Idiosyncrasy and overdominance in the structure of natural communities of arbuscular mycorrhizal fungi: is there a role for stochastic processes?

Abstract

Summary1. Most studies of species abundance patterns focus on conspicuous macroorganisms while microbial communities remain relatively understudied. This bias is a concern given the functional importance and high diversity of microbes. 2. We determine whether a common species abundance distribution (SAD) is observed in communities of a widespread group of soil microbes, the Glomeromycota or arbuscular mycorrhizal (AM) fungi. Using molecular techniques, we intensively sampled the AM fungal community of a woodland-grassland ecotone in Yorkshire, UK. Observed species abundances were compared to theoretical models describing SADs. We also reanalysed 32 previously published data sets in a similar manner. 3. Species abundance distributions in all the AM fungal communities fitted both lognormal and broken-stick models. However, these models consistently and significantly underpredicted the abundance of the most abundant AM fungal taxon. We found that AM fungal communities are typically dominated by a single taxon; representing on average 40% of total abundance within the community. Phylogenetic analysis of the most abundant taxa across data sets showed that the dominant AM fungal type in each community was different and not a widespread generalist. 4. We conclude that a common community structure is present in AM fungal communities from different habitats. The fit to log-normal and broken-stick models suggests the influence of niche differentiation structuring these communities. However, the consistently observed overdominance indicates that local adaptation and stochastic processes may also play important roles in structuring these communities, and we propose a mechanism to explain overdominance in AM fungal communities. 5. Synthesis. This paper applies ecological models derived from studies on larger organisms to microbial communities. Results from this study suggest that a common log-normal SAD is likely to be observed across both microbial and macro taxa. However, due to the distinctive features of microbial biology, some noticeable differences, such as heavy overdominance, may lead to unique structures in microbial communities. This research not only highlights that, to a first approximation, microbial communities follow similar processes and have similar patterns to those of macroorganisms, but also the need for large-scale microbial data sets, if we are to understand the patterns and processes regulating global biodiversity.

Effects of Inoculum Additions in the Presence of a Preestablished Arbuscular Mycorrhizal Fungal Community

“…The pool of nrDNA copies of the AMF community was dominated by G. intraradices, in accordance with observations of highly skewed natural communities being usually dominated by a single taxon (37). However, nrDNA copy numbers per nucleus may vary among AMF isolates (38), and the overall high levels of G. intraradices copy numbers, compared to the other two isolates, cannot be unambiguously related to high levels of biologically relevant units such as nuclei or intraradical fungal structures.…”

Species richness and root colonization of arbuscular mycorrhizal fungi in Syngonanthus elegans, an endemic and threatened species from the Cerrado domain in Brazil

“…This dominance by three species in the community structure has been identified in other Brazilian ecosystems in different habitats such as sand dunes, tropical forest, Cerrado, and agro-ecosystems and is also based on field-collected spores Siqueira, 2006). Molecular data also indicates that species abundance of AMF in natural communities follows the log normal and broken stick model, where communities are dominated by a few species (Dumbrell et al, 2010). Aside from those species, others dominant species were Acaulospora mellea in both sites, Glomus sp.…”

Modularity Reveals the Tendency of Arbuscular Mycorrhizal Fungi To Interact Differently with Generalist and Specialist Plant Species in Gypsum Soils

“…There are case studies on the general abiotic versus biotic effectors of AMF community assembly (7,8). Differences in soil type have been reported to be key factors determining AMF species and community composition (9); this is particularly relevant in stressful environments, such as serpentine soils (10)(11)(12), thermal soils (13), heavy metal soils, and saline soils (14,15).…”