Biochar amendment alters the partitioning of nitrate reduction by significantly enhancing DNRA in a paddy field
Zhijun Wei, Mehmet Şenbayram, Xu Zhao, Chenglin Li, Ke Jin, Min Wu, Mizanur Rahman, Jun Shan, Xiaoyuan Yan
Abstract
Abstract Using 15 N tracer technique, we investigated the potential rates of denitrification, anaerobic ammonium oxidation, dissimilatory nitrate reduction to ammonium (DNRA), and their partitioning among nitrate reduction, as well as the N 2 O emission rates in a paddy soil receiving various biochar (0%, 0.03%, 0.1%, 0.5%, and 1.0%; w / w ) and straw (0.1%) over six consecutive years. Results showed that except for the 1.0% amendment treatment, biochar significantly ( P < 0.05) increased denitrification rates by 10.19‒75.96% compared with non-biochar amended treatment, and that biochar significantly ( P < 0.05) increased DNRA rates by 1.63‒6.84 folds relative to non-biochar amended treatment. Consequently, biochar shifted more NO 3 – partitioning toward DNRA process, as suggested by the increased DNRA/(denitrification + DNRA) ratios from 1.60 to 13.18%. On the other hand, biochar significantly ( P < 0.05) reduced N 2 O emission rates by 61.86–97.65% accompanied by a significant decrease in N 2 O/(N 2 O + N 2 ) ratios (65.29–98.39%), indicating biochar amendment facilitated the reduction of N 2 O to N 2 . The promoting effects of biochar on DNRA rates and DNRA/(denitrification + DNRA) ratios were attributed to the increased carbon availability and the altered nitrate reducer communities. Collectively, our study suggests that biochar amendment in the paddy soil is helpful for N conservation by favoring nitrate partitioning toward DNRA process, which deepens our understanding of how biochar mediates N cycling in the paddy field. Graphical Abstract