Mineral-associated carbon stability weakens the soil organic carbon positive feedback to warming

Soil organic carbon (SOC) pool is the largest terrestrial carbon pool, playing a pivotal role in carbon-climate feedback. However, the response of different SOC fractions to warming 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. POC Q10 slightly increased due to the decrease in carbon quality of POC, while MAOC Q10 remained unchanged because of the nearly constant mineral content under warming. Due to the low Q10, the increase in MAOC content in abandoned croplands would weaken the positive feedback of SOC to climate warming.