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Physiological responses to drought and enhanced UV-B radiation in two contrasting Picea asperata populations

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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 CO2 assimilation 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 CO2 assimilation 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.

Nous avons étudié les réactions de deux populations distinctes de Picea asperata Mast. à une augmentation du rayonnement ultraviolet B (UV-B) dans des conditions d’irrigation adéquate ou de sécheresse dans le but de déterminer les effets du rayonnement UV-B sur la tolérance à la sécheresse. Deux populations distinctes, provenant de régions humide et aride de la Chine, ont été utilisées dans notre étude. Pour les deux populations, la sécheresse diminuait significativement le taux d’assimilation en CO2, la conductance stomatique et le rendement quantique effectif du photosystème II alors qu’elle augmentait significativement la saturation non photochimique et l’activité de la superoxyde dismutase. Comparativement à la population provenant d’un climat humide, la population provenant d’un climat aride était mieux acclimatée au stress hydrique et montrait une activité supérieure de la superoxyde dismutase et de l’ascorbate peroxidase ainsi que des niveaux beaucoup plus faibles de malonaldehyde et de perte d’électrolytes. Par ailleurs, l’enrichissement en rayonnement UV-B a aussi induit une baisse significative du contenu en chlorophylle des deux populations dans des conditions d’irrigation adéquate et une hausse significative des composés qui absorbent les UV chez la population provenant d’un climat humide. Après une saison de croissance d’exposition à différentes intensités d’UVB et différents régimes hydriques, les augmentations de malonaldehyde et de perte d’électrolytes, qui sont des indicateurs de dommages à la membrane cellulaire induits par la sécheresse, étaient moins prononcées lorsque les UV-B étaient combinés à la sécheresse. De plus, un effet additif de la sécheresse et des UV-B sur le taux d’assimilation en CO2 et la conductance stomatique a été observé dans la population provenant du climat humide et sur l’activité de l’ascorbate peroxidase et de saturation non photochimique dans la population provenant du climat aride. Ces résultats indiquent que l’exposition aux UV-B peut réduire certains dommages induits par la sécheresse.

Document Type: Research Article

Publication date: July 1, 2007

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