Abstract: Leaf functional traits have been widely used to characterize plant responses and adaptations to environmental changes. Rhododendron spp. are important horticultural and ecologically valuable species, the heat sensitivity of which limits their survival in low-altitude areas. However, few studies have examined the response of Rhododendron to climate warming based on functional traits. In this study, we compared the differences in leaf morphology \[leaf mass (LM), leaf area (LA), leaf thickness (LT), specific leaf area (SLA)\], leaf dry matter content (LDMC), nutrients \[leaf nitrogen (N), phosphorus (P), nitrogen-phosphorus ratio (N/P)\] and net photosynthetic rate (P_n) of saplings of six Rhododendron species at two altitudes in Dujiangyan area of Sichuan Province. The results showed that: (1) There were significant differences in leaf morphology (except SLA), nutrient concentrations (except leaf P), and P_n among the six Rhododendron species at high altitude (1800 m), but no significant difference in LMDC and P_n between species after transplantation at low altitude (550 m). (2) In general, low-altitude transplantation significantly increased SLA, P_n, N and P, and decreased LM, LA, LT and LDMC. The response magnitudes of these traits were different among different species. (3) For the trait correlations, P_n was significantly positively correlated with SLA, N content and N/P in high-altitude habitats, but not significantly after low-altitude transplantation. These results implied inconsistent sensitivity of different Rhododendron species to temperature increases. Our results can provide a scientific basis for understanding the responses and adaptation of Rhododendron species in the context of global warming.

Key words: climate warming, leaf functional trait, elevation, specific leaf area