PROBING THE DEPTHS OF MICROBIAL COMMUNITY STRUCTURE IN SOIL

An interconnected web of diverse microorganisms largely recognized on the basis of molecular sequence information alone mediates nutrient and energy flow in soil ecosystems. However, accurate description of the microbial networks that drive matter and energy transformation integral to soil ecosystem function remains challenging given the diversity of soil microbial communities and the sensitivity of these communities to soil properties and perturbation. Co-occurrence analysis provides a statistical framework in which to infer microbial community interactions that would otherwise remain cryptic. Here we present guidelines for the development and interpretation of microbial community interaction networks using clustered small subunit ribosomal RNA gene sequences spanning multiple soil horizons in an unmanaged and a disturbed boreal forest in British Columbia. Our networks analysis indicates effects of perturbation were constrained to surficial organic horizons, suggesting that any residual impacts of surface soil disturbance on deeper horizons are unresolvable 13 years post-harvest. Further, building on extant macro-ecology and graph theory, increased connectance, a network property describing the proportion of possible interactions realized, was identified between soil microbial community members following perturbation in the same surface horizons. This network property likely reflects a resilience force that buffers the community against ecological or biogeochemical process changes within the soil milieu. Understanding the eco-evolutionary forces shaping network structure and dynamics will ultimately increase our capacity to predict microbial community responses to forest soil perturbation in a time of climate change.