The Physiological Reaction Of Different Species(Var.) Of Catalpa Bungei Under Drought Stress

Catalpa bungei C.A.Mey ,a representing native Chinese tree, precious quality timber species and a famous garden ornamental tree, has been called "king of wood" since ancient times. The response mechanism of different Catalpa types to drought stress was studied in this paper with two comparative methods, the water controlable pot planting and the PEG penetration stressing. The comprehensive evaluation on drought-resistance of eight Catalpa types was drawn from these studies to provide theoritical bases for the Catalpa bungei forestation in defferent areas. The main results were as follows:certain type of biomass, such as Nanyangqiu and Jinsiqiu, increased under mild and moderate drought stress in plot experiment while the seedling height, ground diameter and biomass readings of the eight types under sever drought stress were all significantly lower than the control groups.Photosynthesis of all the eight types was inhibited in both plot experiment and PEG penetration stressing experiment. The net photosynthetic rate(Pn), stomatal conductance(GS), and water use efficiency decreased with the increase of the intercellular CO₂ concentration(Ci), indicating that the non-stomatal conductance might be the cause of Pn decreasing. Fv/Fm andΦPS II decreased when the drought stress wentl higher. The variation law was obvious in PEG penetration stressing experiment, comparing that the changes of Fv/Fm andΦPS II in plot experiment were different respectively under defferent drought stress levels.The cell membrane permeability, MDA content and SOD activity increased as the drought stress level went higher while the change of relative water content dispalyed the opposite tendency. The praline, soluble protein and soluble sugar also increased when the drought stress level went higher as the osmoregulation substances. But in the end of experiment, some types' SOD activity and osmoregulation substances content decreased under heavy drought stress. The variation laws of these physiological and biochemical indexes were different among different varities(var.).The electrophoresis results indicated that the molecular weight of drought stress proteins were in the range of 14.3-32kD. As was shown under electron microscopy, the metastructures of Jinsiqiu and Qiushu were damaged seriously compared to Nanyangqiu and Yuangjichangguoqiu.By cluster analysis method, the results were concluded that: Zishu and Huiqiu belong to the group with strong drought resistance while Guangyeqiu belong to the weak drought resistance group. Other types drought resistance was moderate. By subject function method, the drought resistance of eight varieties(var.) had the following sequence(from strong to weak):Zishu, Huiqiu, Yuan ji chang guo qiu, Jin si qiu, Qiu shu, Nan yang qiu, Yu qiu-1 and Guangyeqiu.