Patterns and environmental controls of soil organic carbon density in Chinese shrublands

Abstract

The soils of shrublands are important for organic carbon storage in terrestrial ecosystems, but geographical patterns and environmental controls of soil organic carbon (SOC) remain largely understudied compared to other terrestrial ecosystems, leaving a significant gap in our understanding of terrestrial ecosystem carbon budgets. Here, we quantified SOC density (SOCD) and its potential determinants based on a comprehensive dataset with a consistent stratified random sampling of extensive soil profiles down to the parent material or to one meter depth across 1211 sites across China. Our up-to-date estimate of SOCD in Chinese shrublands is an average of 8.36 kg m−2, and ca. 43% of SOC is stored in the upper 20 cm relative to the one meter top soil, which is higher than estimates for shrublands globally. We also observed that SOCD was positively related to shrubland biomass and more so with belowground biomass. Furthermore, SOCD was positively related to mean annual precipitation (MAP), soil total nitrogen (N), phosphorus (P), clay and silt percent, but decreased with increasing mean annual temperature (MAT). Dark felty soils stored the highest SOCD and frigid desert soils stored the lowest. Soil total nitrogen (N), MAP, soil type, MAT, and belowground biomass, soil clay, and pH were the best predictors of total SOCD in Chinese shrublands. We concluded that Chinese shrubland soils store the lowest density of organic carbon so far recorded compared to forests and grasslands, and that the vertical distribution of SOC in Chinese shrublands was much shallower. While both climate (in particular MAP) and soil total N exerted dominant control over geographical patterns of SOCD across Chinese shrublands, soil type also played a significant role. Our study also emphasizes this key role of edaphic variables in determining the SOCD of shrublands and that they should be better incorporated into large-scale assessments of SOC dynamics. Our study extends existing work conducted in forest and grasslands and provides the most up-to-date knowledge on benchmark values for SOCD in Chinese shrublands, with important implications for predicting the fate of C stored in shrubland soils in response to climate change.