil (0–28 cm) and
declined with increasing soil depths. The total decomposed root incorporation was 101 m m− 2 of soil image for 7.5 and 4.3 m inter-row positions, almost twice as high as the recorded at 1.9 m (54 m m− 2) from the trees. Daily root decomposition rates increased during the last rainy season, benefited from numerous dead corn roots, and facilitated by higher soil moisture and temperature. Grasses and Eucalyptus roots at 7.5 m from the tree rows had
shorter longevity than those at 1.9 m, remaining 88 and 152 days less, respectively. Root diameter influenced the decomposition rate as thicker roots (diameter between 1.0 and 2.0 mm) of grasses and Eucalyptus stood in the soil for 243 and 261 days longer than the finest roots (diameter <0.5 mm). Our results highlight that root necromass accretion and decomposition are heterogeneous in ICLF systems. Furthermore, 3-to-5-year-old Eucalyptus trees drive the interactions, creating microclimate conditions that impair corn and palisade grass root production and
reduce root turnover close to the trees. These findings provide a scientific base for managing the ICLF system (spatial and temporal arrangements) and developing models of soil carbon addition via roots in such complex and heterogeneous systems.
... Lower variation in the free proline content was also found in mycorrhizal symbiosis in macadamia, and thus, total soluble sugar was suggested as the major osmolyte 21 . Furthermore, Wu et al. 38 announced that the osmolytes for water balance in plant cells may also originate from total non-structural carbohydrates and ions, i.e., K + , Ca 2+ and Mg 2+ , such as mycorrhizal inoculated citrus. In this case, the lower free proline content under drought was related to the proline biosynthesis and turnover reflected in buffer cellular redox status, resulting in maintenance of plant growth during water shortage 39 . ...
Arbuscular mycorrhizal ecosystem provides sustainability to plant integrity under drought situations. However, host plants that survive in drought frequently lose yield. The potential of Funneliformis mosseae (F), Claroideoglomus etunicatum (C), and Acaulospora fovaeta (A) was assessed to evaluate in indica rice cv. Leum Pua during booting stage under 21-day water withholding. The effects of three inoculation types; (i) F, (ii) F + C (FC), and (iii) F + C + A (FCA), on physiological, biochemical, and yield traits were investigated. The three types showed an induced total chlorophyll content in the host as compared to uninoculated plants. Total soluble sugars and free proline were less regulated by FC and FCA inoculated plants than by F inoculated plants under water deficit conditions. However, the FC and FCA inoculations increased phosphorus content, particularly in the shoots of water-stressed plants. In the three inoculations, the FCA dramatically improved plant osmotic potential adaptability under water deficit stress. Furthermore, even when exposed to the water deficit condition, panicle weight, grain number, and grain maturity were maintained in FCA inoculated plants. According to the findings, the increased osmotic potential and phosphorus content of the FCA-inoculated rice plant provide a protection sign against drought stress and will benefit food security in the future.
... The promotion of photosynthesis under drought stress in AMF plants is linked with higher chlorophyll concentrations. According to Wu and Xia (2006), plants inoculated with AM showed a higher photosynthetic rate under drought stress than non-inoculated ones. As reported by Zhu et al. (2012), chlorophyll concentration of the plants subjected to water deficit stress was enhanced in response to AMF inoculation. ...
Plant-arbuscular mycorrhizal (AM) fungi association is one of the oldest symbiotic relationships between organisms. This relationship may be more important under stress conditions such as drought and can help the host plant tolerate drought. This study was conducted in 2016 and 2017 at the Agricultural Research Farm of Razi University, Kermanshah, Iran to evaluate the effect of AM fungi (AMF) inoculation (with either Funneliformis mosseae or Rhizophagus intraradices) on some physio-biochemical traits of three sunflower cultivars under different soil irrigation treatments (severe water deficit stress, mild water deficit stress and well-watered). In both years, water deficit conditions significantly reduced leaf relative water content (RWC), chlorophyll concentrations (a, b and total) and shoot phosphorus concentration (SPC) while simultaneously increasing shoot proline levels and malondialdehyde (MDA) concentrations. AMF inoculation had positive effects on RWC, chlorophyll concentrations and SPC irrespective of sunflower cultivar and irrigation treatment. Shoot proline concentration and MDA reduced more in AM than non-AM plants. In most cases F. mosseae performed better than R. intraradices in terms of plant performance. Moreover, the improvements caused by AM fungi were more evident under water deficit than well-watered condition. It may be concluded that AM inoculation can alleviate the negative effects of water deficit stress on some important physio-biochemical traits of sunflower grown in the field, and can be considered as a practical and economical approach to improve crop performance in environments exposed to water limitations.
... Microbial inoculation in plants indicates altered efficacies in combating the stress among mycorrhizal plants and proline content act as a dynamic factor to assess stress tolerance [37]. Alternatively, there are also reports which show that AMF inoculation considerably decreased proline accumulation [38] while some studies demonstrate the increase [39][40]. Table 1 and 2. Table 1 and 2. ...
A field study was carried out to determine the interactive effects of two species of arbuscular mycorrhizal fungi [Funneliformis caledonius (Fc) and Glomus bagyarajii (Gb)], Rhizobium (R), and sewage sludge (SS) on the growth, physiology, microbial population and N, P, K content in chickpea grown in autoclaved garden soil (S) and soil mixed with 20% sewage sludge. The growth parameters of chickpea were recorded 60 days after sowing. The plant height, fresh and dry weight, biochemical content (total chlorophyll, carotenoid, protein content and nitrate reductase activity), microbial population (Rhizobial nodule count and percent root colonization by AM fungi) as well as N, P, K content increased significantly on application of 20% sewage sludge in the soil. Microbial inoculation in the sewage sludge amended soil enhanced all plant growth and biochemical parameters. The highest plant growth response was obtained in the treatment SS + R + Gb. The proline content (an indicator of plant stress) was highest in chickpea raised in soil amended with sewage sludge.
... We also verify that the proline content was higher in NM plants than in AM plants under drought stress conditions. A lower proline content suggests improved tolerance to drought (66,67). Therefore, AM symbiosis maintains ROS accumulation in E. grandis seedlings at a relatively stable level by increasing antioxidant abilities under drought stress, thereby reducing damage to cells and alleviating serious damage caused by drought stress. ...
Arbuscular mycorrhizal (AM) fungi play an important role in improving plant growth and development under drought stress. The MAPK cascade may regulate many physiological and biochemical processes in plants in response to drought stress.
... Most of the major physiological processes such as photosynthesis, protein and energy synthesis, and metabolism of lipids are consistently affected in relation to water deficiency [28]. Therefore, drought stress has been shown to influence multiple biological processes and pathways in plants, which subsequently adjust their growth, biomass production and water relations to maintain their productivity [29][30][31]. Many plants show drought-stimulated accumulation of reactive oxygen species (ROS), which may cause oxidation of proteins, DNA materials, carbohydrates, and damage membrane integrity [32][33][34]. ...
Drought stress profoundly affects native desert plants’ survival and performance. Among all the abiotic stresses, drought is considered a major constraint that influences the structure and functions of desert ecosystems. Arid desert ecosystems are characterized by prolonged drought, extreme temperatures, high solar radiation, water scarcity, high salinity, scarcity of soil nutrients, and poor soil structure. Such extreme desert environments are the toughest regions on earth, which present enormous challenges in conserving plant survival, growth and reproduction. Despite the predominance of these environmental conditions, native desert plant species that grow in desert environments develop complex adaptation strategies and resistance mechanisms to ameliorate the abiotic and biotic stresses in the extreme environments including changes in biochemical, physiological, and morphological levels. Arbuscular mycorrhizal fungi (AMF) form positive symbiotic associations with a considerable percentage of terrestrial plants as their host, induce distinct impacts on plant growth and protect plants from abiotic stresses. However, it is necessary to advance our understanding of the complex mechanisms associated with AMF-mediated and other dark septate endophytes (DSE)-mediated amelioration of native desert plants’ drought stress resistance and associated biological adjustments such as changes in hormone balance, water and nutrient status, stomatal conductance and osmotic adjustment, antioxidant activity, and photosynthetic activity. This review provides an overview of the relationships of mycorrhiza and fungal endophytes involved in drought stress tolerance, summarizing the current knowledge and presenting possible mechanisms mediated by AMF to stimulate drought tolerance associated with native desert plants. We discuss the research required to fill the gaps and provide suggestions for future research.
... Facilitation of water uptake by mycorrhizal hyphae is one of the proposed mechanisms in this respect [106]. A large number of studies have shown the stabilization of RWC in shoots of mycorrhizal plants under drought conditions, in contrast to a decrease in RWC in non-mycorrhizal plants [107][108][109][110][111]. Results on absolute water content are almost absent in this type of study. ...
The aim of the present review was to reconsider basic information about various functional aspects related to plant water content and provide evidence that the usefulness of measuring absolute water content in plant sciences is undervalued. First, general questions about water status in plants as well as methods for determining water content and their associated problems were discussed. After a brief overview of the structural organization of water in plant tissues, attention was paid to the water content of different parts of plants. Looking at the influence of environmental factors on plant water status, the differences caused by air humidity, mineral supply, biotic effects, salinity, and specific life forms (clonal and succulent plants) were analyzed. Finally, it was concluded that the expression of absolute water content on a dry biomass basis makes easily noticeable functional sense, but the physiological meaning and ecological significance of the drastic differences in plant water content need to be further elucidated.
... In addition, F. mosseae inoculation reportedly increased Lycopersicon esculentum leaf area (Al-Karaki, 2000) and enhanced Glycyrrhiza uralensis plant biomass (Chen et al., 2017) under greenhouse conditions. Because leaves are a major organ of plant photosynthesis, increasing leaf chlorophyll content could enhance dry matter accumulation and yield in crops (Al-Karaki, 2001;Wu & Xia, 2006). Furthermore, C. annuum root morphology was modified following F. mosseae inoculation, which could contribute to plant growth and fruit yield by enhancing nutrient and water uptake (Chatzistathis et al., 2013;Kapulnik et al., 2010;Wu et al., 2004). ...
Arbuscular mycorrhizal fungi, such as Funneliformis mosseae, are essential components of the soil microbiome that can facilitate plant growth and enhance abiotic and biotic stress resistances. However, the mechanisms via which F. mosseae inoculation influences Capsicum annuum L. plant growth and fruit yield remain unclear. Here, we conducted pot experiments to investigate bacterial and fungal community structures in the rhizosphere of C. annuum plants inoculated with F. mosseae based on 16S ribosomal RNA and internal transcribed spacer gene sequencing. The α‐diversity of bacteria increased significantly following F. mosseae inoculation (p < 0.01); however, there was no significant difference in fungal diversity indices between treatments. The relative abundances of major bacterial phyla, Proteobacteria, Bacteroidetes, and Gemmatimonadetes, together with the fungal phylum Ascomycota, were all higher in inoculated samples than in uninoculated controls. F. mosseae inoculation led to a remarkable enrichment of potentially beneficial genera (e.g., Streptomyces, Sphingomonas, Lysobacter, and Trichoderma), in stark contrast to the depletion of fungal pathogens (e.g., Botryotrichum, Acremonium, Fusarium, and Plectosphaerella). Rhizosphere pathways related to amino acid metabolism and antibiotic biosynthesis were upregulated by F. mosseae inoculation, whereas pathways involved in infectious diseases were downregulated. Thus, F. mosseae inoculation appears to reshape the rhizosphere microbiome, thereby augmenting C. annuum plant growth and fruit yield.
... Under limited irrigation, AMF strains increased growth of tomato plants regardless of irrigation status, and they also restored shoot and root dry weight [189]. Moreover, AMF colonization ameliorated the osmotic adjustment originating not from proline but from non-structural carbohydrates (NSC), Ca 2+ , K + , and Mg 2+ , resulting in the improvement in drought tolerance in the leaves of citrus [190]. The colonization of olive roots by Rhizophagus irregularis DAOM 197,198 significantly reduced the deleterious effect of water deficit stress by up-regulating the primary and secondary metabolism and preserving a high stem water potential level in olive plants (Olea europaea) [191]. ...
Sustainable farming of horticultural plants has been the focus of research during the last decade, paying significant attention to alarming weather extremities and climate change, as well as the pressure of biotic stressors on crops. Microbial biostimulants, including plant growth-promoting bacteria (PGPB) and arbuscular mycorrhizal fungi (AMF), have been proven to increase plant growth via both direct and indirect processes, as well as to increase the availability and uptake of nutrients, boosting soil quality, increasing plants' tolerance to abiotic stress and increasing the overall quality attributes of various horticultural crops (e.g., vegetables, fruit, herbs). The positive effects of microbial biostimulants have been confirmed so far, mostly through symbiotic interactions in the plant-soil-microbes ecosystem, which are considered a biological tool to increase quality parameters of various horticultural crops as well as to decrease soil degradation. However, more research is needed to address future challenges of crop production through revealing the mechanisms of action and identifying response patterns of crops to various microbial products. The present review aims to present the most up-to-date results regarding the practical applications of microbial biostimulants in horticultural species, including case studies of successful paradigms for the most important microbial genera of PGPB and AMF. Moreover, the mechanisms of the actions are briefly described while future remarks are also discussed, aiming to suggest further needs to be addressed for the successful establishment of microbial biostimulants in sustainable horticultural crop production.
Arbuscular mycorrhizal (AM) fungi can enhance the uptake of soil nutrients and water by citrus, promoting its growth. However, the specific mechanisms underlying the action of AM fungi in promoting the growth of citrus were not fully elucidated. This study aimed to explore the role of AM fungi Funneliformis mosseae in the regulatory mechanisms of P. trifoliata growth. Pot experiments combined with non-targeted metabolomics methods were used to observe the growth process and changes in metabolic products of P. trifoliata under the conditions of F. mosseae inoculation. The results showed that F. mosseae could form an excellent symbiotic relationship with P. trifoliata, thereby enhancing the utilization of soil nutrients and significantly promoting its growth. Compared with the control, the plant height, stem diameter, number of leaves, and aboveground and underground dry weight in the F. mosseae inoculation significantly increased by 2.57, 1.29, 1.57, 4.25, and 2.78 times, respectively. Moreover, the root system results confirmed that F. mosseae could substantially promote the growth of P. trifoliata. Meanwhile, the metabolomics data indicated that 361 differential metabolites and 56 metabolic pathways were identified in the roots of P. trifoliata and were inoculated with F. mosseae. This study revealed that the inoculated F. mosseae could participate in ABC transporters by upregulating their participation, glycerophospholipid metabolism, aminoacyl tRNA biosynthesis, tryptophan metabolism and metabolites from five metabolic pathways of benzoxazinoid biosynthesis [mainly enriched in lipid (39.50%) and amino acid-related metabolic pathways] to promote the growth of P. trifoliata.
The most familiar and common mutualistic association existing in the majority of crop plants is the arbuscular mycorrhizal (AM) symbiosis that aids in crop growth and development. In the plant-AM fungal interaction, the fungi acquire carbon from their host plant and in exchange, the fungi increase the supply of important nutrients in particular phosphorous via expanding the roots into the nutrient absorbing sites. Also, the AM fungi enhance crops performance and existence under different abiotic and biotic stresses through different mechanisms. As a natural crop-root colonizer, AM fungi impart essential micro-and macronutrients thereby promoting crop growth and productivity in nutrient-stressed soils. The AM-fungal mediated crop growth promotion involves several pathways and a sequence of multifarious communications between the crop and the fungus. Owing to its crop growth-promoting activity, several AM fungal species are developed into potential bioinoculants for the ecofriendly management of anthropogenic ecosystems like agriculture. In this chapter, we comprehend the existing knowledge on the role of AM fungi in the establishment and survival of crops under normal and stressful environments that hampers crop growth and development like drought, salinity, heavy metals and infestation by pathogens. In addition, the role of AM fungi in crop growth promotion through nutrient uptake and other pathways, application of AM fungi in improving the water relations and nutritional quality in crop species under unfavourable conditions are also discussed. The exploitation of AM fungal symbiosis in agricultural habitats can lead to the creation of self-sustaining ecosystems for future.
Hot deserts impose extreme conditions on plants growing in arid soils. Deserts are expanding due to climate change, thereby increasing the vulnerability of ecosystems and the need to preserve them. Arbuscular mycorrhizal fungi (AMF) improve plant fitness by enhancing plant water/nutrient uptake and stress tolerance. However, few studies have focused on AMF diversity and community composition in deserts, and the soil and land use parameters affecting them. This study aimed to comprehensively describe AMF ecological features in a 5,000 m ² arid hyperalkaline region in AlUla, Saudi Arabia. We used a multimethod approach to analyse over 1,000 soil and 300 plant root samples of various species encompassing agricultural, old agricultural, urban and natural ecosystems. Our method involved metabarcoding using 18S and ITS2 markers, histological techniques for direct AMF colonization observation and soil spore extraction and observation. Our findings revealed a predominance of AMF taxa assigned to Glomeraceae, regardless of the local conditions, and an almost complete absence of Gigasporales taxa. Land use had little effect on the AMF richness, diversity and community composition, while soil texture, pH and substantial unexplained stochastic variance drove their structuring in AlUla soils. Mycorrhization was frequently observed in the studied plant species, even in usually non-mycorrhizal plant taxa. Date palms and Citrus trees, representing two major crops in the region, displayed however a very low mycorrhizal frequency and intensity. AlUla soils had a very low concentration of spores, which were mostly small. This study generated new insight on AMF and specific behavioral features of these fungi in arid environments.
Sessile plants confront the fluctuating harsh environmental conditions and react to alterations in biotic and abiotic components of environments by symbiotic association between plant and biosphere. The origins of stresses are the vicinal environment, which is composed of biotic and abiotic agents. A wide range of molecular mechanisms are opted by the plants for their self-defense. The plant faces harsh conditions due to its molecular battery. Signaling molecules engineer the plants to tolerate the stresses. Transposable elements become active due to living and nonliving agents. Physical and chemical agents cause induction in mutation. These changes are the first driving step in the evolution of plants. During evolution, environmental changes force the plants to adapt or succumb to stress. The plants respond to the ecological conditions by modulating the gene programmer.
Climate changes cause altering rainfall patterns resulting in an increase in drought occurrences globally. These events are disrupting plants and agricultural productivity. To evade droughts, plants try to adapt and modify in the best capacities possible. The plants have adapted by structurally modifying roots, stems, and leaves, as well as modifying functions. Lately, the association of microbial communities with plants has also been proven to be an important factor in aiding resilience. The fungal representatives of the microbial community also help safeguard the plants against drought. We discuss how these fungi associate with plants and contribute to evading drought stress. We specifically focus on Arbuscular mycorrhizal fungi (AMF) mediated mechanisms involving antioxidant defenses, phytohormone mediations, osmotic adjustments, proline expressions, fungal water absorption and transport, morphological modifications, and photosynthesis. We believe understanding the mechanisms would help us to optimize the use of fungi in agricultural practices. That way we could better prepare the plants for the anticipated future drought events.
It has been known that the application of beneficial fungi and compost, has a favourable effect on easing water deficiency stress in plants, hence helping to boost agricultural activities in times of climate uncertainty. In this study, the influence of arbuscular mycorrhizal fungi (AMF) in combination with oil palm empty fruit bunch compost (EFB) on the growth, yield, and physiology of chilli under deficit fertigation was investigated. Throughout the study, five-week-old chilli seedlings were fertigated daily with 100% and 60% of daily evapotranspiration (ET) readings. Three days after transplanting, 10g of sandy soil containing roughly 120-150 mycorrhizal spores was applied to the root zone. Physiological data such as real-time photosynthesis and stomatal conductance were measured at vegetative, early flowering, fruit setting, and maturity or harvesting stages. Meanwhile, yield and morphological measurements were recorded at the end of the study. It was discovered that the addition of EFB to the coconut coir dust media enhanced the beneficial effects of AMF on all parameters including total biomass, chlorophyll fluorescence Fv/Fm, total chlorophylls, photosynthesis rate and stomatal conductance regardless of fertigation levels. The study also revealed that AMF inoculation alone was less effective than non-inoculation + EFB. In conclusion, it is suggested that incorporation of AMF and EFB compost positively affect the yield, growth and physiology of chilli under deficit fertigation.
SPAD (ﻣﻘـﺪار و ﻛﺮﺑﻮﻫﻴـﺪرات ، آزﻣﺎﻳﺸﻲ ﮔﺸﻨﻴﺰ، داروﻳﻲ ﮔﻴﺎه در ﻏﺬاﻳﻲ ﻋﻨﺎﺻﺮ ﺟﺬب زراﻋﻲ ﺳﺎل در 90-1389 ﺑﻪ ﻛﺮت ﺻﻮرت ﺑﻠﻮك ﻗﺎﻟﺐ در ﺷﺪه ﺧﺮد ﻫﺎي ﺗﺼـﺎدﻓﻲ ﻛﺎﻣﻞ ﻫﺎي ﺳـﻪ در ﺗﻜﺮار د داﻧﺸﮕﺎه داروﻳﻲ ﮔﻴﺎﻫﺎن و ﻛﺸﺎورزي ﺗﺤﻘﻴﻘﺎت ﻣﺰرﻋﻪ ر ﺷﺪ اﻧﺠﺎم ﺣﻴﺪرﻳﻪ ﺗﺮﺑﺖ. ﺳﻄﺢ ﺳﻪ ﺷﺎﻣﻞ ﺧﺸﻜﻲ ﺗﻨﺶ ﺗﻴﻤﺎر) 30 ، 60 و 90 ﻇﺮﻓﻴـﺖ درﺻـﺪ زراﻋﻲ (ﻛﻮدي ﺗﻴﻤﺎر و) ورﻣﻲ و داﻣﻲ ﻛﻮد ﻛﺎﻣﻞ، ﺷﻴﻤﻴﺎﻳﻲ ﻛﻮد ﺷﺎﻫﺪ، ﻛﻤﭙﻮﺳﺖ (ﺑﻮد. ﻣﻌﻨﻲ ﮔﻮﻳﺎي ﻧﺘﺎﻳﺞ ﺑﻮدن دار ﻣﻴﺰان ﺑﺮ ﺧﺸﻜﻲ ﺗﻨﺶ ﺷﺎﺧﺺ ﻛﻠﺮوﻓﻴـﻞ ، ﭘﺮوﻟ ﺑﻮد درﺻﺪ ﻳﻚ ﺳﻄﺢ در ﺳﺪﻳﻢ ﺗﺠﻤﻊ و ﭘﺘﺎﺳﻴﻢ ﻓﺴﻔﺮ، ازت، ﺟﺬب ﻛﺮﺑﻮﻫﻴﺪرات، ﻴﻦ،. ﭘﺘﺎﺳﻴﻢ و ﻓﺴﻔﺮ ازت، ﺟﺬب ﻛﺮﺑﻮﻫﻴﺪرات، ﻣﻴﺰان ﺑﺮ ﻧﻴﺰ ﻛﻮدي ﺗﻴﻤﺎر ﻣﻌﻨﻲ درﺻﺪ ﭘﻨﺞ ﺳﻄﺢ در ﭘﺮوﻟﻴﻦ ﻣﻴﺰان ﺑﺮ و درﺻﺪ ﻳﻚ ﺳﻄﺢ در ﺳﺪﻳﻢ ﺗﺠﻤﻊ و ﺷﺪ دار. ﺣﺎل اﻳﻦ ﺑﺎ ﺑـﺮ ﻛﻮدي ﺗﻴﻤﺎر ﺷـﺎﺧﺺ ﻛﻠﺮوﻓﻴـﻞ ﻣﻌﻨـﻲ ﺗـﺎﺛﻴﺮ داري ﻧﺪاﺷﺖ. واژه ﻛﻠﻴﺪي ﻫﺎي : ﻛﻮد ﻏﺬاﻳﻲ، ﻋﻨﺎﺻﺮ ﭘﺮوﻟﻴﻦ، ﺧﺸﻜﻲ، ﺗﻨﺶ ، ﮔﺸﻨﻴﺰ ﻣﻘﺪﻣﻪ ﮔﺸﻨﻴﺰ 1 اﺳـﺖ ﻣﺪﻳﺘﺮاﻧـﻪ ﺑﻮﻣﻲ و ﭼﺘﺮﻳﺎن ﺧﺎﻧﻮاده از ﻳﻜﺴﺎﻟﻪ ﮔﻴﺎﻫﻲ ﻣـﻲ ﻛﺸﺖ اﺳﺎﻧﺲ و ادوﻳﻪ ﺑﺬر، ﺗﻮﻟﻴﺪ ﻣﻨﻈﻮر ﺑﻪ ﻛﻪ ﮔـﺮدد) 41 .(اﺛـﺮات ﻣﺴﻜﻦ و اﻟﺘﻬﺎب ﺿﺪ و ﺧﻮن ﭼﺮﺑﻲ و ﻗﻨﺪ ﻛﺎﻫﻨﺪه) 3 (ﮔﻴـﺎه اﻳـﻦ ﺑـﺮاي اﺳﺖ ﺷﺪه ﮔﺰارش. ﮔﺸﻨﻴﺰ ﺑﻪ ﺳﻨﺘﻲ ﻃﺐ در ﻫﻀـﻢ دﻫﻨـﺪه، ﻧﻴﺮو اﺛﺮات در روﻣﺎﺗﻴﺴـﻤﻲ دردﻫﺎي ﺿﺪ ﺿﺪﻛﺮم، ﻣﺪر، ﺑﺎدﺷﻜﻦ، ﻣﻠﻴﻦ، ﻏﺬا، ﻛﻨﻨﺪه ﺧﻮاب ﻣﻮﺿﻌﻲ، ﻣﺼﺮف اﺳـﺖ ﺷـﺪه داده ﻧﺴﺒﺖ ﺗﺸﻨﺞ ﺿﺪ و ﻣﻔﺮح آور،) 4 .(و ﮔﻴﺎﻫـﺎن رﺷـﺪ ﻛﻨﻨـﺪه ﻣﺤـﺪود ﻋﻮاﻣﻞ ﻣﻬﻤﺘﺮﻳﻦ از ﻳﻜﻲ ﺧﺸﻜﻲ ﺷﺎﻳﻊ اﺳﺖ ﺟﻬﺎن ﺳﺮﺗﺎﺳﺮ در ﻣﺤﻴﻄﻲ ﺗﻨﺶ ﺗﺮﻳﻦ. ﺑـﺮ ﺧﺸـﻜﻲ ﺗﻨﺶ اﺛﺮ و رﺷﺪ ﺗﻨﺶ ﺷﺪت و دوام زﻣﺎن، ﻣﺪت ﮔﻴﺎه، ژﻧﻮﺗﻴﭗ ﺑﻪ ﺑﺴﺘﮕﻲ ﻋﻤﻠﻜﺮد دارد) 11 .(زﻣـﺎن و آﺑـﻲ ﻧﻴﺎز ﺑﺤﺮاﻧﻲ زﻣﺎن از آﮔﺎﻫﻲ و ﺷﻨﺎﺳﺎﻳﻲ ﺑﻨـﺪي 1-داﻧﺸﺠﻮي آزاد داﻧﺸـﮕﺎه اي ﻧﻮﺷـﺎﺑﻪ و اي ادوﻳﻪ داروﻳﻲ، ﮔﻴﺎﻫﺎن ارﺷﺪ ﻛﺎرﺷﻨﺎﺳﻲ ﻛﺮج واﺣﺪ اﺳﻼﻣﻲ *)-ﻣﺴﺌﻮل ﻧﻮﻳﺴﻨﺪه : Email: kharif13@gmail.com (2-اﺳﺘﺎدﻳﺎر ﮔﻴﺎﻫﻲ ﺗﻮﻟﻴﺪات ﮔﺮوه ، ﺣﻴﺪرﻳﻪ ﺗﺮﺑﺖ داﻧﺸﮕﺎه 3-ﻓﺮدوﺳﻲ داﻧﺸﮕﺎه ﻛﺸﺎورزي، داﻧﺸﻜﺪه ﺑﺎﻏﺒﺎﻧﻲ، ﻋﻠﻮم ﮔﺮوه اﺳﺘﺎدﻳﺎر ﻣﺸﻬﺪ 1-Coriandrum sativum L. ذﺧﺎﻳﺮ ﺣﻔﻆ ﺟﻬﺖ در ﻛﺎرآﻣﺪ ﺣﻠﻲ راه ﮔﻴﺎه، ﺑﺤﺮاﻧﻲ ﻧﻴﺎز ﺑﺮاﺳﺎس آﺑﻴﺎري اﺳـﺖ ﺧﺸـﻜﻲ ﺑـﻪ ﮔﻴـﺎه ﺗﺤﻤـﻞ اﻓﺰاﻳﺶ و آﺑﻴﺎري ﻋﻤﻠﻴﺎت ﺑﻬﺒﻮد آﺑﻲ،) 28 .(ﻃ از ﺧﺸﻜﻲ ﺗﻨﺶ ﺗﻮﺳﻌﻪ ﻛﺎﻫﺶ ﺮﻳﻖ ي ﺷـﺎﺧﺺ ﻛﺎﻫﺶ و ﺑﺮگ روزﻧﻪ ﺷﺪن ﺑﺴﺘﻪ ﺑﺮگ، ﺳﻄﺢ روزﻧـﻪ ﻫﺪاﻳﺖ ﻛﺎﻫﺶ ﻫﺎ، ا ي در ﻛـﺎﻫﺶ ، ﺑﺨـﺶ ﺳﺎﻳﺮ و ﻛﻠﺮوﭘﻼﺳﺖ آﺑﮕﻴﺮي ﺳـﻨﺘﺰ ﻛـﺎﻫﺶ ﭘﺮوﺗﻮﭘﻼﺳـﻢ، ﻫـﺎي ﻓﺘﻮﺳـﻨﺘﺰ ﻛـﺎﻫﺶ ﺳـﺒﺐ ﻛﻠﺮوﻓﻴﻞ، و ﭘﺮوﺗﺌﻴﻦ ﻣـﻲ ﻣـﻮاد اﻧﺘﻘـﺎل ﮔـﺮدد، ﺑﺮگ اﺷﺒﺎع ﻣﻮﺟﺐ و ﮔﺮﻓﺘﻪ ﻗﺮار ﺧﺸﻜﻲ ﺗﻨﺶ ﺗﺄﺛﻴﺮ ﺗﺤﺖ ﻓﺘﻮﺳﻨﺘﺰي ﻫﺎ ﻣﻲ ﻓﺘﻮﺳﻨﺘﺰي ﻣﻮاد از ﮔﺮدد ﻧﻤﺎﻳﺪ ﻣﺤﺪود را ﻓﺘﻮﺳﻨﺘﺰ اﺳﺖ ﻣﻤﻜﻦ ﻛﻪ. ﺑﺎ ﻓﺮآورده ﺷﺪن ﻣﺤﺪود رﺷـﺪ ﺧﺸـﻜﻲ، ﺗـﻨﺶ ﺷﺮاﻳﻂ در ﻓﺘﻮﺳﻨﺘﺰي ﻫﺎي ﻣﻲ ﻛﺎﻫﺶ آن ﻋﻤﻠﻜﺮد ً ﻧﻬﺎﻳﺘﺎ و ﮔﻴﺎه ﻳﺎﺑﺪ) 1 .(ﻋـﺎﻟﻲ ﮔﻴﺎﻫـﺎن در ﺗـﻨﺶ ﺑـﻪ ﻣﺘـﺪاول ﭘﺎﺳـﺨﻲ آزاد، ﭘﺮوﻟﻴﻦ ﺗﺠﻤﻊ ﻣﻲ ﺑﺎﺷﺪ) 42 .(ﮔﺰارش ﻣﺜﺒـﺖ ﻫﻤﺒﺴـﺘﮕﻲ وﺟـﻮد ﺑﺮ ﻣﺒﻨﻲ ﻣﺘﻌﺪدي ﻫﺎي ﺑﻴﻦ ﺗﺠﻤﻊ ﺗـﻨﺶ ﺗﺤﺖ اﺳﻤﺰي ﺗﻨﺶ ﺷﺮاﻳﻂ ﺑﻪ ﺳﺎزش و ﭘﺮوﻟﻴﻦ ﻫـﺎي دارد وﺟﻮد ﮔﻴﺎﻫﺎن ﺷﻮري و ﺧﺸﻜﻲ) 13 .(ﭘﺮوﺗﺌﻴﻦ ﺣﻼﻟﻴﺖ ﭘﺮوﻟﻴﻦ و ﻫﺎ آﻧﺰﻳﻢ ﻣﻲ ﻗﺮار ﺗﺎﺛﻴﺮ ﺗﺤﺖ را ﻣﺨﺘﻠﻒ ﻫﺎي آن ﻣﺎﻫﻴـﺖ ﺗﻐﻴﻴﺮ از و دﻫﺪ ﻫـﺎ ﻣﻲ ﺟﻠﻮﮔﻴﺮي ﻛﻨﺪ) 2 .(اﻓـﺰاﻳﺶ آب، ﭘﺘﺎﻧﺴـﻴﻞ ﻛﺎﻫﺶ ﺑﺎ ﺳﻮﻳﺎ و ﻟﻮﺑﻴﺎ در ﻣﻌﻨﻲ ﮔﺮدﻳﺪ ﻣﺸﺎﻫﺪه ﭘﺮوﻟﻴﻦ ﻣﻴﺰان در داري) 23 .(زدن ﺑﺮﻫﻢ ﺑﻪ ﻣﻨﺠﺮ ﺧﺸﻜﻲ و ﺷﻮري ﺗﻨﺶ ﻛﻪ اﺳﺖ ﺷﺪه ﻣﺸﺨﺺ ﺗﻐﺬﻳﻪ ﺗﻌﺎدل ﻣﻲ ﮔﻴﺎﻫﺎن در اي ﺷـﻮﻧﺪ) 21 .(ﺗـﺄﻣﻴﻦ ﺑـﺎ ﺷـﺮاﻳﻂ اﻳـﻦ در
To improve the carbon fixation capacity of crops, HCO3- is applied to the rhizosphere under a suitable pH value, which can enhance the utilization of CO2 by crops. This study aimed to clarify the maximum fixation capacity of HCO3- in tomato plants by exploring the optimal concentration of HCO3- in their cultivation environment. The results showed that the tomato could maintain both the net increase of HCO3- fixation and normal growth, when the maximum concentration of HCO3- in the cultivation surroundings was discovered during the growth period: 25 mmol/L NaHCO3-solution in seed germination, 14 g-NaHCO3/kg-soil in the cotyledon development, 8 to 10 g-NaHCO3/kg-soil during the seedling, 6 g-NaHCO3/kg-soil in the flowering, and 9 g-NaHCO3/kg-soil in the fruiting. However, excessive HCO3- could impair the development of tomato plants, especially the vegetative growth at seedling/flowering stages and the root growth at fruiting stage due to the increased soil pH and EC by HCO3-. On the other hand, H
O produced by the decomposition of HCO3- by tomato plants could alleviate physiological stress under severe conditions. Therefore, HCO3- became the main inorganic carbon source of tomato assimilation under extreme stress. This study provides a data basis for selecting and optimizing the appropriate HCO3- application amount when CO2 is used for agricultural eco-fixation in the form of HCO3- in the future.
Growth of the pioneer grass Miscanthus condensatus, one of the first vegetation to be established on volcanic deposits, is promoted by root-associated fungi, particularly dark septate endophytes (DSE). Fungal taxa within DSE colonize the root of Miscanthus condensatus in oligotrophic Andosol, and their function in plant growth promotion remains largely unknown. We, therefore, comprehensively assessed the composition of the DSE community associated with Miscanthus condensatus root in volcanic ecosystems using the approaches of both metabarcoding (next-generation sequencing) and isolation (culturing). Also, their promotion effects of DSE on plant growth (rice as a proxy) were evaluated by inoculation of core isolates to rice roots. Here, we found: i) 70 % of culturable fungi that colonized Miscanthus condensatus phylogenetically belonged to DSE, ii) 7 orders were identified by both sequencing and culturing methods, and iii) inoculation of DSE isolates (Phialocephala fortinii, P. helvetica, and Phialocephala sp.) validated their effects on rice growth, particularly under an extremely low pH condition (compared to control without inoculation, rice biomass enhanced by 7.6 times after inoculation of P. fortinii). This study helps improve our understanding of the community of Miscanthus condensatus-associated DSE fungi and their functions in promoting plant growth.
How mycovirus-induced hypovirulence in fungi activates plant defense is still poorly understood. The changes in plant fitness and gene expression caused by the inoculation of the fungus Sclerotinia sclerotiorum harboring and made hypovirulent by the mycovirus soybean leaf-associated gemygorvirus-1 (SlaGemV-1) of the species Gemycircularvirus soybe1 were examined in this study. As the hypovirulent fungus (DK3V) colonized soybean Glycine max, plant transcriptomic analysis indicated changes in defense responses and photosynthetic activity, supported by an upregulation of individual genes and overrepresentation of photosystem gene ontology groups. The upregulated genes include genes relating to both pathogen-associated molecular pattern–triggered immunity and effector-triggered immunity as well as various genes relating to the induction of systemic acquired resistance and the biosynthesis of jasmonic acid. Plants colonized with DK3V showed a resistant phenotype to virulent S. sclerotiorum infection. Plant height and leaf area were also determined to be larger in plants grown with the virus-infected fungus. Here, we hypothesize that inoculation of soybean with DK3V can result in the triggering of a wide range of defense mechanisms to prime against later infection. The knowledge gained from this study about plant transcriptomics and phenotype will help prime plant immunity with mycovirus-infected hypovirulent fungal strains more effectively.
[Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .
As a main by-product of anaerobic digestion in biogas plants, biogas slurry contains a high concentration of mineral elements (such as ammonia‑nitrogen and potassium) and chemical oxygen demand (COD). So determining how to dispose the biogas slurry in a harmless and value-added ways is crucial from the perspective of ecological and environmental protections. This study explored a novel nexus between biogas slurry and lettuce, in which the biogas slurry was concentrated and saturated with carbon dioxide (CO2) to serve as a hydroponic solution for lettuce growth. Meanwhile, the lettuce was used to purify the biogas slurry through removing pollutants. Results showed that when concentrating the biogas slurry, the total nitrogen and ammonia nitrogen contents in the biogas slurry decreased with the increase of concentration factor. The CO2-rich 5-time-concentrated biogas slurry (CR-5CBS) was screened as the most suitable hydroponic solution for lettuce growth after comprehensively considering the nutrient element balance, energy consumption of concentrating the biogas slurry and CO2 absorption performance. The quality of lettuce cultivated in CR-5CBS was comparable to that of the Hoagland-Arnon nutrient solution in terms of physiological toxicity, nutritional quality, and mineral uptake. Obviously, the hydroponic lettuce could effectively utilize the nutrients in CR-5CBS to purify CR-5CBS, meeting the standard of reclaimed water quality for agricultural reuse. Interestingly, when the same yield of lettuce is targeted, using CR-5CBS as the hydroponic solution to cultivate lettuce can save about US $151/m3-CR-5CBS for lettuce production compared to the Hoagland-Arnon nutrient solution. This study might provide a feasible method for high-value utilization and harmless disposal of biogas slurry.
Climate change and agricultural practices like unrestricted utilization of insecticides especially fertilizer and pesticides have amplified the effects of inanimate stress on the productivity of crops and degraded the environment. The need of the hour is to adopt eco-friendly crop management techniques, including the usage of arbuscular mycorrhizal fungi (AMF). AMFs are frequently referred to as bio-fertilizers. Mycorrhiza improves the movement and absorption of nutrients from soils, thereby limiting the demand for artificial fertilizers and avoiding the accretion of nutrients in soil. Reduced fertilizer use reduces the effects of fertilizer runoff and leaching on water quality and serves as a cost-effective method for farmers. Inanimate stressors (such as salt, drought, heat, cold, and mineral shortage) have emerged as the most serious dangers to global agricultural productivity. These stresses induce ion toxicity nutritional imbalance, hormonal inequalities which in turn influence plant growth and development, maturity, productivity etc. Some beneficial microorganisms, such as mycorrhizal fungi, live in mutualistic association with the roots of host plant in the rhizospheric region. Mycorrhiza significantly improves host plant resilience to a variety of animate and inanimate stresses. This chapter emphasizes the relevance of mycorrhizal fungi in stress reduction and their beneficial impacts on plants’ production, growth and enlargement.
Fallopia japonica and Impatiens glandulifera are major plant invaders on a global scale that often become dominant in riparian areas. However, little is known about how these species affect interactions in soil–plant systems. The aim of this study was to investigate the impact of both species on abiotic and biotic soil properties, with a special focus on fungi. We investigated eight sites along small streams invaded by F. japonica and I. glandulifera, respectively, and compared each with nearby sites dominated by the native species Urtica dioica. Three different types of samples were collected: bulk soil, rhizosphere soil and roots from invasive and native stands at each site. Bulk soil samples were analysed for soil physicochemical, microbial properties (soil microbial respiration and ergosterol) and soil arthropod abundance (Acari and Collembola). Soil respiration was also evaluated in rhizosphere samples. The fungal community composition of both bulk soil and roots were analysed using a metabarcoding approach. Soil physicochemical properties as well as soil microbial activity, fungal biomass and soil fungal operational unit taxonomic unit (OTU) richness did not differ between invaded and native riparian habitats, indicating only minor belowground impacts of the two invasive plant species. Soil microbial activity, fungal biomass and soil fungal OTU richness were rather related to the soil physicochemical properties. In contrast, Acari abundance decreased by 68% in the presence of F. japonica, while Collembola abundance increased by 11% in I. glandulifera sites. Moreover, root-associated fungal communities differed between the invasive and native plants. In F. japonica roots, fungal OTU richness of all investigated ecological groups (mycorrhiza, endophytes, parasites, saprobes) were lower compared to U. dioica. However, in I. glandulifera roots only the OTU richness of mycorrhiza and saprobic fungi was lower. Overall, our findings show that F. japonica and I. glandulifera can influence the abundance of soil arthropods and are characterized by lower OTU richness of root-associated fungi.
Potatoes are the most highly consumed vegetable in the United States and are the primary source of antioxidants in the American diet. Therefore, technologies and growing methods that aim to enhance the nutritional quality of potatoes can have positive impacts on public health. Based on past success with other food crops, we hypothesized that inoculation with arbuscular mycorrhizal fungi (AMF) would increase both the yield and nutritional quality of potatoes. To test this hypothesis, we grew yellow fleshed (cv. Lehigh) and purple fleshed (cv. Adirondack Blue) potatoes in containers with several monospecific AMF inoculants comprised of Rhizophagus irregularis, Funneliformis mosseae, or Claroideoglumus etunicatum, and one indigenous mixed species population inoculant. Overall, we found that AMF inoculation increased potato tuber yield by up to 23%, antioxidant activity by up to 120%, ergothioneine concentration by up to 9X, and soluble sugar concentration by up to 46%, and that the extent of these increases varied by mycorrhizal species. Future research should examine the extent to which inoculation with the most beneficial AMF species reported here improves yield and nutritional quality in the field setting.
The water relations of mycorrhizal onions ( Allium cepa L.) were compared with those of non-mycorrhizal controls grown under low and high soil phosphorus conditions. Mycorrhizal plants had higher leaf water potentials, higher transpiration rates, higher hydraulic conductivities and lower leaf resistances than did non-mycorrhizal plants grown in low soil phosphorus conditions. When controls were grown under high soil phosphorus conditions, all 4 parameters were not different from those of mycorrhizal plants. The magnitude of the effect of mycorrhizal fungi on the water relations of the host may, in part, be a function of phosphorus nutrition. The differences in leaf water potentials, transpiration rates and leaf resistances are considered to be the result of the differences found in hydraulic conductivities.
Vesicular-arbuscular mycorrhizal (VAM) development of Glomus intraradices Schenck & Smith and growth response of Carrizo citrange [ Poncirus trifoliata (L.) Raf. × Citrus sinensis (L.) Osbeck] and sour orange (C. aurantium L.) seedlings were examined in peat-perlite medium fertilized with 4 levels of superphosphate (SP) and rock phosphate (RP). Loss of P from SP-amended medium was exponential, whereas release of P was linear from RP-amended medium. With SP, root colonization by G. intraradices and growth response of both citrus rootstocks were reduced compared to RP-amended medium. VAM colonization and growth response were less with SP-amended medium than RP, probably because of the initially high available P from SP which inhibited VAM development, and because P later declined to levels insufficient to support maximum growth. When RP was used as a controlled-release source of P, VAM colonization was comparable to that observed in mineral soils. Growth of VAM plants exceeded that of uninoculated plants fertilized with increased levels of soluble P because of P-induced Cu deficiency in absence of VAM. An additional advantage of RP was long-term availability of P, compared to SP which leached within weeks after application to peat-perlite. No further P fertilization may be necessary if RP and VAM inoculum are incorporated into soilless media before planting, whereas repeated application of soluble P would be required for slow-growing woody plants like citrus.
Roots of Carrizo citrange seedlings were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus intraradices or provided an inoculum filtrate (non-VAM plants). Plants were exposed to drought stress after transplanting into large containers filled with a phosphorus amended medium (30 mg g ⁻¹ ). Drought stress caused reduction of phosphorus in leaf tissues and dry matter accumulation in VAM plants. However, phosphorus levels, dry weights, and transpiration of VAM seedlings were greater than non-VAM plants. Mychorrhizal infection appears to improve establishment of citrus into transplant situations by improving phosphorus uptake and reducing plant stress.
To determine the role of endomycorrhizae on water relations and plant growth of geraniums under nonrate-limiting soil P conditions, hybrid seedlings ( Pelargonium X hortorum Bailey cv. Cherry Glow) were planted in moderately high P (40 ppm) media, grown under high (−0.4 MPa) or low (−1 MPa) soil water potential (ψ s ), and either inoculated with VA mycorrhizal fungi [ Glomus mosseae (Nicol. & Gerd.) and G. fasciculatus (Thaxt. sensu Gerd.) Gerd. & Trappe] (VAM) or left as noninoculated controls. Geraniums grown under high moisture had greater shoot growth, more advanced floral development, and higher P uptake than the low moisture plants. Mycorrhizal plants under high moisture conditions had higher P levels than noninoculated plants, while mycorrhizal plants under low moisture regimes had greater shoot growth, more advanced floral formation, and greater N uptake than noninoculated plants. Xylem water potential in leaves (ψ L ) was lower under −1 MPa than −0.4 MPa ψ S moisture regimes and lowest in mycorrhizal geraniums grown under −1 MPa ψ S . One hundred minutes after plants had recovered from water stress, the greatest change in ψ L was recorded for mycorrhizal geraniums acclimatized to low moisture regimes. Geraniums under low moisture regimes are more mycorrhizal-dependent. Total estimated root length and root water conductivity were lower with mycorrhizal geraniums under high water and P regime. Under water stress, the larger mycorrhizal geraniums have greater total water demands than controls. Consequently, mycorrhizal geraniums stressed more rapidly yet more efficiently recovered from water deficits. Data suggests that VAM plants acclimate more efficiently to water stress because of more frequent or extreme drought.
The influence of arbuscular mycorrhizal fungi on drought tolerance and recovery was studied in safflower (Carthamus tinctorius L.) and wheat (Triticum aestivum L.). Plants were grown with and without the mycorrhizal fungus, Glomus etunicatum Becker & Gerd., in nutrient-amended soil under environmentally-controlled conditions to yield mycorrhizal and nonmycorrhizal with similar leaf areas, root length densities, dry weights, and adequate tissue phosphorus. When drought stress was induced, mycorrhizal infection did not affect changes in leaf water, osmotic or pressure potentials, or osmotic potentials of leaf tissue rehydrated to full turgor in either safflower or wheat. Furthermore, in safflower, infection had little effect on drought tolerance as indicated by the level of leaf necrosis. Mycorrhizal wheat plants, however, had less necrotic leaf tissue than uninfected plants at moderate levels of drought stress (but not at severe levels) probably due to enhanced phosphorus nutrition. To determine the effects of infection on drought recovery, plants were rewatered at a range of soil water potentials from –1 to –4 MPa. We found that although safflower tended to recover more slowly from drought after rewatering than wheat, mycorrhizal infection did not directly affect drought recovery in either plant species. Daily water use after rewatering was reduced and was correlated to the extent that leaves were damaged by drought stress in both plant species, but was not directly influenced by the mycorrhizal status of the plants.
Carbohydrates were analyzed in mycorrhizal and nonmycorrhizal citrus rootstock seedlings in greenhouse studies. Inoculated seedlings grew taller or weighed more and their leaves contained greater amounts of total soluble sugar, sucrose, reducing sugars, starch, and total nonstructural carbohydrate per gram of tissue than noninoculated controls, in a low P soil (9–12 ppm). Only the reducing sugars, fructose and glucose, increased slightly in roots of inoculated seedlings over those levels found in uninoculated control seedlings. Levels of reducing sugars were higher in leaves than in roots. Uninoculated seedlings grown in high P soil (210 ppm) were about the same height and their leaves contained levels of total soluble and reducing sugars similar to those in inoculated rootstocks grown in low P soil. It does not appear that these mycorrhizal fungi mobilize sugars as a sink for photosynthate in roots.
Recovery from water stress was studied on similarly sized VA mycorrhizal and non-mycorrhizal rough lemon seedlings (Citrus jambhiri Lush). VA mycorrhiza affected stomatal conductance, photosynthesis and proline accumulation, but not leaf water potential, suggesting that most of the effect of the mycorrhizal association is on stomatal regulation rather than on root resistance.
The effect of arbuscular mycorrhizal (AM) colonisation by Glomus clarum on fruit yield and water use efficiency (WUE) was evaluated in watermelon (Citrullus lanatus) cv. Crimson Sweet F1 under field conditions. Treatments were: (1) well-watered plants without mycorrhizae (WW-M), (2) well-watered plants with mycorrhizae (WW+M), (3) water- stressed plants without mycorrhizae (WS-M) and (4) water-stressed plants with mycorrhizae (WS+M). When soil water tension readings reached –20 and –50 kPa for well-watered (WW) and water-stressed (WS) treatments, respectively, irrigation was initiated to restore the top soil to near field capacity. Water stress reduced watermelon shoot and root dry matter, fruit yield, water use efficiency but not total soluble solids (TSS) in the fruit, compared with the non-stressed treatments. Mycorrhizal plants had significantly higher biomass and fruit yield compared to nonmycorrhizal plants, whether plants were water stressed or not. AM colonisation increased WUE in both WW and WS plants. Macro- (N, P, K, Ca and Mg) and micro- (Zn, Fe and Mn) nutrient concentrations in the leaves were significantly reduced by water stress. Mycorrhizal colonisation of WS plants restored leaf nutrient concentrations to levels in WW plants in most cases. This is the first report of the mitigation of the adverse effect of water stress on yield and quality of a fruit crop.
Arbuscular mycorrhizal fungi (AMF) living symbiotically with host plants enhance plant growth by improving the acquisition
of mineral nutrients and water relations. This study determined the effects of AMF inoculation on growth, benefit/cost and
water-use efficiency (grams dry matter produced per kilogram water evapotranspired) in two durum wheat genotypes (drought
sensitive and drought tolerant) under water-stressed and well-watered conditions. Plants were grown in a low-P silty clay
(Typic Xerochrept) soil mix in a greenhouse. Shoot and root dry matter (DM) and root AMF colonization were higher for well-watered
than for water-stressed plants. The mycorrhizal plants were more water-use efficient than nonmycorrhizal plants. Shoot DM
differences between mycorrhizal and nonmycorrhizal plants represent the benefit derived by plants from AMF-root associations.
Shoot DM differences between mycorrhizal and nonmycorrhizal plants under similar conditions of water treatment represent the
cost to the plant of AMF-root associations. Values of benefit/cost for AMF-root associations were highest when plants were
water-stressed and decreased under well-watered conditions. Genotypic differences in calculated costs and benefits were pronounced.
Benefit/cost analysis may be helpful in evaluating host plant genotypes in order to optimize efficiencies of AMF symbiosis
under different environmental conditions.
Plants of Helianthemum almeriense were micropropagated on MS medium and inoculated in vitro with Terfezia claveryi mycelium on MH medium and vermiculite. Mycorrhizal (M) and non-mycorrhizal (NM) plants were subjected to a drought stress period of 3 weeks in greenhouse conditions with the soil matric potential maintained at –0.5 MPa. Drought stress did not affect the amount of mycorrhizal colonization. The survival rate of M plants at the end of the drought stress period was higher than that of NM plants. The water potential was higher in M plants than in NM plants by 14% in well-watered and 26% in drought stressed plants. Transpiration, stomatal conductance and net photosynthesis were higher in M plants than in NM plants. Transpiration was 92% higher in M plants than in NM plants under drought-stress conditions and 40% when irrigated. Stomatal conductance was 45% and 14% higher and net photosynthesis 88% and 54% higher, respectively, in M than in NM plants. Drought stressed M plants accumulated more N, P and K than drought-stressed NM plants. Reduced negative effects of drought stress on H. almeriense by the desert truffle T. claveryi could be ascribed to specific physiological and nutritional mechanisms, suggesting that this mycorrhizal symbiosis aids adaptation to arid climates.
The arbuscular mycorrhizal (AM) symbiosis is the association between fungi of the order Glomales (Zy- gomycetes) and the roots of terrestrial plants (Harley and Smith, 1983). Conservative estimates suggest that this ancient symbiosis, dating back to the early Devonian age (398 million years ago), affects approx- imately 90% of the Earth's land plant species (Remy et al., 1994). This symbiosis is increasingly being recognized as an important and integral part of nat- ural ecosystems throughout the world. The AM fungus-plant association is a mutually beneficial event: The plant supplies the fungus with carbon (from its fixed photosynthates) while the fungus as- sists the plant in its uptake of phosphate and other mineral nutrients from the soil (Smith and Gianinazzi-Pearson, 1988; Smith and Read, 1997). This bidirectional exchange of nutrients takes place through extensively branched haustoria, termed ar- buscules. In addition to increased nutrition, mycor- rhizal plants also show increased resistance to root pathogens and tolerance to drought stress, and their hormonal balance is altered (Smith and Gianinazzi- Pearson, 1988; Hwang et al., 1992).
Water deficit is considered one of the most important abiotic factors limiting plant growth and yield in many areas on earth. Several eco-physiological studies have demonstrated that the arbuscular mycorrhizal (AM) symbiosis often results in altered rates of water movement into, through and out of the host plants, with consequent effects on tissue hydration and plant physiology. It is now accepted that the contribution of AM symbiosis to plant drought tolerance is the result of accumulative physical, nutritional, physiological and cellular effects. This review considers several aspects that should be investigated at a molecular level in order to gain a whole understanding of the different mechanisms by which the AM symbiosis protects the host plants against the detrimental effects of water deficit.
Mycorrhizal symbiosis can modify plant response to drying soil, but little is known about the relative contribution of soil vs. root hyphal colonization to drought resistance of mycorrhizal plants. Foliar dehydration tolerance, characterized as leaf and soil water potential at the end of a lethal drying episode, was measured in bean plants (Phaseolus vulgaris) colonized by Glomus intraradices or by a mix of arbuscular mycorrhizal fungi collected from a semi-arid grassland. Path analysis modeling was used to evaluate how colonization rates and other variables affected these lethal values. Of several plant and soil characteristics tested, variation in dehydration tolerance was best explained by soil hyphal density. Soil hyphal colonization had larger direct and total effects on both lethal leaf water potential and soil water potential than did root hyphal colonization, root density, soil aggregation, soil glomalin concentration, leaf phosphorus concentration or leaf osmotic potential. Plants colonized by the semi-arid mix of mycorrhizal fungi had lower lethal leaf water potential and soil water potential than plants colonized by G. intraradices. Our findings support the assertion that external, soil hyphae may play an important role in mycorrhizal influence on the water relations of host plants.
This study investigated several aspects related to drought tolerance in arbuscular mycorrhizal (AM) soybean plants. The investigation included both shoot and root tissues in order to reveal the preferred target tissue for AM effects against drought stress. Non-AM and AM soybean plants were grown under well-watered or drought-stressed conditions, and leaf water status, solute accumulation, oxidative damage to lipids, and other parameters were determined. Results showed that AM plants were protected against drought, as shown by their significantly higher shoot-biomass production. The leaf water potential was also higher in stressed AM plants (-1.9 MPa) than in non-AM plants (-2.5 MPa). The AM roots had accumulated more proline than non-AM roots, while the opposite was observed in shoots. Lipid peroxides were 55% lower in shoots of droughted AM plants than in droughted non-AM plants. Since there was no correlation between the lower oxidative damage to lipids in AM plants and the activity of antioxidant enzymes, it seems that first the AM symbiosis enhanced osmotic adjustment in roots, which could contribute to maintaining a water potential gradient favourable to the water entrance from soil into the roots. This enabled higher leaf water potential in AM plants during drought and kept the plants protected against oxidative stress, and these cumulative effects increased the plant tolerance to drought.
The effects of arbuscular mycorrhizal fungi Glomus mosseae on plant growth and osmotic adjustment matter content of trifoliate orange [Poncirus trifoliata (L.) Raf.] seedlings under water stress were studied in potted culture. The results showed that arbuscular mycorrhizal fungi inoculation could increase plant growth, such as plant height, stem diameter, leaf area, shoot dry weight, root dry weight and plant dry weight, when the water content of soil was 20%, 16% and 12%. Arbuscular mycorrhizal fungi inoculation also promoted active absorbing areas of plant root and absorption of P from plant rhizosphere, enhanced the accumulated quantities of soluble sugar content in leaves and roots, and reduced proline content of leaf. Plant inoculated with arbuscular mycorrhiza had higher plant water use efficiency than non-mycorrhizal plants. Drought tolerance of trifoliate orange seedling inoculated with arbuscular mycorrhiza was enhanced. Effects of arbuscular mycorrhizal fungi inoculation on trifoliate orange seedling under 20% and 16% water content of soil were more significant than under 12% water content of soil. Arbuscular mycorrhizal fungi infection was severely restrained by 12% water content of soil. Thus, effects of arbuscular mycorrhizal fungi on plant probably positively related to the arbuscular mycorrhizal inoculated percentage.
The tolerance of lettuce plants (Lactuca sativa L. cv. Romana) to drought stress differed with the arbuscular-mycorrhizal fungal isolate with which the plants were associated. Seven fungal species belonging to the genus Glomus were studied for their ability to enhance the drought tolerance of lettuce plants. These fungi had different traits that affected the drought resistance of host plants. The ranking of arbuscular-mycorrhizal fungal effects on drought tolerance, based on the relative decreases in shoot dry weight, was as follows: Glomus deserticola > Glomus fasciculatum > Glomus mosseae > Glomus etunicatum > Glomus intraradices > Glomus caledonium > Glomus occultum. In this comparative study specific mycorrhizal fungi had consistent effects on plant growth, mineral uptake, the CO(inf2) exchange rate, water use efficiency, transpiration, stomatal conductance, photosynthetic phosphorus use efficiency, and proline accumulation under either well-watered or drought-stressed conditions. The ability of the isolates to maintain plant growth effectively under water stress conditions was related to higher transpiration rates, levels of leaf conductance, and proline, N, and P contents. Differences in proline accumulation in leaves among the fungal symbioses suggested that the fungi were able to induce different degrees of osmotic adjustment. The detrimental effects of drought were not related to decreases in photosynthesis or water use efficiency. Neither of these parameters was related to P nutrition. The differences in P and K acquisition, transpiration, and stomatal conductance were related to the mycorrhizal efficiencies of the different fungi. Our observations revealed the propensities of different Glomus species to assert their protective effects during plant water stress. The greater effectiveness of G. deserticola in improving water deficit tolerance was associated with the lowest level of growth reduction (9%) under stress conditions. The growth of plants colonized by G. occultum was reduced by 70% after a progressive drought stress period. In general, the different protective effects of the mycorrhizal isolates were not associated with colonizing ability. Nevertheless, G. deserticola was the most efficient fungus and exhibited the highest levels of mycorrhizal colonization, as well as the greatest stimulation of physiological parameters.
Photosynthate partitioning was examined in seedings of sour orange (Citrus aurantium L.) and Carrizo citrange (Poncirus trifoliata [L.] Raf. x C. sinensis [L.] Osbeck) grown with split root systems inoculated on one side with vesicular-arbuscular mycorrhizal fungus (Glomus intraradices Schenck and Smith). Source-sink relations were studied without mitigating differences in mineral content or physiological age that can occur in separate plant comparisons, because phosphorus was evenly distributed between leaves on opposite sides of the seedlings. Above-ground portions of each plant were exposed to (14)CO(2) for 8.5 minutes and ambient air for 2 hours, followed by extraction and identification of labeled assimilates. Mycorrhizal halves of root systems accumulated 66 and 68% of the (14)C-labeled photosynthates translocated to roots of sour orange and ;Carrizo' citrange, respectively, as well as an average of 77% greater disintegrations per minute per gram fresh weight. Distribution of (14)C-labeled assimilates was independent of phosphorus effects on photosynthate partitioning in leaves and did not reflect fresh or dry weights of roots or degree of mycorrhizal dependency of the species. Differences in radioactivity between mycorrhizal and nonmycorrhizal root halves after 2 hours indicated at least 3 to 5% of the whole plant (14)C-labeled photosynthates were allocated to mycorrhizae-related events on one side and that twice this amount, or 6 to 10%, might be expected if the entire root system was infected.
Onion plants (Allium cepa L, cv. Downing Yellow Globe) grown in pots and infected by the mycorrhizal fungusGlomus etunicatus Becker and Gerdemann were more drought tolerant than were non-mycorrhizal individials when exposed to several periods of soil water stress separated by periods of high water supply, as shown by greater fresh and dry weights and higher tissue phosphorus levels in the mycorrhizal plants. The tissues of stressed, non-mycorrhizal plants were deficient in P, despite the fact that only non-mycorrhizal plants were fertilized with high levels of P (26 mg P per 440 g soil). Differences in plant water relations (leaf water potentials or transpiration rates) and changes in soil P levels which may have affected plant growth were investigated, and discounted as factors important for the results. The P nutrition of plants has been implicated in the ability of plants to tolerate drought and it was concluded that the ability of the mycorrhizal fungus to maintain adequate P nutrition in the onions during soil water stress was a major factor in the improved drought tolerance. Infection of the root by the fungus was found not to be affected by water stress or P fertilization but fungal reproduction, as determined by spore numbers in the soil, was decreased by water stress and by P fertilization.
Stomatal gas exchange and zeatin riboside levels (as determined by ELISA) of flax (Linum usitatissimum L.) were investigated with regard to an observed growth response of these plants to vesicular-arbuscular mycorrhizal infection, which was shown not to be related to increased nitrogen, phosphorus or potassimum contents of plants. Additionally, the stomatal gas exchange responses of non-mycorrhizal plants to zeatin and abscisic acid were studied by xylem application experiments. In comparison to non-mycorrhizal plants highly infected plants revealed increased transpiration and CO2 assimilation rates, while stomatal density was not affected and the shoot water potential (Ψ) was unchanged or even lowered. These findings indicated that enhanced stomatal opening was not primarily caused by an improved water supply of the shoots. Additionally, respiration rates of leaves of mycorrhizal plants were lower when compared with non-mycorrhizal plants at the end of the experiments. During the beginning of the mycorrhizal infection zeatin riboside levels in roots were temporarely decreased when compared to non-mycorrhizal plants, whereas levels where increased in shoots. However, when the symbiosis had established colonized roots revealed significantly higher zeatin riboside than those of non-mycorrhizal plants. Significant growth responses of shoots and roots due to mycorrhizal infection were preceded by higher zeatin riboside levels in the respective organs. Zeatin applied alone into the vascular system of non-mycorrhizal flax did not affect stomatal gas exchange, whereas abscisic acid applied alone decreased transpiration and CO2 assimilation rates. Additional application of zeatin, however, partially reversed abscisic acid-mediated effects and improved transpiration and CO2 assimilation rates showing analogy to the mycorrhizal infection. These results leed to the conclusion, that the enhanced internal Cytokinin levels are involved in the improved photosynthesis and growth of mycorrhizal flax.
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Seedlings of five citrus rootstocks were grown in a low phosphorus (P) sandy soil and were either (1) inoculated with Glomus intraradices Schenck & Smith, (2) non‐inoculated and fertilized with P, or (3) non‐inoculated without added P. The order of mycorrhizal dependency (MD) of the five rootstocks was sour orange = Cleopatra mandarin > Swingle citrumelo > Carrizo citrange > trifoliate orange. The less dependent rootstocks, trifoliate orange and its hybrid Carrizo citrange, had greater leaf P, finer roots (greater length per unit of dry root) and slower growth rates than sour orange and Cleopatra mandarin. Rootstocks with lower MD also generally had greater hydraulic conductivity of roots, and greater transpiration and CO 2 assimilation rates. Under well‐watered conditions, VAM plants of all five rootstocks did not differ in morphology, anatomy or physiology from non‐mycorrhizal plants fertilized with P of similar size, growth rate and P status.
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Carrizo citrange (CC) and sour orange (SO) seedlings were grown in a low phosphorus (P) sandy soil and either inoculated with Glomus intraradices Schenck & Smith or fertilized with soluble P. Mycorrhizal seedlings had nutritionally sufficient levels of leaf P, non‐mycorrhizal plants of similar size were P‐deficient. The root–shoot ratio of both rootstocks was reduced by mycorrhizal colonization, but root hydraulic conductivity per unit root length of mycorrhizal CC and SO was more than twice that of non‐mycorrhizal seedlings under well‐watered conditions. Mycorrhizal plants also had significantly higher transpiration rates when standardized on a root length basis, and greater transpiration appeared to be related to the increased conductivity of roots. Flow of water to roots via hyphae alone could not account for the greater water uptake by mycorrhizal roots. Apparently, mycorrhizal enchancement of P nutrition was primarily responsible for the greater conductivity of roots since no differences were found between root hydraulic conductivity of mycorrhizal and non‐mycorrhizal CC of equal P status under well‐watered conditions.
Red clover Trifolium pratense L. plants were grown in a factorial design with four levels of added P and with and without a mycorrhizal inoculum, to test
the separate effects of P nutrition and infection on plant water relations. Under well-watered conditions, only uninfected
plants on very low P soil showed reduced stomatal conductance and these had the lowest leaf P concentrations. During droughting,
only plants with very high leaf P concentrations maintained high conductance. There was no evidence of increased water uptake
by mycorrhizal plants. This and other evidence suggests that mycorrhizal effects on water relations are secondary consequences
of changes in P nutrition which are, in any case, inconsistent.
Vesicular-arbuscular mycorrhizae may increase resistance of plants to drought by a number of mechanisms, such as increased root hydraulic conductivity, stomatal regulation, hyphal water uptake and osmotic adjustment. However, a substantial contribution of vesicular-arbuscular mycorrhizal (VAM) hyphae to water uptake has not been demonstrated unequivocally. The objective of this investigation was to examine the contribution of hyphae from two VAM fungi to water uptake and transport by the host plant. Lettuce (Lactuca sativa L.) plants were grown in a container divided by a screen into two compartments. One was occupied by roots, the other only by VAM hyphae, which the screen permitted to pass. Roots were colonized by the VAM fungi Glomus deserticola or Glomus fasciculatum, or were left uninoculated but P-supplemented. Water was supplied to the hyphal compartment at a distance of 10 cm from the screen (root). CO2 exchange rate, water-use efficiency, transpiration, stomatal conductance and photosynthetic phosphorus-use efficiency of VAM or P-amended control plants were evaluated at three levels of water application in the hyphal compartment. Results indicate that much of the water was taken up by the hyphae in VAM plants. VAM plants, which had access to the hyphal compartment, had higher water and nutrient contents. G. deserticola functioned efficiently under water limitation and mycelium from G. fasciculatum-colonized plants was very sensitive to water in the medium. This discrepancy in VAM behaviour reflects the various abilities of each fungus according to soil water levels. Different abilities of specific mycelia were also expressed in terms of nutritional and leaf gas-exchange parameters. G. fasciculatum caused a significant increase in net photosynthesis and rate of water use efficiency compared to G. deserticola and P-fertilized plants. In contrast, the G. deserticola treatment was the most efficient affecting N, P and K nutrition, leaf conductance and transpiration. Since no differences in the intra- and extra-radical hyphal extension of the two endophytes were found, the results demonstrate that mycorrhizal hyphae can take up water and that there are considerable variations in both the behaviour of these two VAM fungi and in the mechanisms involved in their effects on plant water relations.
The beneficial effect of mycorrhization on photosynthetic gas exchange of host plants under drought conditions could be related to factors other than changes in phosphorus nutrition and water uptake. Our objective was to study the influence of drought on phytohormones and gas exchange parameters in Medicago sativa L. cv. Aragón associated with or in the absence of arbuscular mycorrhizal (AM) fungi and/or nitrogen-fixing bacteria. Four treatments were used: (1) plants inoculated with Glomus fasciculatum (Taxter sensu Gerd.) Gerdemann and Trappe and Rhizobium meliloti 102 F51 strain (MR); (2) plants inoculated with only Rhizobium (R); (3) plants inoculated with only mycorrhizae (M); and (4) non-inoculated plants (N). When endophytes were well established, treatments received different levels of phosphorus and nitrogen in the nutrient solution in order to obtain plants similar in size. Sixty days after planting, plants were subjected to two cycles of drought and recovery. Midday leaf water potential (Ψ), CO2 exchange rate (CER), leaf conductance (gw) and transpiration (T), as well as leaf and root abscisic acid (ABA) and cytokinin concentrations were measured after the second drought period. Gas exchange parameters were determined by infrared gas analysis. Cytokinins and ABA levels in tissues were analysed by ELISA and HPLC, respectively. Nodulated R and MR plants had the lowest ABA concentrations in roots under well-watered conditions. Water stress increased ABA concentrations in leaves of N, R and MR plants, while ABA concentration in M plants did not change. The highest production of ABA under water deficit was in the roots of non-mycorrhizal plants. The ratio of ABA to cytokinin concentration strongly increased in leaves and roots of non-mycorrhizal plants under drought. By contrast, this ratio was lowered in roots of M plants and remained unchanged in leaves and roots of MR plants when stress was imposed. The highest leaf conductances and transpirational fluxes under well-watered conditions were those of nitrogen-fixing R and MR plants, but these results were not impaired with increased CO2 exchange rates. Photosynthesis, leaf conductance and transpiration rates decreased in all treatments when stress was imposed, with the strongest decrease occurring in non-mycorrhizal plants. The relationships found between these gas exchange parameters and the hormone concentrations in stressed alfalfa tissues suggest that microsymbionts have an important role in the control of gas exchange of the host plant through hormone production in roots and the ABA/cytokinin balance in leaves. The most relevant effect of mycorrhizal fungi was observed under drought conditions.
IntroductionConcepts of Mycorrhizae and SymbiosisMycorrhizal Development and Some Biochemical Interactions Between Host and FungusDisease ResistanceNutrient UptakePlant StressMycorrhizal Fungi in Horticultural Crop ProductionConclusion
Literature Cited
Bethlenfalvay, G. J., Brown, M. S., Ames, R. N. and Thomas, R. S. 1988. Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake. ‐ Physiol. Plant. 72: 565–571.
Soybean [ Glycine max (L.) Merr.] plants were grown in pot cultures and inoculated with the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe or provided with P fertilizer (non‐VAM plants). After an initial growth period (21 days), plants were exposed to cycles of severe, moderate or no drought stress over a subsequent 28‐day period by rewatering at soil water potentials of ‐1.0, ‐0.3 or ‐0.05 MPa. Dry weights of VAM plants were greater at severe stress and smaller at no stress than those of non‐VAM plants. Phosphorus fertilization was applied to produce VAM and non‐VAM plants of the same size at moderate stress. Root and leaf P concentrations were higher in non‐VAM plants at all stress levels. All plants were stressed to permanent wilting prior to harvest. VAM plants had lower soil moisture content at harvest than non‐VAM plants. Colonization of roots by G. mosseae did not vary with stress, but the biomass and length of the extraradical mycelium was greater in severely stressed than in non‐stressed plants. Growth enhancement of VAM plants relative to P‐fertilized non‐VAM plants under severe stress was attributed to increased uptake of water as well as to more efficient P uptake. The ability of VAM plants to deplete soil water to a greater extent than non‐VAM plants suggests lower permanent wilting potentials for the former.
Four Glomus species/isolates from arid, semi-arid and mesic areas were evaluated for their effects on growth and water use characteristics
of young Citrus volkameriana (′Volkamer′ lemon) under well-watered conditions, followed by three soil-drying episodes of increasing severity (soil moisture
tensions of –0.02, –0.06, and –0.08 MPa) and recovery conditions. Arbuscular mycorrhizal (AM) plants were also compared to
non-AM plants given extra phosphorus (P) fertilizer. AM plants and non-AM plants had similar shoot size (dry weight and canopy
area), but all AM fungus treatments stimulated root growth (dry weight and length). Leaf P concentrations were 12–56% higher
in AM plants than non-AM plants. Enhanced root growth was positively correlated with leaf P concentration. In general, AM
plants had greater whole-plant transpiration than non-AM plants under well-watered conditions, under mild water stress and
during recovery from moderate and severe soil drying. This suggests a faster recovery from moisture stress by AM plants. AM
plants had lower leaf conductance than non-AM plants when exposed to severe soil drying. Although the greatest differences
were between AM and non-AM plants, plants treated with Glomus isolates differed in colonization level, leaf P concentration, root length, transpiration flux and leaf conductance.
We examined the influence of Glomus intraradices on nonhydraulic signaling of soil drying, in a drought-avoiding plant having stomates that are extremely sensitive to changes
in soil moisture. Cowpea [Vigna un
guiculata (L.) Walp. 'White Acre'] seedlings were grown in a greenhouse with root systems split between two pots. The 2×3×2 experimental
design included two levels of mycorrhizal colonization (presence or absence of Glomus intraradices Schenck & Smith UT143), three levels of phosphorus fertilization within each mycorrhizal treatment and two levels of water
(both pots watered or one pot watered, one pot allowed to dry). Stomatal conductance was mostly similar in fully watered mycorrhizal
and nonmycorrhizal controls. However, g
s
of half-dried, nonmycorrhizal plants was reduced on fewer days and to a lesser extent than g
s
of half-dried, mycorrhizal plants, perhaps related to quicker soil drying in mycorrhizal pots. The partial soil drying treatment
had little effect on leaf relative water content or osmotic potential, indicating that declines in g
s
and leaf growth were induced by some nonhydraulic factor. Leaf growth was inhibited only in nonmycorrhizal plants, evidently
due to a difference in phosphorus nutrition between mycorrhizal and nonmycorrhizal plants. The mycorrhizal effect on g
s
was not associated with phosphorus nutrition. Inhibition of g
s
was directly related to extent of soil drying, while inhibition of leaf growth was inversely related to extent of soil drying.
Vesicular-arbuscular mycorrhizal fungi can affect the water balance of both amply watered and droughted host plants. This
review summarizes these effects and possible causal mechanisms. Also discussed are host drought resistance and the influence
of soil drying on the fungi.
The response of 49 pea cultivars with different drought tolerance was studied. The tolerance to stress was determined according to the grain yield or the harvest index in rainfed farming. In these conditions variability among the genotypes in turgor maintenance, measured as the slope of the turgor potential (ψp) function against water potential (ψw), was observed. The cultivars, which best maintained turgor, were those which were more drought-tolerant. Turgor maintenance was significantly related to osmotic adjustment (OA). However, OA does not explain all the variability observed in dψp/dψw. Therefore, other factors such as tissue elasticity may also be influential. Soluble carbohydrate concentration increased (from 1.5 to 7 times) when the studied cultivars were subjected to water stress. The lines with a conventional leaf-type, showed a greater sugar content than semileafless lines when watered as well as when subjected to desiccation. The stimulation of sugar levels induced by drought was proportional to OA. During stress, the average soluble sugar content of all cultivars would be equivalent to 17.3% or 8.6% of ψs100, if all carbohydrates were present in the tissue as monosaccharides or disaccharides, respectively. This suggests that sugars play an important role in OA in peas. The free proline level also increased (from 4 to 40 times) in response to water stress. However, the contribution of this amino acid to ψs100 was small (approximately 1%) and no significant relationship was observed between proline content and OA. The cultivars which accumulated more proline had lower water contents upon turgor loss. This seems to indicate that proline may play a role in minimizing the damage caused by dehydration.
Pepper plants (Capsicum annuum L. cv. Orlando) were used to compare the effects of NaCl and KCl on osmotic adjustment, water relations, and gas exchange. Thus, two different saline treatments, 60 mM NaCl and 60 mM KCl, were applied and different measurement times (1, 2, 3 and 10 days) were assayed in order to determine the effect of the treatment duration on the parameters studied. Reductions in root hydraulic conductance, stomatal conductance and net assimilation of CO2 were observed after NaCl and KCl addition. Mineral composition of leaf sap was also determined and it was observed that Cl− and NO3− were the main anions used by pepper plants to achieve the osmotic adjustment. Also, salinity induced a decrease in the concentrations of Ca2+ and Mg2+ in leaves. Osmotic regulation by organic solutes was also determined, by analysis of the contents of sugars and amino acids. It appeared that sucrose was the main carbohydrate accumulated by the plants in order to maintain turgor. However, the degree of osmotic adjustment observed indicated that changes in leaf turgor occurred after either saline treatment, for all application times, suggesting that pepper plants could not adjust their water relations sufficiently. Thus, Na+ and K+ exerted a toxic effect on pepper plants mainly by affecting the plant water relations, although the effect of Na+ on water relations parameters was more significant than that of K+.
The domestication of halophytes has been proposed as a strategy to expand cultivation onto unfavorable land. However, halophytes mainly have been considered for their performance in extremely saline environments, and only a few species have been characterized in terms of their tolerance and physiological responses to moderately high levels of salinity. Salvadora persica is an evergreen perennial halophyte capable of growing under extreme conditions, from very dry environments to highly saline soils. It possesses high potential economic value as a source of oil and medicinal compounds. To quantify its response to salinity, S. persica seedlings were exposed to 200 mM NaCl for 3 weeks, and growth, leaf gas exchange and solute accumulation were measured. The presence of NaCl induced a 100% increase in fresh weight and a 30% increase in dry weight, relative to non-salinized controls. Increases in fresh weight and dry weight were not associated with higher rates of net CO2 assimilation, however. Analysis of ion accumulation revealed that S. persica leaves accumulated Na+ as a primary osmoticum. The concentration of Na+ in leaves of salinized plants was ∼40-fold greater than that measured in non-salinized controls, and this was associated with significant reductions in leaf K+ and Ca2+ concentrations. In addition, a significant accumulation of proline, probably associated with osmotic adjustment and protection of membrane stability, occurred in roots of salinized plants.
This study set out to determine the effect of drought stress on nitrate reductase (NR, EC 1.6.6.1.) activity in mycorrhizal plants, and to see if the maintenance of this enzymatic activity under stress conditions is a factor involved in the drought tolerance of mycorrhizal plants. Lactuca sativa L. plants were inoculated with three arbuscular mycorrhizal (AM) fungi, Glomus deserticola (Trappe. Bloss. and Menge), G. fasciculatum (Thax. and Gerd.) Gerd. and Trappe or G. mosseae (Nicol. and Gerd.) Gerd and Trappe or remained uninoculated (plus or less P fertilization). The plants were grwn under controlled conditions at constant soil water potential (close to −0.04 MPa) or at −0.17 MPa during the last six weeks of plant growth. Results obtained showed that mycorrhizal plants had higher NR activity (NRA) than the uninoculated treatments, particularly under water stress conditions. Control plants had 57% less NRA than G. deserticola-colonized ones under well watered conditions, with a reduction in NRA of 79% when the plants were subjected to drought stress. Under well-watered conditions the P-fertilized plants showed similar or higher growth and P content than the G. mosseae and G. fasciculatum mycorrhizal ones, the NRA being lower in P-fertilized than in AM plants. These results suggest that either the AM fungi increase the NRA in the host plant (regardless of the P content) or the AM fungi have such enzymatic activity per se. Besides, under the experimental conditions, plants colonized by different AM fungi showed different NR activities. It was concluded that drought stress decreased NRA, but much less in mycorrhizal than in uninoculated plants. This effect may be a factor in the drought tolerance of mycorrhizal plants.
Osmotic adjustment in Rosa hybrida L. cv Samantha was characterized by the pressure-volume approach in drought-acclimated and unacclimated plants brought to the same level of drought strain, as assayed by stomatal closure. Plants were colonized by either of the vesicular-arbuscular mycorrhizal fungi Glomus deserticola Trappe, Bloss and Menge or G. intraradices Schenck and Smith, or were nonmycorrhizal. Both the acclimation and the mycorrhizal treatments decreased the osmotic potential (Psi(pi)) of leaves at full turgor and at the turgor loss point, with a corresponding increase in pressure potential at full turgor. Mycorrhizae enabled plants to maintain leaf turgor and conductance at greater tissue water deficits, and lower leaf and soil water potentials, when compared with nonmycorrhizal plants. As indicated by the Psi(pi) at the turgor loss point, the active Psi(pi) depression which attended mycorrhizal colonization alone was 0.4 to 0.6 megapascals, and mycorrhizal colonization and acclimation in concert 0.6 to 0.9 megapascals, relative to unacclimated controls without mycorrhizae. Colonization levels and sporulation were higher in plants subjected to acclimation. In unacclimated hosts, leaf water potential, water saturation deficit, and soil water potential at a particular level of drought strain were affected most by G. intraradices. G. deserticola had the greater effect after drought preconditioning.
The purpose of this study was to test the hypothesis that vesicular arbuscular mycorrhizal (VAM) fungi affect net assimilation of CO(2) (A) of different-aged citrus leaves independent of mineral nutrition effects of mycorrhizae. Citrus aurantium L., sour orange plants were grown for 6 months in a sandy soil low in phosphorus that was either infested with the VAM fungus, Glomus intraradices Schenck & Smith, or fertilized with additional phosphorus and left nonmycorrhizal (NM). Net CO(2) assimilation, stomatal conductance, water use efficiency, and mineral nutrient status for expanding, recently expanded, and mature leaves were evaluated as well as plant size and relative growth rate of leaves. Nutrient status and net gas exchange varied with leaf age. G. intraradices-inoculated plants had well-established colonization (79% of root length) and were comparable in relative growth rate and size at final harvest with NM plants. Leaf mineral concentrations were generally the same for VAM and NM plants except for nitrogen. Although leaf nitrogen was apparently sufficient for high rates of A, VAM plants did have higher nitrogen concentrations than NM at the time of gas exchange measurements. G. intraradices had no effect on A, stomatal conductance, or water use efficiency, irrespective of leaf age. These results show that well-established VAM colonization does not affect net gas exchange of citrus plants that are comparable in size, growth rate, and nutritional status with NM plants.
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