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.