Differential impacts of asymmetric winter warming and symmetric year-round warming on leaf nutrient and resorption in an alpine meadow

Nutrient resorption before leaf senescence is an important nutrient conservation mechanism for plants, which can maximize plant fitness, and thus ecosystem functions and stability, especially when the ecosystems were subjected to warming. Yet, temperature increased non-uniformly among seasons, with stronger increase in winter than other seasons, particularly in high latitudes such as the Tibetan Plateau. However, our knowledge of the responses of nutrient resorption to asymmetric seasonal warming remains unknown. Here, we investigated the effects of long-term (10-yr) symmetric year-round warming and asymmetric winter warming on nitrogen (N) and phosphorus (P) resorption of four plant functional groups (13 common species from grasses, forbs, legumes and sedges) in a Tibetan alpine meadow. Across functional groups, year-round warming decreased green and senesced leaf N and P concentrations, and N resorption efficiency (NRE), while winter warming increased senesced leaf P concentration and decreased P resorption efficiency (PRE). Such responses dependent on functional groups, with grasses remained stable, and legumes were the most responsive. Senesced leaf N and P concentrations of legumes (e.g., Melilotoides archiducis-nicolai) reduced under year-round warming, and senesced leaf P concentration of forbs (e.g., Saussurea pulchra and Aster diplostephioides) increased under winter warming, suggesting that, due to plant-soil feedbacks, legumes would gain competitive superiority in N- and P-acquisition over other functional groups under year-round warming, and forbs would be disadvantaged in P-acquisition under winter warming. Green leaf P and NRE decreased more under year-round warming, and PRE decreased more under winter warming, which implied that year-round warming potentially elicits relative P-limitation and winter warming elicits relative N-limitation.Overall, our findings underlie that the differential responses to asymmetric winter warming and symmetric year-round warming should be considered when predicting the response of alpine plants to climate warming, which will provide new insights into the community composition and plant-soil feedbacks under climate warming.