The Effect Of Water Stress In Soil On Photosynthetic Characteristics Of Populus Szechuanica Var. Tibetica

Environmental deterioration posed great threat on the survival and development of people,especially the drought which was one of the most serious disasters. Populus szechuanica var. tibetica was used as the experiment material in the study .Four kinds of the water stress was simulated with the method of water controlling. The effect of the water stress was studied on the photosynthetic characteristics of Populus szechuanica var. tibetica to provide the main theoretical basis for the selection and management of the trees. It also had the great significance for us to utilize the plant more effectively and enhance the productivity of the forest and protect the environment.The Chia of Populus szechuanica var. tibetica decreased gradually with the increasing of the water stress, but the Chib did not change obviously.The Chia/b increased gradually under the mild or moderate drought, but decreased under the serious drought.With the escalation of water stress in soil, net photosynthetic rate of Populus szechuanica var. gradually decreased, stomatal conductance also showed one kind of trend of gradual decrease. The intercellular carbon dioxide of Populus szechuanica var. decreased under the mild water stress. But with the escalation of water stress, when the water stress was moderate and severe, the concentration of intercellular carbon dioxide showed the trend of increase. The stomatal limitation of Populus szechuanica var. increased under the mild drought stress but decreased under moderate and severe drought stress. With the escalation of water stress in soil, daily average value of leaf transpiration rate of Populus szechuanica var. tibetica decreased. There were great differences of transpiration rate between Populus szechuanica var. under moderate and severe drought stress and Populus szechuanica var. under normal water treatment. The efficiency of water of Populus szechuanica var. under mild drought stress was higher than that under normal treatment. The efficiency of water utilization under moderate and severe water stress was obviously lower than that under normal treatment. It had been showed that appropriate intensity of water stress in soil could elevate the efficiency of water utilization of Populus szechuanica var.Four empirical models of light-response curve of leaf net photosynthesis, such as nonrectangular hyperbolic model, rectangular hyperbolic model, modified rectangular hyperbolic model and index function model, were tested to compare their fitness in this paper and the application of four empirical models in study on photosynthesis light response of Populus szechuanica var. tibetica was discussed. The results showed that the parameters of light-response curve simulated by modified rectangular hyperbolic model were more accurate than other models.The apparent quantum yield (AQY),maximum net photosynthetic rate (Pmax),light saturation point (LSP),dark respiration rate (Rd) declined gradually with the decrease of the water in soil, but the light compensation point (LCP) increased. Certain adaptability of Populus szechuanica var. tibetica appeared to light drought and medium drought setted in the study, but it was out of condition to severe drought. Both of the adaptability to low light environment and high light environment and the ability to use low light and high light of Populus szechuanica var. tibetica reduced under drought stress, but both still remained at a high level, basically able to adapt to arid and semi-arid condition in North China.