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

• • Grassland topsoil exhibited the highest carbon content (40.36±22.92 g·kg−1) but also the highest variability (CV=0.57), indicating heterogeneous carbon storage potential across karst landscapes. • • Forestland showed the most stable carbon and nitrogen contents (CV=0.35 and 0.26, respectively) with nitrogen content of 2.89±0.76 g·kg−1, suggesting that forest soils provide reliable carbon and nitrogen sequestration. • • Cultivated land had the lowest carbon (34.06±14.57 g·kg−1) and nitrogen (2.50±0.65 g·kg−1) contents, with moderate variability (CV=0.43 for C), highlighting the negative impact of agricultural management on soil organic matter. • • Across all land use types, soil carbon and nitrogen were strongly positively correlated (r>0.5, P<0.001), indicating coupled dynamics that are critical for predicting carbon-nitrogen interactions under land use change.