Search

The soil carbon reservoir is the largest carbon reservoir in terrestrial ecosystems and consists of soil organic and inorganic carbon stocks. Previous studies have mainly focused on the soil organic carbon (SOC) stock, and limited information is available about the soil inorganic carbon (SIC) stock. The Chinese Loess Plateau (CLP), which is located in the arid and semi-arid region of China, is an important inorganic carbon reservoir, with a thick soil layer that is rich in calcium carbonate. However, there are few reports on the SIC stock and its spatial distribution in this region. In the current study, the SIC densities and stocks for various soil types and land use patterns were evaluated based on 495 profiles with 2470 soil samples across the CLP, which were collected from the Chinese Second National Soil Survey. The results showed that in the top 1m of soil across the CLP, the average SIC density is 17.04kg/m², and the total SIC stock is approximately 10.20 Pg C (1 Pg=1015g). The SIC stock of the CLP accounts for approximately 18.4% of the total SIC stock throughout China. The average values of the SIC stock in the 0-20, 20-50 and 50-100cm depths of the CLP are 2.39, 2.92 and 4.89 Pg, respectively. Under different land use patterns, the order of the average SIC density is farmland≈grassland > forest in all soil layers. For the various soil types, the SIC density in the 0-100cm layer is the highest in alkaline soil and lowest in subalpine meadow soil, whereas the SIC stock is highest in loessial soil, eolian sandy soil and sierozem, and the lowest in subalpine meadow soil. These differences are largely a result of the area occupied by each soil type and the climate conditions. The results of this study provide basic information about carbon reservoir in China and contribute to our understanding of the SIC stock on the CLP as it relates to the carbon balance of terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Land use and topography strongly influence soil organic C (SOC) and N accumulation in eroded hilly regions. However, their combined effects and the underlying mechanism remain unclear. In this study, five land uses and three topographic positions across an eroded hilly watershed of the Loess Plateau were selected to investigate their effects on SOC and N accumulation. The restored grassland, shrubland and woodland (25 to 30years) increased SOC and total N by 32% to 119% in the slope and 17% to 81% in the gully, respectively compared with the cropland. These restored vegetation increased soil dissolved organic C (DOC) and microbial biomass C and N (MBC and MBN) by 1.1- to 3.0-fold in the slope and 30% to 108% in the gully, respectively. Similar increases were observed in soil aggregates, MBN/total N, soil C:N and microbial C:N ratios. These improvements were higher in the shrubland than in the other land uses. The SOC significantly decreased from the gully to the slope, and the magnitudes decreased in a sequence of cropland, grassland, shrubland and woodland. Soil DOC, total N, and MBN also decreased from the gully to the slope in the cropland, but remained unchanged in the grassland, shrubland, and woodland. Land use (P <0.05), topographic position (P <0.05), and their interaction (P <0.1) influenced SOC, total N, DOC, MBC, MBN, soil C:N and microbial C:N ratios. There were close relationships among soil aggregates, SOC and total N, and DOC, MBC and MBN. Therefore, land use, topographic position (erosion and deposition), and their interactions regulate SOC and N accumulation and their labile fractions in the eroded hilly region at a watershed scale. Our results suggested that converting cropland to shrubland is an initial strategy to restore degraded ecosystems and increase soil C sequestration in eroded hilly region of the Loess Plateau. [Copyright &y& Elsevier]