Enhancing plant-derived carbon is key to building stabilized soil organic carbon with perennial crops

Plant- and microbial derived carbon (C) are the main components of soil organic carbon (SOC), however, their relative contributions to soil fractions with different stability remain uncertain. Particulate organic carbon (POC) and mineral associated organic carbon (MAOC) are considered to have different formation mechanisms and different stabilities. Here, 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 the two C fractions.

The results showed that the two perennial crops had higher POC and MAOC than maize at 0–20 cm soil depth, with higher proportions of POC in SOC. Microbial necromass was linked to the perennials’ higher POC, as festulolium and grass-clover showed higher fungal and bacterial necromass in POC at 0–20 cm. In contrast, maize showed significantly higher microbial necromass C in MAOC than festulolium and grass-clover. Total microbial necromass C accounted for only 30% of POC and 31% of MAOC across all systems, suggesting that plant-derived C could dominate these two C pools. However, no statistical differences were detected in the lignin phenols content in POC and MAOC at 0–20 cm. Our results challenge the conventional assumption that necromass C dominates MAOC, highlighting the significance of plant-derived C in POC and MAOC, which could have a greater influence on soil C sequestration than previously thought.