Spatial variation of soil organic carbon fractions and decomposition rates in temperate grasslands and their multi-factor driving mechanisms

Temperate grasslands represent a significant component of the global terrestrial carbon pool, and the spatial patterns and decomposition dynamics of their soil organic carbon fractions are directly linked to ecosystem carbon stability and climate change feedbacks; thus, clarifying the mechanisms underlying these variations is of substantial scientific importance. This study aims to identify how diverse environmental factors regulate the contents and standardized decomposition rates of major soil organic carbon fractions and to characterize their spatial differentiation at the regional scale. Based on transects established along typical environmental gradients in temperate grasslands, combined with soil particle-size fractionation, controlled laboratory incubation experiments, and a multifactor variance decomposition model, this study systematically evaluates the influences of climate, vegetation, soil physicochemical properties, and mineral composition on the behavior of distinct carbon fractions. The results reveal pronounced spatial heterogeneity in the contents of various organic carbon fractions along regional gradients, with clear differences among grassland types. In contrast, their standardized decomposition rates generally exhibit opposing spatial trends, characterized by lower decomposition rates in areas with higher carbon contents. Mechanistic analyses further indicate that climate and mineralogical factors are the dominant variables governing the distribution of carbon-fraction contents, with mineral effects particularly evident in fine particle-associated fractions, whereas decomposition rates are jointly regulated by mineralogy, soil physicochemical attributes, and climatic conditions. Overall, the study uncovers significant heterogeneity in the spatial patterns and process controls of soil organic carbon fractions in temperate grasslands, providing essential parameters for improving the representation of soil-carbon dynamics in Earth system models and offering important scientific support for carbon-sink assessment and ecological management in temperate grassland ecosystems.