Land-use effects on organic and inorganic carbon patterns in the topsoil around Qinghai Lake basin, Qinghai-Tibetan Plateau

Abstract

Soil carbon (C) pool contains organic carbon (SOC) and inorganic carbon (SIC). A detailed understanding of SOC and SIC is meaningful and essential for precisely assessing the effects of land-use on soil C stocks. Alpine grassland around Qinghai Lake basin has experienced extensive land-use changes due to the cultivation of native grassland and vegetation recovery on cropped land. However, limited information is available about the changes and distribution patterns of soil C pool with land-use in this region. Here, three land-use types were chosen, including natural alpine grassland (NG), and a pair of restored grassland (RG) and farmland (FL), to examine the effects of cultivation and restoration on SOC and SIC horizontal patterns and vertical distributions in the upper 30cm soil layer. Land-use changed the ratio of SOC/SIC without affecting the net soil total C accumulation in this area. The NG had the highest SOC (96.0MgCha−1) and lowest SIC (19.8MgCha−1) stocks, while the FL had the opposite result, with the average of SOC and SIC stocks was 65.0 and 57.7MgCha−1, respectively. After 10-year restoration, SOC stock increased to 73.2MgCha−1, while SIC decreased to 47.8MgCha−1 in the RG. The vertical distribution of SOC and SIC changed sharply with depth in the NG but gently in the RG, and with little changes in the FL. Stepwise regression analysis manifested that soil nitrogen and pH were the main determinants for the redistribution patterns of SOC and SIC with land-use. In addition, ordinary regression analysis revealed a significant negative correlation between SIC content and aboveground biomass of the respective vegetation. The results demonstrated that land-use had affected the horizontal and vertical patterns of SOC and SIC synchronously, and indicated SIC stocks played crucial roles for estimating the C sequestration capacity in the restoration and farmland ecosystems around Qinghai Lake basin. Moreover, the results of this study provided an interesting snapshot of the compensation relationship between SOC and SIC stocks with land-use, and suggested that the changes of soil properties and plant above- and belowground biomass resulting from cultivation and restoration were potentially responsible for the transformation of soil C forms.