Variations and Drivers of Soil Extracellular Enzyme Activities and Ecoenzymatic Stoichiometry Across Elevation Bands in Baishanzu National Park

This study focused on carbon (C), nitrogen (N), and phosphorus (P) nutrient cycling in the montane ecosystem of Baishanzu National Park. We investigated variations in soil extracellular enzyme activities and ecoenzymatic stoichiometric characteristics along an elevational gradient and analyzed the relative effects of plant diversity and soil physicochemical factors on soil extracellular enzyme activities and their stoichiometric characteristics. A total of 48 plots were established across four elevation bands, including 700～900 m (evergreen broadleaved forest), 1100～1300 m (coniferous and broadleaved mixed forest), 1300～1500 m (coniferous forest), and 1500～1700 m (shrubland). Plant diversity was surveyed, and surface soil samples from the 0～20 cm layer were collected. Soil physicochemical properties and the activities of five extracellular enzymes involved in C, N, and P cycling were measured, including β-1,4-glucosidase (BG), cellobiohydrolase (CBH), β-1,4-N-acetylglucosaminidase (NAG), L-leucine aminopeptidase (LAP), and acid phosphatase (AP). Ecoenzymatic stoichiometric ratios were calculated, and vector analysis, Mantel tests, and redundancy analysis were used to identify the major factors associated with soil extracellular enzyme activities and their stoichiometric characteristics. The results showed that soil extracellular enzyme activities differed markedly among elevation bands. The activities of BG, CBH, LAP, and AP generally increased with elevation and reached their highest values at 1500～1700 m, whereas NAG activity was highest at 1100～1300 m and 1500～1700 m. The ecoenzymatic C/N ratio was lowest at 1100～1300 m, the ecoenzymatic C/P ratio was lowest at 700～900 m, and the ecoenzymatic N/P ratio was highest at 1100～1300 m. Vector analysis showed that vector length (VL) increased with elevation, whereas vector angle (VA) decreased but remained greater than 45° across all elevation bands, indicating stronger P limitation at lower elevations and stronger C limitation at higher elevations. Soil moisture content (SM) and pH were important factors associated with soil extracellular enzyme activities and their stoichiometric characteristics across elevation bands. Soil physicochemical factors such as soil organic carbon (SOC), dissolved organic carbon (DOC), and total inorganic nitrogen (TIN) were also closely related to changes in enzyme activities, whereas plant diversity indices showed relatively weak correlations with soil extracellular enzyme activities and their stoichiometric characteristics. Overall, soil extracellular enzyme activities and ecoenzymatic stoichiometry differed markedly among elevation bands in Baishanzu National Park, and soil microorganisms exhibited varying degrees of C and P limitation.