The application years of biochar affect CH4 emission by negatively methanogens and increased rice yield

Biochar influences CH 4 emissions, methane-associated microbial communities, and rice yields. However, the effects of biochar application over different durations remain unclear. This study investigated the impact of biochar application on CH 4 emissions, methane-associated microbial communities, and rice yield across different years. Five treatments were assessed based on the year of biochar application (NB: applied in April 2023; FB: applied in April 2016) along with three biochar application rates (CK: 0 t‧ha −1 ; NB15, FB15: 15 t‧ha −1 ; NB45, FB45: 45 t‧ha −1 ). Biochar application improved the physical and chemical properties of the soil, with NB45 exhibiting the most pronounced effect. Compared with CK, CH 4 emissions increased under NB conditions but decreased under FB conditions. Additionally, emissions were higher at lower biochar application rates than at higher rates across all years. These trends were associated with shifts in the abundance of methanogenic and methane-oxidising bacteria in the soil. Biochar reduced the pmoA / mcrA ratio in paddy soil, with FB45 showing the greatest reduction. The composition of methanogenic and methane-oxidising bacterial species differed significantly between NB and FB soils, with Chloroflexota exhibiting the highest relative abundance in both bacterial groups. Biochar application enhanced CH 4 metabolism in methanogenic and methane-oxidising bacteria, with the strongest effect observed under the NB treatment. Moreover, biochar application significantly improved rice yield, increasing by 9.27 %, 12.58 %, 13.50 %, and 14.68 % under the NB15, NB45, FB15, and FB45 treatments, respectively. Overall, biochar effectively reduced CH 4 emissions, modulated the structure and function of methane-associated microbial communities, and enhanced rice yield. • Corn straw biochar improved the soil's physical and chemical properties in both the 1st (NB) and 8th (FB) years. • NB15, NB45, FB15, and FB45 increased rice yield by 9.27 %, 12.58 %, 13.50 %, and 14.68 %, respectively. • NB increased CH 4 emissions, while FB, in contrast, and emissions were higher for low than for high biochar applications. • Methanogenic and methane-oxidising bacterial species in NB and FB soils differed significantly and reduced pmoA/mcrA . • NB and FB enhance CH 4 metabolism by methanogenic and methane-oxidising bacteria in soil.