Soil organic carbon pool of grassland soils on the Qinghai-Tibetan Plateau and its global implication.

A study of carbon (C) storage in the 0-0.75-m profile of soils subtending various types of grasslands on the Qinghai-Tibetan Plateau showed that the organic carbon content of the 1,627,000 km2 of such lands in the region reaches 33.52 Pg of C. Organic carbon is mainly stored in the meadow and steppe soils of the Plateau, which combined, represents 23.2 Pg of C stored in organic form. This represents 23.44% of China's total organic soil-stored carbon and 2.5% of the global pool of soil carbon as of 1996. Carbon emissions from the grassland soils were estimated based on the two major modes of emission: (i) natural soil respiration and (ii) shifts in net C flux to/from soil due to land-use changes and their potential influence on organic matter decomposition. Annual soil respiration-driven CO2 emissions from the grassland soils of the plateau reached 1.17 Pg C year(-1), accounting for 26.4% of China's total soil respiration and 1.73% of global soil respiration. Because the grassland area accounts for 1.02% of the global terrestrial land and 16.9% of China's total terrestrial land, this CO2 emission rate is significantly higher than the country's mean annual rate (approx. 4.2 Pg C year(-1)) and even higher than the global mean rate (approx. 68 Pg C year(-1)). In the last 30 years, approximately 3.02 Pg C have been emitted from the grassland soils of the plateau due to land-use changes and grassland degradation. The total CO2 emissions rate from the grassland soils of the plateau reached 1.27 Pg C year(-1). Protecting grasslands on the Qinghai-Tibetan Plateau is of great importance in limiting global climate change.