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Carbon flow into soil and external hyphae from roots of mycorrhizal cucumber plants
New Phytologist
Abstract
Cucumber (Cucumis sativus L.) plants grown in PVC tubes with a partially sterilized soil-sand mixture were inoculated with the vesicular-arbuscular mycorrhizal fungus Glomus fasciculatum (Thaxter) Gerdemann & Trappe emend. Walker & Koske or left uninoculated. The soil column of each PVC tube was divided into a root and a hyphal compartment by a mesh bag (60 μm), which retained the roots but allowed external hyphae to pass. Inoculated plants rapidly became infected and an extensive mycelium developed. Three weeks after seedling emergence plants were labelled with 14CO2 for 16 h. The distribution of 14C within the plants and the 14C flow into external hyphae and soil were measured during an 80 h chase period. Below-ground respiration in mycorrhizal plants accounted for 27% of the photo assimilated 14C. Organic 14C in the soil represented 3˙1 % of the fixed 14C, and 26 % of this was located in external hyphae.
Based on conservative assumptions concerning dry weight of internal mycorrhizal infection and growth yield of the fungus, it was estimated that mycorrhizal events consumed 20 % of photoassimilated 14C. The specific incorporation of C by the external mycelium in the hyphal compartment was 41 μg C mg−1 dry wt. d−1.
The importance of external VA mycorrhizal hyphae for the distribution of plant-derived C in the soil volume and as a substrate source for the soil biota is discussed.
... In addition, the contribution of AM fungi to the C cycle also depends on both the extraradical hyphae (ERH) and exudates from AM fungal hyphae such as glomalin which can contribute to soil C aggregation and soil quality enhancement (Wright and Upadhyaya 1996;Tisdall et al. 1997;Zhu and Miller 2003;Zhang et al. 2016). However, several studies show that plant C allocated to hyphae was high enough to cause depression of host plant growth in some experiments, especially in nutrient-limited areas or at the establishment stages of roots and hyphae (Jakobsen 1999;Gavito et al. 2019). Thus, understanding the mechanisms by which AM fungi promote soil C storage is helpful. ...
... Inoculation with the AM fungus increased the concentration and total amount of 13 C in the plants (Figs. 3 and 4). This is supported by previous studies showing that AM fungi increase the C fixation capacity of their host plants by enhancing photosynthesis (Hoeksema et al. 2010;Jakobsen and Rosendahl 1990;Al-Karaki 2000;Drigo et al. 2010;Olsson et al. 2010). We also observed significantly higher 13 C concentrations in the intermediate leaves and roots in the mycorrhizal treatment as well as higher concentrations of 13 C in the young and senescent leaves and stems than in non-mycorrhizal controls (Fig. 3c). ...
... This is consistent with a previous study in which 14 C was fixed by plants and then transferred to AM fungi within a few minutes (Clemmensen et al. 2013). In fact, AM fungi contain 5 to 20% of the photosynthetic C (Jakobsen and Rosendahl 1990;Johnson et al. 1997). Therefore, AM fungi are regulators of C flux pools from above-to below-ground (Zhu and Miller 2003). ...
A three-compartment culture system was used to study the mechanism by which the AM fungus Funneliformis mosseae influences host plant growth and soil organic carbon (SOC) content in a northwest China coal mining area. A ¹³CO2 pulse tracing technique was used to trace the allocation of maize photosynthetic C in shoots, roots, AM fungus, and soil. Carbon accumulation and allocation in mycorrhizal (inoculated with Funneliformis mosseae) and non-mycorrhizal treatments were detected. AM fungal inoculation significantly increased the ¹³C concentration and content in both above- and below-ground plant parts and also significantly enhanced anti-aging ability by increasing soluble sugars and catalase activity (CAT) in maize leaves while reducing foliar malondialdehyde content (MDA) and leaf temperature and promoted plant growth. AM fungi also increased P uptake to promote maize growth. Soil organic carbon (SOC), glomalin, microbial biomass carbon (MBC), and nitrogen (MBN) contents increased significantly after inoculation. A mutually beneficial system was established involving maize, the AM fungus and the microbiome, and the AM fungus became an important regulator of C flux between the above- and below-ground parts of the system. Inoculation with the AM fungus promoted plant growth, C fixation and allocation belowground to enhance soil quality. A positive above-belowground feedback appeared to be established.
... Theses arbuscules and cells are separated by the periarbuscular space [66,67]. The plant exchanges up to 20% of its carbon molecules from photosynthesis with AMF [69,70], in the form of carbohydrates [71] and fatty acids [72], against various macroand micro-nutrients, taken from the soil via the extra-radical mycelium [73], such as phosphates [74], sulphates [75], nitrogen molecules [76], potassium [77], copper [77], iron [73,78], zinc [78], calcium, manganese, magnesium [79], and finally water [80,81]. Arbuscules have an average lifespan of 8.5 days, during which they are active for up to 5 days [82], and disappear by senescence, leaving the plant cell in its original state [83]. ...
... Also, AMF naturally contribute to better carbon sequestration in soils [89,91]: the improvement of soil aggregation by glomalin prevents the degradation and the leaching of soil organic matter [92]. AMF absorb carbon molecules from the plant's photosynthesis for their development and functioning [69,70]. This is not without consequences for the plant, because it creates a carbon sink for the plant: AMF will modify the primary carbon metabolism of the mycorrhizal plant, by deregulating photosynthesis and reducing the accumulation of photosynthates, to such an extent that a slowdown in growth has sometimes been observed in the establishment stage of AMF-plant symbiosis [93,94]. ...
Arbuscular mycorrhizal fungi (AMF) are soil microorganisms living in symbiosis with most terrestrial plants. They are known to improve plant tolerance to numerous abiotic and biotic stresses through the systemic induction of resistance mechanisms. With the aim of developing more sustainable agriculture, reducing the use of chemical inputs is becoming a major concern. After providing an overview on AMF history, phylogeny, development cycle and symbiosis benefits, the current review aims to explore the potential of AMF as biostimulants and/or biocontrol agents. Nowadays, AMF inoculums are already increasingly used as biostimulants, improving mineral nutrient plant acquisition. However, their role as a promising tool in the biocontrol market, as an alternative to chemical phytosanitary products, is underexplored and underdiscussed. Thus, in the current review, we will address the mechanisms of mycorrhized plant resistance to biotic stresses induced by AMF, and highlight the various factors in favor of inoculum application, but also the challenges that remain to be overcome.
... Theses arbuscules and cells are separated by the periarbuscular space [63,64]. The plant exchanges up to 20% of its carbon molecules from photosynthesis with AMF [66,67], in the form of carbohydrates [68] and fatty acids [69], against various macro-and micronutrients, taken from the soil via the extra-radical mycelium [70], such as phosphates [71], sulphates [72], nitrogen molecules [73], potassium [74], copper [74], iron [70,75], zinc [75], calcium, manganese, magnesium [76], and finally water [77,78]. Arbuscules have an average lifespan of 8.5 days, during which they are active for up to 5 days [79], and disappear by senescence, leaving the plant cell in its original state [80]. ...
... AMF absorb carbon molecules from the plant's photosynthesis for their development and functioning [66,67]. This is not without consequences for the plant, because it creates a carbon sink for the plant: AMF will modify the primary carbon metabolism of the mycorrhizal plant, by deregulating photosynthesis and reducing the accumulation of photosynthates, to such an extent that a slowdown in growth has sometimes been observed in the establishment stage of AMF-plant symbiosis [90,91]. ...
Arbuscular mycorrhizal fungi (AMF) are soil microorganisms living in symbiosis with most terrestrial plants. They are known to improve plant tolerance to numerous abiotic and biotic stresses through the systemic induction of resistance mechanisms. With the aim of developing a more sustainable agriculture, reducing the use of chemical inputs is becoming of a major concern. After providing an overview on the AMF history, phylogeny, development cycle and the symbiosis benefits, the current review aims at exploring the potential of AMF as biostimulants and/or biocontrol agents. Nowadays, AMF inoculums are already increasingly used as biostimulants, improving mineral nutrient plant acquisition. However, their role as promising tool into the biocontrol market, as alternative to chemical phytosanitary products, is underexplored and discussed. Thus, in the current review, we will address the mechanisms of mycorrhized plant resistance to biotic stresses induced by AMF, and highlight the various factors in favor of inoculum application, but also the challenges that remain to be overcame.
... Interactions between soil bacteria and plant-associated hyphae are likely shaped by resource dynamics. Plants share up to 20% of photosynthates with their mycorrhizal symbionts [29,30], which can rapidly transport these resources to surrounding bacteria [24,31]. Because fungi may explore a volume of soil that is two orders of magnitude greater than the area explored by plant roots [32], they may exert a substantial effect on soil microbiome structure and function. ...
... This suggests that R. irregularis and S. bescii modified edaphic conditions in some way that broadly supported bacterial resilience to water limitation. Plant-associated fungi can exude plant-derived C [24,[29][30][31][32], promote biofilm formation [88], enhance soil aggregation through their interactions with other soil biota [14,89], and facilitate bacterial transport through soil [90]. Together, these fungalmediated processes could help maintain soil connectivity, microbial activity, and nutrient cycling under water-limited conditions, thereby preventing bacterial dormancy and death despite a substantial decline in soil moisture. ...
Drought disrupts soil microbial activity and many biogeochemical processes. Although plant-associated fungi can support plant performance and nutrient cycling during drought, their effects on nearby drought-exposed soil microbial communities are not well resolved. We used H 2 ¹⁸ O quantitative stable isotope probing (qSIP) and 16S rRNA gene profiling to investigate bacterial community dynamics following water limitation in the hyphospheres of two distinct fungal lineages ( Rhizophagus irregularis and Serendipita bescii ) grown with the bioenergy model grass Panicum hallii . In uninoculated soil, a history of water limitation resulted in significantly lower bacterial growth potential and growth efficiency, as well as lower diversity in the actively growing bacterial community. In contrast, both fungal lineages had a protective effect on hyphosphere bacterial communities exposed to water limitation: bacterial growth potential, growth efficiency, and the diversity of the actively growing bacterial community were not suppressed by a history of water limitation in soils inoculated with either fungus. Despite their similar effects at the community level, the two fungal lineages did elicit different taxon-specific responses, and bacterial growth potential was greater in R. irregularis compared to S. bescii -inoculated soils. Several of the bacterial taxa that responded positively to fungal inocula belong to lineages that are considered drought susceptible. Overall, H 2 ¹⁸ O qSIP highlighted treatment effects on bacterial community structure that were less pronounced using traditional 16S rRNA gene profiling. Together, these results indicate that fungal–bacterial synergies may support bacterial resilience to moisture limitation.
... AM fungi are obligate biotrophs that require the roots of a living host to grow and complete their life stages (Kehri et al., 2018). They colonize plant roots in exchange for carbohydrates, up to 20% of photosynthetically fixed, organic carbon (C)-based compounds (C) (Jakobsen and Rosendahl, 1990;Smith and Read, 2008), and provide their plant hosts with mineral nutrients required for plant growth (Jakobsen et al., 1992;Luginbuehl et al., 2017). ...
Taxonomic identification of arbuscular mycorrhizal (AM) fungal spores extracted directly from the field is sometimes difficult because spores are often degraded or parasitized by other organisms. Single-spore inoculation of a suitable host plant allows for establishing monosporic cultures of AM fungi. This study aimed to propagate AM fungal spores isolated from maize soil using single spores for morphological characterization. First, trap cultures were established to trigger the sporulation of AM fungal species. Second, trap cultures were established with individual morphotypes by picking up only one spore under a dissecting microscope and transferring it to a small triangle of sterilized filter paper, which was then carefully inoculated below a root from germinated sorghum seeds in each pot and covered with a sterile substrate. All pots were placed in sunbags and maintained in a plant growth room for 120 days. Spores obtained from single spore trap cultures from each treatment, maize after oats (MO), maize after maize (MM), maize after peas (MP), and maize after soybean (MS), were extracted using the sieving method. Healthy spores were selected for morphological analysis. Direct PCR was conducted by crushing spores in RNAlater and applying three sets of primer pairs: ITS1 × ITS4, NS31 × AML2, and SSUmcf and LSUmBr. Nucleotide sequences obtained from Sanger sequencing were aligned on MEGA X. The phylogenetic tree showed that the closest neighbors of the propagated AM fungal species belonged to the genera Claroideoglomus, Funneliformis, Gigaspora, Paraglomus, and Rhizophagus. The morphological characteristics were compared to the descriptive features of described species posted on the INVAM website, and they included Acaulospora cavernata, Diversispora spurca, Funneliformis geosporus, Funneliformis mosseae, Gigaspora clarus, Gigaspora margarita, Glomus macrosporum, Paraglomus occultum, and Rhizophagus intraradices. These findings can provide a great contribution to crop productivity and sustainable management of the agricultural ecosystem. Also, the isolate analyzed could be grouped into efficient promoters of growth and mycorrhization of maize independent of their geographical location.
... Meanwhile, AM hyphae entail a lower carbon construction cost (Fitter 1991), a higher P-acquisition rate per unit of length compared with fine roots (Jakobsen et al. 1992) and allow nutrient acquisition beyond the root-depletion nutrient-impoverished zone. AM colonization might, therefore, be favorable to growth in less infertile soil (Treseder and Allen 2002), provided that the potential increase in photosynthesis associated with greater nutrient translocation to leaves (Eissenstat et al. 1993) offsets the higher respiration cost of colonized fine roots (Jakobsen and Rosendahl 1990). The latter is supported by our study, as more abundant species displaying large-diameter and high AM colonization also exhibited high SLA, leaf [N], and [P], suggesting high mass-based photosynthetic activities (Wright et al. 2004). ...
Background and aims
Unravelling how fundamental axes of leaf and fine-root trait variation correlate and relate to nutrient availability is crucial for understanding plant distribution across edaphic gradients. While leaf traits vary consistently along soil nutrient availability gradients, the response of fine-root traits to the same gradients has yielded inconsistent results.
Methods
We studied leaf and root trait variation among 23 co-occurring plant species along a 2-million-year soil chronosequence to assess how leaf and root traits coordinate and whether this axis of trait variation relates to soil fertility.
Results
Leaf and root trait variation was primarily structured by mycorrhizal association types. However, when considering community-level traits weighted by plant species abundance, soil nutrient availability was an important driver of trait distribution. Leaves that support rapid growth on younger more fertile soils were associated with roots of larger diameter and arbuscular mycorrhizal colonization. In contrast, leaves that favor nutrient conservation on nutrient-impoverished soil were associated with greater root-hair length and phosphorus-mobilizing root exudates proxied by leaf manganese concentration. At the species level, leaf and root trait variation patterns deviated from the community-wide results, as leaves that support either rapid growth or survival were associated with a wide range of root trait syndromes.
Conclusions
Our results highlight the challenge of generalizing a specific set of root-trait values that consistently meet the requirements of leaves supporting rapid growth or survival. Hence, the leaf economic spectrum's ability to capture variation in carbon gain may not be reflected by the root economic space.
... These strategies have a carbon and nitrogen cost so that treesif they have evolved control of their carbon allocationcould reduce investment in strategies when nutrients are abundant or light becomes limiting (Bloom et al., 1985;Treseder & Vitousek, 2001). Mycorrhizal fungi can cost up to 20% of the net carbon fixed by plants (Jakobsen & Rosendahl, 1990;Lynch et al., 2005), and root phosphatase enzymes are between 15% and 20% nitrogen on a mass basis (Wang et al., 2007). Accordingly, as phosphorus becomes limiting, trees would increase investment in root phosphatase and mycorrhizal fungi. ...
Nutrient limitation may constrain the ability of recovering and mature tropical forests to serve as a carbon sink. However, it is unclear to what extent trees can utilize nutrient acquisition strategies – especially root phosphatase enzymes and mycorrhizal symbioses – to overcome low nutrient availability across secondary succession.
Using a large‐scale, full factorial nitrogen and phosphorus fertilization experiment of 76 plots along a secondary successional gradient in lowland wet tropical forests of Panama, we tested the extent to which root phosphatase enzyme activity and mycorrhizal colonization are flexible, and if investment shifts over succession, reflective of changing nutrient limitation. We also conducted a meta‐analysis to test how tropical trees adjust these strategies in response to nutrient additions and across succession.
We find that tropical trees are dynamic, adjusting investment in strategies – particularly root phosphatase – in response to changing nutrient conditions through succession. These changes reflect a shift from strong nitrogen to weak phosphorus limitation over succession. Our meta‐analysis findings were consistent with our field study; we found more predictable responses of root phosphatase than mycorrhizal colonization to nutrient availability.
Our findings suggest that nutrient acquisition strategies respond to nutrient availability and demand in tropical forests, likely critical for alleviating nutrient limitation.
... In the last decade, increasing attention has been devoted to the hyphosphere of arbuscular mycorrhizal (AM) fungi, which are obligatory symbionts of plants. Given that AM fungal mycelia vastly extend in soil (from 82 to 111 m cm −3 in prairie and 52 to 81 m cm −3 in ungrazed pasture [13]) and mobilize between 4 and 20% of the total carbon (C) synthesized by plants [14,15], they can be considered as key players in ecosystems, enabling bacterial activity (e.g., solubilization of organic phosphorus (P)) by excretion of compounds used as nutrients or acting as signals at their surface [16]. This hyphosphere interface thus represents a huge biological market for C and nutrients (especially P) with trade-offs between AM fungi and bacteria [17]. ...
Background
Fungi and bacteria coexist in a wide variety of environments, and their interactions are now recognized as the norm in most agroecosystems. These microbial communities harbor keystone taxa, which facilitate connectivity between fungal and bacterial communities, influencing their composition and functions. The roots of most plants are associated with arbuscular mycorrhizal (AM) fungi, which develop dense networks of hyphae in the soil. The surface of these hyphae (called the hyphosphere) is the region where multiple interactions with microbial communities can occur, e.g., exchanging or responding to each other’s metabolites. However, the presence and importance of keystone taxa in the AM fungal hyphosphere remain largely unknown.
Results
Here, we used in vitro and pot cultivation systems of AM fungi to investigate whether certain keystone bacteria were able to shape the microbial communities growing in the hyphosphere and potentially improved the fitness of the AM fungal host. Based on various AM fungi, soil leachates, and synthetic microbial communities, we found that under organic phosphorus (P) conditions, AM fungi could selectively recruit bacteria that enhanced their P nutrition and competed with less P-mobilizing bacteria. Specifically, we observed a privileged interaction between the isolate Streptomyces sp. D1 and AM fungi of the genus Rhizophagus, where (1) the carbon compounds exuded by the fungus were acquired by the bacterium which could mineralize organic P and (2) the in vitro culturable bacterial community residing on the surface of hyphae was in part regulated by Streptomyces sp. D1, primarily by inhibiting the bacteria with weak P-mineralizing ability, thereby enhancing AM fungi to acquire P.
Conclusions
This work highlights the multi-functionality of the keystone bacteria Streptomyces sp. D1 in fungal-bacteria and bacterial-bacterial interactions at the hyphal surface of AM fungi.
3XiVYVBxkNucerLC-WX6ofVideo Abstract
... Short-term experiments using 14CO2 showed that photoassimilates were transported to the fungi, with most 14C labeling found in soluble sugars in mycorrhizal roots and hyphae. Estimates from Jakobsen and Rosendahl [13] suggested that 20% of the plant's carbon budget is allocated to AMF. Hexose sugars were identified as the primary carbon source for AMF by Shachar-Hill et al. [14], while Pfeffer et al. [15] demonstrated that AMF synthesized lipids from dextrose and fructose in roots, transferring these lipids to external hyphae. ...
Since its initial discovery and investigation two centuries ago, mycorrhizal symbiosis has evolved from a concept to a firmly established phenomenon within the realm of beneficial mutualistic symbioses. In the first two decades of the twenty-first century, significant strides have been made in understanding and harnessing the potential of arbuscular mycorrhizal fungi (AMF). This chapter traces the trajectory of mycorrhizal symbiosis research, with a focus on AMF, elucidating its historical development and contemporary advancements. Beginning with an exploration of the evolution of symbiosis as a concept, we delve into the historical context that shaped our understanding of mycorrhizal symbiosis. Through meticulous research and argumentation, the acceptance of mycorrhizal symbiosis as a vital ecological process has been solidified. Drawing from recent research, we showcase the remarkable achievements in AMF studies, including a deeper understanding of AMF communities' natural distribution across various ecosystems such as agriculture, forests, and grasslands. Additionally, we highlight breakthroughs in elucidating the mechanisms underlying AMF formation and their multifaceted roles in nutrient uptake, carbon metabolism, pest inhibition, plant health improvement, and bioremediation. Central to our discussion are the revelations concerning the enigmatic structure and function of arbuscules, along with the intricate symbiotic ultrastructural interface. Moreover, we explore the confirmed interactions between AMF and global environmental changes, paving the way for innovative applications of AMF in mitigating the effects of such changes. Looking ahead, we identify opportunities for further exploration and application of AMF while acknowledging current challenges and limitations. By envisioning the future prospects of AMF research and applications, we aim to catalyze the advancement of mycorrhizology and biological symbioses, fostering a deeper understanding of these intricate ecological relationships and their potential for sustainable development.
... El principal atributo de esta interacción simbiótica (por lo general mutualista), es la transferencia bidireccional de nutrientes: las plantas proveen a los hongos de un microhábitat (dentro de sus raíces) y energía (carbohidratos derivados de la fotosíntesis), esenciales para su supervivencia y crecimiento; aunque las estimaciones pueden variar, se ha sugerido que las plantas podrían destinar entre 10 y 30% de sus fotosintatos para mantener la relación con los HMA (Jacobsen y Rosendahl, 1990;Finlay y Söderström, 1992). A cambio, los hongos forman extensas redes de hifas (células alargadas con diámetros de pocas micras características de los hongos, que en su conjunto se denomina micelio) de manera extrarradical, es decir fuera de las raíces, en el suelo. ...
El bosque mesófilo de montaña (BMM) ocupa ~1% del territo mexicano. Concentra una gran riqueza biológica, un notable grado de endemismos y provee varios servicios ecosistemicos. Sin embargo, se encuentra amenazado por actividades antropogénicas. Debido a su importancia para la conservación de la biodiversidad y de los servicios ambientales que proveen, los BMM se consideran uno de los ecosistemas más amenazados del mundo. Varios esfuerzos se han realizado para entender los efectos del cambio de uso de suelo sobre los organismos y sus interacciones bajo una perspectiva de ecología funcional, con el propósito de aplicar métodos novedosos de restauración y conservación. Los hongos micorrizógenos arbusculares (HMA) son un grupo clave de la biota del suelo que pueden contribuir a la restauración de ecosistemas degradados. Por lo tanto, entender el efecto del cambio de uso de suelo sobre la diversidad de HMA y sus plantas hospederas es importante.
En Cumbres de Huicicila, Nayarit; se seleccionó un fragmento de BMM y aledaño a éste, el cafetal que lo ha sustituido. Se colectó suelo para extraer, y estimar la abundancia y riqueza de especies de HMA.
se registrarón 9 y 10 especies para el BMM y cafetal respectivamente, éste último presentando la mayor abundancia. Aunque se ha reportado una riqueza similar entre el BMM y su cafetal asociado, como en este estudio, la riqueza encontrada fue menor comparada con otros estudios. También, contrario a otros estudios la abundancia fue mayor en el cafetal. Es probable que diversidad de HMA y plantas no esté correlacionada, pero el ecotono podría explicar la mayor abundacia de esporas en el cafetal. Por lo tanto, sería recomendable usar herramientas moleculares para determinar el papel que tiene el cambio de uso de suelo sobre la diversidad de los HMA y sus plantas hospederas en ambas comunidades vegetales.
... Understanding the individual and combined impacts of perturbations on AM fungi is important because they are a critical component of most terrestrial ecosystems. Forming mutualistic relationships with at least 80% of terrestrial plant species, AM fungi acquire and translocate mineral nutrients from the soil to their hosts in exchange for carbon (C) derived from plant photosynthesis (Smith and Read, 2008;Smith and Smith, 2012); numerous studies demonstrate that non-defoliated plants can transfer upwards of 20% of recently assimilated photosynthetic C to AM fungi through their hyphal network (Douds et al., 1988;Jakobsen and Rosendahl, 1990;Johnson et al., 2002). Defoliation, defined here as the removal of leaf material and hence plant photosynthetic tissue, a typical feature of mown and grazed grasslands and can potentially lead to a decrease in primary productivity (Bethlenfalvay and Dakessian, 1984;Bethlenfalvay et al., 1985;Smith and Read, 2008). ...
... Arbuscular mycorrhizal fungi (AMF, phylum Mucoromycota, subphylum Glomeromycotina) form symbiotic associations with over 80% of vascular plant families (Sch€ ubler et al., 2001;Spatafora et al., 2016) and facilitate plant nutrient uptake in exchange for photosynthetically derived carbon (C) (Smith & Read, 2008;Willis et al., 2013). Arbuscular mycorrhizal fungi consume 6.2% of plant photosynthate C on average (Hawkins et al., 2023) and grow extensive hyphal networks into soil (Jakobsen & Rosendahl, 1990;Tome et al., 2015), which can account for 15-30% of the soil microbial biomass (Leake et al., 2004;Parniske, 2008;Qin et al., 2017), and explore a soil volume substantially larger than fine roots alone (See et al., 2022). The composition, exudates, and interactions of AMF hyphae with plant roots and soil microbes play a critical and complex role in soil C processes (Wei et al., 2019;Domeignoz-Horta et al., 2021;Horsch et al., 2023). ...
Arbuscular mycorrhizal fungi (AMF) transport substantial plant carbon (C) that serves as a substrate for soil organisms, a precursor of soil organic matter (SOM), and a driver of soil microbial dynamics. Using two‐chamber microcosms where an air gap isolated AMF from roots, we ¹³CO2‐labeled Avena barbata for 6 wk and measured the C Rhizophagus intraradices transferred to SOM and hyphosphere microorganisms.
NanoSIMS imaging revealed hyphae and roots had similar ¹³C enrichment. SOM density fractionation, ¹³C NMR, and IRMS showed AMF transferred 0.77 mg C g⁻¹ of soil (increasing total C by 2% relative to non‐mycorrhizal controls); 33% was found in occluded or mineral‐associated pools.
In the AMF hyphosphere, there was no overall change in community diversity but 36 bacterial ASVs significantly changed in relative abundance. With stable isotope probing (SIP)‐enabled shotgun sequencing, we found taxa from the Solibacterales, Sphingobacteriales, Myxococcales, and Nitrososphaerales (ammonium oxidizing archaea) were highly enriched in AMF‐imported ¹³C (> 20 atom%). Mapping sequences from ¹³C‐SIP metagenomes to total ASVs showed at least 92 bacteria and archaea were significantly ¹³C‐enriched.
Our results illustrate the quantitative and ecological impact of hyphal C transport on the formation of potentially protective SOM pools and microbial roles in the AMF hyphosphere soil food web.
... New Phytologist more C-efficient (Raven et al., 2018). A similar pattern may occur in low-P soils, where a greater soil volume has to be explored to acquire exchangeable P. Arbuscular mycorrhizal hyphae incur a lower C construction cost than fine roots (Raven et al., 2018), but potentially a higher C respiration cost (Jakobsen & Rosendahl, 1990). Consequently, the varying advantages of symbiosis may have promoted soil exploration through AM hyphae for some species, enabling spatial resource partitioning among species with varying levels of dependency to mycorrhizal symbiosis (Steidinger et al., 2015). ...
Soil phosphorus (P) is a growth‐limiting nutrient in tropical ecosystems, driving diverse P‐acquisition strategies among plants. Particularly, mining for inorganic P through phosphomonoesterase (PME) activity is essential, given the substantial proportion of organic P in soils. Yet, the relationship between PME activity and other nutrient‐acquisition root traits remains unclear.
We measured root PME activity and commonly measured root traits, including root diameter, specific root length (SRL), root tissue density (RTD), and nitrogen concentration ([N]) in 18 co‐occurring species across soils with varying P availability to better understand trees response to P supply.
Root [N] and RTD were inversely related, and that axis was not clearly related to soil P supply. Both traits, however, correlated positively and negatively with PME activity, which responded strongly to P supply. Conversely, root diameter was inversely related to SRL, but this axis was not related to P supply.
This pattern suggests that limiting similarity influenced variation along the diameter–SRL axis, explaining local trait diversity. Meanwhile, variation along the root [N]–RTD axis might best reflect environmental filtering. Overall, P availability indicator traits such as PME activity and root hairs only tended to be associated with these axes, highlighting limitations of these axes in describing convergent adaptations at local sites.
... Plants can acquire soil P through their roots, but P acquisition through AMF is generally more C efficient than direct root uptake, particularly at low soil P concentrations [2,3]. AMF, on the other hand, consume 2-20% of plant photosynthates [1,4]. Despite this high C investment by plants in AMF, plants generally benefit from this symbiosis [5], and accordingly plants acquire the majority of P through associated AMF [6][7][8]. ...
Arbuscular mycorrhizal fungi (AMF) are plant root symbionts that provide phosphorus (P) to plants in exchange for photosynthetically fixed carbon (C). Previous research has shown that plants—given a choice among AMF species—may preferentially allocate C to AMF species that provide more P. However, these investigations rested on a limited set of plant and AMF species, and it therefore remains unclear how general this phenomenon is. Here, we combined 4 plant and 6 AMF species in 24 distinct plant-AMF species compositions in split-root microcosms, manipulating the species identity of AMF in either side of the root system. Using ¹⁴ C and ³² P/ ³³ P radioisotope tracers, we tracked the transfer of C and P between plants and AMF, respectively. We found that when plants had a choice of AMF species, AMF species which transferred more P acquired more C. Evidence for preferential C allocation to more beneficial AMF species within individual plant roots was equivocal. However, AMF species which transferred more P to plants did so at lower C-to-P ratios, highlighting the importance both of absolute and relative costs of P acquisition from AMF. When plants had a choice of AMF species, their shoots contained a larger total amount of P at higher concentrations. Our results thus highlight the benefits of plant C choice among AMF for plant P acquisition.
... Here, we investigated whether AM fungi, that are part of the plant root microbiome, are themselves also similarly able to interact with microbes. AM fungi do not only transfer mineral nutrients to the host plants, but also relocate 5-20% of photosynthates from the plant to the surrounding environment [48,49]. As such, the AM hyphae provide space and nutrients for microbes to grow on and have been shown that the AM hyphosphere microbiome is different from the bulk soil [22,23]. ...
Background
Plant microbiomes play crucial roles in nutrient cycling and plant growth, and are shaped by a complex interplay between plants, microbes, and the environment. The role of bacteria as mediators of the 400-million-year-old partnership between the majority of land plants and, arbuscular mycorrhizal (AM) fungi is still poorly understood. Here, we test whether AM hyphae-associated bacteria influence the success of the AM symbiosis.
Results
Using partitioned microcosms containing field soil, we discovered that AM hyphae and roots selectively assemble their own microbiome from the surrounding soil. In two independent experiments, we identified several bacterial genera, including Devosia, that are consistently enriched on AM hyphae. Subsequently, we isolated 144 pure bacterial isolates from a mycorrhiza-rich sample of extraradical hyphae and isolated Devosia sp. ZB163 as root and hyphal colonizer. We show that this AM-associated bacterium synergistically acts with mycorrhiza on the plant root to strongly promote plant growth, nitrogen uptake, and mycorrhization.
Conclusions
Our results highlight that AM fungi do not function in isolation and that the plant-mycorrhiza symbiont can recruit beneficial bacteria that support the symbiosis.
Aik4iJYbzAos1E2c5U4cFFVideo Abstract
... The transfer of photosynthates from the host plants to the AM fungal intraradical hyphae and then to extraradical hyphae before release to the soil matrix is a well-known method by which AMF sequester C in soil (Solaiman 2014). AM fungi have an indirect impact on C sequestration in soils and cause a 4-20% drain of carbon from the host plant to their hyphae (Jakobsen and Rosendahl 1990). They directly affect soil C sequestration by increasing the number and turnover of extraradical hyphae in the bulk soil and rhizosphere. ...
The Himalayan region is one of the planet’s most distinctive mountain ecosystems as a result of its geography, altitude, and biological diversity. Mountain ecosystems throughout the world are being affected by overuse of resources, widespread land conversion, and climate change. Despite their rich biodiversity and diverse ecosystems, mountains are facing an increasing pressure from land conversion, industrialization, and climate change. Between 2000 and 2025, food production in developing nations, now estimated at 1223 million metric tonnes (Mt), should increase by 778 million Mt, or 2.5% annually, to fulfill the demands of an expanding population and an anticipated change in diet. SOC is regarded as the most important indicator of soil quality and agricultural sustainability. Focusing on improving soil quality and agronomic productivity per unit area through an increase in the soil organic carbon pool provides the most additional advantages among all the others. Adopting suggested management techniques on arable lands and degraded soils would improve soil quality. Cropland deterioration is accelerated by increased agricultural activity, and restoration has been controlled by modifying the vegetation on the land. However, little is known about the crucial microbiome that fuels the degradation of organic materials linked to plants during vegetation regeneration. Ecological rehabilitation of deteriorated areas has gradually increased public awareness and sparked widespread concern around the world. Thus, this chapter will focus on the role of microbes and their functioning in enhancing SOC and in the restoration of the degraded agricultural ecosystems.
... A quick transformation of sucrose into hexoses (within a plant) and hexoses into lipids and trehaloses (in fungal structures) maintains the gradient of concentrations which promotes the diffusion of carbohydrates via the contact zone (Harrison, 1996). The increase in the expression of plant transporter genes of hexoses in arbuscular mycorrhizal roots may be a mechanism to control the outfl ow of carbon to the fungal symbiont (the export of carbohydrates from the plant cells and the reverse absorption of hexoses from the interphase apoplast) (Jakobsen and Rosendahl, 1990;Bravo et al, 2017;Martino and Crawford, 2021). ...
Aim. A review of the literature to establish the mechanisms of the main mutualistic interactions that are important for the potential application of symbiotic fungi as biofertilizers, bioprotectors and bioregulators for more sustainable and so-called greening agriculture, soil restoration and understanding the role of microsymbionts in natural ecosystems. Methods. Comparative analysis of scientific literature. Results. Root mycorrhization is a potent factor of plant growth intensification, metabolic processes activation and macro-organism development improvement. Mycorrhiza formation is notable for angiosperms and gymnosperms, yet many representatives of bryophytes, ferns, and mosses also reveal (other) close symbiotic relations with fungi. Mycorrhizal fungi account for about 10 % of identified fungal species, including essentially all of the Glomeromycota and substantial fractions of the Ascomycota and Basidiomycota. De- pending on the fungal structures and microsymbiont position in tissues or cells of the macrosymbiont, arbuscular, ericoid, arbutoid, monotropoid, orchid mycorrhiza and so-called ectendomycorrhiza, and ectomycorrhiza are distinguished. This review gives an overview of the signalling interaction between partners and the bidirectional mechanism of nutrient exchange or other mutual benefits. Conclusions. Microscopic saprophytic fungi, capable of penetrating plant roots and playing a critical role in plant adaptation to abiotic and biotic stressors, are of special interest in mutualistic symbioses. In addition, while forming mutualistic symbioses with plants, the saprophytic fungi promote bio- mass increase and enhance the food traits of plants. The type of interaction depends on both micro- and macrosymbiot; it may in some cases and for some organisms fluctuate from mutualistic, commensalistic to antagonistic, even parasitic interactions, demonstrating different stages of mutualism evolution and co-habitation and/or evolution of plants and fungi. A better understanding of the diverse roles of symbiotic microorganisms in ecosystems will improve the ways of their application in agriculture.
... However, Zhang [22] indicated that both microbes and plants were self-sufficient, and few interactions occurred in suitable and appropriate interaction environments. These contradictory results suggest that the diverse associations between AMF and diazotrophs are known to be regulated by resource availability [17], tolerant or sensitive plant cultivars [64], and the physiological status of host plants [65]. In this study, co-occurrence network analysis revealed a higher positive correlation between AMF and diazotrophs in MG3.8 soybean than in the other earlier MG genotypes, and the correlation included a lower number of nodes and edges and average connectivity ( Figure 3 and Table 2), indicating that the different MG genotypes profoundly influenced the facilitative interaction between AMF and diazotrophs. ...
Soybeans can simultaneously form tripartite symbiotic associations with arbuscular mycorrhizal fungi (AMF) and diazotrophs. However, no studies have explored whether soybean genotypes differing in their maturity groups (MGs) may have implications for the recruitment of rhizosphere soil AMF and diazotrophs. We investigated the diversity and community compositions of AMF and diazotrophs in three soybean genotypes differing in their maturity groups (MG) using high-throughput sequencing. The soybean MGs were MG1.4, MG2.2, and MG3.8, representing early, standard, and late maturity, respectively, for the study region. Soil chemical properties and yield-related traits were determined, and co-occurrence network patterns and drivers were also analyzed. The results obtained demonstrated that AMF richness and diversity were relatively stable in the three soybean genotypes, but noticeable differences were observed in diazotrophs, with late maturity being significantly higher than early maturity. However, there were differences in AMF and diazotrophic composition among different MG genotypes, and the changes in the proportion of dominant species in the community were necessarily related to MG genotypes. Co-occurrence network analysis showed that the positive correlation between AMF and diazotrophs gradually decreased in earlier MG genotypes than in the other later MG genotypes. The results of the structural equation model analysis showed that soil organic carbon, AMF, diversity of soil nutrients, and extracellular enzyme activities were important factors driving soybean yield change, with organic carbon accounting for more than 80% of the pathways analyzed. These results suggest that soybean genotype selection based on MG plays an important role in recruiting both AMF and diazotrophic communities, and in comparison to AMF, diazotrophs are more responsive to the different MG genotypes.
... El principal atributo de esta interacción simbiótica (por lo general mutualista), es la transferencia bidireccional de nutrientes: las plantas proveen a los hongos de un microhábitat (dentro de sus raíces) y energía (carbohidratos derivados de la fotosíntesis), esenciales para su supervivencia y crecimiento; aunque las estimaciones pueden variar, se ha sugerido que las plantas podrían destinar entre 10 y 30% de sus fotosintatos para mantener la relación con los HMA (Jacobsen y Rosendahl, 1990;Finlay y Söderström, 1992). A cambio, los hongos forman extensas redes de hifas (células alargadas con diámetros de pocas micras características de los hongos, que en su conjunto se denomina micelio) de manera extrarradical, es decir fuera de las raíces, en el suelo. ...
Este libro reúne algunas de las investigaciones qué surgieron a raíz de una pregunta inicial. ¿Qué efecto ha tenido, sobre la diversidad de hongos micorrizógenos, la producción de café sobre el área que ocupaba el bosque mesófilo de montaña en Nayarit? En la búsqueda de un sitio adecuado para llevar a cabo el estudio, donde colindara bosque y cafetal, dimos con Cumbres de Huicicila, en el municipio de Compostela. Ahí, en las partes menos accesibles de las cañadas que ahora producen café bajo sombra, saltan a la vista los imponentes helechos arborescentes que indican la presencia de pequeños fragmentos a los que ha sido reducido el bosque mesófilo. Esta comunidad vegetal destaca por su diversidad y fragilidad; es la que más especies de plantas presenta si se considera la poca superficie de terreno que ocupa (zonas húmedas y protegidas de macizos montañosos) y la mayoría de sus especies no son capaces de vivir en otros ambientes. Además de su importancia en el mantenimiento de patrones naturales en el flujo de arroyos y ríos que nacen de su escorrentía. Durante el desarrollo de esta investigación, surgieron otros temas que fueron abordados también, como conocer la diversidad de plantas que crecen bajo los árboles en el bosque y el cafetal, así como la diversidad de musgos y sus parientes en el bosque.
Finalmente, este libro es una invitación y una provocación a conocer algunos de los aspectos de este importante ecosistema y pretende motivar a las futuras generaciones de biólogos y sociedad en general a valorar y conservar los pocos bosques mesófilos de montaña que aún tenemos.
... El principal atributo de esta interacción simbiótica (por lo general mutualista), es la transferencia bidireccional de nutrientes: las plantas proveen a los hongos de un microhábitat (dentro de sus raíces) y energía (carbohidratos derivados de la fotosíntesis), esenciales para su supervivencia y crecimiento; aunque las estimaciones pueden variar, se ha sugerido que las plantas podrían destinar entre 10 y 30% de sus fotosintatos para mantener la relación con los HMA (Jacobsen y Rosendahl, 1990;Finlay y Söderström, 1992). A cambio, los hongos forman extensas redes de hifas (células alargadas con diámetros de pocas micras características de los hongos, que en su conjunto se denomina micelio) de manera extrarradical, es decir fuera de las raíces, en el suelo. ...
Este libro reúne algunas de las investigaciones qué surgieron a raíz de una pregunta inicial. ¿Qué efecto ha tenido, sobre la diversidad de hongos micorrizógenos, la producción de café sobre el área que ocupaba el bosque mesófilo de montaña en Nayarit? En la búsqueda de un sitio adecuado para llevar a cabo el estudio, donde colindara bosque y cafetal, dimos con Cumbres de Huicicila, en el municipio de Compostela. Ahí, en las partes menos accesibles de las cañadas que ahora producen café bajo sombra, saltan a la vista los imponentes helechos arborescentes que indican la presencia de pequeños fragmentos a los que ha sido reducido el bosque mesófilo. Esta comunidad vegetal destaca por su diversidad y fragilidad; es la que más especies de plantas presenta si se considera la poca superficie de terreno que ocupa (zonas húmedas y protegidas de macizos montañosos) y la mayoría de sus especies no son capaces de vivir en otros ambientes. Además de su importancia en el mantenimiento de patrones naturales en el flujo de arroyos y ríos que nacen de su escorrentía. Durante el desarrollo de esta investigación, surgieron otros temas que fueron abordados también, como conocer la diversidad de plantas que crecen bajo los árboles en el bosque y el cafetal, así como la diversidad de musgos y sus parientes en el bosque. Finalmente, este libro es una invitación y una provocación a conocer algunos de los aspectos de este importante ecosistema y pretende motivar a las futuras generaciones de biólogos y sociedad en general a valorar y conservar los pocos bosques mesófilos de montaña que aún tenemos.
... These fungi are obligate symbionts relying on the plant host for their growth and survival. Up to 20 % of photosynthetic products can be diverted from the plant to the maintenance of mycorrhizal structures (Jakobsen and Rosendahl, 1990;Bryla and Eissenstat, 2005). In exchange for carbon compounds, the AMF provide the host plant with nutrients (especially P) and water improving their tolerance to a variety of biotic and abiotic stresses, including salinity (Smith and Read, 2008). ...
... At early stage of crop growth, AM fungal inoculated plants showed an increase in root mass while the shoot masses were similar. This may be attributed to the utilization of carbon for establishment of functional symbiosis as reported by Jakobsen and Rosendahl (1990). ...
A Field experiment was conducted at Tamil Nadu Agricultural University, Coimbatore during winter 2011-12 to study the influence of maize (Zea mays) under different intercropping systems, mycorrhizal inoculation and fertilizer levels on root growth and grain yield of hybrid maize under irrigated condition. The experiment was laid out in split – split plot design. The results revealed that the root parameters such as root length, root volume, root dry mass, root- shoot ratio and root colonization were higher under sole maize, inoculation of mycorrhiza and fertilizer levels. Regarding the treatment combinations, 100% RDF along with mycorrhizal inoculation recorded significantly better root parameters. With regard to the yield, sole maize recorded the highest grain and stover yield (8,531 and 12,560 kg ha -1 , respectively). Also mycorrhizal inoculated treatments recorded the highest grain and stover yield (8,892 and 12,849 kg ha -1 , respectively). Regarding the treatment combinations, sole maize along with mycorrhizal inoculation and 125% RDF recorded significantly higher yield parameters and yield. However, the yield was comparable with maize + cowpea intercropping along with mycorrhizal inoculation and application of 100% RDF.
... They also have a direct effect on soil structure, which is particularly relevant in agricultural environments, in which cultivation, traffic and low levels of organic matter tend to damage soil structure. According to Jakobsen and Rosendahl [115], host plants can transfer up to 20% of fixed carbon to their fungal partners and mycorrhizae can produce significant biomass in agricultural soils [116]. ...
The growing interest in mycorrhizal fungi in agriculture is related to their symbiotic relationships with cultivated plants. Thanks to functional genomics approaches, mycorrhizae and symbioses with host plants have emerged for their features. Besides improving nutritional supply, plant-fungal interactions increase plants' tolerance to abiotic stresses such as drought, salinity and cold, as well as their resistance to diseases. Recent studies have investigated the interactions between plants and mycorrhizae, however the mechanisms often remain unclear. Indeed, plants in the field are affected by various stresses and results often appear contradictory. This review is aimed at presenting the most relevant studies in this field in order to highlight the possible benefits of mycorrhizal interactions and their application in agriculture. Abstract The growing interest in mycorrhizal fungi in agriculture is related to their symbiotic relationships with cultivated plants. Thanks to functional genomics approaches, mycorrhizae and symbioses with host plants have emerged for their features. Besides improving nutritional supply, plantefungal interactions increase plants' tolerance to abiotic stresses such as drought, salinity and cold, as well as their resistance to diseases. Recent studies have investigated the interactions between plants and mycorrhizae, however the mechanisms often remain unclear. Indeed, plants in the field are affected by various stresses and results often appear contradictory. This review is aimed at presenting the most relevant studies in this field in order to highlight the possible benefits of mycorrhizal interactions and their application in agriculture.
... Both absorption ne roots and their associated mycorrhizal fungi are major organs for nutrient acquisition (van der Heijden et al. 2015), however, there is competition and trade-offs between these two nutrient access mechanisms, as both ne roots and their associated mycorrhizal fungi require the allocation of underground C for growth and maintenance (Lynch 2005). Mycorrhiza can obtain nutrients more e ciently than roots, but mycorrhiza requires more C because hyphae turnover is very fast (Jakobsen and Rosendahl 1990). Studies have shown that trees rely more on ne roots than mycorrhizal fungi for nutrients acquired during the longterm addition of large amounts of N (Ma et al. 2021). ...
Background and aims
Fine root longevity and turnover respond to changes in soil nitrogen (N) determine plants’ performance at elevated N-level under global N-deposition. This study was conducted to understand the fine root dynamics of N-fixing and non-N-fixing tree species at elevated N-level by N fertilization.
Methods
To determine fine root dynamics (biomass, length density, longevity, and turnover rate) under N-fertilization, a three-year fertilization experiment at 150 g CO(NH2)². m− 2 year− 1 was conducted for two N-fixing species and two non-N-fixing tree species.
Results
Fine root biomass of the two N-fixing tree species was lower than that of non-N-fixing tree species. N-fertilization decreased root length density, root surface area, and root volume of all tree species. The fine root turnover rate of N-fixing trees was higher but root longevity was lower than that of non-N-fixing species. For all four species, N fertilization decreased fine root turnover rate but increased fine root longevity. Moreover, both the root turnover rate and root longevity of the two N-fixing tree species were more sensitive than the two non-N-fixing tree species to N fertilization. The proportion of long-lived roots of non-N-fixing tree species was higher than that of N-fixing tree species.
Conclusion
Fine roots of N-fixing tree species have shorter longevity and faster turnover rate than that of non-N-fixing tree species. The fine root longevity and turnover of N-fixing tree species were more sensitive to elevated N-level than that of non-N-fixing species at elevated N-level, they have different response strategies to the increase of soil N.
... Common mycorrhizal networks partition mineral nutrients among interconnected neighboring plants 10,11,12,13 . Plants may receive up to 80% of their phosphorus and 25% of their nitrogen requirements from AM fungi, while providing up to 20% of their total fixed carbon to the fungi in return 14 . Recent in vitro root organ culture work has found that CMNs preferentially exchange mineral nutrients with host roots that provide the most carbon to the fungi 11,12 . ...
... Arbuscular mycorrhizal fungi are obligate biotrophs that belong to the Glomeromycota monophyletic phylum (Parniske, 2008). Through the symbiotic relation, AMF incorporates sugars and lipids synthesised by the plant (upto 20% of the photosynthesis products may be consumed by AMF as reported by Jakobsen and Rosendahl (1990)), and plants incorporate minerals (i.e. phosphorus) and water (Trivedi et al., 2020). ...
In a global context of climate change and loss of biodiversity, phytoremediation appears as a viable strategy to recover polluted soil. Phytoremediation is defined as a strategy to recover polluted soils by means of plants and the associated microorganisms. Arbuscular mycorrhizal fungi (AMF) are one of the most widespread soil microorganisms, they live in symbiosis with 70% of terrestrial plants. In the symbiotic relation, the fungal partner incorporates carbohydrates and lipids facilitated by the plant and the plant incorporates minerals facilitated by the fungal partner. Then, the inclusion of AMF in phytoremediation strategies should become a priority, not only because the presence of AMF will help the plant to adapt to the polluted soil but also because it could enhance the incorporation of carbon to the soil. In addition, the actual context of global biodiversity loss prioritizes the study of local populations in order to promote the incorporation of the local biodiversity to soil management, that includes phytoremediation. In the present work we aimed to taxonomically characterise four AMF populations obtained from Ricinus communis rhizospheric Cr(VI) polluted soil. In addition, we aimed to study the symbiosis and the mineral uptake of some elements, including phosphorus and chromium, in R. communis plants associated with each AMF population and re-exposed to Cr(VI). We found that three AMF populations grouped near Rhizophagus and one near Paraglomus accessions and that the four AMF populations were tolerant to the re-exposure to 8 ppm Cr(VI) substrate concentration. Finally, from the mineral content analysis, our results strongly suggest that Paraglomus sp., a taxon which appeared earlier in the evolution of AMF, was the population that best adapted to the re-exposure of 8 ppm Cr(VI). Thus, we suggest that future phytoremediation studies should include taxa from this early diverged genus.
... The driving force behind mycorrhizal fungi is photosynthetically derived organic C, which fuels biomass growth, production of protons, organic acids, chelators, and enzymes that increase mineral weathering, and allow the selective uptake of nutrients by mycorrhiza. Overall, about 2-15% of the plant C-photosynthate (up to 26% between arbuscular mycorrhiza Glomus fasciculatum and cucumber plant) is typically invested into supporting their fungal symbionts [154][155][156][157] , adding up to a transfer of C from plants to mycorrhiza yielding globally~12% of the terrestrial C cycle 65 , mycorrhizal networks have transformative effects on soil physicochemical properties via their inputs of organic matter and selective uptake of elements and water. As such, BW can be seen as part of a solar-to-chemical energy conversion by plants into mycorrhiza, which partly links belowground C allocation to mineral weathering and nutrient acquisition 158 and allows to sustain the extended and dynamic fungi-mineral interface area. ...
Rock weathering is a key process in global elemental cycling. Life participates in this process with tangible consequences observed from the mineral interface to the planetary scale. Multiple lines of evidence show that microorganisms may play a pivotal—yet overlooked—role in weathering. This topic is reviewed here with an emphasis on the following questions that remain unanswered: What is the quantitative contribution of bacteria and fungi to weathering? What are the associated mechanisms and do they leave characteristic imprints on mineral surfaces or in the geological record? Does biogenic weathering fulfill an ecological function, or does it occur as a side effect of unrelated metabolic functions and biological processes? An overview of efforts to integrate the contribution of living organisms into reactive transport models is provided. We also highlight prospective opportunities to harness microbial weathering in order to support sustainable agroforestry practices and mining activities, soil remediation, and carbon sequestration.
... The phylum Glomeromycota currently comprises approximately 150 described species distributed among 10 genera, most of which are defined primarily by spore morphology and was instituted based on rDNA phylogenies of living members (Schüssler et al. 2001;Redecker and Raab 2006). AMF are known to be a vital part of most terrestrial ecosystems and have been recognized to play an important role in the pathway of carbon flux in the soil-plant-atmosphere continuum through the mycelia they produce (Jacobsen and Rosendhal 1990;Johnson et al. 2002), ultimately affecting carbon fluxes and nutrient dynamics. Also, AMF participate in various aspects of global change and in regulating ecosystem responses. ...
Cacao (Theobroma cacao) is both an economically and ecologically important crop worldwide especially in the Philippines, a tropical country suitable for its growth and cultivation. The association of this crop with arbuscular mycorrhizal fungi (AMF) is an understudied field but the benefits reported from this symbiosis highlights their irreplaceable role in enhancing growth conditions by facilitating the uptake of phosphorus, increasing yield through increased plant health and productivity, and in several ecological aspects such as soil biological dynamics and ecological processes that are carried out in cacao plant community. This paper proposed the different areas of improving cacao ecology that need to gain attention in the Philippines to augment the measures being undertaken to boost the country’s cacao plantations. This includes more research on areas of soil physicochemical properties, AMF genetic and functional diversity in cacao communities, and resistance to diseases of AMF-associated cacao trees. The ecology of the AMF-cacao association is an essential part of developing effective AMF inocula for the ultimate purpose of increasing the yield of cacao. Appropriate application of AMF could increase the overall yield of the country’s cacao plantations and can be translated to improving food security and many other economic gains.
... −AMF/−P: without AMF inoculation and without parasite; −AMF/+P: without AMF inoculation and with parasite; +AMF/−P: with AMF inoculation and without parasite; +AMF/+P: with AMF inoculation and with parasite. Rosendahl, 1990;Kucey & Paul, 1982). Direct competition for C between AMF and the parasite may thus have limited AMF growth and thereby suppressed the effect of AMF on decomposition ( Figure 5). ...
Parasitic plants have been shown to affect soil‐organic‐matter (SOM) decomposition, but the mechanism is unknown. As arbuscular mycorrhizal fungi (AMF) can affect decomposition and compete with parasitic plants for carbon, we hypothesized that parasitic plants can indirectly regulate SOM decomposition by suppressing the effects of AMF on decomposition.
To test this hypothesis, we conducted two container experiments in which the herbaceous plant Bidens pilosa was inoculated with the AMF Rhizophagus intraradices or not, and Cuscuta australis or not. In one experiment, we provided SOM within hyphae‐in‐growth bags as ¹³C‐/¹⁵ N‐labelled maize leaves and in the other experiment as phytate‐P. We assessed growth and nutrient uptake of B. pilosa, growth of C. australis, the SOM remaining in the hyphae‐in‐growth bags, and the bacterial communities.
Parasitization increased the ¹³C and decreased the organic P remaining in the bags, but only in the presence of the extraradical AMF hyphae. AMF decreased the ¹³C and increased the organic P remaining in the absence of the parasite, but not in the presence of the parasite.
Our results demonstrate that parasitic plants can regulate the decomposition of organic materials indirectly by suppressing the effect of the extraradical AMF hyphae on decomposition. In other words, parasitic plants can regulate SOM decomposition indirectly via a multitrophic cascading effect. Our study helps to unravel the mechanisms of a sophisticated hidden ecological process, and is an important step forward in elucidating the roles of parasitic plants in soil nutrient cycling.
Read the free Plain Language Summary for this article on the Journal blog.
... L'apport fongique de ces minéraux décrits précédemment au niveau de la zone arbusculaire se traduit par un échange d'une source de carbone vers les CMAs -montré pour la première fois par Ho & Trappe (1973) -nécessaire pour l'accomplissement de leur cycle biologique. On considère que la plante transférerait plus de 20% de son carbone provenant des photosynthétats (Jakobsen & Rosendahl, 1990;Wright et al., 1998) permettant un enrichissement du sol en matière carbonée Graham, 2000). Les CMAs obtiendraient majoritairement leur source de carbone au sein de la racine de l'hôte au travers de l'action de transporteurs de monosaccharides (MST) fongique, capable de lier les sucres avec une forte affinité (Schussler et al., 2006;Helber et al., 2011). ...
La symbiose mycorhizienne à arbuscule (MA) est une association mutualiste s’établissant entre les racines des plantes et des champignons du sol appartenant à l’embranchement des Gloméromycètes. Dans cette association, le champignon agit comme un fertilisant naturel, fournissant à la plante divers minéraux (phosphore, mais aussi azote et soufre …) en échange de sources de carbone indispensables à son développement. Une caractéristique originale de ces champignons est leur très large spectre d’hôte : de l’ordre de 80% des espèces végétales ont l’aptitude à former cette symbiose, et certains espèces de champignons MA ne semblent pas avoir de limitation de spectre d’hôte. Les champignons MA possèderaient-ils des « clés universelles » de compatibilité cellulaire avec leur hôte, ou de contournement de l’immunité végétale ? Pour aborder cette problématique, nous avons entrepris l’étude du sécrétome du champignon MA Rhizophagus irregularis dont plusieurs données génomiques étaient disponibles. Les microorganismes eucaryotes sécrètent en effet dans leur environnement des protéines agissant sur leurs structures exogènes (paroi cellulaire), leur environnement, et pouvant agir sur l’immunité des cellules hôtes. Ces protéines sécrétées (SPs) sont dans ce dernier cas appelées « effecteurs ». Sur la base de deux assemblages différents, un catalogue de 872 SPs de R. irregularis (RiSPs) a été défini pour lesquelles les profils d’expression dans trois plantes hôtes ont été comparés. Nous avons également comparé ces SPs à celles que nous avons définies sur une autre espèce de champignon MA, Gigaspora rosea. Après enrichissement du catalogue de RiSPs avec des séquences de petite taille identifiées sur un assemblage transcriptomique propre, puis sélection des candidats dont les cadres de lecture sont robustes et présentant un niveau d’expression élevé (FC>10) dans les 3 hôtes testés, un jeu de 33 RiSPs d’intérêt a été défini, dont 18 ont été sélectionnées pour effectuer des analyses fonctionnelles. En absence de protocole de transformation de ces champignons, l’analyse fonctionnelle a porté sur la cytolocalisation de protéines de fusion RiSP:citrine dans les cellules végétales par surexpression dans des feuilles de tabac et des racines de luzerne tronquée. Différents compartiments cellulaires sont ciblés par ces RiSPs, très souvent le compartiment vacuolaire. Des approches par surexpression in planta de plusieurs candidats RiSP ont permis d’identifier une activité stimulatrice de 3 RiSPs sur l’établissement de la symbiose. Parallèlement, des essais de stimulation de la symbiose MA par apport exogène de différents SPs sur plantules en cours de mycorhization en chambre ont été initiés. Ils devront être poursuivis sur les 3 candidats issus du crible de surexpression. En perspective, l’évaluation de la spécificité d’action de ces SPs sur la symbiose MA comparativement à d’autres interactions plante-champignon ouvrira la voie à des essais d’application au champ.
... Se han realizado investigaciones sobre la estructura y función de los micelios vegetativos de HFMA utilizando microcosmos y cámaras transparentes de dos dimensiones para poder observar las redes hifales sin destruirlas (Finlay & Read, 1986;Friese & Allen, 1991), sin embargo, estas metodologías han presentado limitantes para el estudio de la frecuencia de anastomosis directamente. Por otro lado, se han realizado estudios extrayendo el micelio del suelo, pero esto dificulta la obtención de redes intactas y así poder hacer un seguimiento continuo de este proceso (Jakobsen & Rosendhal, 1990;). Estas metodologías entregaron evidencia cualitativa sobre la estructura del micelio, pero no permitieron evidenciar en detalle los mecanismos involucrados en la formación de las redes hifales. ...
RESUMEN La anastomosis es un proceso de fusión entre las ramas de hifas de los hongos, muy común en hongos basidiomicetos y ascomicetos. Este proceso también, se ha reportado en hongos formadores de micorrizas arbusculares (HFMA). Los HFMA tienen importancia ecológica y económica ya que forman simbiosis con más del 60% de las plantas del planeta, jugando un papel fundamental en la toma y distribución de nutrientes de los ecosistemas. La anastomosis en los HFMA ha sido estudiada en las etapas pre-simbiótica y simbiótica utilizando diversas aproximaciones metodológicas, las cuales son nombradas y comparadas en esta revisión. En este trabajo se abordan los diferentes patrones que se han identificado para este mecanismo en los HFMA. Este proceso se asocia con la formación de redes extensas de micelios y con el flujo de material citoplasmático y genético dentro de estas redes, y por esta razón, se discuten los principales hallazgos sobre el rol que cumple la anastomosis en la biología y ecología de los HFMA. Finalmente, se identifican las posibles ventajas y desventajas que puede ofrecer este mecanismo cuando se ésta considerando realizar desarrollos biotecnológicos con estos hongos.
... To build up symbioses with mycorrhizal fungi is an alternative strategy for plants against P deficiency (Clark and Zeto, 2000). In the mycorrhizal symbiosis system, it is usually considered that the plants offer carbon and energy to the fungi (Jakobsen and Rosendahl, 1990), and employ the fungi to enhance P acquisition in various ways . The fungal hyphae are far thinner and longer than fine roots, therefore the symbioses could provide considerable extra root area, extend to distant places to overcome the 'P depletion zones' near root surfaces (Lewis and Quirk, 1967), and explore the soil micro-pores and particles that roots could not reach (Clark and Zeto, 2000). ...
Aims
Plant roots show various functional strategies in soil phosphorus (P) acquisition. Under limited soil phosphatase activity, P deficiency is the main concern, and roots either invest carbon (C) to produce higher levels of phosphatase or establish more symbioses with mycorrhizal fungi. However, these strategies and their interactions are not clear. Furthermore, few studies have investigated trade-offs of functional traits in woody species associated with different types of mycorrhizal partners.
Methods
Here we examined the abilities to release acid phosphatase (AP) and the colonization ratio by arbuscular and ectomycorrhizal fungi for fine roots of 15 woody species growing in a tropical common garden in Xishuangbanna, China. We also measured acid phosphatase activities of bulk soils under the canopy of target trees.
Results
Soil and root AP activities exhibited a positive correlation, indicating that roots actively produced AP to acquire P even bulk soil AP was increasing. We found a significantly negative correlation (P = 0.02) between mycorrhizal colonization ratio and root-released AP activity across target species, reflecting a trade-off between these two P acquisition strategies.
Conclusions
Our findings suggest a trade-off of resource allocation between these two strategies at both species and individual levels, and provide information on the overall mechanism of P acquisition by fine roots that they either ‘do it by themselves’ or ‘rely on mycorrhizal partners’. These two strategies might be integrated into the collaboration gradient of the root economics space.
... associations with approximately 72% terrestrial plant species (Brundrett and Tedersoo 2018). Arbuscular mycorrhizal (AM) symbiosis allows host plants to obtain essential nutrients, and in turn, the host plants invest part of their photosynthates to their fungal partners (Jakobsen and Rosendahl 1990;Johnson et al. 2002;van der Heijden et al. 2015). Among the mineral nutrients with improved uptake in mycorrhizal plants, inorganic phosphorus (P) is by far the most recognized and studied, with the AMF contribution to plant P uptake reaching up to 90% (Smith and Smith 2011;Smith et al. 2004). ...
Background and aims
The acquisition of nitrogen (N) captured via arbuscular mycorrhizal (AM) hyphal networks is a major pathway in the N uptake of host plants. However, the relative contribution of arbuscular mycorrhizal fungi (AMF) to N uptake in different species has not been well quantified.
Methods
Two dominant plant species in semiarid steppes, i.e., Leymus chinensis (a C3 grass) and Cleistogenes squarrosa (a C4 grass), were selected. We conducted a greenhouse manipulation experiment that involved specifically designed microcosms combined with ¹⁵ N labelling techniques to quantify the relative contribution of AMF to plant N uptake under high and low levels of available soil N.
Results
AMF contributed more to N uptake in L. chinensis than that in C. squarrosa. For L. chinensis, AM symbiosis suppressed plant growth under low soil N conditions but improved plant growth under high soil N conditions, contributing c. 23% and 20% of the total plant N, respectively. For C. squarrosa, AM symbiosis consistently inhibited plant growth under both low and high soil N conditions, contributing only 9% and 7% of the plant N uptake, respectively.
Conclusions
AMF contributed significantly to N uptake in the C3 grass of L. chinensis but not in the C4 grass of C. squarrosa. Our findings indicate that AMF may modify the relative fitness of the two dominant grass species on the Mongolian Plateau through their influence on plant growth and N uptake in the face of increasing global N deposition.
... for 70-100% of the plants' overall Pi acquisition [18,19]. In return, up to 20% (approximately 5 billion tonnes of carbon per year) of photosynthesis products (e.g., sugar and lipids) are transferred from plants to AM fungi [20][21][22], indicating the pivotal role of AM fungi in regulating carbon fluxes between the atmosphere and the biosphere [23]. Furthermore, AM hyphae provide an efficient pathway to distribute plant-fixed carbon into soil pores and onto mineral surfaces, where it can be chemically or physically protected from microbial attack [24]. ...
Arbuscular mycorrhizal (AM) fungi and soil invertebrates represent a large proportion of total soil biomass and biodiversity and are vital for plant performance, soil structure, and biogeochemical cycling. However, the role of soil invertebrates in AM fungi development remains elusive. In this opinion article, we summarize the ecological importance of AM fungi and soil invertebrates in the plant–soil continuum and highlight the effects of soil invertebrates on AM fungal hyphae development and functioning. In a context of global change, we envision that better mechanistic understanding of the complex feedback via chemical signaling pathways across the interactions between soil invertebrates and AM fungi is critical to predict their ecological consequences and will open new avenues for promoting ecosystem resilience and sustainability.
El presente capítulo integra información biológica y ecológica sobre un importante grupo de especies de plantas categorizadas como malezas, que pueden ser nativas o introducidas. Las malezas forman una parte muy importante de la estructura y composición de los tres principales tipos de bosque templados de la cuenca del río Magdalena (CRM).
El objetivo de la obra es dar a conocer el papel que juegan las especies de plantas introducidas y las especies con comportamiento malezoide, en la estructura de los bosques templados de la CRM. Se presenta información sobre el origen, la distribución y las estrategias de estas plantas para permanecer en la comunidad. Este capítulo será un elemento imprescindible para conocer el estado de conservación de los diferentes tipos de vegetación que conforman la CRM y para determinar algunas
estrategias de monitoreo en áreas donde las malezas y/o especies introducidas tienen un impacto sobre las especies características de los bosques templados del centro de México. El libro completo puede ser usado como material didáctico, pues permite a estudiantes, profesores
y público en general conocer un área de suma importancia ambiental para la
Ciudad de México; hace énfasis en el conocimiento sobre el origen y la biología de las malezas, sean estas nativas o introducidas. Asimismo, fomenta la difusión del conocimiento y del área de estudio, involucrando en este proceso a la población responsable de su conservación y aprovechamiento.
Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with the majority of land plants and deliver a wide range of soil-based ecosystem services. Due to their conspicuous belowground lifestyle in a...
The relationship between biodiversity and multitrophic ecosystem functions (BEF) remains poorly studied in forests. There have been inconsistent reports regarding the significance of tree diversity effects on ecosystem functions, which may be better understood by considering critical biotic interactions of trees.
This study investigates the role of tree‐mycorrhizal associations that may shape forest BEF relationships across multiple ecosystem functions. We used a field experiment (MyDiv) that comprises 10 deciduous tree species associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EcM) fungi to create gradients in species richness (1, 2, 4 species) and different mycorrhizal communities (only AM‐species [AM fungi associated tree species] or EcM‐species [EcM fungi associated tree species], or a combination of both). We investigated the effects of tree species richness and mycorrhizal types on crucial multitrophic ecosystem functions (foliage damage, predation [using artificial caterpillars] and soil fauna feeding activity [~0–10 cm]) and assessed how these effects were mediated by stand characteristics.
Overall, we found that tree species richness and mycorrhizal types strongly affected multitrophic ecosystem functions. Compared to monocultures, 4‐species mixtures with both mycorrhizal types experienced significantly lower foliage damage. The mixtures of EcM‐species supported significantly higher predation (i.e. a greater proportion of artificial caterpillars being attacked), and this effect strengthened with tree species richness. The effects of tree species richness on soil fauna feeding activity were negative across all mycorrhizal types in the lower soil layer. Moreover, we showed that tree diversity effects were mediated by above‐ground tree biomass, vertical structural complexity and leaf quality, with the dominating mechanisms largely depending on the mycorrhizal types.
Synthesis. Tree species richness affected multitrophic ecosystem functioning by (1) directly decreasing the proportion of foliage damage in the communities with both mycorrhizal types, where AM‐species benefited from mixing with EcM‐species, and (2) increasing predation rates via changes in the vertical structural complexity in mixtures of EcM‐species. Our results highlight the importance of considering mycorrhizal types for managing well‐functioning mixed‐species forests and contribute to broadening the mechanistic understanding of the context‐dependent BEF relationships in forests.
In arbuscular mycorrhizal (AM) symbiosis, sugars in root cortical cells could be exported as glucose or sucrose into peri‐arbuscular space for use by AM fungi. However, no sugar transporter has been identified to be involved in sucrose export. An AM‐inducible SWEET transporter, GmSWEET6, was functionally characterised in soybean, and its role in AM symbiosis was investigated via transgenic plants. The expression of GmSWEET6 was enhanced by inoculation with the cooperative fungal strain in both leaves and roots. Heterologous expression in a yeast mutant showed that GmSWEET6 mainly transported sucrose. Transgenic plants overexpressing GmSWEET6 increased sucrose concentration in root exudates. Overexpression or knockdown of GmSWEET6 decreased plant dry weight, P content, and sugar concentrations in non‐mycorrhizal plants, which were partly recovered in mycorrhizal plants. Intriguingly, overexpression of GmSWEET6 increased root P content and decreased the percentage of degraded arbuscules, while knockdown of GmSWEET6 increased root sugar concentrations in RNAi2 plants and the percentage of degraded arbuscules in RNAi1 plants compared with wild‐type plants when inoculated with AM fungi. These results in combination with subcellular localisation of GmSWEET6 to peri‐arbuscular membranes strongly suggest that GmSWEET6 is required for AM symbiosis by mediating sucrose efflux towards fungi.
Poplar is a short-rotation woody crop frequently studied for its significance as a sustainable bioenergy source. The successful establishment of a poplar plantation partially depends on its rhizosphere-a dynamic zone governed by complex interactions between plant roots and a plethora of commensal, mutualistic, symbiotic, or pathogenic microbes that shape plant fitness. In an exploratory endeavor, we investigated the effects of a consortium consisting of ectomycorrhizal fungi and a beneficial Pseudomonas sp. strain GM41 on plant growth (including height, stem girth, leaf, and root growth) and as well as growth rate over time, across four Populus trichocarpa genotypes. Additionally, we compared the level of total organic carbon and plant exometabolite profiles across different poplar genotypes in the presence of the microbial consortium. These data revealed no significant difference in plant growth parameters between the treatments and the control across four different poplar genotypes at 7 weeks post-inoculation. However, total organic carbon and exometabolite profiles were significantly different between the genotypes and the treatments. These findings suggest that this microbial consortium has the potential to trigger early signaling responses in poplar, influencing its metabolism in ways crucial for later developmental processes and stress tolerance. K E Y W O R D S beneficial bacteria, metabolomics, mycorrhizal fungi, poplar exometabolites, total organic carbon
Large scale biofuel production from lignocellulosic feedstock is limited by the financial and environmental costs associated with growing and processing lignocellulosic material and the resilience of these plants to environmental stress. Symbiotic associations with arbuscular (AM) and ectomycorrhizal (EM) fungi represent a potential strategy for expanding feedstock production while reducing nutrient inputs. Comparing AM and EM effects on wood production and chemical composition is a necessary step in developing biofuel feedstocks. Here, we assessed the productivity, biomass allocation, and secondary cell wall composition of greenhouse grown Populus tremuloides inoculated with either AM or EM fungi. Given the long-term goal of reducing nutrient inputs for biofuel production, we further tested the effects of nutrient availability and nitrogen:phosphorus stoichiometry on mycorrhizal responses. Associations with both AM and EM fungi increased plant biomass by 14% to 74% depending on the nutrient conditions but had minimal effects on secondary cell wall composition. Mycorrhizal plants, especially those inoculated with EM fungi, also allocated a greater portion of their biomass to roots, which could be beneficial in the field where plants are likely to experience both water and nutrient stress. Leaf nutrient content was weakly, but positively correlated with wood production in mycorrhizal plants. Surprisingly, phosphorus played a larger role in EM plants compared to AM plants. Relative nitrogen and phosphorus availability was correlated with shifts in secondary cell wall composition. For AM associations the benefit of increased wood biomass may be partially offset by increased lignin content, a trait that affects downstream processing of lignocellulosic tissue for biofuels. By comparing AM and EM effects on the productivity and chemical composition of lignocellulosic tissue, this work links broad functional diversity in mycorrhizal associations to key biofuels traits and highlights the importance of considering both biotic and abiotic factors when developing strategies for sustainable biofuel production.
In terrestrial ecosystems, arbuscular mycorrhizal fungi (AMF)-land plant symbiosis helps plant for nutrient uptake and, protection from abiotic and abiotic stresses. It is important to study the AMF-plant relationship to fully realize the potential to exploit for plant growth, maintenance and establishment in different ecosystem. Therefore, the objective of this study was to determine the diversity, abundance and population densities of AMF and quantify root colonization of the indigenous trees in Munessa forest. To this end, composite fine roots and soil samples were collected from seven dominant indigenous trees within 10 m x10 m plots in the forest. AMF spores were extracted for taxonomic identification and AMF root colonization was determined. A total of 39 AMF morphotypes belonging to 7 genera were recovered. Of which, Glomus was the most dominant genus followed by Acaulospora , Glomus rubiform e was the most dominant species followed by Acaulospora myriocarpa . The highest genus and species richness was recorded from Croton macrostachyus and Millettia ferruginea in this study. Mean AMF spore density was significantly different ( p < 0.05) among indigenous trees, ranging from 859.6 spores/100g of dry soil under Albizia shimperiana to2829.52 spores/100g of dry soil under Pouteria adolfiifriedericii . The highest hyphal and vesicular colonizations were observed in Millettia ferruginea (71%) and Celtis Africana (36.37%) respectively. Albizia shimperiana was the least colonized tree by all AMF structures. AMF spore density was positively correlated with soil available phosphorus ( p < 0.05). Extensive studies are required to select AMF for growth promotion and recruitment of tree seedlings for plantation and, restoration of forest vegetation and rehabilitation of degraded lands.
Aufgrund des Klimawandels führen immer öfter Dürreereignisse zu Ernteausfällen in der Landwirtschaft. Eine Adaptionsstrategie wäre eine intelligente Nutzung der Wasserressourcen des Bodens durch eine komplementäre Erschließung von Wurzelräumen durch Flach- und Tiefwurzler sowie eine hydraulische Wasserumverteilung zwischen benachbarten Pflanzenspezies innerhalb angepasster Mischkultursysteme. Durch den sogenannten Hydraulic Lift-Effekt (HL) transportieren Tiefwurzler insbesondere in der Nacht Wasser aus feuchten Bodenzonen aufgrund von Wasserpotentialgradienten in sehr trockene obere Bodenzonen, wovon Flachwurzler profitieren können. Die Bedeutung gemeinsamer Mykorrhiza-Netze (Common mycorrhizal networks; CMN) für eine hydraulische Wasserumverteilung zwischen Ackerpflanzen wurde auf der Feldskala bislang nicht quantifiziert. Ziel dieser Studie ist es, die Bedeutung unterschiedlicher Transportwege für eine hydraulische Wasserumverteilung unter verschiedenen biotischen und abiotischen Umgebungs-bedingungen zu untersuchen und die Relevanz von CMN für die hydraulische Wasserumverteilung zu prüfen. Hyphensysteme von arbuskulären Mykorrhizen (AM) könnten die hydraulische Wasserumverteilung in Ackerkulturen signifikant erhöhen, da diese die Pflanzen miteinander vernetzen und im Vergleich zu Pflanzenwurzeln bei noch größerer Trockenheit Wasser aus dem Boden entnehmen können.
In einem Feldversuch und einem Topfexperiment im Gewächshaus wurden Wasserbewegungen im Boden Pflanze Atmosphäre-Kontinuum mit ²H Isotopentracern verfolgt, welche durch Infiltrations-schläuche in tiefere Bodenschichten bzw. in untere Topfkompartimente zugegeben wurden. Mit einem Cavity Ring-Down Spektrometer wurde die Isotopensignatur des transpirierten Wassers der Versuchspflanzen in situ gemessen und mit Sonden die Bodenfeuchte ermittelt. Zur Beurteilung des physiologischen Zustands der Versuchspflanzen wurde die stomatäre Leitfähigkeit der Pflanzen-blätter gemessen sowie die Pflanzenhöhe und die Erträge erfasst. Im Gewächshausversuch wurden verschiedene Topfvarianten mit unterschiedlichen Möglichkeiten der pflanzlichen Interaktion verwendet, um mögliche Transportwege für eine hydraulische Wasserumverteilung separat zu quantifizieren. Zur Beurteilung abiotischer und biotischer Faktoren auf eine hydraulische Wasserumverteilung wuchsen Zea mays (Mais), Sorghum bicolor (Zucker Hirse), Medicago sativa (Luzerne), Linum usitatissimum (Lein) und Helianthus annuus (Sonnenblume) in unterschiedlichen Kombinationen in den Versuchstöpfen für eine Zeit von 100 Tagen mit einer Trockenphase am Versuchsende. Im Feldversuch wurden verschiedene Feldvarianten mit fünf Reihen Z. mays zwischen tiefwurzelnden M. sativa angelegt, wobei letztere am Versuchsende zum Teil geschnitten wurden. Um den Einfluss von Begleitpflanzen auf die Kolonisationsrate der Wurzeln von Z. mays mit AM im Zusammenhang mit einer möglichen hydraulischen Wasserumverteilung von M. sativa zu Z. mays zu untersuchen, wurde in verschiedenen Feldvarianten Z. mays zudem mit Zwischensaaten von Plantago lanceolata (Spitzwegerich) oder mit zufällig aufkeimenden Wildpflanzen kombiniert.
Im Feld war anhand der erhobenen Messdaten keine signifikante hydraulische Wasserumverteilung von geschnittenen oder ungeschnittenen M. sativa zu Z. mays nachweisbar, obgleich bei der Feldvariante mit Wildpflanzen ein höherer Wassergehalt festgestellt wurde als bei den anderen Feldvarianten bei zugleich erhöhter Kolonisationsrate der Wurzeln des Z. mays mit AM. Bei der Feldvariante mit P. lanceolata als Zwischensaat war die Kolonisationsrate der Wurzeln von Z. mays geringer als bei der Feldvariante mit Z. mays in Monokultur. Somit war keine Förderung der CMN durch P. lanceolata feststellbar. Die Kolben-Erträge waren bei Z. mays in Monokulturbeständen am höchsten und am geringsten bei der Feldvariante mit Wildpflanzen. Der dichte Bestand der M. sativa könnte die Abundanz von Wurzeln in der oberen Bodenzone aufgrund des hohen intraspezifischen Konkurrenzdrucks verringert und die Wurzeln mehr in tiefere Bodenbereiche getrieben haben, was die Interaktion mit den Wurzelsystemen des Z. mays und eine hydraulische Wasserumverteilung gemindert haben könnte. Die Beurteilung der hydraulischen Wasserumverteilung zwischen den Pflanzen beim Gewächshausversuch war nicht möglich, da die Versuchspflanzen nicht nur in den dafür vorgesehenen Topfkompartimenten wuchsen, sondern selbst die verschiedenen Wasser-quellen in den Kompartimenten erschlossen. Eine Pflanzeninteraktion zwischen L. usitatissimum und S. bicolor wurde anhand einer 18 % geringeren Pflanzenhöhe von S. bicolor in Mischkultur als in Monokultur festgestellt, trotz einer begrenzten Interaktionsmöglichkeit durch die Unterbindung des Wurzelkontakts durch Trennung in mehrere Topfkompartimente und einer ausbleibenden Verknüpfung der Pflanzen über CMN.
Die Experimente zeigten, dass Gemeinschaften von AM in Ackerkulturen durch eine verringerte Bodenbearbeitung und assoziierte Wildpflanzengemeinschaften gesteigert werden können. Der abiotische Faktor der physikalischen Bodenbearbeitung und der biotische Faktor der Konkurrenz um Nährstoffe können entscheidender für das Wachstum von Z. mays sein als der Kolonisationsgrad der Wurzeln mit AM, eine Nährstoffumverteilung über gemeinsame Mykorrhiza-Netze, positive Pflanzeninteraktionen oder eine mögliche hydraulische Wasserumverteilung von tiefwurzelnden M. sativa. Durch die geringe Abundanz von Wurzeln im Oberboden sind M. sativa vermutlich in engen Beständen nicht geeignet für einen HL. Tiefwurzelnde Pflanzenspezies, die wenig Nährstoffe verbrauchen, andere Kulturpflanzen nicht beschatten und durch ein dimorphes Wurzelsystem einen dichten Kontakt zum Wurzelsystem eines Flachwurzlers herstellen, sind wahrscheinlich in Mischkultursystemen am effektivsten, um den Effekt einer hydraulischen Wasserumverteilung bei Dürre zu nutzen.
Rangelands provide different ecosystem services to satisfy human needs. Although grazing management in southern Patagonia is mostly characterized by extensive continuous grazing, rotational grazing management may improve plant productivity and its associated microbiome. Arbuscular mycorrhizal (AM) symbioses play an important role in the functioning of arid rangelands. However, in most arid and semiarid grasslands, little is known about the environment-plant-symbiont interaction under different defoliation frequencies and contrasting growth conditions. In this context, the objective of the present study was to evaluate the response of Rytidosperma virescens native grass and the associated AM fungi under different defoliation frequency treatments (plants undefoliated, two clippings with 50-d intervals between defoliations, four clippings with 30-d intervals, and six clippings with 21-d intervals) and two growth conditions (field and greenhouse) in a 150-d experiment. Defoliation frequency with 21-d clipping intervals negatively affected plants and AM colonization. We found a negative linear relationship between AM colonization and removal of aboveground biomass and a positive relationship with root biomass and leaf area of R. virescens plants. We determined that the appropriate recovery period for rotational grazing systems should be at least 50 d (threshold) to optimize forage production and AM symbiosis during spring-summer seasons. Sustainable grazing management practices should be designed to improve or restore AM communities to maintain positive feedback with plant development.
Background
Most plants have a hyphosphere, the thin zone of soil around extraradical hyphae of arbuscular mycorrhizal (AM) fungi, which extends beyond the rhizosphere. This important interface has critical roles in plant mineral nutrition and water acquisition, biotic and abiotic stress resistance, mineral weathering, the formation of soil macroaggregates and aggregate stabilization, carbon (C) allocation to soils and interaction with soil microbes.
Scope
This review focuses on the hyphosphere of AM fungi and critically appraises the important findings related to the hyphosphere processes, including physical, chemical and biological properties and functions. We highlight ecological functions of AM fungal hyphae, which have profound impacts on global sustainability through biological cycling of nutrients, C sequestration in soil, release of greenhouse gas emissions from soil and the diversity and dynamics of the microbial community in the vicinity of the extraradical hyphae.
Conclusions
As a critical interface between AM fungi and soil, hyphosphere processes and their important ecological functions have begun to be understood and appreciated, and are now known to be implicit in important soil processes. Recent studies provide new insights into this crucial zone and highlight how the hyphosphere might be exploited as a nature-based solution, through understanding of interactions with the microbiome and the impacts on key processes governing resource availability, to increase sustainability of agriculture and minimize its environmental impact. Uncovering hyphosphere chemical and biological processes and their subsequent agricultural, ecological and environmental consequences is a critical research activity.
Soil functions as a vital living ecosystem that sustains plants, animals, and humans. Soil is not an inert medium, but it contains living organisms such as bacteria, fungi, and other microbes that are foundation of an elegant symbiotic ecosystem. The majority of plants live in close association with the diversity of soil microorganisms. They play an essential role in establishing symbiotic associations and thereby contributing to the growth of plant and indeed help in maintaining soil health. In the rhizosphere, a myriad of plant–microbe interactions occurs; therefore, the microorganisms that inhabit the rhizosphere are of great significance. Among a variety of soil microorganisms, the microbes such as rhizobacteria and arbuscular mycorrhizal fungi play very significant role in facilitating nutrient supply to their host plants and improve soil fertility. The use of plant materials in soil works as a conditioner and influences the carbon, phosphorus, and nitrogen cycles in soil–plant system. The process of mineralization in the soil contributes to the circulation of these nutrients, which is actually achieved by the action of saprophytic and pathogenic microorganisms. Shrinking cultivable land coupled with increasing population has created an increasing and immediate demand for new technologies. In recent era, nanofertilizers are a booming field. Nanotechnology acts as driver for modern-day smart and efficient practice. They are also helping in the maintenance of soil nutrients, stimulate plant growth, and provide resistance to disease. In the present review, a holistic view of the interaction of soil, plant, and microbes, sequestration of minerals, and role of nanotechnology in maintaining the soil health have been discussed.
Soils, particularly agricultural soils, are home to a plethora of microbial communities capable of sequestering soil carbon. In this framework, arbuscular mycorrhizal fungi (AMF) play a pivotal role. This universal group of fungi form an obligate symbiotic relationship with the roots of higher plants leading to improved nutrient uptake and abiotic and biotic stress resistance. In addition, these fungi secrete a group of glycoproteins called glomalin or glomalin-related soil protein (GRSP) that sustain soil health, cement soil aggregates, and sequester soil C in a stable form. AMF symbiosis and GRSP production are however influenced by numerous aspects, including crop and soil management practices. Besides plant and soil type, soil management practices also influence AMF diversity and abundance. The soil carbon sequestration via AMF and GRSP is achievable if AMF supporting agricultural practices are employed. This chapter summarizes the cumulative role of AMF and GRSP in forming and stabilizing soil aggregates for long-term C storage, the influence of AMF-mediated agricultural practices to sequester soil carbon and improve soil quality traits.
Several isolates of bacteria and fungi from soil, together with cells released directly from soil, were studied with respect to buoyant density and dry weight. The specific volume (cubic centimeters per gram) of wet cells as measured in density gradients of colloidal silica was correlated with the percent dry weight of the cells and found to be in general agreement with calculations based on the partial specific volume of major cell components. The buoyant density of pure bacterial cultures ranged from 1.035 to 1.093 g/cm, and their dry-matter content ranged from 12 to 33% (wt/wt). Average values proposed for the conversion of bacterial biovolume into biomass dry weight are 1.09 g/cm and 30% dry matter. Fungal hyphae had buoyant densities ranging from 1.08 to 1.11 g/cm, and their dry-matter content ranged from 18 to 25% (wt/wt). Average values proposed for the conversion of hyphal biovolume into biomass dry weight are 1.09 g/cm and 21% dry matter. Three of the bacterial isolates were found to have cell capsules. The calculated buoyant density and percent dry weight of these capsules varied from 1.029 g/cm and 7% dry weight to 1.084 g/cm and 44% dry weight. The majority of the fungi were found to produce large amounts of extracellular material when grown in liquid cultures. This material was not produced when the fungi were grown on either sterile spruce needles or membrane filters on an agar surface. Fungal hyphae in litter were shown to be free from extracellular materials.
A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.
The rhizosphere region is a variable zone containing a proliferation of microorganisms inside and outside the plant root. Many compounds are both taken up and passed out. Under normal growth conditions the rhizosphere exists because of the continuous loss of many forms of plant metabolites, which are rapidly utilized by microorganisms. Consequently, these rhizosphere microorganisms are in a position to affect both subsequent loss of material from the roots and nutrient uptake by the roots. In natural ecosystems an equilibrium develops between the plant and microorganisms that is affected only by the normal growth of plant and seasonal changes in the environment. However, in agriculture, man continually changes the normal equilibrium by manifold means. (e.g., plant monoculture, herbicide, fungicide and pesticide treatments, fertilizer application, and cultivation), all of which modify subsequent plant growth and the associated rhizosphere biota. Because of the importance of agriculture, the majority of work on the rhizosphere and its effects on plant growth has involved research on crop plants and, although this has provided great insight into rhizosphere—plant interactions in these relatively few species, some care should be taken in extrapolating such results to all natural ecosystems. With this proviso, we attempt to show, first, the effect the plant has on development and maintenance of the rhizosphere and, second, the influence the rhizosphere has on plant physiology and consequently crop productivity, highlighting areas of research likely to be rewarding both scientifically and commercially in the future. We do not attempt a complete review of the literature, since there have been reviews on many aspects of rhizosphere biology in recent years (Barber, 1978; Hale, et al. 1978; Newman, 1978; Balandreau and Knowles, 1978; Hale and Moore, 1979; Bowen, 1979, 1980, 1982; Woldendorp, 1981; Foster and Bowen, 1982; Lynch, 1982, 1983; Subba Rao, 1982a; Suslow, 1982), but rather choose specific examples to illustrate our major points.
The release of organic materials by roots of maize and wheat was studied using a growth chamber with a14CO2 atmosphere at constant total CO2 concentration and constant specific activity. The distribution of14C within shoots, roots and soil was determined for both plants after 4 and 6 weeks. After 6 weeks, 1.5% of the total amount of14C fixed by maize was found as a residue in the soil, while for wheat this figure was 2.0%. Rhizosphere14CO2 production was measured in a second experiment and plants were harvested after 3, 4, 5 and 6 weeks growth. The rhizosphere14CO2 evolution by wheat accounted for some 20% of the total amount of fixed14C and was a constant value throughout the growth period. Root-derived products were slowly incorporated by the soil microbial biomass to a maximum of 20% of the residual soil14C content after 6 weeks growth.
A two-compartment growth chamber in which the aboveground plant materials were exposed to ¹⁴CO2 and the belowground portion was exposed to ¹⁵N2 under normal atmospheric pressure was designed for carbon and nitrogen transfer studies. Vicia faba infected with vesicular-arbuscular fungus Glomus mossae and non-mycorrhizal plants fixed similar quantities of N2 at an age of 6½ wk. Approximately 0.10 mg N was fixed∙g⁻¹ dry plant materials∙day⁻¹ and 40 mg C∙g⁻¹ dry matter day⁻¹ were synthesized by mycorrhizal and non-mycorrhizal fababeans during 48 h exposure to ¹⁴CO2 at 6½ wk with no apparent difference in yield of dry matter. The non-mycorrhizal plants transferred 37% of the fixed ¹⁴C beneath ground. The mycorrhizal ones transferred 47% of the fixed ¹⁴C beneath ground. Most of the difference could be accounted for in the belowground respiration. The ¹⁴CO2 produced by root-microbial systems of the mycorrhizal fababeans was twice as great as that of the nonmycorrhizal; both contained active rhizobium.
The amounts of carbon released into soil from roots of wheat and barley seedlings grown under three environmental conditions
for 3 weeks with shoots in constant specific activity 14CO2 are reported. This carbon loss was measured as respired 14CO2 from both the root and the accompanying microbial population and as root derived 14C-labelled organic C compounds in the soil. With a 16 h photoperiod, growth at 15 °C constant or 18 °C day/14 °C night gave
a loss of 33–40% of the total net fixed carbon (defined as 14C retained in the plant plus 14C lost from the root). The proportion of 14C translocated to the roots that was released into the soil did not change with temperature, so carbon distribution within
the plant must have changed. With a 12 h photoperiod and a temperature regime of 18 °C/14 °C carbon loss from the roots was
decreased to 17–25% of the total fixed carbon.
The root system of ryegrass was more efficient than that of white clover in stabilizing aggregates of Lemnos loam because ryegrass supported a larger population of vesicular-arbuscular mycorrhizal hyphae in the soil. Electron micrographs show that the hyphae were covered with a layer of amorphous material, probably polysaccharide, to which clay particles appear firmly attached.
S ummary
The ability of several species of vesicular–arbuscular (VA) mycorrhizal fungi to form hyphae in soil was compared in two glasshouse experiments. We measured the length of hyphae in soil and related this to the length of infected root. Species of VA mycorrhizal fungi differed in the length of external hyphae produced per cm of infected root. Glomus fasciculatum (Thaxter sensu Gerd.) Gerd. and Trappe produced less external hyphae per cm infected root than did Gigaspora calospora (Nicol. and Gerd.) Gerd. at all harvest times and when inoculum was either placed in a band below the seed or mixed throughout the soil. Glomus tenue (Greenall) Hall and Acaulospora laevis Gerd. and Trappe both produced similar lengths of external hyphae per cm infected root to that formed by G. calospora .
Differences among isolates of VA mycorrhizal fungi in the distribution of hyphae in soil may be as important as differences in the length of external hyphae when selecting fungi that are effective at increasing nutrient uptake.
Carbon uptake and allocation in plants that were largely dependent on microbial symbionts for N and P was compared to that in plants given inorganic fertilizer. Soybeans (Glycine max L. Merr.) were grown in sterilized soil and were either left uninoculated, or were inoculated with Rhizobium japonicum (Kirschner), or both R. japonicum and Glomus fasciculatum (Thaxter sensu Gerd.). Uninoculated plants were given N and/or P fertilizer at rates required to produce plants similar in size to inoculated plants. Carbon flows to plant parts, root nodules and vesicular-arbuscular mycorrhizas were measured in six- and nine-week-old plants by determining the distributions of 14C after pulse labelling with 14CO2.
Root nodules in non-mycorrhizal plants utilized 9% of total photosynthate; this was increased to 12% in nodulated, mycorrhizal plants. Mycorrhizas used 17% of the total photosynthate of six-week-old plants; this fell to 8% after nine weeks. Rates of 14CO2 fixation in leaves of nodulated or nodulated plus mycorrhizal plants were up to 52% higher than in plants without microbial symbionts. Part of the increase was due to higher specific leaf area in plants colonized by symbionts, but other factors such as source-sink relationships, starch mobilization and leaf P concentrations were also involved in the host-plant adaptations to the C demand of the microbial endophytes.
Leek plants (Allium porrum) were grown on partially sterilized soil either inoculated (M) or not (NM) with the vesicular-arbuscular mycorrhizal fungus, Glomus mosseae. They were pulse-fed with 14CO2 in an apparatus which allowed CO2 subsequently respired either by the shoots or by the roots plus soil to be separately monitored. There were three experiments. In two, plants were harvested 48 h after labelling and in the third after 214 h. At harvest, the distribution of 14C between shoot, root, soil organic matter and root washings was measured.
Similar growth curves for M and NM plants were obtained by supplying extra phosphorus to the latter, so that C distributions for both treatments could be compared directly. In all three experiments, about 7 % more of the total fixed C was translocated from shoot to root in M plants compared to NM plants. In the third experiment, this extra translocate could be accounted for by increased root respiration plus increased loss of C to the soil but, despite this drain, M and NM plants had equal rates of C assimilation per unit of leaf area. However, shoots of M plants had a lower content of dry matter and hence higher assimilation rates expressed on a dry matter basis.
Increased hydration is suggested as a mechanism whereby leaf area and hence C assimilation increases in mycorrhizal plants and which offsets the effects of the drain imposed by the mycorrhizas.
Mycorrhizal and non-mycorrhizal onion seedlings were grown in individual soil chambers in which roots were confined to one side of a barrier. External hyphae of Glomus fasciculatus arising from mycorrhizal roots grew into an adjacent volume of soil. 32P was injected into soil at 1-cm intervals up to a distance of 8 cm from the confined roots. Relatively high levels of radioactivity were subsequently detected in root segments of mycorrhizal plants at all distances from tracer injection. High levels of radioactivity were detected also in leaf segments of mycorrhizal plants. Radioactivity of root or leaf segments of non-mycorrhizal plants did not exceed background level at any distance from tracer injection. 32P did not move more than 7.5 mm from the point of injection as indicated by gross autoradiography. Absorption of phosphate and its trans-location to the host by hyphae of G. fasciculatus can extend the phosphate uptake zone of mycorrhizal onions to at least 7 cm from the root surface.
Wheat and bailey plants were grown for 3 weeks in a constant environment chamber containing approximately atmospheric concentrations of carbon dioxide (0.03%) labelled with 14C. The roots of the plants were maintained under sterile or non-sterile conditions in soil contained in sealed pots which were regularly flushed with air. This enabled the quantities of 14C-labelled carbon dioxide produced in the soil by plant and microbial activity to be separately assessed. At harvest, the 14C and total carbon contents of the roots and shoots and of the water-soluble and insoluble material present in the soil were measured.
These procedures enabled both the amounts of organic materials released into soil by the roots of growing plants and the effects of micro-organisms on the process to be determined. Under sterile conditions between 5 and 10% of the photosynthetically fixed carbon may be released by roots compared with 12–18% by the roots of plants growing in unsterilized soil. These latter values are equivalent to 18–25% of the dry matter increments of the plants. The results indicate also that the increased evolution of carbon dioxide by cropped as compared to fallow soils can largely be ascribed to the immediate utilization by micro-organisms of substances released by roots.
Carbon flows to vesicular-arbuscular mycorrhizal fungi and rhizobial symbionts of 4- to 5-week-old faba beans, Vicia faba L., were measured by determining the distribution of 14CO2-C fixed by above-ground plant parts. Mycorrhizal fungi of both nodulated and non-nodulated hosts utilized ca. 4% of the C fixed by their hosts. Nodules utilized 6% of the C fixed by non-mycorrhizal hosts and 12% of the C fixed by mycorrhizal hosts. Measured rates of CO2 fixation for symbiotic beans were higher than for non-symbiotic beans. Nodulated root systems of mycorrhizal beans fixed more 15N2 than nodulated root systems of non-mycorrhizal plants. An increase in nodule biomass for plants infected with both rhizobia and mycorrhizal fungi was concluded to be the major factor increasing N2 fixation rates.
A colorimetric method measuring the conversion of fungal chitin to glucosamine has been used to estimate the intensity of vesicular-arbuscular mycorrhizal infection in roots. The technique has been used successfully with four plant genera and with four different endophytes.
A method of length estimation based on Newman's (1966) line intersect principle was developed and tested during a programme of root growth investigation in wheat. The length of sample roots when spread over a flat surface was found to relate to the number of intercepts made with the vertical and horizontal lines of an underlying grid. The versatility of the method was tested using 1/2 × 1/2, 1 × 1, 2 × 2 and 3 × 3 cm grid square sizes. Length estimates to 10 m required a maximum of 5-6 min for coefficients of variation of 5% or less.
The utilization of plant‐ and soil‐C by the microbial biomass in the rhizosphere of maize plants was investigated as a function of root proximity. The plants were cultivated in pots with divided root chambers and their shoots supplied with ¹⁴ CO 2 for 23 days. Subsequently the individual soil zones were analyzed for organic C, ¹⁴ C, biomass C and biomass ¹⁴ C.
Plant roots induced a 197% increase in microbial biomass and a 5.4% decrease in soil organic C compared with an 1.2% decrease in the unplanted control soil. The contributions of plant‐ and soil‐C to this increased microbial growth amounted to 68% and 32% respectively. Biomass‐ ¹⁴ C corresponded to 1.6% of the total photosynthetically fixed ¹⁴ C, to about 15% of the organic ¹⁴ C‐input into the rhizosphere and to 58% of the plant carbon remaining in soil after the removal of roots. 20% of this biomass‐ ¹⁴ C was found outside the immediate root zone.
These results demonstrate that growing roots are a significant C‐source for the microbial biomass and render an additional fraction of soil‐C available to microbial utilization. The efficiency of C‐utilization by the rhizosphere biomass is lower than values obtained with liquid cultures in laboratory experiments. The supply of plant‐C to the microbial biomass outside the immediate root vicinity indicates that the overall volume of the maize rhizosphere is greater than what has been supposed so far.
Considerable progress has been made during the last decade towards understanding and quantifying the input and turnover of plant carbon in the rhizosphere. This was made possible by the development (partially by the authors) and combination of appropriate new methods, such as: –homogeneous labelling of whole plants with ¹⁴ C
–distinction between root and microbial respiration
–separation of soil zones of known distances from the roots
–determination of microbial soil biomass.
These methods were applied to study the following aspects: –release of organic plant carbon into the soil by growing roots
–utilization of this plant carbon by the microbial biomass in the rhizosphere
–related influence on the turnover of soil organic matter, and
–spatial range of such root influence in the soil.
About 19% of the total photosynthetic production of the investigated plants was released into the rhizosphere as organic material. Most of this (15%) was transformed by the rhizosphere microorganisms into CO 2 , while only a small fraction (4%) remained in the soil, mainly as microbial cells (2.5%). As a result, microbial rhizosphere biomass increased considerably. Relative to the organic C‐input, however, the incorporation of root derived carbon by the microbial biomass was remarkably low (13%).
Along with the increase in microbial rhizosphere biomass, the presence of plant roots also enhanced the decomposition of soil organic matter and affected soil aggregate stability. Root carbon and root influences were even detected up to 20 mm away from the roots. This may be partially attributed to the contribution of root derived volatiles. Accordingly, both the actual volume of the rhizosphere and its metabolic significance is greater than what has so far been assumed. Possible interactions involving root, soil and microbial carbon are discussed.
The flow of carbon from plant roots through the microbial biomass is one of the key processes in terrestrial ecosystems. Roots release considerable amounts of organic materials which are utilized by microbes as substrate for biosynthesis and energy supply. The fate of photosynthates and other organic material in the soil-root environment under different conditions was studied using 14C-tracers. Soil structure and texture had a large effect on the turnover of the 14C-labelled materials through the microbial biomass. Finer, clayey soils tended to be more ‘preservative’ than coarser, sandy soils, i.e. larger amounts of 14C were incorporated in microbial biomass and soil organic matter fractions in clayey soils than in sandy soils.
The soil nutrient status also appeared to affect organic matter turnover. At limiting plant-nutrient concentrations the utilization of 14C-labelled photosynthates seem to be hampered. Plants roots influenced the transformation of glucose and crop residues and the effect was attributed to plant-induced changes in mineral nutrients status. The mechanisms of this process and the consequences are discussed.
A number of areas for future research are identified, including the potentials for manipulating rhizodeposition.
Soybean plants colonized by the vesicular-arbuscular mycorrhizal (VAM) fungusGlomus fasciculatum were grown in pot cultures utilizing a composite greenhouse rooting medium. Development of fungal mycelia inside and outside
the host root and total fungal biomass were determined from assays of fungal chitin. Growth and phosphorus uptake by VAM plants
and uncolonized controls were compared. Mycotrophic growth in VAM plants occurred during the final six weeks of the 19-week
growth period, when the concentration of available soil P fell below 10 μg P/g soil. Growth enhancement was most pronounced
in the reproductive organs. The data suggest a relationship between the initiation of the reproductive phase in the host and
the cessation of growth in the endophyte. Source-sink relationships and P availability appear to be factors influencing interactions
between the symbionts.
Water-soluble14C-labelled organic material, released into soil from roots of wheat and maize plants, was recovered with a mild percolation
technique, without disturbing the root-soil interface. Extraction yields were relatively high for the14C materials (up to 11% of residual soil14C for 6 weeks maize) illustrating the water soluble character of the freshly added material. The complexation potential of
the soil extracts was evaluated by adding57Co,65Zn and54Mn to the extract and determining their distribution among the organic fractions by a gel filtration technique. The results
show that within four weeks a micro-environment is created around a plant root, characterized by an accumulation of root-derived
organic materials. In parallel with this time dependent accumulation, a gradual shift from ionic metal to higher molecular
weight forms occurred. The three metals were increasingly complexed throughout the growth period. Extracts from a fallow soil
complexed minor amounts of the added tracer (6.4%; 1.9% and 0.2% for57Co,65Zn and54Mn respectively) while cropped soil extracts after 6 weeks complexed 61%; 16% and 6% of respectively Co, Zn and Mn in the
case of maize, and 31%, 15% and 1% in the case of wheat. Although the effects are most pronounced in the case of Co and maize,
evidence is given for similar effects with wheat and the other metals. The results indicate that the physicochemical status
of transition metals in the rhizosphere is entirely different from that in the bulk soil.
Tomato and pea seedlings were grown for 14d and 28d with shoots in constant specific activity14CO2 and the amounts and distribution of carbon within the plants and of that released into the soil from the roots were measured.
The estimates of carbon loss were derived from measurements of14CO2 respired from both the root and the accompanying microbial population and from the root derived14C-labelled organic carbon compounds in the soil. The relationship between plant growth and the loss of carbon and distribution
of carbon within the plants are discussed.
A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.RésuméUne méthode spectrophotométrique est décrite pour le dosage du phosphate dans l'eau de mer, an moyen de molybdate d'ammonium, en présence d'acide ascorbique et d'antimoinc. Il se forme rapidement un composé violet bleu, renfermant antimoine et phosphore dans un rapport atomique de 1:1.ZusammenfassungBeschreibung einer Methode zur Bestimmung von Phosphat in Mecrwasser mit Hilfe von Ammoniummolybdat in Gegenwart von Ascorbinsäure und Antimon. Der gebildete blau-violette Komplex wird spektrophotometrisch gemessen.
A group of technical procedures and devices are described which have proved useful in the study of the effects of carbon dioxide concentration on soil invertebrates and microbes. They include: (i) Methods for handling carbon dioxide-air mixtures.1.(ii) Methods for measuring carbon dioxide concentration in small air samples. (A brief review of available techniques is followed by a description of a micro-electrolytic method using a plastic syringe and the construction and use of buried Polythene sacs for field use.)2.(iii) Methods for maintaining carbon dioxide concentrations in small closed containers using carbon dioxide buffers.
The mechanism responsible for phosphorus inhibition of vesicular-arbuscular mycorrhiza formation in sudangrass (Sorghum vulgare Pers.) was investigated in a phosphorus-deficient sandy soil (0.5 micrograms phosphorus per gram soil) amended with increasing levels of phosphorus as superphosphate (0, 28, 56, 228 micrograms per gram soil). The root phosphorus content of 4-week-old plants was correlated with the amount of phosphorus added to the soil. Root exudation of amino acids and reducing sugars was greater for plants grown in phosphorus-deficient soil than for those grown in the phosphorus-treated soils. The increase in exudation corresponded with changes in membrane permeability of phosphorus-deficient roots, as measured by K(+) ((86)Rb) efflux, rather than with changes in root content of reducing sugars and amino acids. The roots of phosphorus-deficient plants inoculated at 4 weeks with Glomus fasciculatus were 88% infected after 9 weeks as compared to less than 25% infection in phosphorus-sufficient roots; these differences were correlated with root exudation at the time of inoculation. For plants grown in phosphorus-deficient soil, infection by vesicular-arbuscular mycorrhizae increased root phosphorus which resulted in a decrease in root membrane permeability and exudation compared to nonmycorrhizal plants. It is proposed that, under low phosphorus nutrition, increased root membrane permeability leads to net loss of metabolites at sufficient levels to sustain the germination and growth of the mycorrhizal fungus during pre- and postinfection. Subsequently, mycorrhizal infection leads to improvement of root phosphorus nutrition and a reduction in membrane-mediated loss of root metabolites.
A comparison was made of water-soluble root exudates and extracts of Sorghum vulgare Pers. grown under two levels of P nutrition. An increase in P nutrition significantly decreased the concentration of carbohydrates, carboxylic acids, and amino acids in exudates, and decreased the concentration of carboxylic acids in extracts. Higher P did not affect the relative proportions of specific carboxylic acids and had little effect on proportions of specific amino acids in both extracts and exudates. Phosphorus amendment resulted in an increase in the relative proportion of arabinose and a decrease in the proportion of fructose in exudates, but did not have a large effect on the proportion of individual sugars in extracts. The proportions of specific carbohydrates, carboxylic acids, and amino acids varied between exudates and extracts. Therefore, the quantity and composition of root extracts may not be a reliable predictor of the availability of substrate for symbiotic vesicular-arbuscular mycorrhizal fungi. Comparisons of the rate of leakage of compounds from roots with the growth rate of vesicular-arbuscular mycorrhizal fungi suggest that the fungus must either be capable of using a variety of organic substrates for growth, or be capable of inducing a much higher rate of movement of specific organic compounds across root cell membranes than occurs through passive exudation as measured in this study.
Microbiological and biochemical aspects of the rhizosphere
- A D Rovira
- B M Mcdougall
- A D Rovira
- B M Mcdougall
Interactions between soil micro-arthropods and endomycorrhizal associations of higher plants. In: Ecological Interactions in Soil
- R D Finlay
- Oxford
- J H Graham
- R T Leonard
- J A Menge
FiNLAY, R. D. (1985). Interactions between soil micro-arthropods and endomycorrhizal associations of higher plants. In: Ecological Interactions in Soil (Ed. by A. H. Fitter), pp. 319-331. Blackwell Scientific Publisher, Oxford. GRAHAM, J. H., LEONARD, R. T. & MENGE, J. A. (1981).
Quantification of \esicular-arbuscular mycorrhizae in plant roots
- P P Kormanik
- A.-C Mcgraw
KoRMANiK, P.P. & MCGRAW, A.-C. (1982). Quantification of
\esicular-arbuscular mycorrhizae in plant roots. In: Methods
and Principles of Mycorrhizai Research (Ed. by \. C. Schenck),
pp. 37-45. American Phytopathologica! Societ\, St. Paul.
The eftect of phosphorus on the formation of hyphae in soil bv the vesicular-arbuscular mycorrhizal fungus Buoyant densities and dry-matter contents of microorganisms: Conversion of a measured biovolume into biomass
- L K Abbott
- A D Robson
- G De Boer
- L Bakken
- R Olsen
ABBOTT, L. K., ROBSON, A. D. & DE BOER, G. (1984). The eftect of phosphorus on the formation of hyphae in soil bv the vesicular-arbuscular mycorrhizal fungus, Glomus fasciculatum Nezv Phytologist 97, 437^46. BAKKEN, L, R. & OLSEN, R. A. (1983). Buoyant densities and dry-matter contents of microorganisms: Conversion of a measured biovolume into biomass. Applied and Environmental Micro-biology 45, 1188-1195.
United States Department of Agriculture Effects of vesicular-arbuscular mycorrhiza on ^'C and '"N distribution in nodulated faba beans The chemical environment for fungal growth, 2. Carbon sources Arthropods as con-sumers of vesicular-arbuscular mycorrhizal fungi
- P C Pang
- E A Paul
Estimation of Available Phosphorus in Soils bv Extraction with NaHCO.^. Circular no. 939, United States Department of Agriculture. PANG, P. C. & PAUL, E. A. (1980). Effects of vesicular-arbuscular mycorrhiza on ^'C and '"N distribution in nodulated faba beans. Canadian Journal of Soil Science 60, 241 250. PERLMAN, D. (1965). The chemical environment for fungal growth, 2. Carbon sources. In: The Eungi An Advanced Treatise, Vol. 1 (Ed. by G. C. Ainsworth & A. S. Sussman), pp. 479-489. Academic Press, New York. RABATIN, S. C. & STINNER, B. R. (1985). Arthropods as con-sumers of vesicular-arbuscular mycorrhizal fungi. Mvcologia 77, 320-322.
Microbiological and biochemical aspects of the rhizosphere Quan-titati\e and qualitative effects of phosphorus on extracts and exudates of sudangrass roots in relation to \ esicular-arbuscular mycorrhiza formatic^n
- A D Rovira
- B L M Mcdougai
- S M Schwab
- J A Menge
- R T Leonard
RoviRA, A. D. & McDoUGAi.L, B. M. (1967). Microbiological and biochemical aspects of the rhizosphere. In: Soil Biochemistry, Vol. 1 (Ed. by A. D. McLaren & Ci. H. Peterson), pp. 417 463. Marcel Dekker, New York. SCHWAB, S. M., MENGE, J. A. & LEONARD, R. T. (1983). Quan-titati\e and qualitative effects of phosphorus on extracts and exudates of sudangrass roots in relation to \ esicular-arbuscular mycorrhiza formatic^n. Plant Physiology 73, 761 765.
Carbon loss from the roots of tomato and pea seedlings grown m soil Energy losses by the plant in rhizodeposition The infiuence of the rhizosphere on crop productivity
- J M Wihpi 's
- J M Whipps
- M Lynch
WiHPi's, J. M. (1987). Carbon loss from the roots of tomato and pea seedlings grown m soil. Plant and Soil 103, 95 100. WHIPPS, J. M. & LYNCH, j. M. (1985). Energy losses by the plant in rhizodeposition. Annual Proceedings of the Phytochemical Journal of Europe 26, 59 71. WHIPPS, J. M. & LVNCH, J. M. (1986). The infiuence of the rhizosphere on crop productivity. In :.4di'ances in M icrobial Ecology, Vo! 9 (Ed. by K. C. Marshall), pp. 187 244. Plenum Press, New York.
Carbon requirements of vesicular-arbuscular mycorrhizas
- D Harris
- E A Pail
HARRIS, D. & PAIL, E. A. (1987). Carbon requirements of
vesicular-arbuscular mycorrhizas. In: Ecophysiology of VA
Mycorrhizai Plants (Ed, by G. R. Safir), pp. 93-105. CRC
Press, Boca Raton, Florida.
Interactions between soil micro-arthropods and endomycorrhizal associations of higher plants
- R D Finlay
FiNLAY, R. D. (1985). Interactions between soil micro-arthropods
and endomycorrhizal associations of higher plants. In:
Ecological Interactions in Soil (Ed. by A. H. Fitter), pp.
319-331. Blackwell Scientific Publisher, Oxford.
Iiffect of plant roots on carbon metabolism of soil microbial biomass
- H M Fielal
- D Sauerbeck
FIELAL, H. M. & SAUERBECK, D. (1986). Iiffect of plant roots on
carbon metabolism of soil microbial biomass. Zeitschrift fiir
Pfiansenernaehrungen
und Bodenkunde 149, 181-188.
Carbon turnover in the rhizosphere
- H M Helal
- D Sai'erbeck
HELAL, H. M. & SAI'ERBECK, D. (1989). Carbon turnover in the
rhizosphere.
Zeitschrift
fiir Pfianzenernaehrungen und
Bodenkunde 152, 211-216.
Microbiological and biochemical aspects of the rhizosphere
- A D Rovira
- B L M Mcdougai
RoviRA, A. D. & McDoUGAi.L, B. M. (1967). Microbiological and
biochemical aspects of the rhizosphere. In: Soil Biochemistry,
Vol. 1 (Ed. by A. D. McLaren & Ci. H. Peterson), pp. 417 463.
Marcel Dekker, New York.
Estimation of Available Phosphorus in Soils by Extraction with NaHCO2. Circular no. 939 United States Department of Agriculture
- R Olsen
- C V Cole
- F S Watanabe