Opposite patterns of soil organic and inorganic carbon along a climate gradient in the alpine steppe of northern Tibetan Plateau.

• SOC increased with increasing precipitation, but the reverse for SIC in alpine steppe. • SOC density decreased with soil depth, but SIC density increased with depth. • Biological processes drive SOC profiles, while abiotic factors determine SIC patterns. • SIC comprises about 10% of C storage in alpine steppe soils of the Tibetan Plateau. Both soil organic carbon (SOC) and inorganic carbon (SIC) are important components of soil carbon storage. However, few studies have attempted to estimate the magnitude and patterns of SIC in arid areas. We measured the concentrations of SOC and SIC in alpine steppe grasslands along a climate gradient in the Tibetan Plateau. At all sites, an opposing trend was found in the distribution of SOC compared with SIC. SOC increased with increasing precipitation, while SIC decreased. Within sites, SOC decreased with soil depth, while SIC increased. Among the variables considered, soil total nitrogen (TN) and soil water content explained the most variability in SOC (r2 = 0.95 for TN, r2 = 0.93 for soil water content), and soil pH had the highest correlation with SIC (r2 = 0.90). This finding indicates that SOC is closely related to biological processes, such as biomass input and litter accumulation, while SIC is determined by abiotic factors such as chemical and physical processes of soil formation. SOC and SIC densities showed that the SOC pool comprised 91% of total carbon (TC) storage in these alpine steppe soils. A decrease in SOC density occurred with depth, but this pattern was the opposite for SIC density in all soil profiles. These findings help to characterize the C cycle in the alpine steppe of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]