Altitudinal distribution of soil organic and inorganic carbon in a dry alpine rangeland of northern Qinghai-Tibetan Plateau

Abstract. The spatial patterns of soil carbon in water-constrained alpine ecosystems have been rarely investigated. It remains unclear how changes in biotic and abiotic factors with altitude would shape the distribution of soil carbon stocks when plant communities are co-limited by water and low temperature. To address this uncertainty, we investigated changes in soil organic carbon (SOC) and inorganic carbon (SIC) along an altitudinal gradient between 3000–4000 m asl, in the northern Qinghai-Tibetan Plateau. Our results showed that the total soil carbon density (TCD) and the SOC density (SOCD) increased with increases in altitude, but the SIC density (SICD) displayed a pattern of nonlinear change along the altitudinal gradient with a peak at the mid-slope of the range. While SIC dominated the soil carbon pool, accounting for 64–90 % of TCD, the proportion of SOC increased from 10 to 36 % of the TCD with increases in altitude. The increases in SOCD with altitude were associated with changes from scrub-dominated vegetation cover to herbaceous plant communities and decreasing MAT, which together attributed to increased level of plant-derived carbon inputs and reduced SOC mineralization at higher altitudes. Whereas variations in SICD were mainly explainable by changes in soil C/N and soil water content (SWC), and likely resulted from non-linear changes in factors related to inorganic carbon production and leaking losses. Findings from this study help fill the knowledge gap on the underlying controls of SOC and SIC distribution along the altitudinal gradient in water- and low temperature-constrained alpine rangeland.