Soil Enzyme Activities and Microbial Nutrient Limitation Between Restored Vegetation and Primary Forest on the Loess Plateau

Abstract

Vegetation restoration aims to recover ecosystem functions in degraded landscapes, yet differences in soil microbial functioning between restored vegetation and primary forests remain poorly understood. In this study, we investigated extracellular enzyme activities (EEAs) and ecoenzymatic stoichiometry in plantation, secondary grassland, and primary forest on the Loess Plateau and evaluated the relative contributions of multiple environmental factors to their variations. The results showed that grassland exhibited higher EEAs than plantation and primary forest. Vector lengths (1.34–1.38) indicated greater microbial C limitation in plantation than in grassland and primary forest, whereas vector angles (40.60–43.21°) indicated predominantly greater N than P limitation across vegetation types. Soil organic carbon, slope gradient, and alkaline phosphatase were the main predictors of EEAs, microbial C limitation, and microbial N/P limitation, respectively. In addition, microbial biomass stoichiometric homeostasis varied among vegetation types, with comparatively weak homeostasis in plantation and strict homeostasis in grassland. Overall, grassland was characterized by high enzyme investment and relatively low microbial nutrient limitation, suggesting that natural secondary succession following cropland abandonment may support favorable soil microbial functioning on the Loess Plateau.