Insight into mitigation mechanisms of N2O emission by biochar during agricultural waste composting.

[Display omitted] • Biochar added at the beginning of composting reduced 55% of total N 2 O emission. • N 2 O emission showed significant relationships with most environmental factors. • Biochar mitigated N 2 O mainly by regulating the physicochemical properties of compost. • Genes and enzymes influenced the overall effect of environmental factors to N 2 O. The effects and mitigation mechanisms of biochar added at different composting stages on N 2 O emission were investigated. Four treatments were set as follows: CK: control, B B10% : +10 % biochar at beginning of composting, B B5%&T5% : +5% biochar at beginning and + 5 % biochar after thermophilic stage of composting, B T10% : +10 % after thermophilic stage of composting. Results showed that treatment B B10% , B B5%&T5% , and B T10% reduced total N 2 O emissions by 55 %, 37 %, and 36 %, respectively. N 2 O emission was closely related to most physicochemical properties, while it was only related to amoA gene and hydroxylamine oxidoreductase. Different addition strategies of biochar changed the contributions of physicochemical properties, functional genes and enzymes to N 2 O emission. Organic matter and C/N contributed 23.7 % and 27.6 % of variations in functional gene abundances (P < 0.05), respectively. pH and C/N (P < 0.05) contributed 37.3 % and 17.3 % of variations in functional enzyme activities. These findings provided valuable insights into mitigating N 2 O emissions during composting. [ABSTRACT FROM AUTHOR]