Patterns of SOC and soil 13C and their relations to climatic factors and soil characteristics on the Qinghai-Tibetan Plateau

SOC inventory and soil delta C-13 were widely used to access the size of soil C pool and to indicate the dynamics of C input and output. The effects of climatic factors and soil physical characteristics and plant litter input on SOC inventory and soil delta C-13 were analyzed to better understand the dynamics of carbon cycling across ecosystems on the Qinghai-Tibetan Plateau. Field investigation was carried out along the two transects with a total of 1,875 km in length and 200 km in width. Sixty-two soil profiles, distributed in forest, meadow, steppe, and cropland, were stratified sampled every 10 cm from 0 to 40 cm. Our result showed that SOC density in forest and meadows were much higher than in steppe and highland barley. In contrast, delta C-13 in forest and meadow were lower than in steppe and highland barley. Soil delta C-13 tended to enrich with increasing soil depth but SOC decline. SOC and delta C-13 (0-40 cm) were correlated with different climatic factors in different ecosystems, such that SOC correlated negatively with MAT in meadow and positively with MAP in steppe; delta C-13 correlated positively with MAT in meadow and steppe; and delta C-13 also tended to increase with increasing MAT in forest. Of the variation of SOC, 55.15 % was explained by MAP, pH and silt content and 4.63 % was explained by the interaction between MAT and pH across all the ecosystems except for the cropland. Meanwhile, SOC density explained 27.40 % of variation of soil delta C-13. It is suggested that different climatic factors controlled the size of the soil C pool in different ecosystems on the Tibetan Plateau. SOC density is a key contributor to the variation of soil delta C-13.