Carcass decay inhibits denitrification indirectly by regulating the microbiota and physicochemical properties in a model water system

Abstract Animal carcass decomposition is involved in nitrogen (N) cycle in the aquatic ecosystems, for example denitrification, volatilization and leaching. The denitrification process is a crucial part of the nitrogen cycle, helping to alleviate biological toxicity resulting from nitrate accumulation. However, it is still unknown whether and how cadaver decay affects the denitrifiers and their activity in river water. In this study, six denitrifiers (encoding napA , narG , nirK , nirS , norB and nosZ , respectively) and denitrifying activity were investigated in a model water system with nitrogen pollution from corpse decomposition using high‐throughput sequencing, real‐time quantitative PCR and denitrifying enzyme activity (DEA) assay. Cadaver decay increased the quantity and altered the composition of denitrifying microbiota. Multiple regression on distance matrices revealed that corpse decay had a significantly greater impact on the denitrification communities than temperature. To our surprise, the DEA decreased in the contaminated water by cadavers. The multiple regression models revealed that the abundance of denitrifying taxa and the gene copies may jointly predict changes in DEA, with highest contribution coming from the norB ‐type Hydrogenophaga . Further, the partial least squares path model (PLS‐PM) showed that corpse decay indirectly inhibited DEA via the denitrification community and water physicochemical properties. Synthesis and applications . This study provides important insights into how cadaver decomposition can reduce denitrification activity in water systems. These findings can assist us in scientifically managing and remediating polluted water bodies.