Impacts of seasonal grazing on soil enzymes, physicochemical properties, and vegetation in alpine meadows

Alpine grasslands of the Qinghai–Tibet Plateau (QTP) are vital for regional biodiversity and nutrient cycling but are increasingly affected by grazing-induced degradation. This study examined the effects of seasonal grazing (spring, summer, autumn, winter) on soil extracellular enzyme activities, key physicochemical properties, and plant biomass in alpine meadows of the QTP. Over two consecutive years (2021–2022), pre- and post-grazing soil and vegetation samples were collected from replicated seasonal grazing plots. Enzyme activities were analyzed in relation to biomass of dominant plant functional groups: Cyperaceae, Poaceae, Leguminosae, and miscellaneous grasses. Enzymes were categorized by function into nutrient cycling (phosphatase, hydroxylamine reductase), organic matter degradation (amylase, cellulase, chitinase, glucosidase, polyphenol oxidase), and proteolysis (alkaline proteases). The results revealed distinct seasonal patterns in enzymatic activity and plant biomass. Amylase (3066 μgd⁻¹g⁻¹) and hydroxylamine reductase (466 μgd⁻¹g⁻¹) activities were significantly higher during winter grazing (p < 0.05), while chitinase (40 μgd⁻¹g⁻¹) and cellulase (675 μgd⁻¹g⁻¹) peaked during spring. Glucosidase activity was highest under summer grazing, while alkaline proteases exhibited minimal seasonal variation. Plant biomass varied by season: Cyperaceae dominated in winter, Poaceae in autumn, and miscellaneous grasses in summer, whereas Leguminosae biomass remained consistently low. Pearson correlation analysis showed significant correlations between elevated amylase (p < 0.05) and hydroxylamine reductase (p < 0.01) activities with increased Cyperaceae biomass in winter. Similarly, higher chitinase activity (p < 0.01) during spring was positively correlated with the growth of miscellaneous grasses. These findings reveal that seasonal grazing alters soil enzymatic activity, influencing plant growth and species composition, and underscore the need for adaptive grazing strategies to sustain soil health and ecosystem resilience in alpine meadows.