Dissimilatory nitrate reduction to ammonium dominates nitrate reduction in long-term low nitrogen fertilized rice paddies

Abstract

Dissimilatory nitrate reduction to ammonium (DNRA) and diazotrophic N2 fixation contribute to nitrogen (N) supply in rice paddies, whereas denitrification contributes to N loss. Continuous N fertilization in rice paddies is known to increase denitrification and reduce N2 fixation, however little is known about its effect on DNRA and the NO3− partitioning between DNRA and denitrification. Here, we investigated the rates of DNRA, denitrification and N2 fixation, and their relevant microbial gene abundances, in long-term high and low N fertilized rice paddies using a 15NO3− tracer, an acetylene reduction assay and quantitative PCR analysis, in laboratory incubation studies. We observed that DNR..