## 1 Introduction  
The photosynthesis activity of alpine vegetation and its response to the changing environment has been an attractive topic for centuries [1, 2] due to its unparalleled scientific and social significance. In alpine regions, plants along the altitudinal gradient usually habituate themselves well to local environmental conditions, thus their physiological traits vary over relatively short horizontal distances [1, 3]. Due to the unique combination of extreme environmental stresses along the altitude gradient, such as low temperature and high light intensity, large amounts of special materials for evolutionary studies on adaptation strategies can be found in alpine regions, which appeals to numerous ecologists and evolutionists [1, 3, 4, 5]. The special combination of environmental stresses also makes the alpine area a natural laboratory for vegetation-climate interaction research. Environmental variables that often appear with collinearity decouple along the elevation gradient, which can be of benefit in clarifying the response of photosynthesis to the environment under wild conditions [1]. Considering the specificity of this habitat, the findings and mechanisms of adaptation in high-altitude regions can be different from those in other regions, such as high-latitude regions [7], therefore, research on the alpine vegetation-climate interaction is invaluable. Understanding the altitudinal variations in unique traits of alpine plants and their environmental sensitivity will help in revealing their adaptation mechanism in mountain areas, describing the impact of climate change on vegetation, and predicting the degree of biological negative feedback to the changing climate. However, the altitudinal patterns of vegetation changes are still under discussion. Altitudinal factors can affect vegetation in diverse aspects. Studies have demonstrated that the phenological behavior of vegetation in alpine regions varies significantly with altitude. [PERSON] et al. discovered higher phenological sensitivity to temperature in spring in regions with higher altitudes, which highlights the vulnerability of alpine vegetation in the context of global warming [8]. This study also found a reduced number of accumulated growing degree days before the growing season at high altitudes, which was consistent with the growth efficiency hypothesis suggesting that less heat is required for the green-up date in colder habitats. Apart from phenological properties, studies have also demonstrated that vegetation structure and some physiological traits change along with altitude [9; 10]. Alpine plants were found to adjust their individual plant biomass allocation in the Tibetan Plateau [11; 12]. According to that research, as altitude increases, plants increase their biomass proportion to below-ground storage organs in order to resist environmental stress. Ground research on variations in 13 traits of grassland and forest in the European Alps also demonstrated variations of plants along the elevation gradient, showing that stress factors such as cold and a short growing season can impact the growth and reproduction of alpine plants and constrain them to a limited number of strategies [13]. Based on published data on 210 species at 25 sites, a re-analysis study successfully modeled increasing photosynthetic capacity and decreasing primary production along the Amazon-Andes, and managed to test the emerging theory that photosynthetic traits and primary production depend on optimal acclimation and adaptation to the environment [14]. These results suggest that plants' adaptation to their unique local circumstances can play an important role in the formation of altitudinal trait differences. Variations in phenotypes across altitudes generally reflects the long-term effects of harsh environmental conditions and short growing seasons on vegetation in higher regions [15].