Carbon amendment rather than nitrate fertilization dominated the reassembly of the total, denitrifying, and DNRA bacterial community in the anaerobic subsoil

Purpose Carbon amendment can steer both denitrifying and dissimilatory nitrate reduction to ammonium (DNRA) bacterial communities to reduce nitrate leaching. The purpose of this study was to uncover changes in the abundance and diversity of denitrifying and DNRA bacterial communities by carbon amendment in anaerobic subsoil. Methods High throughput sequencing and qPCR analyses of narG , napA , nirK , nirS , nrfA , and 16S rRNA were used to identify changes in the abundance and diversity of total, denitrifying, and DNRA bacterial communities in the subsoil as responses to straw amendment under 0, 800, or 1600 kg N ha −1 nitrate fertilization. Results The straw amendment resulted in over 81% of reduction in nitrate leaching, 3.2–5.1 folds’ increase in dissolved organic matter (DOM), 102.2–147.5% of increase in the total N content in subsoil, and 2.6–43.1 folds’ increase of narG , napA , nirK , nirS , nrfA , and 16S rRNA , as compared to the corresponding non-amended control. The straw amendment could explain 32–52% of the variation in the community composition of total, denitrifying, and DNRA bacteria, and it also enriched denitrifying Proteobacteria, DNRA bacteria of Nitrospira or Planctomycetes, and cellulose degraders such as Cellulomonas , Opitutus , and Lysinibacillus . These responding communities formed a co-occurrence network of high density, highlighting the importance of carbon amendment on the reassembly of microbial communities in the anaerobic subsoil. Conclusion Straw amendment in the subsoil greatly reduced nitrate leaching via straw decomposer, dissimilatory, and assimilatory nitrate-reducing bacterial communities.