Long-term manure amendment promotes the formation of soil particulate and mineral-associated organic carbon following straw incorporation

Soil organic carbon (SOC) sequestration in agroecosystems has been regarded as an effective strategy to restore soil fertility, sustain productivity and meet the targets of climate change. However, it remains unclear on the underlying mechanisms of long-term fertilization regulating the formation of SOC fractions (particulate organic carbon, POC; mineral-associated organic carbon, MAOC). Here, a one-year laboratory incubation experiment was conducted to quantity the POC and MAOC formation and uncover underlying mechanisms using a 13 C-labelled straw tracing approach in two texture-contrasting soils collected from 29-year history fertilization field trials (unfertilized, control; mineral fertilizer, NPK; mineral fertilizer plus manure application, NPKM) at the Urumqi (UQ) and Gongzhuling (GZL) sites. Results showed that NPKM treatment strongly increased straw-derived SOC by 38–42%, POC by 39–76% and MAOC by 28–53% compared to the corresponding NPK and control treatment, with more pronounced increase in MAOC in the GZL relative to UQ sites. The 52–81% of the straw-derived SOC was stored as MAOC across soils and treatments after year-around incubation. The straw-derived MAOC showed positive relationships with PLFAs abundances, fungal k-strategies taxa and microbial carbon use efficiency, implying close linkage between MAOC formation and microbial C anabolism. In contrast, the increased straw-derived POC in the manure-amended soils primarily resulted from enhanced aggregate stability. The relative higher contribution of straw-derived POC to SOC in the GZL soil primarily resulted from greater physical protection via aggregation as compared to UQ soil. Overall, these findings suggested that long-term manure amendment help facilitate POC and MAOC formation via physical protection and microbial metabolism mechanisms, respectively, providing perspectives for optimizing fertilization practices to enhance soil C sequestration in agricultural ecosystems.