Spatial variation of deep soil inorganic carbon under different land use types and its driving factors in the Loess Plateau

Abstract

Since the implementation of the large-scale land use converted from farmland, the soil carbon storage has changed significantly in the Loess Plateau. Previous studies mainly focused on soil organic carbon (SOC), the response of soil inorganic carbon (SIC) to afforestation projects remains inconclusive, especially in deep soil. In order to systematically explore the impact of land use change on the spatial distribution of SIC, 10 sites in the Loess Plateau including forestlands, shrublands, grasslands, and farmlands (control) at each site were selected using regional-scale paired experiments. Soil samples were collected in the layers of 0–300 cm depth, totaling 1800 soil samples. The results showed that (1) In the east-west direction, land use converted from farmland increased the shallow (0–100 cm) soil inorganic carbon storage (SICS), with grassland having the largest SICS. However, land use converted from farmland promoted the deep (100–300 cm) SIC loss, and shrublands had the largest SIC loss. In the north-south direction, land use converted from farmland promoted SIC loss in shallow and deep soils, with the largest SIC loss in forestlands in shallow soils and shrublands in deep soils. Overall grasslands were more favorable for SIC sequestration at the regional scale. (2) In the region, the increase in SIC sequestration was more significant in shallow soils than in deeper soils in the east-west direction. However, in the north-south direction, larger carbon loss in shallow soils was found. (3) The spatial variation of SIC in the Loess Plateau was affected by climate, land use types and soil properties. Climate is dominant, and the indirect effect of climate factor is the largest in both shallow (0.45) and deep (0.48) soils. Soil properties can directly affect the distribution of SIC, with the direct effects of 0.31 and −0.39 in shallow and deep soils, respectively. In addition, land use types indirectly affect SIC by acting on soil properties. In this study, through evaluating the sequestration benefits of deep SIC after afforestation through paired experiments at the regional scale, we found that grassland is the optimal choice for SIC sequestration in the study area. The finding could provide scientific support for land use management and carbon sequestration strategies in the Loess Plateau.