Maize-soybean rotation with straw return improves carbon stabilization efficiency by distinctively allocating soil carbon pool fractions in northeast China

Straw return (ST) and maize-soybean rotation (MS) are recognized agronomic strategies for enhancing soil organic carbon (SOC). However, their combined effects on SOC stabilization and underlying mechanisms remain unclear, particularly regarding carbon use efficiency and stabilization pathways. A split-plot field experiment was conducted in Northeast China to evaluate the effects of straw return and maize–soybean rotation on SOC fractions, microbial necromass accumulation, extracellular enzyme activities, soil respiration, and crop yield. Our results showed that ST with MS promoted SOC stability and higher grain yield. Notably, ST with MS achieved comparable SOC levels with lower C input and soil respiration, indicating higher C stabilization efficiency. This was associated with increased contribution of MAOC to SOC (1.68-5.11%), but decreased for POC, reflecting a shift toward more stable C pools. Compared with continuous cropping, MS increased MBC (8.21-8.24%), DOC (10.76-14.74%), and MNC (13.42-41.43%), while enhancing soil enzymes activity and alleviating microbial N limitation. Random forest and partial least squares path modeling identified MAOC as the key driver of SOC, with MBC indirectly promoting MAOC formation via MNC accumulation. These findings demonstrate that the integration of straw return and crop rotation could be considered as effective practices to improve SOC stability and crop yield, provide a theoretical framework for synergistically optimizing soil C sequestration and food production strategies as well.