The assembly mechanisms underlying microbial community abundance, biotic interactions, and diversity over space and time are unresolved, particularly in benthic microbial mats distributed along environmental gradients. Experimental enrichment of nutrient-limited microbial mats from the Florida Everglades along a nutrient subsidy-salinity stress gradient stimulated autotrophic and heterotrophic metabolism, growth, and diversity independent of autotroph-heterotroph interactions across treatments and space. These results suggest spatial segregation of autotrophic and heterotrophic components within mats. Considering only the diatom component of Everglades mats over space and time, the subsidy-stress gradient controlled diatom compositional turnover at broad spatial scales while environmental and dispersal-based processes structured diatom communities at the regional scale and environmental processes independent of the environmental gradient at the temporal scale. These results indicate environmental gradients may not necessarily increase connectivity and dispersal across space, and temporal microbial diversity is driven at the local and regional scales by environmental heterogeneity in benthic microbial communities.
