Different types of biochar reduce N2O emissions by mediating the interplay of multiple factors during composting

Biochar has been proven to effectively mitigate the emission of N 2 O which is a potent greenhouse gas by regulating inorganic nitrogen transformation, while the conversion of organic nitrogen and its effect on N 2 O emission remain unclear. In this research, the impacts of different types of biochar on organic/inorganic nitrogen transformation and the evolution of core microbial communities during composting were investigated to reveal the mechanism of N 2 O emission. Four groups were set: CK (blank group), RSB, WSB, and CSB was added with 10 % rice, wheat, and corn straw biochar, respectively. The results showed that biochar increased the content of organic and inorganic nitrogen. In comparison with CK, the cumulative N 2 O emissions were decreased by 70.12 %, 56.63 % and 65.38 % in RSB, WSB, and CSB, respectively. The core microorganisms related to nitrogen transformation were increased with biochar addition. N 2 O shared significantly positive relationship with NH 4 + -N ( P < 0.05), but negative correlation with hydrolysable unknown-N ( P < 0.05). Redundancy analysis showed that organic matter was the only significant factor ( P < 0.05), contributing 63.9 % and 56.5 % variations of core microorganisms in WSB and CSB, respectively. Partial least squares path model indicated that the core microorganisms were directly influenced by environmental factors in all treatments, while N 2 O emissions were mainly indirectly affected by the interactions between each factor. This study reveals the mechanism of N 2 O emission mediated by biochar from a new perspective of simultaneous transformation of organic and inorganic nitrogen, which is of great significance for mitigation of N 2 O during organic waste composting. THN: total hydrolyzed organic nitrogen; AN: amine-N; AAN: amino acid-N; HUN: hydrolysable unknown-N. ** P < 0.01. • Rice, wheat and corn straw biochar reduced N 2 O emission by 70.12 %, 56.63 % and 65.38 %. • N 2 O emission was significantly correlated with NH 4 + -N and HUN ( P < 0.05). • Biochar increased the core microorganisms related to nitrogen transformation. • OM was the driving factor for core microbes in wheat and corn straw biochar groups. • N 2 O emission was mainly affected by the interactions between multiple variables.