The effect of drought and enhanced UV-B radiation on the growth and physiological traits of two contrasting poplar species

Cuttings of Populus kangdingensis and P. cathayana originating from high and low altitudes in south-west China, respectively, were used to determine the effect of drought and enhanced UV-B radiation and their combination on plant growth and physiological traits in a greenhouse during one growing season. In both species, cuttings grown under drought conditions exhibited reduced growth and more abscisic acid (ABA) accumulation than did plants kept under well-watered conditions. Enhanced UV-B radiation significantly reduced plant growth and influenced ascorbate peroxidase (APX) activity, proline concentration, the amount of UV-B absorbing compounds and carbon isotope composition (δ13C) in both species, while it hardly affected ABA accumulation. However, partial differences in responses to each stress were observed between the two species. In P. cathayana, the additive effect of both stresses on plant height and leaf area was observed, and drought significantly increased the free proline concentration. In contrast, distinctly higher APX activity, and ABA and δ13C levels were observed in P. kangdingensis when compared to P. cathayana. Moreover, an increase in the amount of UV-B absorbing compounds was detected in P. kangdingensis both after the treatment with UV-B alone as well as after its application to drought-stressed plants. In P. cathayana, superoxide dismutase (SOD) activity showed a significant increase under enhanced UV-B, while a pronounced increase in the amount of UV-B absorbing compounds was observed only under the combination of the two stresses. Our results suggest that P. kangdingensis, originating from high altitude and being apparently adapted to drought and high levels of UV-B, exhibits greater tolerance to drought and enhanced UV-B radiation than does P. cathayana originating from lower altitude.