Understanding the ecology of soil aggregation: interrelationships between arbuscular mycorrhizal fungi and associated microbiota

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Soil aggregation is a crucial aspect of agricultural sustainability and ecosystem functioning. Arbuscularmycorrhizal fungi (AMF) have a prominent role in the process of soil aggregation. As a ubiquitous and significant portion of soil microbial biomass AMF also exert potentially strong influences on the microbial communities associated with the mycorrhizal symbiosis. Our central hypotheses are that (a) soil microbial communities will be changed by AMF as a function of AMF species and mycorrhizosphere compartment; (b) and that these altered microbial communities are functionally significant in soil aggregation.The soil zone under influence by the mycorrhizal symbiosis (the mycorrhizosphere) can be conceptualized to consist of the hyphosphere (the soil under influence of AMF hyphae in soil) and the rhizosphere (the AMFinfluenced zone surrounding the root). The remaining soil is referred to as bulk soil. In this proposal we are explicitly distinguishing among these compartments, since different potential mechanisms for microbial community change act in each zone. Further, there are significant differences among AMF species/ isolates in their influences on plants and soil (in particular aggregation), and hence we propose a comparative approach using several isolates of AMF. Soil microbial communities will be assessed by DGGE analyses. Soil aggregation will be assessed by measuring soil aggregate distribution and water stability.This research will enhance our understanding of the microbial ecology of the AMF symbiosis and our knowledge of organism interactions in soil aggregation.