Treeline ecotone drives the soil physical, bio-chemical and stoichiometry properties in alpine ecosystems of the western Himalaya, India

The alpine treeline ecotones represent one of the most sensitive ecosystems, functioning as first responder of global climate change. However, the soil nutrient dynamics within the alpine ecotone across varying altitudinal gradients remain insufficiently explored. The present study investigated soil physical and biochemical properties in the forest, ecotone and meadow zone in three soil depths: 0–10, 10–20, and 20–30 cm. Our findings revealed soil moisture, pH, organic carbon (SOC), total nitrogen (TN), available phosphorus (AP), SOC/TN and SOC/AP were higher in meadow compared to forest. The SOC (mean) was higher in the meadow (5.68 %) and ecotone (5.02 %) than in forest (4.08 %). The TN increased in order: forest (0.33 %) < ecotone (0.47 %) < meadow (0.52 %). The AP decreased in order: forest (0.048 %) > ecotone (0.037 %) and > meadow (0.035 %). The soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial biomass phosphorus (MBP) ranged from 125 to 400 µg g─1, 3–12 µg g─1 and 0.12–4.63 µg g─1, respectively with higher values in ecotone, possibly due to warming-induced increased shrubification in alpine ecosystem. Principal component analysis (PCA) showed ecotone influenced by most of the soil parameters. ANOVA reveals significant differences in soil physical, chemical, biological, and stoichiometry due to soil layers, sites, and sites × depths interaction (P < 0.05). The results indicated SOC, TN, AP, MBC, MBN, and MBP decreased with soil layers. Significant correlations between soil nutrients and microbial biomass showed strong linkages. Compared to forest and ecotone, the higher MBC/MBN ratio in meadow region indicated shifting of microbes towards the fungal community dominance. Our findings indicated changes in the ecosystem along an altitudinal gradient directly influence the cycling of soil and microbial nutrients and stoichiometry. Thus, our findings will improve understanding for managing and conserving alpine ecosystems in long run.