Soil inorganic carbon stock in the Tibetan alpine grasslands

As the largest carbon pool in the terrestrial biosphere, soil carbon stock consists of organic and inorganic components. However, previous studies dominantly concentrated on soil organic carbon (SOC) stock, and little is known about the magnitude and patterns of soil inorganic carbon (SIC). In this study, we evaluated the magnitude of SIC stock in the Tibetan alpine grasslands using data from 405 profiles surveyed from 135 sites across the plateau during 2001-2004. Kriging interpolation was conducted to interpolate site-level observations to the regional level. We also compared spatial and vertical distributions of SIC stock with the corresponding patterns of SOC stock in the Tibetan alpine grasslands. Our results showed that SIC stock in the top 1 meter in the Tibetan alpine grasslands was approximately 15.2 Pg C (1 Pg = 10(15) g), with an average density (amount per area) of 13.46 kg C m(-2). SIC density exhibited different spatial and vertical distributions in comparison with SOC density. Spatially, SIC density in the alpine steppe was larger than that in the alpine meadow, in contrast to SOC distribution. Vertically, SIC stock in the upper 30 and 50 cm accounted for 47.6% and 71.6%, respectively, of that in the upper 1 meter, with lower proportions than that of SOC stock in the same interval (67.8% and 83.3%). In total, SIC stock in the Tibetan alpine grasslands was about 2.1 times the corresponding SOC stock, accounting for 28.5% of the total SIC stock in China. These results highlight that SIC stock in the Tibetan grasslands could make a significant contribution to China's terrestrial carbon balance.