Opposing effects of maize straw and its biochar on soil N2O emissions by mediating microbial nitrification and denitrification in a subtropical Moso bamboo forest

Abstract Straw and biochar amendments markedly influence soil N 2 O emissions in subtropical Moso bamboo forests, but the microbial mechanisms driving these responses remain elusive. This study aimed to assess the contrasting influences of maize straw and its derived biochar on soil N 2 O emissions in a subtropical Moso bamboo forest. Straw amendment (5 t C ha −1 ) stimulated N 2 O emission by 16–27% ( P < 0.05). However, biochar addition (5 t C ha −1 ) decreased the concentrations of NH 4 + by 11–14%, NO 3 − by 11–15% and water-soluble organic nitrogen for 14–17%, and decreased the abundances of ammonia-oxidising bacterial amoA by 40–45%, nirK by 30–36%, nirS by 24–32% and associated genera Nitrosospira , Mesorhizobium , Bradyrhizobium , Rhizobium , Pseudomonas , and Cupriavidus . Biochar also decreased the activities of enzymes related to organic N hydrolysis (protease and urease) and denitrification (nitrate reductase and nitrite reductase), and thus decreased N 2 O emissions by 17–20% ( P < 0.05). Furthermore, biochar enhanced the abundance of nosZ gene (by 40–46%) and its dominant genera ( Mesorhizobium , Bradyrhizobium , and Azospirillum ), which facilitated N 2 O reduction. In contrast, straw inhibited the growth of these dominant genera and lowered the abundance of nosZ gene (by 24–38%). These results highlight the varied responses of nitrification and denitrification processes and hence N 2 O emission to the application of straw and biochar in soils of a subtropical Moso bamboo forest. Graphical Abstract Highlights Maize straw enhances but its biochar lowers N 2 O emissions Biochar decreases organic N hydrolysis and denitrifying enzyme activities Biochar reduces the abundances of AOB amoA , nirK and nirS and dominant genera Biochar promotes the abundances of nosZ gene and its dominant genera