Soil Total, Microbial and Enzymatic C : N : P Stoichiometry Associated with Depth and Land-Use Types in a Typical Karst Depression

Abstract Land use significantly alters soil enzyme activity and microbial nutrient metabolism by regulating the coupled biogeochemical carbon, nitrogen, and phosphorus cycles. While these mechanisms have been well studied for surface soils (0–30 cm), they remain to be clarified for deeper soil layers (>50 cm), particularly in karst regions. We therefore examined the C : N : P stoichiometry of the soil–microbe–enzyme system across the 0–200 cm profile under five land-use types (grassland, cane field, plantation forest, orchard land, and secondary forest) in a typical karst depression in southern China. Grassland exhibited a significantly lower soil C : N ratio than cane field and secondary forest, while orchard land exhibited the highest soil C : P and N : P, microbial biomass C : N and C : P, and enzymatic C : P and N : P ratios. The lower soil and microbial biomass C : N, C : P, and N : P ratios observed here indicate co-limitation by N and P, which intensified with depth. Correlation and redundancy analyses revealed strong correlations between soil properties and microbial and enzyme metrics, with soil organic carbon and total nitrogen content being key regulators of microbial biomass stoichiometry, while soil bulk density and the C : N ratio were the primary drivers of enzyme activity. Partial least squares path modeling revealed that the soil modifications owing to land use significantly influenced microbial and enzymatic stoichiometry. These findings highlight the critical impacts of land use and soil depth on C : N : P stoichiometry in karst depression ecosystems, providing essential insights for soil health assessment and sustainable land management.