Nutrient Limitation Mechanisms of Natural Succession of Karst Vegetation Based on Soil Chemometrics and Enzyme Metrology

Background and Aims: Karst ecosystems suffer from thin soil layers and severe nutrient limitation, while the interactive regulation of vegetation succession and restoration duration on soil C–N–P and microbial enzyme limitation remains unclear. This study aimed to disentangle individual and coupled effects of succession stage and 14-year restoration on soil stoichiometry and extracellular enzyme-based nutrient limitation in karst. Methods: We established five natural succession gradients (HS–MS) with fixed plots sampled in 2008 and 2022. Soil physicochemical properties and ecoenzyme stoichiometry (ecoenzyme stoichiometry, EEA; EEA ratios, vector length/angle) of eight soil enzymes (including hydrolases and oxidoreductases) were measured; two-way ANOVA, redundancy analysis (RDA) and correlation analysis were applied to quantify factor interactions. Results: N:P and available nitrogen:total nitrogen (AN:TN) decreased significantly over restoration; EEA stoichiometry remained stable across succession. Vector angle < 45° indicated the persistence of nitrogen limitation. The restoration duration of secondary succession masked the independent effects of community succession on most soil variables, with three coupling modes (masking, activation, synergism) identified for C, N, P and Ca2+:Mg2+. Conclusion: Long-term restoration reshaped karst soil nutrient pools and aggravated N limitation. Stage-targeted nitrogen activation and phosphorus mobilization strategies were proposed for differentiated karst ecological restoration.