Climate, plant and microorganisms jointly influence soil organic matter fractions in temperate grasslands.

Soil organic carbon (SOC) plays a critical role in mitigating climate change. Conceptualizing SOC into particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) helps us more accurately predict the responses of organic carbon, with varying chemical composition, molecular size, and degree of association with soil minerals, to environmental changes. To assess the controlling factors of particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), plant and soil samples were collected from 54 temperate grassland sites in Northern China, and the impacts of climate, plants, soil properties and microorganisms on POC and MAOC contents were analyzed. The results indicated that POC slightly dominated temperate grassland topsoils. Climate, plants, and microorganisms could predict a significant portion of the variation in POC and MAOC contents. Microbial factors, represented by fungal and bacterial biomass and necromass carbon, explained 56.6 % and 46.7 % of the variation in POC and MAOC contents, respectively. These findings indicate that the potential of POC in soil carbon storage cannot be ignored, and microorganisms should be considered when studying the dynamics and accumulation of POC and MAOC.