Stochastic Processes Structure Both Abundant and Rare Microbial Communities Involved in Riverine Nitrification and Denitrification Across China

ABSTRACT Both abundant and rare microorganisms are critical in regulating soil biogeochemical processes such as nitrification and denitrification. However, the community assembly mechanisms of abundant and rare microorganisms involved in nitrification and denitrification remain unclear, especially at large scales. Here, using high‐throughput sequencing of archaeal amoA , bacterial amoA , nirK , and nirS genes, we investigated the biogeographic patterns and assembly mechanisms of nitrifying and denitrifying communities in multiple habitats (riparian rhizosphere soils, riparian bulk soils, and channel sediments) of 30 rivers along a latitudinal gradient in China. The results showed that the α‐ and β‐diversity of nitrifying and denitrifying communities usually decreased with increasing latitude. Nitrifying and denitrifying communities presented a significant distance‐decay relationship (DDR), and the DDR slopes were steeper for abundant subcommunities than for rare subcommunities. Latitude, climate, vegetation, and soil properties (e.g., pH and carbon content) were important in explaining community composition variation. Our results indicate that community assemblies of nitrifiers and denitrifiers were mainly affected by stochastic processes, with those of denitrifiers and abundant nitrifiers being governed by dispersal limitation and those of rare nitrifiers by undominated processes (also known as ecological drift). To our knowledge, this is one of the few studies showing that stochastic rather than deterministic processes dominate the community assembly of abundant and rare microorganisms involved in nitrification and denitrification across China, comprising 25% of the Asian continent. Our findings have potential implications for predicting soil microorganism responses to environmental change.