Mineral-associated carbon stability weakens the positive feedback of soil organic carbon to warming in abandoned croplands

Natural recovery can enhance soil organic carbon (SOC) accumulation in abandoned croplands. However, the response of different SOC fractions to warming in abandoned croplands remains unclear. Here, categorizing SOC into particulate and mineral-associated organic carbon (POC and MAOC) with physical fractionation, we investigated the responses of POC and MAOC content and temperature sensitivity (Q10) to warming, and explored the underlying mechanisms through a 3-year in situ warming experiment (open-top chambers, +1.6°C) in abandoned croplands across China (latitude: 22.33-46.58°N). Our results indicated that POC content remained unchanged while MAOC content significantly increased under warming. Changes in POC and MAOC content were mainly influenced by changes in belowground biomass and microbial necromass carbon, respectively. Warming affected the Q10 of POC and MAOC by influencing carbon quality and mineral protection, respectively. The Q10 of MAOC was significantly lower than that of POC regardless of the warming or control treatment, suggesting that MAOC represented the most persistent and least vulnerable carbon fraction within SOC. Therefore, the increase in MAOC content in abandoned croplands would weaken the positive feedback of SOC to climate warming.