Effects of biochar and 3,4-dimethylpyrazole phosphate (DMPP) on soil ammonia-oxidizing bacteria and nosZ-N2O reducers in the mitigation of N2O emissions from paddy soils

Abstract

Paddy fields are an important source of nitrous oxide (N2O) emission. The application of biochar or the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) to paddy soils have been proposed as technologies to mitigate N2O emissions, but their mechanisms remain poorly understood. An experiment was undertaken to study the combined and individual effects of biochar and DMPP on N2O emission from a paddy field. Changes in soil microbial community composition were investigated. Four fertilized treatments were established as follows: fertilizer only, biochar, DMPP, and biochar combined with DMPP; along with an unfertilized control. The application of biochar and/or DMPP decreased N2O emission by 18.9–39.6% compared with fertilizer only. The combination of biochar and DMPP exhibited higher efficiency at suppressing N2O emission than biochar alone but not as effective as DMPP alone. Biochar promoted the growth of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), while DMPP suppressed AOB and increased AOA. Applying biochar with DMPP reduced the impact of DMPP on AOB. The nirS-/nirK- denitrifiers were decreased and nosZ-N2O reducers were increased by DMPP and the combination of DMPP and biochar. The abundance of the nirK gene was increased by biochar at the elongation and heading stages of rice development. Compared with fertilizer only, the application of biochar and/or DMPP promoted the abundance of nosZ genes. These results suggest that applying biochar and/or DMPP to rice paddy fields is a promising strategy to reduce N2O emissions by regulating the dynamics of ammonia oxidizers and N2O reducers.