Understanding the relative role of ecological neutrality and niche based competition in structuring the soil community: a comparative field study on arbuscular mycorrhizal fungi and microarthropods

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Soil biota represents a unique opportunity for testing competing models of community assembly since it is characterized by an astonishing diversity. Surprisingly, there are only a few studies that directly addressed neutral (demographic stochasticity with limited dispersal) vs. niche (competition with environmental heterogeneity) processes in the soil. We will study the assemblages formed by arbuscular-mycorrhizal fungi (AMF), collembolans and oribatid mites in a natural grassland and we will test four hypotheses: (1) at the smallest scale of the study (the single plant canopy) community is randomly assembled (ecological drift); (2) at the plot scale (≈ 1m), distance between plants is the main predictor of community similarities (dispersal limitation); (3) at larger scales (transects, 5-10 m), that encompass environmental heterogeneities (e.g. soil texture and moisture), species composition varies randomly (niche overlap); (4) at all scales geographic distances is sufficient to predict species distribution. Soil will be characterized by key variables such as moisture, pH and organic C. AMF communities will be assessed molecularly, in the roots and the soil, while microarthropods will be assessed morphologically. There are no comparative studies that addressed in detail the different scales at which assemblages of different organisms may diverge. This is a topical issue, given the functional role of AMF and microarthropods in the ecosystem (e.g. carbon cycling). This research will enhance our understanding of processes shaping natural communities.