Different roles of biochar in mitigating greenhouse gas emissions from paddy fields in northern and southern China

Abstract

Global warming is a serious threat to human survival and development, ranking among the most formidable challenges humanity faces. Mitigating greenhouse gas (GHG) emissions, the main driver of climate warming, has become an urgent priority. As a unique soil amendment, biochar has substantial potential for reducing GHG emissions. Here, we summarizes and analyzes the differences in the role of biochar in carbon sequestration and GHG emission reduction mechanisms in paddy soils between northern and southern China, and reviews how biochar affects CH₄ and N₂O emissions, improves soil physical and chemical properties, and enhances rice growth in both regions. In southern China, initial crop residues and higher field temperatures create an optimal environment for methanogens; meanwhile, biochar promotes favorable conditions for methanotrophic bacteria. In contrast, the northern climate with repeated freeze-thaw cycles affects microbial the changes through the changes in soil temperature and structure, which in turn affects GHG emission mechanisms, as well as substrate availability. Northern soils have higher concentrations of substrates necessary for microbial reactions that facilitate nitrification processes related to N₂O emissions. Therefore, the effect of biochar applied in the south to reduce CH₄ emissions is more prominent, while the effect on mitigating N₂O emissions is more prominent in the north. The rice cultivation system combined with freeze-thaw cycles significantly contributes to the observed differences between the two regions. This review provides theoretical guidance and a decision-making basis for the use of biochar to reduce GHG emissions in paddy soils, thereby advancing toward the China's agricultural carbon peak goal.