Al/Fe Mineral Controls on Soil Organic Carbon Stock Across Tibetan Alpine Grasslands

Adequate understanding of the controlling factors of soil carbon (C) stock is crucial for improving the predictability of Earth System Models in exploring terrestrial C-climate feedback. Current studies, however, mainly focus on climatic and edaphic variables and rarely explore the effects of mineral protection in regulating soil organic carbon (SOC) stock over broad geographic scale. Particularly, the relative importance of mineral protection compared with other factors is unclear. Based on large-scale soil inventory, here we filled this knowledge gap by exploring the effects of Al/Fe-(hydr) oxides on SOC and three C fractions across Tibetan alpine grasslands via linear regression, partial correlation, and variance partitioning analyses, and also by comparing the degree of mineral protection in alpine grasslands with other ecosystems. Our results showed that SOC and C fractions across Tibetan alpine grasslands were regulated by Al/Fe-(hydr) oxides, with the incorporation of mineral variables increasing the explained variations by 10.1% for SOC content, 13.4% for coarse particulate organic matter, 12.6% for microaggregate associated C, and 21.9% for silt and clay associated C. Moreover, the contribution of mineral effects exceeded that of climatic and edaphic factors, particularly in the silt and clay associated C fraction. In addition, about 15.812.0% of SOC pools were associated with Fe, which was equal to or higher than those in temperate and tropical-subtropical ecosystems. Taken together, these results demonstrate the significant role of Al/Fe minerals in the stabilization of SOC across Tibetan alpine grasslands, highlighting the importance of incorporating C-mineral interactions into ESMs for better understanding the terrestrial C-climate feedback