Conclusions
The present study investigated the impacts of different land-use types on denitrification-related microbial communities and associated functional groups in freshwater rivers. Compared with natural land uses, anthropogenic land uses (agriculture and urbanization) increased N concentrations in river water, altering microbial community structure. The anthropogenic land uses also shaped microbial functional groups and stimulated microbially-mediated denitrification in the river basins. The results of the present study could facilitate the estimation of land-use type impacts on freshwater ecosystems through the analysis of microbial functional groups. These conclusions will provide scientific references for the impact of anthropogenic land on ecology of freshwater rivers and land quality improvement in the Qinling Mountains. We recommend further studies based on quantitative PCR, metagenomics, and metatranscriptomics approaches to verify our findings. Furthermore, it is necessary to determine the threshold N concentrations for denitrification efficiency in ecosystems other than freshwater rivers, which can facilitate the control of denitrification or N2O emissions caused by anthropogenic disturbance.