Adaptability to elevated temperature and nitrogen addition is greater in a high-elevation population than in a low-elevation population of Hippophae rhamnoides

Hippophae rhamnoides L. is a broadleaf deciduous woody shrub occurring in southwest China, where it has been widely used in ecological restoration. In this study we investigated growth and physiological responses of 2-year-old healthy seedlings to elevated temperature, nitrogen (N) addition and their combination in two contrasting populations from high and low elevations. In closed-top chamber experiments, two populations were subjected to two temperature conditions (ambient temperature and temperature elevated by 2.2 ± 0.2°C) and two N levels (0 and 25 g N m−2 a−1). Compared with the control, increases in total leaf area (TLA), total chlorophyll content (TC), light-saturated photosynthetic rate (Pmax), guaiacol peroxidase activity (POD), catalase activity (CAT) and carbon isotope composition (δ13C) were greater in the high-elevation population than in the low-elevation population under elevated temperature. On the other hand, decreases in root and shoot biomass ratio (RS), TC, Pmax, light saturation point (LSP), light compensation point (LCP), superoxide dismutase (SOD), POD, CAT and δ13C were lower in the high-elevation population than in the low-elevation population under N addition. Moreover, the combination of elevated temperature and N addition decreased RS, Pmax, apparent quantum efficiency (Φ), SOD, POD and δ13C significantly more in the low-elevation population than in the high-elevation population. These results demonstrated that there are different adaptive strategies among H. rhamnoides populations, the high-elevation population exhibiting higher adaptability to elevated temperature and N addition than the low-elevation population.