Impact of Land Use Types on Topsoil Carbon and Nitrogen and Their Spatial Distribution Characteristics in the Karst Area of the Yunnan-Guizhou Plateau: A Case Study of the Sancha River Basin
This study investigates the effects of different land use types on topsoil carbon (C) and nitrogen (N) contents and their spatial distribution in the lower reaches of the Sancha River Basin, a karst region of the Yunnan-Guizhou Plateau. Grid sampling collected 0–20 cm topsoil from forestland (n=23), cultivated land (n=25), and grassland (n=32). Total C and N were measured. Results showed that topsoil C content followed grassland (40.36±22.92 g·kg−1) > forestland (37.05±12.83 g·kg−1) > cultivated land (34.06±14.57 g·kg−1), while N content followed forestland (2.89±0.76 g·kg−1) > grassland (2.67±1.19 g·kg−1) > cultivated land (2.50±0.65 g·kg−1). One-way ANOVA revealed no significant differences among land use types (P>0.05). Soil C and N were significantly positively correlated across all land uses (r>0.5, P<0.001). Coefficient of variation (CV) indicated grassland had the highest C variability (0.57), while forestland showed the most stable C and N (CV=0.35 and 0.26, respectively). Cultivated land had CVs of 0.43 for C and 0.26 for N. Spatially, forestland exhibited concentrated high C values with significant N heterogeneity; grassland had higher C in southern and eastern areas but scattered distribution, with generally low and variable N; cultivated land showed uniform but lowest C and N. Land use types significantly drive topsoil C and N dynamics through vegetation input, soil disturbance, and management practices, underscoring the importance of rational land use planning for enhancing carbon sink functions and sustainable development in karst watersheds.