Ecoenzymatic C: N: P stoichiometry reveals microbial nutrient limitations across seasonal, depth, and disturbance gradients in Shorea robusta forest soils of the Western Himalaya, India

Abstract Background and aims Logging threatens nutrient (C, N, P) retention in Shorea robusta forests, disrupting biogeochemical cycles by altering vegetation regeneration and soil biochemical feedbacks. Yet, combined effects of disturbance and seasonality on microbial biomass, extracellular enzyme activities (EEAs), and stoichiometry remain underexplored, particularly under nutrient-limited, climate-sensitive conditions. Methods This study investigated how seasonal shifts, soil depths, and four disturbance regimes (no disturbance (ND): < 5% basal area removal, low disturbance (LD): < 20%, moderate disturbance (MD): < 50%, and high disturbance (HD): > 50%) shape microbial biomass and C-, N-, and P-cycling enzymes (cellobiosidase, β-glucosidase, β-acetyl-glycosaminidase, urease, acid/alkaline phosphatase). It also explored relationships with understory vegetation (Shannon diversity (H′), fine root biomass (FRB)) and soil physicochemical properties. Results Microbial biomass and enzyme activities peaked in MD stands during monsoon. LD and HD stands exhibited reduced C: N and C: P EEAs ratios, suggesting elevated P limitation. Depth-wise EEAs stoichiometry indicated increased constraints on C and P in deeper layers. Vector analysis identified C and P as limiting elements, with partial alleviation at HD. Structural equation modeling revealed stronger P than N limitation, driven by understory H′, FRB, microbial traits, and soil nutrients. Positive correlations between microbial biomass, EEAs, and nutrient limitation indices suggest microbial activity is shaped more by nutrient availability than by strict stoichiometric homeostasis. Conclusions Overall, this study illustrates seasonality, depth, and disturbance interactively govern microbial nutrient dynamics in sal forests, revealing microbial adaptability under shifting environmental constraints and implications for nutrient cycling and ecosystem resilience.