Influence Of Biochar On Methane Emission From Paddy Soil Under Elevated Atmospheric Carbon Dioxide And Temperature

Rice cropping system, one of the main agro-ecosystems in China, has been considered to be among the major anthropogenic sources of methane (CH4). Many studies have demonstrated that elevated atmospheric carbon dioxide (CO2) and temperature would significantly influence CH4 emission from paddy fields. As the new environmentally friendly material, incorporating biochar into paddy soil has been shown previously to reduce CH4 emission from paddy rice under ambient temperature and CO2 However, whether biochar addition could still exert a positive effect on decreasing CH4 emission from paddy soil will be of great importance to our combatting climate change under elevated temperature and CO2. Therefore, in this study, we combined elevated temperature and CO2 with biochar’s role in carbon sequestration and greenhouse gas mitigation, and examined the ability of rice straw-derived biochar to reduce CH4 emission from paddy soil under elevated temperature (+3℃) and CO2 concentrations (700 ppm). Meanwhile, through q-PCR analysis, we tried to elucidate the responses of abundances of mtehanogens and methanotrophs to biochar incorporation. The main results are summarized as follows:(1) In a growth chamber system, the effects of rice straw-derived biochar on CH4 emission from paddy soil under elevated temperature and CO2 concentrations were investigated. Results showed that variations of temperature and CO2 concentration had different influences on CH4 emissions during the rice growing season. Our results revealed that CH4 emissions were reduced under elevated temperature or elevated CO2 alone, where cumulative CH4 emissions were reduced by 70.9% and 54.4%, respectively, compared with those treatments under ambient temperature and CO2 (CK). Elevating temperature and CO2 simultaneously did not exert any significant effects on the cumulative CH4 emissions. Similar to the results of most researches, biochar addition could not only inhibit CH4 emissions by 97.2% in ambient environment, but also significantly reduce cumulative CH4 emissions by 39.5% under simultaneously elevated temperature and CO2 condition.(2) Through analyzing rice plant growth, soil physicochemical and microbial characteristics, we studied the responses of CH4 production and oxidation to biochar incorporation under simultaneously elevated temperature and CO2 condition. Results showed that elevated temperature alone inhibited rice plants growth and most mesophilic methanogens, which decreased soil methanogenic activity at heading time and the release of CH4 through rice plants. CO2 enrichment alone strikingly promoted the biomass of rice plants, which might bring more available oxygen to the rhizosphere soil. These variations might lead to the decreased CH4 emissions by improving pmoA gene abundance and decreasing the soil methanogenic activity. Correlation analysis showed that reduced CH4 release was mainly attributable to the decreased activity of methanogens along with the increased CH4 oxidation activity and pmoA gene abundance of methanotrophs caused by biochar addition through affecting soil environment.