Effects of stimulated warming on nutrient allocation between vegetative and reproductive growth in Carex and Potentilla in an alpine Gongga grassland

In this study, alpine grasslands at altitudes of 4 130 and 3 850 m in Yajiageng Canyon located on the eastern slope of Gongga Mountain in the Hengduan Mountains, were selected as research sites. Two warming methods -open-top chamber (OTC) warming and turf-down (downward-move) warming- were used to simulate climate warming. The effects of five-years warming on the morphological, physiological, chemical, and phenological traits of Carex and Potentilla species at different altitudes were analyzed. In addition, the correlation between aboveground biomass and various functional traits was examined to clarify the adaptive characteristics of nutrient utilization strategies in terms of reproduction and vegetative growth. The results showed that: (1) OTC warming significantly increased the aboveground biomass, height, and coverage of Carex at the 4 130 m site, while downward move warming significantly increased the aboveground biomass and height at the 3 850 m site. For Potentilla, only downward-move warming significantly increased the aboveground biomass and height at the 4 130 m site ( P < 0.05 ). (2) OTC warming significantly reduced nitrogen and phosphorus content while increasing the C/N ratio in Carex at both altitudes. Downward-move warming significantly increased the δ¹³C abundance of Carex at 3 850 m. OTC warming significantly decreased the specific leaf area and nitrogen content of Potentilla at the 3 850 m site, while downward-move warming reduced the C/P ratio and δ¹³C abundance of Potentilla at the 4 130 m site (P < 0.05). (3) Both OTC and downward-move warming advanced the budding and flowering phases of Carex at both sites; however, the duration of the reproductive growth period varied. (4) Carex tends to invest more resources in the vegetative growth phase under moderate warming, resulting in increased aboveground biomass. Under more intense warming, Carex allocates more resources to reproductive growth, prioritizing survival, which leads to no significant change in aboveground biomass. There were observable differences in nutrient uptake capacities between alpine herbs at 4 130 and 3 850 m under OTC and downward-move warming treatments. To adapt to climate warming, alpine herbs their aboveground biomass by modifying the duration of reproductive growth and balancing nutrient investment between reproductive and vegetative stages.