Abstract: Aims Frequent drought events have significantly influenced the growth and survival of plants. However, it is not yet clear how the physiological and ecological characteristics of different alpine plants respond to droughts in different seasons. Methods Based on a simulated seasonal drought experiment, this study investigated the antioxidants, osmotic regulation substances, functional traits and photosynthetic parameters of the leaves of eight typical alpine plants, and analyzed the effects of drought in different seasons on the antioxidant and osmotic regulation systems and photosynthesis of alpine plants. Important findings Our results showed that: Overall, the response of plant leaf antioxidants to seasonal droughts was not significant, but interspecific differences were evident. Poa crymophila adapted to seasonal drought primarily through increased catalase (CAT) and peroxidase (POD) activities, whereas Stipa aliena and Carex przewalskii relied more on superoxide dismutase (SOD) activity (-25 - 38%). Autumn drought increased the content of malondialdehyde (MDA) (32 - 35%), while growing season drought significantly enhanced the plant CAT activity (122% - 161%). Plant leaf osmoregulatory substances responded significantly to seasonal droughts, with interspecific variations. The soluble protein content in the leaves of Poa crymophila increased by 73% under summer drought. Potentilla saundersiana increased by 47% during the drought of the growing season. The contents of proline and soluble sugar are sensitive to autumn drought and decrease (36-45%). There is a synergistic mechanism among the systems, and the osmotic regulation - antioxidant system shows a significant correlation (proline content and SOD: r = -0.19**;) Soluble protein and POD: r = 0.128*), specific leaf area was negatively correlated with CAT activity (r = -0.14*), leaf dry matter was positively correlated with proline content (r = 0.18**), and N/P was negatively correlated with SOD (r =-0.18**). It is worth noting that photosynthesis and defense metabolism show a seasonally dependent trade-off: Under spring drought, the net photosynthetic rate (Pn) is negatively correlated with POD and CAT (r = -0.41*, -0.35*), and during autumn drought, Pn is significantly negatively correlated with proline (r = -0.39*), revealing the seasonal dependence of resource allocation. This study proposed the framework of "seasonally specific defense strategies", revealing the regulatory pathways by which alpine plants respond to seasonal drought through the synergistic interaction of functional traits and physiological metabolic dynamics, providing a theoretical basis for the adaptive management of alpine grassland ecosystems under climate change.

Key words: Alpine meadow, Climate change, Drought response mechanisms, Functional traits, Net photosynthetic rate, Osmotic adjustment, Reactive oxygen species metabolism