Physiological responses to drought and enhanced UV-B radiation in two contrastingPicea asperatapopulations

Abstract

The responses of two Picea asperata Mast. populations to enhanced ultraviolet B (UV-B) radiation under well-watered and drought conditions were investigated to further elucidate the effect of UV-B radiation on drought tolerance. Two P. asperata populations originating from wet- and dry-climate regions in China were employed. Drought significantly decreased the CO2assimilation rate, stomatal conductance, and effective photosystem II quantum yield, while it significantly increased nonphotochemical quenching and the activity of superoxide dismutase in both populations. Compared with the wet-climate population, the dry-climate population was more acclimated to drought stress and showed much higher superoxide dismutase and ascorbate peroxidase activities and much lower levels of malondialdehyde and electrolyte leakage. Enhanced UV-B radiation also induced a significant decrease in chlorophyll content in both populations under well-watered conditions and a significant increase in UV-absorbing compounds in the wet-climate population. After exposure to different UV-B radiation levels and watering regimes over one growing season, the increases in malondialdehyde and electrolyte leakage, which are indicators of damage to the cellular membrane induced by drought, were less pronounced under the combination of enhanced UV-B radiation and drought than they were under well-watered conditions without enhanced UV-B radiation. In addition, an additive effect of drought and UV-B radiation on the CO2assimilation rate and stomatal conductance was observed in the wet-climate population and on the activity of ascorbate peroxidase and nonphotochemical quenching in the dry-climate population. These results suggest that the UV-B exposure may have alleviated some of the damage induced by drought.