Effects of water stress on physiological and biochemical characteristics of Populus×euramericana cv.‘Neva' seedlings

I- 107 Populus euramericana seedlings growing in pots were subjected to four different water treatments( normal irrigation,light drought,moderate drought and severe drought) in this experiment. The contents of tissue water,osmotic regulation substances,MDA and activities of antioxidant enzymes in leaves of poplar were tested. The results showed that with the increasing extent and duration of water stress,the leaf relative water content and free water content of I- 107 Populus euramericana seedlings decreased significantly. The bound water content and the ratio of bound water to free water in leaves rose gradually under light water stress,but had a trend of increasing firstly and decreasing then under moderate and severe water stress. With regard to praline content,it had no significant difference with the control under light stress,while was significantly higher than the control under either moderate or severe stress. The leaf soluble protein content increased consistently under light stress,however,had a trend of first up then down under both moderate and severe stress. The activities of superoxide dismutase( SOD) and catalase( CAT) decreased after an initial increase and the malondialdehyde( MDA) content had a significant increase. As a result,the I-107 Populus euramericana seedlings had relatively stronger mechanisms of antioxidant defense and osmotic regulation under light water stress,but decreased significantly under both moderate and severe water stress.