Community assembly and coexistence in communities of arbuscular mycorrhizal fungi

Abstract

Arbuscular mycorrhizal fungi are asexual, obligately symbiotic fungi with unique morphology and genomic structure, which occupy a dual niche, that is, the soil and the host root. Consequently, the direct adoption of models for community assembly developed for other organism groups is not evident. In this paper we adapted modern coexistence and assembly theory to arbuscular mycorrhizal fungi. We review research on the elements of community assembly and coexistence of arbuscular mycorrhizal fungi, highlighting recent studies using molecular methods. By addressing several points from the individual to the community level where the application of modern community ecology terms runs into problems when arbuscular mycorrhizal fungi are concerned, we aim to account for these special circumstances from a mycocentric point of view. We suggest that hierarchical spatial structure of arbuscular mycorrhizal fungal communities should be explicitly taken into account in future studies. The conceptual framework we develop here for arbuscular mycorrhizal fungi is also adaptable for other host-associated microbial communities.

Figure 1

Applying the combination of a filter model of community assembly and neutral processes for AM fungi. The regional pool of AM fungi consists of species present in the soil and in the roots of the host community. Through local or long-distance dispersal and chance, species reach local habitats. The environmental filter prevents species whose environmental tolerances do not overlap with local conditions from entering the community. The host filter allows colonization only for compatible fungal partners, thus further removing species. The local community reflects the cumulative effects of these processes, and in turn influences them through feedbacks. Horizontal interactions within the symbiotic community and with other non-host species also affect local communities. Local communities in turn contribute to the regional species pools with autochtonous propagule input. The capital letters refer to different AM fungal species. Ellipses with different lines depict different root system communities. Details of the depicted community assembly and coexistence model elements can be found in the section 'Factors affecting AM fungal community assembly: review of the elements of the proposed model' in the main text.

Figure 2

Hierarchical scale-dependent community system in AM fungi. At a given spatial (or temporal) scale, multiple processes influence the assembly of AM fungal communities. Relative importance of assembly processes changes with spatial scale, causing idiosyncrasy in response to different assembly factors, when the hierarchical spatial structure is not explicitly considered.