Carbon sequestration through straw amendment: multi-pool dynamics within soil organic carbon

Straw amendment is widely practiced to stabilize soil structure and increase soil organic carbon (SOC) stocks. Given SOC’s complex composition, the multi-pool responses to straw amendment and their interrelationships remain unclear. Here, we conducted a meta-analysis of 3206 paired measurements to assess the effects of straw on functional (particulate and mineral-associated organic carbon, POC, and MAOC), aggregate-associated (macro- and micro-aggregates, and silt–clay-associated C), and microbial pools (microbial biomass, MBC; necromass C). We found that the straw amendment increased SOC by 16 ± 0.9 % compared to control, with POC and MAOC pools rising by 33 ± 3.2 % and 9.6 ± 2.6 %, respectively. The POC accumulation was linked to greater straw C input and hydrolytic enzyme activity, and showed a stronger association with macroaggregate-C, highlighting that improved aggregation plays a key role in SOC gains under straw amendment. Initially, the POC, macroaggregate-C, and their ratio to SOC increased within 5 years, but later declined in the more-than-10-year duration period, suggesting that C entered pools with rapid turnover rates and likely underwent multiple cycles of microbial decomposition over time. The increase in microbial necromass C after five years of straw amendment confirmed increased microbial C modification and stabilization, thereby increasing the residence time of C in the soil. The study provided mechanistic insights into the effects of straw amendment on the SOC pools and their stability at the global scale, which underscores the importance of adopting multi-pool strategies in croplands.