Organics composition and microbial analysis reveal the different roles of biochar and hydrochar in affecting methane oxidation from paddy soil

Biochar and hydrochar, as valuable and eco-friendly soil remediation materials from greenwaste, have potential to enhance methane oxidation in paddy soil. But the mechanism of biomass carbon on the improvement of methane-oxidizing bacteria communities in paddy soil has not been adequately elucidated. In the present study, the effect of different-temperature rice straw-based biomass carbon (RB400, RB600, RH250 and RH300) on methane oxidation were investigated by analyzing the soil dissolved organic matter (DOM), physicochemical properties and changes in microbial community structure. The results of the 17-day incubation experiment showed that the methane oxidation rate increased under all types of biomass carbon in the first 6 days. The enhancement of methane oxidation rate was more pronounced for biochar compared to hydrochar, with RB600 being the most effective treatment. The result of excitation-emission matrix (EEM) fluorescence spectroscopy showed that less DOM were released from the soil in the biochar treatments compared to the hydrochar treatments and protein-like were detected only in the hydrochar group. Microbial analysis further showed that hydrochar inhibited the growth of Bacillus, Methylobacter, and Methylocystis, while RB600 significantly increased the relative abundance of methanotrophs (responsible for methane oxidation), such as Methylocystis and Methylobacter, which was consistent with their different effects on the methane oxidation rate. Moreover, from the analysis of principal component analysis (PCA) and canonical correspondence analysis (CCA), Methylobacter and Methylocystis were negatively respond to H/C of biomass carbon. The present study provides a deeper understanding of the effect of biomass carbon obtained by different processes on methane oxidation when applied to soil from the perspective of organic matter and microbial communities. [Display omitted] •Methanotrophs were not suitable for growth in RH at lower pH.•Methanotrophs were suitable for growth in RB that released less DOM.•The aromaticity of biomass carbon had a positive link with methanotrophs.•The abundance of methanotrophs decreased due to the high H/C of RH.•RB600 has enhanced methane oxidation rate significantly in the first 6 days.