Microaggregates regulated by edaphic properties determine the soil carbon stock in Tibetan alpine grasslands

Abstract

Soil carbon (C) stock and aggregate associated C are controlled by complex interactions among climate, edaphic, plant, and microbial factors. However, the relative contribution of these abiotic and biotic factors to variations in soil aggregate associated C and their effects on soil C stock are rarely evaluated. In this study, we investigated the influences of climatic, edaphic, plant, and microbial drivers on soil aggregate associated C and their relative contribution to soil C stock, based on a transect study across 45 sites in alpine grasslands on the Tibetan Plateau where stores a large amount of soil C. Microaggregate associated C contributed most to soil C stock, followed by macroaggregate associated C and silt + clay associated C. The variations of each aggregate associated C were related to changes in soil bulk density, soil available nitrogen, soil total nitrogen, root biomass, and bacteria diversity. Among these determinants, the edaphic factors (e.g., bulk density, soil available nitrogen, and total nitrogen) contributed most to the variation of soil C stock, primarily by changing the microaggregate associated C. Our findings highlight the vital roles of soil physicochemical properties in determining aggregate associated C and soil C stabilization across Tibetan alpine grasslands.