Effects Of Drought Stress And Re-watering On Growth And Physiology Of Phoebe Zhennan Seedlings

Pot experiments were conducted with 7 drought treatments (watering to 80% field capacity, then stopping watering, followed by drought stress of 30,25,20,15,10, 5 and 0 day) on two-year-old seedlings of Phoebe zhennan. The change of growth and physiological indicators of Phoebe zhennan in different treatment of drought stress were determined and analyzed. Physiological indicators of Phoebe zhennan after re-watering were determined, and the mechanism of drought resistance of Phoebe zhennan was explored. Some theoretical basis of habitat selection and water management measure for scientific development of Phoebe zhennan seedling and young tree was suggested. The results were showed as follows:1) The diameter and height increment were both inhibited under drought stress. With the intensified drought stress, the diameter increment and the height increment decreased significantly (P<0.05).2) With the intensification of drought stress, soil water content (SWC) decreased significantly (P<0.05). At the early stage of stress, Relative water content of leaves (LRWC) of Phoebe zhennan not significantly decreased, but began to significantly decreased (P<0.05) in the mid stage.3) The total amount of photo synthetic pigment increased first and then decreased under drought stress, that of mild stress, moderate stress and severe stress showed the significant difference. The ratio of chlorophyll a and chlorophyll b (Ch1 a/b) overall decreased under drought stress. The net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of Phoebe zhennan seedlings significantly decreased (P<0.05), intercellular CO2 concentration (Ci) decreased at first and then increased under drought stress. With the increase of drought stress, the apparent quantum yield (AQY), the maximum net photosynthetic rate (Pnmax), light saturation point (LSP) decreased, and light compensation point (LCP) increased. Meanwhile, carboxylation rate of enzyme RuBP (CE), CO2 saturation point (CSP) decreased, and CO2 compensation point (CCP) increased.4) With the increase of drought stress, the concentration of soluble sugar (SS) increased dramatically(P<0.05), that of proline (Pro) overall increased. The concentration of soluble protein (SP) increased at first and then decreased under drought stress.5) With the increase of drought stress, The concentration of O2·- and H2O2 overall increased. The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and the concentration of ascorbic acid (AsA) increased at first and then decreased under drought stress. The concentration of malondialdehyde (MDA) increased significantly (P<0.05).6) After re-watering the seedling for 10 days, the net photosynthetic rate (Pn), stomatal conductance (Gs) and the transpiration rate (Tr) continually increased, the change of intercellular CO2 concentration (Ci) trend tended to be gentle, except for severe stress treatment, there was no significant difference between other treatments. After re-watering the seedling for 10 days, the concentration of soluble sugar (SS), soluble protein (SP), proline (Pro), ascorbic acid (AsA), malondialdehyde (MDA), and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) had no significant difference with DO (CK).