Factors controlling the contributions of bacterial and fungal residue carbon to soil organic carbon in grassland ecosystems

Soil microbial residue carbon (MRC) plays an important role in the accumulation and stabilization of soil organic carbon (SOC) in grassland ecosystems. Numerous studies to date show that soil bacterial MRC and fungal MRC have different effects on SOC stability, however, there is a lack of understanding about what regulates the contributions of the bacterial MRC and fungal MRC to SOC in large-scale grassland ecosystems. In this study, we selected nine alpine and temperate grassland ecosystems to quantify the effects of biotic (plant and microbial) and abiotic (climate and soil) factors on the bacterial and fungal MRC/SOC. The results showed that 1) Both biotic and abiotic factors explained 97% and 89% of the variations in the bacterial MRC/SOC and fungal MRC/ SOC, respectively. Compared with the fungal MRC/SOC, the bacterial MRC/SOC could be explained more by the biotic and abiotic factors. 2) The bacterial MRC/SOC was clearly correlated with climate and increased as the mean annual temperature increased and decreased as the mean annual precipitation increased. The bacterial MRC/SOC was negatively correlated with the soil phosphorus stoichiometry. 3) The fungal MRC/SOC was significantly correlated with mean annual temperature and was negatively correlated with the ratio of carbon to nitrogen. Our study demonstrates that the bacterial and fungal MRC/SOC respond differently to environmental changes, which can contribute to the regulation of soil carbon sequestration in grassland ecosystems by modulating different soil microbial communities under climate change.