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.     

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.     

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.     

Changes in arbuscular mycorrhizal fungal communities during invasion by an exotic invasive plant

Exotic invasive plants can show strong plant–soil feedback responses, but little is known about time scales for significant changes in soil microbial communities to occur after invasion. Previous work has suggested that plant invasions can modify arbuscular mycorrhizal (AM) fungal community structure. However, there is a lack of understanding about how long it takes for these changes to develop. To test this we investigated temporal changes in AM fungal communities colonising the invasive plant Vincetoxicum rossicum (Apocynaceae). We hypothesised that AM fungal community structure would change in a particular direction during the invasion process. We collected soil from two sites with a long history of invasion by this plant, with each site having paired invaded and uninvaded plots. Soil from these plots was used in a glasshouse experiment to characterise AM fungal community structure in the roots of V. rossicum at different times throughout a simulated growing season. AM fungal community structure differed between invaded and uninvaded plots. However, contrasting with our hypothesis, AM fungal communities colonising V. rossicum growing in soil from uninvaded plots did not change towards those in plants growing in previously invaded soil. Our data suggest that changes to AM fungal communities in the presence of V. rossicum require longer than the first growing season after establishment to develop.     

Testing Potential Effects of Maize Expressing the Bacillus thuringiensis Cry1Ab Endotoxin (Bt Maize) on Mycorrhizal Fungal Communities via DNA- and RNA-Based Pyrosequencing and Molecular Fingerprinting

The cultivation of genetically modified (GM) crops has increased significantly over the last decades. However, concerns have been raised that some GM traits may negatively affect beneficial soil biota, such as arbuscular mycorrhizal fungi (AMF), potentially leading to alterations in soil functioning. Here, we test two maize varieties expressing the Bacillus thuringiensis Cry1Ab endotoxin (Bt maize) for their effects on soil AM fungal communities. We target both fungal DNA and RNA, which is new for AM fungi, and we use two strategies as an inclusive and robust way of detecting community differences: (i) 454 pyrosequencing using general fungal rRNA gene-directed primers and (ii) terminal restriction fragment length polymorphism (T-RFLP) profiling using AM fungus-specific markers. Potential GM-induced effects were compared to the normal natural variation of AM fungal communities across 15 different agricultural fields. AM fungi were found to be abundant in the experiment, accounting for 8% and 21% of total recovered DNA- and RNA-derived fungal sequences, respectively, after 104 days of plant growth. RNA- and DNA-based sequence analyses yielded most of the same AM fungal lineages. Our research yielded three major conclusions. First, no consistent differences were detected between AM fungal communities associated with GM plants and non-GM plants. Second, temporal variation in AMF community composition (between two measured time points) was bigger than GM trait-induced variation. Third, natural variation of AMF communities across 15 agricultural fields in The Netherlands, as well as within-field temporal variation, was much higher than GM-induced variation. In conclusion, we found no indication that Bt maize cultivation poses a risk for AMF.     

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.     

Preferential Colonization of Solanum tuberosum L. Roots by the Fungus Glomus intraradices in Arable Soil of a Potato Farming Area

The symbiosis between plant roots and arbuscular mycorrhizal (AM) fungi has been shown to affect both the diversity and productivity of agricultural communities. In this study, we characterized the AM fungal communities of Solanum tuberosum L. (potato) roots and of the bulk soil in two nearby areas of northern Italy, in order to verify if land use practices had selected any particular AM fungus with specificity to potato plants. The AM fungal large-subunit (LSU) rRNA genes were subjected to nested PCR, cloning, sequencing, and phylogenetic analyses. One hundred eighty-three LSU rRNA sequences were analyzed, and eight monophyletic ribotypes, belonging to Glomus groups A and B, were identified. AM fungal communities differed between bulk soil and potato roots, as one AM fungal ribotype, corresponding to Glomus intraradices, was much more frequent in potato roots than in soils (accounting for more than 90% of sequences from potato samples and less than 10% of sequences from soil samples). A semiquantitative heminested PCR with specific primers was used to confirm and quantify the AM fungal abundance observed by cloning. Overall results concerning the biodiversity of AM fungal communities in roots and in bulk soils from the two studied areas suggested that potato roots were preferentially colonized by one AM fungal species, G. intraradices.     

The interactions between plant life form and fungal traits of arbuscular mycorrhizal fungi determine the symbiotic community

Arbuscular mycorrhizal (AM) fungi have traditionally been considered generalist symbionts. However, an increasing number of studies are pointing out the selectivity potential of plant hosts. Plant life form, determined by plant life history traits, seems to drive the AM fungal community composition. The AM fungi also exhibit a wide diversity of functional traits known to be responsible for their distribution in natural ecosystems. However, little is known about the role of plant and fungal traits driving the resultant symbiotic assemblages. With the aim of testing the feedback relationship between plant and fungal traits on the resulting AM fungal community, we inoculated three different plant life forms, i.e. annual herbs, perennial herbs and perennial semi-woody plants, with AM fungal communities sampled in different seasons. We hypothesized that the annual climate variation will induce changes in the mean traits of the AM fungal communities present in the soil throughout the year. Furthermore, the association of plants with different life forms with AM fungi with contrasting life history traits will show certain preferences according to reciprocal traits of the plants and fungi. We found changes in the AM fungal community throughout the year, which were differentially disrupted by disturbance and altered by plant growth form and plant biomass. Both plant and fungal traits clearly contributed to the resultant AM fungal communities. The revealed process can have implications for the functioning of ecosystems since changes in dominant plant life forms or climatic variables could influence the traits of AM fungal communities in soil and hence ecosystem processes.     

Diversity of arbuscular mycorrhizal fungi colonising roots of the grass species<Emphasis Type="Italic"> Agrostis capillaris</Emphasis> and<Emphasis Type="Italic"> Lolium perenne</Emphasis> in a field experiment

Analysis of arbuscular mycorrhizal (AM) fungal diversity through morphological characters of spores and intraradicular hyphae has suggested previously that preferential associations occur between plants and AM fungi. A field experiment was established to investigate whether AM fungal diversity is affected by different host plants in upland grasslands. Indigenous vegetation from plots in an unimproved pasture was replaced with monocultures of either Agrostis capillaris or Lolium perenne. Modification of the diversity of AM fungi in these plots was evaluated by analysis of partial sequences in the large subunit (LSU) ribosomal RNA (rDNA) genes. General primers for AM fungi were designed for the PCR amplification of partial sequences using DNA extracted from root tissues of A. capillaris and L. perenne. PCR products were used to construct LSU rDNA libraries. Sequencing of randomly selected clones indicated that plant roots were colonised by AM fungi belonging to the genera Glomus, Acaulospora and Scutellospora. There was a difference in the diversity of AM fungi colonising roots of A. capillaris and L. perenne that was confirmed by PCR using primers specific for each sequence group. These molecular data suggest the existence of a selection pressure of plants on AM fungal communities.     

The effects of arbuscular mycorrhizal (AM) fungal and garlic mustard introductions on native AM fungal diversity

Introduced, non-native organisms are of global concern, because biological invasions can negatively affect local communities. Arbuscular mycorrhizal (AM) fungal communities have not been well studied in this context. AM fungi are abundant in most soils, forming symbiotic root-associations with many plant species. Commercial AM fungal inocula are increasingly spread worldwide, because of potentially beneficial effects on plant growth. In contrast, some invasive plant species, such as the non-mycorrhizal Alliaria petiolata, can negatively influence AM fungi. In a greenhouse study we examined changes in the structure of a local Canadian AM fungal community in response to inoculation by foreign AM fungi and the manipulated presence/absence of A. petiolata. We expected A. petiolata to have a stronger effect on the local AM fungal community than the addition of foreign AM fungal isolates. Molecular analyses indicated that inoculated foreign AM fungi successfully established and decreased molecular diversity of the local AM fungal community in host roots. A. petiolata did not affect molecular diversity, but reduced AM fungal growth in the greenhouse study and in a in vitro assay. Our findings suggest that both introduced plants and exotic AM fungi can have negative impacts on local AM fungi.     

Relative Importance of Deterministic and Stochastic Processes in Driving Arbuscular Mycorrhizal Fungal Assemblage during the Spreading of a Toxic Plant

Both deterministic and stochastic processes are expected to drive the assemblages of arbuscular mycorrhizal (AM) fungi, but little is known about the relative importance of these processes during the spreading of toxic plants. Here, the species composition and phylogenetic structure of AM fungal communities colonizing the roots of a toxic plant, Ligularia virgaurea, and its neighborhood plants, were analyzed in patches with different individual densities of L. virgaurea (represents the spreading degree). Community compositions of AM fungi in both root systems were changed significantly by the L. virgaurea spreading, and also these communities fitted the neutral model very well. AM fungal communities in patches with absence and presence of L. virgaurea were phylogenetically random and clustered, respectively, suggesting that the principal ecological process determining AM fungal assemblage shifted from stochastic process to environmental filtering when this toxic plant was present. Our results indicate that deterministic and stochastic processes together determine the assemblage of AM fungi, but the dominant process would be changed by the spreading of toxic plants, and suggest that the spreading of toxic plants in alpine meadow ecosystems might be involving the mycorrhizal symbionts.     

Effect of environmental gradient in coastal vegetation on communities of arbuscular mycorrhizal fungi associated with Ixeris repens (Asteraceae)

The community structure of arbuscular mycorrhizal (AM) fungi associated with Ixeris repens was studied in coastal vegetation near the Tottori sand dunes in Japan. I. repens produces roots from a subterranean stem growing near the soil surface which provides an opportunity to examine the effects of an environmental gradient related to distance from the sea on AM fungal communities at a regular soil depth. Based on partial sequences of the nuclear large subunit ribosomal RNA gene, AM fungi in root samples were divided into 17 phylotypes. Among these, five AM fungal phylotypes in Glomus and Diversispora were dominant near the seaward forefront of the vegetation. Redundancy analysis of the AM fungal community showed significant relationships between the distribution of phylotypes and environmental variables such as distance from the sea, water-soluble sodium in soil, and some coexisting plant species. These results suggest that environmental gradients in the coastal vegetation can be determinants of the AM fungal community.     

Alien plants associate with widespread generalist arbuscular mycorrhizal fungal taxa: evidence from a continental‐scale study using massively parallel 454 sequencing

Aim The biogeography of arbuscular mycorrhizal (AM) fungi is poorly understood, and consequently the potential of AM fungi to determine plant distribution has been largely overlooked. We aimed to describe AM fungal communities associating with a single host‐plant species across a wide geographical area, including the plant’s native, invasive and experimentally introduced ranges. We hypothesized that an alien AM plant associates primarily with the geographically widespread generalist AM fungal taxa present in a novel range. Location Europe, China. Methods We transplanted the palm Trachycarpus fortunei into nine European sites where it does not occur as a native species, into one site where it is naturalized (Switzerland), and into one glasshouse site. We harvested plant roots after two seasons. In addition, we sampled palms at three sites in the plant’s native range (China). Roots were subjected to DNA extraction, polymerase chain reaction (PCR) and 454 sequencing of AM fungal sequences. We analysed fungal communities with non‐metric multidimensional scaling (NMDS) ordination and cluster analysis and studied the frequency of geographically widespread fungal taxa with log‐linear analysis. We compared fungal communities in the roots of the palm with those in resident plants at one site in the introduced range (Estonia) where natural AM fungal communities had previously been studied. Results We recorded a total of 73 AM fungal taxa. AM fungal communities in the native and introduced ranges differed from one another, while those in the invasive range contained taxa present in both other ranges. Geographically widespread AM fungal taxa were over‐represented in palm roots in all regions, but especially in the introduced range. At the Estonian site, the palm was colonized by the same community of widespread AM fungal taxa as associate with resident habitat‐generalist plants; by contrast, resident forest‐specialist plants were colonized by a diverse community of widespread and other AM fungal taxa. Main conclusions AM fungal communities in the native, invasive and experimentally introduced ranges varied in taxonomic composition and richness, but they shared a pool of geographically widespread, non‐host‐specific taxa that might support the invasion of a generalist alien plant. Our dataset provides the first geographical overview of AM taxon distributions obtained using a single host‐plant species.     

Mycorrhizal fungal growth responds to soil characteristics,but not host plant identity,during a primary lacustrine dune succession

Soil factors and host plant identity can both affect the growth and functioning of mycorrhizal fungi. Both components change during primary succession, but it is unknown if their relative importance to mycorrhizas also changes. This research tested how soil type and host plant differences among primary successional stages determine the growth and plant effects of arbuscular mycorrhizal (AM) fungal communities. Mycorrhizal fungal community, plant identity, and soil conditions were manipulated among three stages of a lacustrine sand dune successional series in a fully factorial greenhouse experiment. Late succession AM fungi produced more arbuscules and soil hyphae when grown in late succession soils, although the community was from the same narrow phylogenetic group as those in intermediate succession. AM fungal growth did not differ between host species, and plant growth was similarly unaffected by different AM fungal communities. These results indicate that though ecological filtering and/or adaptation of AM fungi occurs during this primary dune succession, it more strongly reflects matching between fungi and soils, rather than interactions between fungi and host plants. Thus, AM fungal performance during this succession may not depend directly on the sequence of plant community succession.     

Host plant species effects on arbuscular mycorrhizal fungal communities in tallgrass prairie

Symbiotic associations between plants and arbuscular mycorrhizal (AM) fungi are ubiquitous in many herbaceous plant communities and can have large effects on these communities and ecosystem processes. The extent of species-specificity between these plant and fungal symbionts in nature is poorly known, yet reciprocal effects of the composition of plant and soil microbe communities is an important assumption of recent theoretical models of plant community structure. In grassland ecosystems, host plant species may have an important role in determining development and sporulation of AM fungi and patterns of fungal species composition and diversity. In this study, the effects of five different host plant species [Poa pratensis L., Sporobolus heterolepis (A. Gray) A. Gray, Panicum virgatum L., Baptisia bracteata Muhl. ex Ell., Solidago missouriensis Nutt.] on spore communities of AM fungi in tallgrass prairie were examined. Spore abundances and species composition of fungal communities of soil samples collected from patches within tallgrass prairie were significantly influenced by the host plant species that dominated the patch. The AM fungal spore community associated with B. bracteata showed the highest species diversity and the fungi associated with Pa. virgatum showed the lowest diversity. Results from sorghum trap cultures using soil collected from under different host plant species showed differential sporulations of AM fungal species. In addition, a greenhouse study was conducted in which different host plant species were grown in similar tallgrass prairie soil. After 4 months of growth, AM fungal species composition was significantly different beneath each host species. These results strongly suggest that AM fungi show some degree of host-specificity and are not randomly distributed in tallgrass prairie. The demonstration that host plant species composition influences AM fungal species composition provides support for current feedback models predicting strong regulatory effects of soil communities on plant community structure. Differential responses of AM fungi to host plant species may also play an important role in the regulation of species composition and diversity in AM fungal communities. Received: 29 January 1999 / Accepted: 20 October 1999     

Soil nutritional status, not inoculum identity, primarily determines the effect of arbuscular mycorrhizal fungi on the growth of Knautia arvensis plants

Arbuscular mycorrhizal (AM) symbiosis is among the factors contributing to plant survival in serpentine soils characterised by unfavourable physicochemical properties. However, AM fungi show a considerable functional diversity, which is further modified by host plant identity and edaphic conditions. To determine the variability among serpentine AM fungal isolates in their effects on plant growth and nutrition, a greenhouse experiment was conducted involving two serpentine and two non-serpentine populations of Knautia arvensis plants grown in their native substrates. The plants were inoculated with one of the four serpentine AM fungal isolates or with a complex AM fungal community native to the respective plant population. At harvest after 6-month cultivation, intraradical fungal development was assessed, AM fungal taxa established from native fungal communities were determined and plant growth and element uptake evaluated. AM symbiosis significantly improved the performance of all the K. arvensis populations. The extent of mycorrhizal growth promotion was mainly governed by nutritional status of the substrate, while the effect of AM fungal identity was negligible. Inoculation with the native AM fungal communities was not more efficient than inoculation with single AM fungal isolates in any plant population. Contrary to the growth effects, a certain variation among AM fungal isolates was revealed in terms of their effects on plant nutrient uptake, especially P, Mg and Ca, with none of the AM fungi being generally superior in this respect. Regardless of AM symbiosis, K. arvensis populations significantly differed in their relative nutrient accumulation ratios, clearly showing the plant’s ability to adapt to nutrient deficiency/excess.     

TRFLP analysis reveals that fungi rather than bacteria are associated with premature yeast flocculation in brewing

Premature yeast flocculation (PYF) is a sporadic fermentation problem in the brewing industry that results in incomplete yeast utilization of fermentable sugars in wort. Culture-independent, PCR-based fingerprinting techniques were applied in this study to identify the associations between the occurrence of the PYF problem during brewery fermentation with barley malt-associated microbial communities (both bacteria and fungi). Striking differences in the microbial DNA fingerprint patterns for fungi between PYF positive (PYF +ve) and negative (PYF ?ve) barley malts were observed using the terminal restriction fragment length polymorphism (TRFLP) technique. The presence of terminal restriction fragments (TRFs) of 360–460 bp size range, for fungal HaeIII restriction enzyme-derived TRFLP profiles appeared to vary substantially between PYF +ve and PYF ?ve samples. The source of the barley malt did not influence the fungal taxa implicated in PYF. TRFLP analysis indicates bacterial taxa are unlikely to be important in causing PYF. Virtual digestion of fungal sequences tentatively linked HaeIII TRFs in the 360–460 bp size range to a diverse range of yeast/yeast-like species. Findings from this study suggest that direct monitoring of barley malt samples using molecular methods could potentially be an efficient and viable alternative for monitoring PYF during brewery fermentations.     

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.     

Divergent phenologies may facilitate the coexistence of arbuscular mycorrhizal fungi in a North Carolina grassland

Interest in the diversity of arbuscular mycorrhizal (AM) fungal communities has been stimulated by recent data that demonstrate that fungal communities influence the competitive hierarchies, productivity, diversity, and successional patterns of plant communities. Although natural communities of AM fungi are diverse, we have a poor understanding of the mechanisms that promote and maintain that diversity. Plants may coexist by inhabiting disparate temporal niches; plants of many grasslands are either warm or cool season specialists. We hypothesized that AM fungi might be similarly seasonal. To test our hypothesis, we tracked the sporulation of individual AM fungal species growing within a North Carolina grassland. Data were collected in 1996 and 1997; in 1997, sampling focused on two common species. We found that AM fungi, especially Acaulospora colossica and Gigaspora gigantea, maintained different and contrasting seasonalities. Acaulospora colossica sporulated more frequently in the warm season, but Gi. gigantea sporulated more frequently in the cool season. Moreover, AM fungal species were spatially aggregated at a fine scale. Contrasting seasonal and spatial niches may facilitate the maintenance of a diverse community of AM fungi. Furthermore, these data may illuminate our understanding of the AM fungal influence on plant communities: various fungal species may preferentially associate with different plant species and thereby promote diversity in the plant community.