Differences in growth and physiological traits of two poplars originating from different altitudes as affected by UV-B radiation and nutrient availability.

Cuttings of Populus kangdingensis and Populus cathayana originating from altitudes of 3500 and 1500 m in southwestern China, respectively, were grown for one growing season in the field under ambient or ambient plus supplemental ultraviolet-B (UV-B) radiation with two levels of nutrients. In both species, enhanced UV-B radiation significantly increased UV-B absorbing compounds and guaiacol peroxidase (GPX) activity, while no significant effects were observed in photosynthetic pigments and proline content. On the other hand, cuttings grown with high-nutrient availability had larger leaf area, higher total biomass and GPX activity as well as higher water use efficiency (WUE) (as measured by stable carbon isotope composition, delta(13)C) when compared with low-nutrient conditions, while UV-B absorbing compounds and ascorbic acid (AsA) content significantly decreased. Differences in responses to enhanced UV-B radiation and nutrient availability were observed between the two species. Nutrient-induced increases in chlorophyll a, chlorophyll b and total chlorophyll as well as in carotenoids were greater in P. kangdingensis than in P. cathayana. In P. cathayana, enhanced UV-B radiation significantly decreased leaf area and total biomass, while it significantly increased WUE and ascorbate peroxidase (APX). In contrast, such changes were not observed in P. kangdingensis. In addition, the effects of enhanced UV-B radiation on leaf area, total biomass and UV-B absorbing compounds were closely related to the nutrient status. Our results indicated that P. kangdingensis, which originates from the altitude of 3500 m and is apparently adapted to low-nutrient and high-UV-B habitats, exhibits better tolerance to enhanced UV-B radiation and greater growth under low-nutrient availability than does P. cathayana originating from the altitude of 1500 m.