Experimental warming alleviates leaf-level physiological stress of Kobresia pygmaea in alpine meadows on the Northeastern Qinghai-Tibet Plateau

Climate warming can strongly influence alpine plant physiology, but the leaf-level responses of dominant alpine meadow species to warming may vary across elevation and growing-season stages. These spatial and seasonal patterns remain insufficiently known. We examined the physiological responses of Kobresia pygmaea on the northeastern Qinghai-Tibet Plateau to long-term passive open-top chamber (OTC) warming across four elevations (3691, 3786, 3981, and 4131 m a.s.l.) from July to September. Across all sites and months, OTC warming increased mean near-surface air temperature by 1.34 °C and surface soil temperature by 1.32 °C, while reducing relative humidity by 5.16% and surface soil moisture by 5.17%. Warming reduced leaf malondialdehyde by 20.2% and proline by 45.3%, suggesting lower membrane lipid peroxidation and reduced osmotic adjustment. Superoxide dismutase activity increased slightly by 2.4%, whereas peroxidase activity increased by 26.3%, indicating enzyme-specific antioxidant regulation. Chlorophyll a, chlorophyll b, and total chlorophyll increased by 72.0%, 66.2%, and 70.2%, respectively. Three-way ANOVA showed significant effects of warming, month, elevation, and their interactions on most physiological indicators. Moderate OTC warming improved the leaf-level physiological status and photosynthetic pigment capacity of K. pygmaea during the growing season. These benefits were season- and elevation-dependent and occurred under a concurrent drying microclimate. The results provided evidence of a leaf-level physiological response to warming by the dominant species in alpine meadows.