Small‐ and large‐scale patches shape benthic microbial community structure and functional gene composition in streams at the subcontinental scale

Abstract

Streams process organic matter as water moves along the land-to-ocean continuum, making important contributions to global biogeochemical cycles. Yet, predicting stream microbial metabolism associated with biogeochemical transformations at broad spatial scales remains challenging. Using the National Ecological Observatory Network database, we investigated ecological relationships between microbial communities and environmental conditions at the subcontinental scale. We found that microbial community composition and function were best explained by site and substrate type. However, when field replicates were combined, stream physico-chemical characteristics became strong predictors. Additionally, oxic and anoxic nitrogen- and methane-related gene abundances varied with substrate type and coexisted in epipsammon samples, but not in epilithon. Overall, water quality appeared to act as a subcontinental scale environmental filter on microbial communities. However, this influence was secondary to the high spatial heterogeneity induced by small-scale patches. Thus, nested spatial scales must be considered to fully understand benthic microbial communities' role in stream biogeochemistry.