Growth and physiological responses to drought and elevated ultraviolet-B in two contrasting populations of Hippophae rhamnoides

In the southeast of the Qinghai-Tibetan Plateau of China, sea buckthorn ( Hippophae rhamnoides L.), which is a thorny nitrogen-fixing deciduously perennial shrub, has been widely used in forest restoration as the pioneer species. In our study, two contrasting populations from the low and high altitudinal regions were employed to investigate the effects of drought, ultraviolet-B (UV-B) and their combination on sea buckthorn. The experimental design included two watering regimes (well watered and drought stressed) and two levels of UV-B (with and without UV-B supplementation). Drought significantly decreased total biomass, total leaf area and specific leaf area (SLA), and increased root/shoot ratio, fine root/coarse root ratio and abscisic acid content (ABA) in both populations. However, the high altitudinal population was more responsive to drought than the low altitudinal population. On the other hand, elevated UV-B induced increase in anthocyanins in both populations, whereas the accumulation of UV-absorbing compounds occurred only in the low altitudinal population. The drought-induced enhancement of ABA in the high altitudinal population was significantly suppressed in the combination of drought and elevated UV-B. Moreover, significant drought × UV-B interaction was detected on total biomass in both populations, total leaf area and fine root/coarse root in the low altitudinal population, and SLA in the high altitudinal population. These results demonstrated that there were different adaptive responses between two contrasting populations, the high altitudinal population exhibited higher tolerance to drought and UV-B than the low altitudinal population.