Decadal soil carbon sequestration under straw management: Relative roles of stable carbon inputs and microbial carbon...

Enhancing soil organic carbon (SOC) sequestration in rice paddies is crucial for climate change mitigation, yet the mechanisms by which straw management regulates SOC accumulation, particularly through the microbial carbon pump (MCP) and stable carbon inputs, remain poorly understood. This study investigated the effects of three straw management practices on SOC dynamics and the underlying mechanisms based on a decade-long field experiment in a rice-paddy system. Three treatments were compared: straw removal (SR), straw incorporation (SI), and straw biochar amendment (SBA). We quantified soil physicochemical properties, phytolith-occluded carbon (PhytOC), microbial necromass carbon, and SOC fractions to identify key drivers of SOC changes. Results showed that the SBA and SI treatments increased total SOC by 30.5 % and 16.8 %, respectively, compared to the SR treatment. These changes were primarily attributed to the effects of straw management on stable carbon inputs and microbial-mediated carbon sequestration. Specifically, compared with the SR treatment, both SBA and SI treatments significantly improved the microbial carbon pump, thereby increasing mineral-associated organic carbon (MAOC). Additionally, SBA treatment contributed a higher amount of stable PhytOC than the SI treatment, and significantly enhanced particulate organic carbon (POC) formation. These findings demonstrate that straw biochar amendment provides superior long-term SOC stabilization through enhanced stable carbon inputs and strengthened microbial-mediated carbon sequestration. This study provides practical guidance for optimizing straw management strategies to maximize carbon sequestration in paddy ecosystems.