Biochar reduces gaseous emissions during poultry manure composting: Evidence from the evolution of associated functional genes

Biochar has demonstrated the potential in mitigating pollutant gaseous emission during composting. However, little is known about the difference among biochars derived from different plant feedstocks on the critical genes' expression and microbial communities’ succession for gaseous emissions. In this study, the effects of biochar (from wood chips, cornstalks, and rice husks) on gaseous emissions during chicken manure composting were investigated. Environmental factors, bacterial communities, and functional genes related to CH4, N2O, NH3, and H2S emissions were analyzed to reveal the reduction pathways of different biochar amendments during composting. Results showed that all biochar treatments improved the seed germination index of the compost from unmature (55.74%) to mature (70.28–75.23%). The CH4, N2O, NH3, and H2S emissions from all biochar-treated composts were reduced by 18.93–27.47%, 35.74–52.82%, 1.26–36.38%, and 8.57–24.14%, respectively, and the cornstalk biochar had the highest emission reduction performance. Temperature, pH, and NH4+ were the major environmental factors that affected Lactobacillus and Bacillus activities, which critically influenced the CH4, N2O, NH3, and H2S emissions during composting. Furthermore, cornstalk biochar mainly improved pmoA for CH4 reduction, whereas wood chip biochar increased amoA for NH3 oxidation. Rice husk biochar mostly decreased nirS and nirK and increased norB, narG, and nosZ during N2O reduction. Cornstalk biochar also increased dsrB and decreased aprA during H2S reduction. Overall, cornstalk biochar was determined to be an optimal additive for simultaneously improving compost maturity and reducing gaseous pollutant emissions during chicken manure composting. This study verified the mechanisms of three plant derived biochars in pollutant gas control in composting, and thus provided evidence for facilitating the sustainable development of composting technologies.