Vegetation changes drive alterations in soil nutrients, heavy metals and microbial traits in alpine meadows

With ongoing global warming, vegetation succession in alpine meadows has become increasingly prominent, substantially altering soil ecological processes. To investigate the patterns and regulatory mechanisms of soil nutrient, heavy metal, and microbial trait changes during vegetation succession, we selected a typical alpine vegetation succession sequence-ranging from grassland to shrubland to mixed forest-in Shangri-La, China. Using a space-for-time substitution approach, we systematically analyzed changes in soil nutrients, heavy metals, and microbial properties (including enzyme activities and microbial biomass) across different succession stages. Our results revealed significant differences in soil nutrients, heavy metals, and microbial characteristics along the succession gradient. Notably, soil enzyme activities, microbial biomass, and concentrations of Cu, Zn, Cr, As, and Cd were lowest in the shrubland co-dominated by Rhododendron racemosum Franch. And Quercus monimotricha (Hand.-Mazz.) Hand.-Mazz. (G2). With the progression of vegetation succession, all measured soil nutrients-except for total potassium (TK)-including available potassium (AK), available phosphorus (AP), soil organic carbon (SOC), pH, total nitrogen (TN), and total phosphorus (TP), exhibited significant increases at the late successional stage, represented by the mixed forest co-dominated by Quercus monimotricha (Hand.-Mazz.) Hand.-Mazz. and Picea asperata Mast. (QG). Soil nutrients and heavy metals jointly drove microbial dynamics, with their combined effects explaining 50.0% of the observed variation. Among these, heavy metals had a greater independent explanatory power (35.0%) than soil nutrients (11.3%). This study provides theoretical support and scientific evidence for understanding ecosystem stability mechanisms and guiding ecological restoration in climate-sensitive alpine regions.