Addition of cellulose and hemicellulose degrading microorganisms intensified nitrous oxide emission during composting.

[Display omitted] • Composting with cellulose and hemicellulose-degrading microorganisms inoculated. • Microbial inoculation promoted AOB and denitrifying bacteria derived N 2 O production. • Microbial inoculation increased AOB amoA and denitrifying nirK gene abundances. • Microbial inoculation enhanced N 2 O reduction to N 2 by increasing nosZ Ⅰ and nosZ ⅠⅠ. This study aims to clarify the mechanisms underlying effects of inoculating cellulose and hemicellulose-degrading microorganisms on nitrous oxide (N 2 O) emissions during composting with silkworm excrement and mulberry branches. Inoculation with cellulose and hemicellulose–degrading microorganisms resulted in significant increases of total N 2 O emission by 10.4 ± 2.0 % (349.1 ± 6.2 mg N kg−1 dw) and 26.7 ± 2.1 % (400.6 ± 6.8 mg N kg−1 dw), respectively, compared to the control (316.3 ± 3.6 mg N kg−1 dw). The stimulation of N 2 O emission was attributed to the enhanced contribution of ammonia-oxidizing bacteria (AOB) and denitrifying bacteria to N 2 O production, as evidenced by the increased AOB amoA and denitrifying nirK gene abundances. Moreover, microbial inoculation stimulated N 2 O reduction to N 2 owing to increased abundances of nosZ Ⅰ and nosZ ⅠⅠ genes. These findings highlight the necessity to develop cost-effective and environmentally friendly strategies to reduce N 2 O emissions when cellulose and hemicellulose-degrading microorganisms are inoculated during composting. [ABSTRACT FROM AUTHOR]