Organic and inorganic carbon in the topsoil of the Mongolian and Tibetan grasslands: pattern, control and implications

[摘要] Soil carbon (C) is the largest C pool in the terrestrial biosphere and includesboth inorganic and organic components. Studying patterns and controls ofsoil C help us to understand and estimate potential responses of soil C toglobal change in the future. Here we analyzed topsoil data of 81 sitesobtained from a regional survey across grasslands in the Inner Mongolia andon the Tibetan Plateau during 2006–2007, attempting to find the patterns andcontrols of soil inorganic carbon (SIC) and soil organic carbon (SOC). Theaverages of inorganic and organic carbon in the topsoil (0–20 cm) across thestudy region were 0.38% and 3.63%, ranging between 0.00–2.92% and0.32–26.17% respectively. Both SIC and SOC in the Tibetan grasslands(0.51% and 5.24% respectively) were higher than those in the InnerMongolian grasslands (0.21% and 1.61%). Regression tree analysesshowed that the spatial pattern of SIC and SOC were controlled by differentfactors. Chemical and physical processes of soil formation drive the spatialpattern of SIC, while biotic processes drive the spatial pattern of SOC. SICwas controlled by soil acidification and other processes depending on soilpH. Vegetation type is the most important variable driving the spatialpattern of SOC. According to our models, given the acidification rate inChinese grassland soils in the future is the same as that in Chinesecropland soils during the past two decades: 0.27 and 0.48 units per 20 yrin the Inner Mongolian grasslands and the Tibetan grasslands respectively,it will lead to a 30% and 53% decrease in SIC in the Inner Mongoliangrasslands and the Tibetan grasslands respectively. However, negativerelationship between soil pH and SOC suggests that acidification willinhibit decomposition of SOC, thus will not lead to a significant generalloss of carbon from soils in these regions.

[学科分类] 地球化学与岩石