Microbial and plant-derived carbon contributions to particulate and mineral-associated organic carbon in perennial and annual cropping systems

• Plant- and microbial-derived C contributions to soil POC and MAOC were quantified. • Perennials showed significantly higher POC and MAOC than maize at 0–20 cm. • Microbial necromass C, not lignin phenols, was linked to higher POC for perennials. • Microbial necromass C accounted for 29% of POC and 36% of MAOC at 0–20 cm. • In this study, POC and MAOC could be dominated by plant-derived C. Perennial cropping systems hold great potential to enhance soil organic carbon (SOC) stocks and contribute to climate change mitigation. However, the effects of perennial crops on SOC fractions with different stabilities remain poorly understood. Particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) are considered to have different formation mechanisms and different stabilities. Plant- and microbial-derived carbon (C) are the main origins of SOC, yet their relative contributions to POC and MAOC remain unclear. Here, based on an 11-year experiment, we compared two perennial cropping systems (festulolium and grass-clover) with an annual cropping system (maize), to investigate their effects on soil POC and MAOC, and quantify the contribution of plant- and microbial-derived C to these two soil C fractions using lignin phenols and amino sugars as biomarkers. The soil of the two perennials had higher POC and MAOC than maize at 0–20 cm soil depth, with higher proportions of POC in SOC. The higher POC of the two perennials was linked to their significantly higher fungal and bacterial necromass C in POC. Total microbial necromass C accounted for only 29% of POC and 36% of MAOC at 0–20 cm across all systems, suggesting that plant-derived C dominates these two C pools. However, no significant differences were detected in the lignin phenols content in POC and MAOC at 0–20 cm. Our results challenge the conventional assumption that microbial necromass C dominates MAOC, highlighting the role of plant-derived C in POC and MAOC, which could have a greater influence on soil C sequestration in climates with low mean annual temperature than previously assumed. Given that only two biomarkers were used, interpretations should not be extrapolated beyond their analytical scope.