Land use change and climatic-topographic factors drive spatial heterogeneity of soil pH in karst watersheds of Southwest China

• A high-resolution map (150 m) of the soil pH in the karst watershed was produced first. • The soil pH in the karst watershed is predominantly neutral to slightly alkaline. • Parent materials, land use, and topography strongly influence the soil pH distribution. • Climate, topography, and land use integration are crucial for assessing soil pH. Soil pH is a critical determinant of nutrient availability and microbial activity, strongly influencing terrestrial ecosystem functions and productivity. Understanding its spatial distribution is essential for sustainable land-use management. However, the effects of land use change on soil pH in karst regions with high habitat heterogeneity (e.g., complex microtopography, abrupt changes in soil thickness, and high spatial variability in rock exposure rates) are less well understood. Here, we present a comprehensive investigation of the spatial distribution and drivers of the 0–5 cm soil pH at 2755 sampling points in a typical karst watershed in Southwest China. Our results revealed significant spatial heterogeneity in the soil pH within the watershed, predominantly ranging from neutral (6.6–7.3) to slightly alkaline (7.4–7.8), with noticeable acidification trends in localized areas. This spatial pattern was influenced by topography (e.g., slope and slope position), land use type, parent material, and soil type. Notably, native karst vegetation (arbor-shrub mixed forestland) was more effective at maintaining neutral soil conditions, whereas garden land tended to contribute to soil acidification. These findings indicate that human activities, such as agricultural practices, can alter native vegetation and soil properties, significantly affecting the acid‒base buffering capacity of the soil. Additionally, the average annual rainfall, temperature, and soil thickness shaped the spatial distribution of soil pH in the watershed, which was related to hydrodynamic differences. Notably, the direct and indirect effects of geography, climate, rock exposure rate, and land use on soil pH highlight the complex interactions among various elements of karst ecosystems. These findings indicate that in regions with high soil heterogeneity, comprehensively considering the impacts of various factors, such as topography, microclimate, vegetation, and land use, on soil pH values at the watershed scale is necessary. The implementation of tailored management measures can effectively maintain the soil acid‒base balance, promoting ecosystem productivity.