The turnover of community composition across space and time – beta diversity – can be differentially influenced by local (e.g., environmental) and regional (e.g., dispersal) assembly mechanisms that can determine how resilient community biodiversity is to change. However, relatively little is known of how the mechanisms underlying beta diversity are affected at multiple spatial and temporal scales along environmental gradients, particularly in microbial communities sensitive to environmental disturbance and physically contained within microhabitats. We assessed the beta diversity of a periphytic diatom metacommunity across an environmental subsidy (nutrients) and chemical stress (salinity) gradient and identified the spatial and temporal extents of the local and regional mechanisms structuring metacommunity turnover using variation partitioning. The study was conducted along a freshwater-oligohaline coastal gradient within the Florida Everglades, USA among 16 sites over 8 years.
We found higher spatial and temporal environmental variability within the low subsidy-stress, freshwater region of the gradient that was attributed to high variability in drought physical stress. Metacommunity environmental conditions were defined spatially and temporally by the subsidy-stress gradient. Spatial beta diversities were highest at the metacommunity and inter-region scale, but temporal turnover was low across and within regions except for the high subsidy-stress, brackish region. The variation of spatial beta diversity was partitioned into assembly mechanisms for each region: the metacommunity and between regions were environmentally structured, indicative of species sorting processes. Environmental and spatial factors were significant within regions, indicative of coincident species sorting and spatial-based processes at the regional scale that fluctuated spatiotemporally. Temporally, the metacommunity and each region correlated strongly with non-gradient environmental factors and variability in subsidy and drought stress. These findings suggest environmental gradients structure microbial communities at the metacommunity spatial scale, while both local and regional controls structure communities spatially within a region and environmental controls regulate community assembly temporally at metacommunity and regional scales independent of spatial environmental gradients.