Achieving synergistic high yield and methane mitigation in rice under co-application of biochar and mild alternate wetting and drying via enhancing root-produced brassinosteroids

This study aimed to examine whether the co-application of biochar and mild alternate wetting and drying (Mild AWD) could synergistically achieve high rice yields and mitigate methane (CH₄) emissions by optimizing brassinosteroid (BRs)-driven root functions. In a two-year field trial, two rice cultivars were cultivated under continuous flooding (CF) and Mild AWD, with paired treatments of applying or not applying biochar made from wheat straw. Results showed that the co-application of biochar and Mild AWD significantly increased grain yield (14.1 % in 2023 and 15.0 % in 2024) and reduced CH₄ emissions (64.2 % in 2023 and 67.1 % in 2024), although N₂O emissions increased. However, the increase in N₂O emissions did not offset the overall benefits of reduced global warming potential (GWP) and greenhouse gas intensity (GHGI) resulting from CH₄ emission reduction. The co-application of biochar and Mild AWD enhanced grain yield by promoting carbon assimilate accumulation and efficient transport from vegetative organs to grains, supported by improved root activity. Moreover, elevated BRs levels in rice roots strengthened the ascorbate-glutathione cycle, rapidly scavenging excessive reactive oxygen species (ROS), maintaining cellular antioxidant capacity and root activity, and inhibiting ROS-induced aerenchyma formation. This, in turn, elevated the levels of specific organic acids (malic acid, citric acid, and succinic acid) in root exudates, enhancing soil CH₄ oxidation activity and ultimately reducing CH₄ emissions, GHGI, and GWP in the paddy ecosystem. Overall, this study highlights a synergistic strategy for high-yield rice production and CH₄ mitigation through the co-application of biochar and Mild AWD, facilitated by enhanced root-produced BRs.