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

This study aims to clarify the mechanisms underlying effects of inoculating cellulose and hemicellulose-degrading microorganisms on nitrous oxide (N2O) emissions during composting with silkworm excrement and mulberry branches. Inoculation with cellulose and hemicellulose–degrading microorganisms resulted in significant increases of total N2O 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 N2O emission was attributed to the enhanced contribution of ammonia-oxidizing bacteria (AOB) and denitrifying bacteria to N2O production, as evidenced by the increased AOB amoA and denitrifying nirK gene abundances. Moreover, microbial inoculation stimulated N2O reduction to N2 owing to increased abundances of nosZⅠ and nosZⅠⅠ genes. These findings highlight the necessity to develop cost-effective and environmentally friendly strategies to reduce N2O emissions when cellulose and hemicellulose-degrading microorganisms are inoculated during composting.