Communities of arbuscular mycorrhizal fungi in Stipa krylovii (Poaceae) in the Mongolian steppe

We examined arbuscular mycorrhizal (AM) fungi colonizing the roots of Stipa krylovii, a grass species dominating the grasslands of the steppe zone in Hustai and Uvurkhangai in Mongolia. The AM fungal communities of the collected S. krylovii roots were examined by molecular analysis based on the partial sequences of a small subunit of ribosomal RNA gene as well as AM fungal colonization rates. Almost all AM fungi detected were in Glomus-group A, and were divided into 10 phylotypes. Among them, one phylotype forming a clade with G. intraradices and G. irregulare was the most dominant. Furthermore, it was also found that most of the phylotypes include AM fungi previously detected in high altitude regions in the Eurasian Continent. Significant correlations were found among soil total N, total plant biomass and AM fungal colonization ratio, which suggested that higher plant biomass may be required for the proliferation of AM fungi in the environment. Meanwhile, redundancy analysis on AM fungal distribution and environmental variables suggested that the effect of plant biomass and most soil chemical properties on the AM fungal communities were not significant.     

Local adaptation to soil hypoxia determines the structure of an arbuscular mycorrhizal fungal community in roots from natural CO₂ springs

The processes responsible for producing and maintaining the diversity of natural arbuscular mycorrhizal (AM) fungal communities remain largely unknown. We used natural CO(2) springs (mofettes), which create hypoxic soil environments, to determine whether a long-term, directional, abiotic selection pressure could change AM fungal community structure and drive the selection of particular AM fungal phylotypes. We explored whether those phylotypes that appear exclusively in hypoxic soils are local specialists or widespread generalists able to tolerate a range of soil conditions. AM fungal community composition was characterized by cloning, restriction fragment length polymorphism typing, and the sequencing of small subunit rRNA genes from roots of four plant species growing at high (hypoxic) and low (control) geological CO(2) exposure. We found significant levels of AM fungal community turnover (β diversity) between soil types and the numerical dominance of two AM fungal phylotypes in hypoxic soils. Our results strongly suggest that direct environmental selection acting on AM fungi is a major factor regulating AM fungal communities and their phylogeographic patterns. Consequently, some AM fungi are more strongly associated with local variations in the soil environment than with their host plant's distribution.     

Wheat cultivars form distinctive communities of root-associated arbuscular mycorrhiza in a conventional agroecosystem

Background and aims

The effect of plant species on their root-associated arbuscular mycorrhizal (AM) fungi is well studied, but how this effect operates at the cultivar level remains poorly understood. This study investigates how wheat cultivars shape their AM fungal communities.

Methods

Twenty-one new wheat cultivars were traditionally cultivated in a dryland of northwestern China, and their agronomic traits, soil characteristics and the abundance and community composition of AM fungi were measured.

Results

Both spore community in soils and AM fungal phylotypes inside roots were significantly influenced by cultivar even though hyphal abundance, spore density and AM fungal diversity were similar across cultivars. Three out of 16 AM fungal phylotypes interacted with most cultivars, whilst some phylotypes preferred to colonize cultivars with similar agronomic traits. Six wheat cultivars, all which had hosted 6 AM fungal phylotypes, seemed to be generalists. Nestedness analysis and stochastic model fitting revealed that the AM fungal communities colonizing roots were codetermined by deterministic and stochastic processes.

Conclusions

A complex pattern of cultivar-AM fungal interactions was observed in this study, and our results highlight that the host effect on the community assembly of AM fungi could be operating on the level of plant cultivar.     

Effect of plant species on communities of arbuscular mycorrhizal fungi in the Mongolian steppe

Communities of arbuscular mycorrhizal (AM) fungi were investigated in Stipa krylovii, Leymus chinensis (Poaceae), Allium bidentatum (Liliaceae), and Astragalus brevifolius (Fabaceae) in the Mongolian steppe to examine the effect of plant species on the communities in this study. The AM fungal communities were examined by molecular analysis based on the partial sequences of a small subunit of the ribosomal RNA gene. The sequences obtained were divided into 23 phylotypes by the sequence similarity >98%. Many of the AM fungal phylotypes included AM fungi previously detected in high-altitude regions in the Tibet and Loes plateaus, which suggested that these AM fungi may have wide distribution with stressful conditions of aridity and coldness. Among the 23 phylotypes, 12 phylotypes were found in all four plants, and 87.4% of the all obtained sequences were affiliated into these 12 types. For the distribution of the AM fungal phylotypes, overlapping of the phylotypes among the four plant species were significantly higher than that simulated by random chance. These results suggested that AM fungal communities were less diversified among the examined plant species.     

Rapid change of AM fungal community in a rain-fed wheat field with short-term plastic film mulching practice

Plastic film mulching (PFM) is a widely used agricultural practice in the temperate semi-arid Loess Plateau of China. However, how beneficial soil microbes, arbuscular mycorrhizal (AM) fungi in particular, respond to the PFM practice is not known. Here, a field experiment was performed to study the effects of a 3-month short-term PFM practice on AM fungi in plots planted with spring wheat (Triticum aestivum L. cv. Dingxi-2) in the Loess Plateau. AM colonization, spore density, wheat spike weight, and grain phosphorus (P) content were significantly increased in the PFM treatments, and these changes were mainly attributable to changes in soil properties such as available P and soil moisture. Alkaline phosphatase activity was significantly higher in PFM soils, but levels of AM fungal-related glomalin were similar between treatments. A total of nine AM fungal phylotypes were detected in root samples based on AM fungal SSU rDNA analyses, with six and five phylotypes in PFM and no-PFM plots, respectively. Although AM fungal phylotype richness was not statistically different between treatments, the community compositions were different, with four and three specific phylotypes in the PFM and no-PFM plots, respectively. A significant and rapid change in AM fungal, wheat, and soil variables following PFM suggested that the functioning of the AM symbiosis had been changed in the wheat field under PFM. Future studies are needed to investigate whether PFM applied over a longer term has a similar effect on the AM fungal community and their functioning in an agricultural ecosystem.     

Contrasting preferences of arbuscular mycorrhizal and dark septate fungi colonizing boreal and subarctic Avenella flexuosa

Arbuscular mycorrhizal (AM) and dark septate endophytic (DSE) fungi are ubiquitous in grass roots, but their colonizations may vary according to latitudinal gradient and site conditions. We investigated how vegetation zone (boreal vs. subarctic), humus thickness, and site openness affect root fungal colonizations of the grass Avenella flexuosa. More precisely, we hypothesized that AM and DSE fungal colonizations would have different responses to environmental conditions such that AM fungi could be more common in boreal zone, whereas we expected DSE fungi to be more affected by the amount of humus. We found site openness to affect AM and DSE fungi in a contrasting manner, in interaction with the vegetation zone. AM colonization was high at open coastal dunes, whereas DSE fungi were more common at forested sites, in the boreal zone. Humus thickness affected AM fungi negatively and DSE fungi positively. To conclude, the observed AM and DSE fungal colonization patterns were largely contrasting. AM fungi were favored in seashore conditions characterized by thin humus layer, whereas DSE fungi were favored in conditions of higher humus availability.     

Arbuscular mycorrhizal dynamics in a chronosequence of Caragana korshinskii plantations

Arbuscular mycorrhizal (AM) fungi in a chronosequence of 5–42-year-old Caragana korshinskii plantations in the semi-arid Loess Plateau region of northwestern China were investigated. AM fungi colonization, spore diversity and PCR-denatured gradient gel electrophoresis-based AM fungal SSU rRNA gene sequences were analyzed. AM fungi colonization [measured as the percent of root length (%RLC), vesicular (%VC) and arbuscular (%AC) colonization] and spore density were significantly correlated with sampling month, but not with plant age, except for %RLC. The percent of vesicular colonization was negatively correlated with soil total nitrogen and organic carbon, and spore density was negatively correlated with soil moisture and available phosphorus. Ten distinguishable AM fungal spore morphotypes, nine Glomus and one Scutellospora species, were found. Nine AM fungal Glomus phylotypes were identified by sequencing, but at each sampling time only four to six AM fungal phylotypes were detected. The AM fungal community was significantly seasonal, whereas the AM fungal species richness did not increase with plantation age. A significant change in AM fungal colonization and community composition over an annual cycle was observed in this study, and our results suggest that the changes of AM are the product of the interaction between host phenology, soil characteristics and habitat. Understanding these interactions is essential if habitat restoration is to be effective.     

Effects of arbuscular mycorrhiza on community composition and seedling recruitment in temperate forest understory

Arbuscular mycorrhizal (AM) fungal communities can influence the species composition of plant communities. This influence may result from effects of AM on seedling recruitment, although the existing evidence is limited to experimental systems. We addressed the impact of AM fungi on the plant community composition and seedling recruitment of two species – Oxalis acetosella and Prunella vulgaris – in a temperate forest understory. We established a field experiment over two years in which soil fertility (using fertilizer to enhance and sucrose to decrease fertility) and the activity of AM fungi (using fungicide) was manipulated in a factorial design. Species richness, diversity and community composition of understory plants were not influenced by soil fertility or AM fungal activity treatments. However, plant community composition was marginally significantly affected by the interaction of these treatments as the effect of AM fungal activity became evident under enhanced soil fertility. Suppression of AM fungal activity combined with decreased soil fertility increased the number of shoots of herbaceous plants. Unchanged activity of AM fungi enhanced the growth of O. acetosella seedlings under decreased soil fertility, but did not influence the growth of P. vulgaris seedlings. We conclude that the role of AM fungi in structuring plant communities depends on soil fertility. AM fungi can have a strong influence on seedling recruitment, especially for those plants that are characteristic of the habitat.     

Interactive influence of light intensity and soil fertility on root-associated arbuscular mycorrhizal fungi

Background and aims

Soil nutrients and light have major effects on the economics of arbuscular mycorrhizal (AM) symbioses. This study tests the main and interactive effects of soil fertility and light on AM fungal community.

Methods

We conducted a 3 year mesocosm experiment with a full two factorial design: light (full light or shade) and soil fertility (unfertilized or fertilized), on the Qinghai-Tibetan Plateau. Plant traits, soil characteristics and the AM fungal communities inside roots and in soils were measured.

Results

Shade reduced AM colonization of roots, fertilization reduced the hyphal abundance in the soil, and both factors reduced species richness of AM fungi inside plant roots. Fertilization exacerbated the negative impacts of shade on AM fungal abundance and diversity. We observed 15 phylotypes of AM fungi inside roots and ten morphotypes of AM fungal spores in the soil. Taxa responded differently to shade and fertilization and there was little congruence between the responses of fungi inside the roots and in the spore community.

Conclusions

Our findings indicate that both shade and fertilization reduce the abundance of AM fungi, but the two factors have different effects on the quality of plant roots as habitat for AM fungi.     

Arbuscular mycorrhizal fungal community divergence within a common host plant in two different soils in a subarctic Aeolian sand area

There is rising awareness that different arbuscular mycorrhizal (AM) fungi have different autoecology and occupy different soil niches and that the benefits they provide to the host plant are dependent on plant-AM fungus combination. However, the role and community composition of AM fungi in succession are not well known and the northern latitudes remain poorly investigated ecosystems. We studied AM fungal communities in the roots of the grass Deschampsia flexuosa in two different, closely located, successional stages in a northern Aeolian sand area. The AM fungal taxa richness in planta was estimated by cloning and sequencing small subunit ribosomal RNA genes. AM colonization, shoot δ ¹³C signature, and %N and %C were measured. Soil microbial community structure and AM fungal mycelium abundance were estimated using phospholipid (PLFA) and neutral lipid (NLFA) analyses. The two successional stages were characterized by distinct plant, microbial, and fungal communities. AM fungal species richness was very low in both the early and late successional stages. AM frequency in D. flexuosa roots was higher in the early successional stage than in the late one. The AM fungal taxa retrieved belonged to the genera generally adapted to Arctic or extreme environments. AM fungi seemed to be important in the early stage of the succession, suggesting that AM fungi may help plants to better cope with the harsh environmental conditions, especially in an early successional stage with more extreme environmental fluctuations.     

Arbuscular mycorrhizal and dark septate endophytic fungi at 5,500 m on a glacier forefront in the Qinghai-Tibet Plateau, China

Arbuscular mycorrhizal (AM) and dark septate endophytic (DSE) fungi are rarely studied at extremely high elevations. Here, AM and DSE colonization in two dominant plant species (Melandrium apetalum and Poa litwinowiana) were microscopically observed on the forefront of Zhadang Glacier (5,500 m above sea level) in the Qinghai-Tibet Plateau, China. The AM fungal taxa were also identified by molecular methods. Both AM and DSE fungi synchronously colonized these two plant species, but AM dominated in M. apetalum and DSE dominated in P. litwinowiana. A total of five AM fungal spore morphotypes (Acaulospora capsicula, Diversispora sp., Glomus constrictum, G. eburneum and Glomus sp.) were found in the rhizosphere soils. Molecular identification revealed two AM fungal phylotypes: one Claroideoglomus phylotype from roots and one Diversispora phylotype from spores. These results extend the elevation at which both AM and DSE are known to occur.     

Ninety-year-, but not single, application of phosphorus fertilizer has a major impact on arbuscular mycorrhizal fungal communities

Background and aims

Arbuscular mycorrhizal (AM) fungi play a significant role in P nutrition of crops in agriculture, but P accumulation in the soil, e.g., application of P-fertilizer, generally reduces AM fungal colonization. The impact of long-term application of chemical fertilizer on AM fungal communities was investigated with respect to the time scale.

Methods

Soils were collected from four plots with different fertilizer management in the long-term experimental field established in 1914. Lotus japonicus was grown in the soils in a greenhouse, while Glycine max was grown in the plots in the field. DNA was extracted from their roots, and the diversity and community compositions were analyzed based on occurrence of the AM fungal phylotypes defined by sequence similarity in the LSU rDNA.

Results

The 90-year-application of N and K in the absence of P increased AM fungal diversity and resulted in formation of a distinctive fungal community compared with those in the other treatments. This effect was not cancelled by single application of P. Whereas the impact of balanced application of N, P, and K was ambiguous.

Conclusion

These observations suggest that the presence/absence of P-fertilizer has a major impact on AM fungal communities, but the action may appear only on a long time scale.     

Influence of commercial inoculation with Glomus intraradices on the structure and functioning of an AM fungal community from an agricultural site

The use of commercial arbuscular mycorrhizal (AM) inoculants is growing. However, we know little about how resident AM communities respond to inoculations under different soil management conditions. The objective of this study was to simulate the application of a commercial AM fungal inoculant of Glomus intraradices to soil to determine whether the structure and functioning of that soil’s resident AM community would be affected. The effects of inoculation were investigated over time under disturbed or undisturbed soil conditions. We predicted that the introduction of an infective AM fungus, such as G. intraradices, would have greater consequences in disturbed soil. Using a combination of molecular (terminal restriction length polymorphism analysis based on the large subunit of the rRNA gene) and classical methods (AM fungal root colonization and P nutrition) we found that, contrary to our prediction, adding inoculant to soil containing a resident AM fungal community does not necessarily have an impact on the structure of that community either under disturbed or undisturbed conditions. However, we found evidence of positive effects of inoculation on plant nutrition under disturbed conditions, suggesting that the inoculant interacted, directly or indirectly, with the resident AM fungi. The inoculant significantly improved the P content of the host but only in presence of the resident AM fungal community. In contrast to inoculation, soil disturbance had a significant negative impact on species richness of AM fungi and influenced the AM fungal community composition as well as its functioning. Thus, we conclude that soil disturbance may under certain conditions have greater consequences for the structure of resident AM fungal communities in agricultural soils than commercial AM fungal inoculations with G. intraradices.     

The Effect of Sulfur on the Composition of Arbuscular Mycorrhizal Fungal Communities During the Pod-Setting Stage of Different Soybean Cultivars

This study sought to investigate the effect of sulfur levels on changes in the fungal community composition of arbuscular mycorrhizae (AM) at the pod-setting stage and the relationship between the amount of applied sulfur and AM fungal diversity in different soybean cultivars. The objective of the research was to determine the optimal sulfur application level for different soybean cultivars and to improve soybean yield and quality from the perspective of AM fungal diversity. Three soybean cultivars, Heinong 44, Heinong 48, and Heinong 37, were selected as study materials. In addition to 0.033?g each of N, P₂O₅ and K₂O per kg of soil, 0, 0.02, 0.04, or 0.06?g of elemental sulfur was applied to each kg of soil for the four treatment groups, S1, S2, S3, and S4, respectively. The AM fungal community structure was analyzed in the soil and root of different soybean cultivars using the PCR-DGGE technology. The results indicated a significant effect of sulfur on the AM fungal community structure in the roots and rhizospheric soil of different soybean cultivars. The three soybean cultivars in group S2 exhibited the highest diversity in AM fungus. Significant changes in the dominant fungal species were observed in the DGGE fingerprints of each sample, and Glomus, Funneliformis, Rhizophagus, and Claroideoglomus fungi were the dominant species of AM fungus in the roots and soil of soybean. The application of an appropriate amount of sulfur improved the diversity of AM fungi in roots and rhizospheric soil of different soybean cultivars.     

Mechanical soil disturbance as a determinant of arbuscular mycorrhizal fungal communities in semi-natural grassland

While the effect of disturbance on overall abundance and community composition of arbuscular mycorrhizal (AM) fungi has been researched in agricultural fields, less is known about the impact in semi-natural grasslands. We sampled two AM plant species, Festuca brevipila and Plantago lanceolata, from an ongoing grassland restoration experiment that contained replicated plowed and control plots. The AM fungal community in roots was determined using nested PCR and LSU rDNA primers. We identified 38 phylotypes within the Glomeromycota, of which 29 belonged to Glomus A, six to Glomus B, and three to Diversisporaceae. Only three phylotypes were closely related to known morphospecies. Soil disturbance significantly reduced phylotype richness and changed the AM fungal community composition. Most phylotypes, even closely related ones, showed little or no overlap in their distribution and occurred in either the control or disturbed plots. We found no evidence of host preference in this system, except for one phylotype that preferentially seemed to colonize Festuca. Our results show that disturbance imposed a stronger structuring force for AM fungal communities than did host plants in this semi-natural grassland.     

Distribution of fungal endophytes in roots of Stipa krylovii across six vegetation types in grassland of northern China

To explore the biogeographical patterns of endophytic fungal communities on a large scale, we surveyed fungal endophytes in roots of Stipa krylovii from six vegetation types in grassland along a 3200 km west–east transect in northern China. Pyrosequencing of samples collected from 18 sites (three sites per vegetation type) revealed that Pleosporales, Hypocreales, Agaricales, and Xylariales were the dominant fungal orders in roots of S. krylovii. The dominant genera were Marasmius, Fusarium, Acremonium, Sarcinomyces, and Monosporascus, and these genera were distributed differently among the six vegetation types. In a variation partitioning analysis, vegetation type, geographical distance, and environmental parameters (mean annual precipitation and air temperature, soil organic carbon, soil total nitrogen, pH, elevation) explained 98.2% of variation in the endophyte fungal community, and environmental parameters explained more variation than did vegetation type or geographical distance. Mean annual precipitation was the major significant factor influencing endophytic fungal communities.     

Changes of AM Fungal Abundance along Environmental Gradients in the Arid and Semi-Arid Grasslands of Northern China

Arbuscular mycorrhizal (AM) fungi are ubiquitous symbionts of higher plants in terrestrial ecosystems, while the occurrence of the AM symbiosis is influenced by a complex set of abiotic and biotic factors. To reveal the regional distribution pattern of AM fungi as driven by multiple environmental factors, and to understand the ecological importance of AM fungi in natural ecosystems, we conducted a field investigation on AM fungal abundance along environmental gradients in the arid and semi-arid grasslands of northern China. In addition to plant parameters recorded in situ, soil samples were collected, and soil chemo-physical and biological parameters were measured in the lab. Statistical analyses were performed to reveal the relative contribution of climatic, edaphic and vegetation factors to AM fungal abundance, especially for extraradical hyphal length density (HLD) in the soil. The results indicated that HLD were positively correlated with mean annual temperature (MAT), soil clay content and soil pH, but negatively correlated with both soil organic carbon (SOC) and soil available N. The multiple regressions and structural equation model showed that MAT was the key positive contributor and soil fertility was the key negative contributor to HLD. Furthermore, both the intraradical AM colonization (IMC) and relative abundance of AM fungi, which was quantified by real-time PCR assay, tended to decrease along the increasing SOC content. With regard to the obvious negative correlation between MAT and SOC in the research area, the positive correlation between MAT and HLD implied that AM fungi could potentially mitigate soil carbon losses especially in infertile soils under global warming. However, direct evidence from long-term experiments is still expected to support the AM fungal contribution to soil carbon pools.     

Diversity of Rhizosphere Soil Arbuscular Mycorrhizal Fungi in Various Soybean Cultivars under Different Continuous Cropping Regimes

Recent studies have shown that continuous cropping in soybean causes substantial changes to the microbial community in rhizosphere soil. In this study, we investigated the effects of continuous cropping for various time periods on the diversity of rhizosphere soil arbuscular mycorrhizal (AM) fungi in various soybean cultivars at the branching stage. The soybean cultivars Heinong 37 (an intermediate cultivar), Heinong 44 (a high-fat cultivar) and Heinong 48 (a high-protein cultivar) were seeded in a field and continuously cropped for two or three years. We analyzed the diversity of rhizosphere soil AM fungi of these soybean plants at the branching stage using morphological and denaturing gradient gel electrophoresis (DGGE) techniques. The clustering analysis of unweighted pair-group method with arithmetic averages (UPGMA) was then used to investigate the AM fungal community shifts. The results showed that increasing the number of years of continuous cropping can improve the colonization rate of AM fungi in different soybean cultivars at the branching stage. The dominant AM fungi in the experimental fields were Funneliformismosseae and Glomus spp. The number of years of continuous cropping and the soybean cultivar both had obvious effects on the diversity of AM fungi, which was consistent with the results of colonization rate analysis. This study establishes a basis for screening dominant AM fungi of soybean. In addition, the results of this study may be useful for the development of AM fungal inoculants.     

Growth response of crops to soil microbial communities from conventional monocropping and tree-based intercropping systems

Background and aims

Recent studies have shown that tree-based intercropping (TBI) systems support a more diverse soil microbial community compared to conventional agricultural systems. However, it is unclear whether differences in soil microbial diversity between these two agricultural systems have a functional effect on crop growth.

Methods

In this study, we used a series of greenhouse experiments to test whether crops respond differently to the total soil microbial community (Experiment 1) and to arbuscular mycorrhizal (AM) fungal communities alone (Experiment 2) from conventionally monocropped (CM) and TBI systems.

Results

The crops had a similar growth response to the total soil microbial communities from both cropping systems. However, when compared to sterilized controls, barley (Hordeum vulgare) and canola (Brassica napus) exhibited a negative growth response to the total soil microbial communities, while soybean (Glycine max) was unaffected. During the AM fungal establishment phase of the second experiment, ‘nurse’ plants had a strong positive growth response to AM fungal inoculation, and significantly higher biomass when inoculated with AM fungi from the CM system compared to the TBI system. Soybean was the only crop species to exhibit a significant positive growth response to AM fungal inoculation. Similar to the total soil microbial communities, AM fungi from the two cropping systems did not differ in their effect on crop growth.

Conclusion

Overall, AM fungi from both cropping systems had a positive effect on the growth of plants that formed a functional symbiosis. However, the results from these experiments suggest that negative effects of non-AM fungal microbes are stronger than the beneficial effects of AM fungi from these cropping systems.     

The role of local environment and geographical distance in determining community composition of arbuscular mycorrhizal fungi at the landscape scale

Arbuscular fungi have a major role in directing the functioning of terrestrial ecosystems yet little is known about their biogeographical distribution. The Baas-Becking hypothesis (‘everything is everywhere, but, the environment selects'') was tested by investigating the distribution of arbuscular mycorrhizal fungi (AMF) at the landscape scale and the influence of environmental factors and geographical distance in determining community composition. AMF communities in Trifolium repens and Lolium perenne roots were assessed in 40 geographically dispersed sites in Ireland representing different land uses and soil types. Field sampling and laboratory bioassays were used, with AMF communities characterised using 18S rRNA terminal-restriction fragment length polymorphism. Landscape-scale distribution of AMF was driven by the local environment. AMF community composition was influenced by abiotic variables (pH, rainfall and soil type), but not land use or geographical distance. Trifolium repens and L. perenne supported contrasting communities of AMF, and the communities colonising each plant species were consistent across pasture habitats and over distance. Furthermore, L. perenne AMF communities grouped by soil type within pasture habitats. This is the largest and most comprehensive study that has investigated the landscape-scale distribution of AMF. Our findings support the Baas-Becking hypothesis at the landscape scale and demonstrate the strong influence the local environment has on determining AMF community composition.