The Response Of Seedlings Of Larix Principis-rupprechtii And Pinus Tabuliformis To Drought Stress And Evaluation Of Drought Resistance

With the global climatic change increasingly,drought has become one of the main limiting factors of vegetation growth and recovery.Larix principis-rupprechtii and Pinus tabuliformis are the dominant tree species in North China,have played important roles in the vegetation restoration,soil and water conservation,and improve the ecological environment.In order to reveal drought stress coping strategies and evaluate drought-resistant abilities of Larix principis-rupprechtii and Pinus tabuliformis,we conducted field water control trails,to study morphology,growth and photosynthetic physiological changes of 2-year-seedling of Larix principis-rupprechtii and Pinus tabuliformis affected by drought stress.The results are expected to provide some basic information for forest tree breeding,plantation built and vegetation reconstruction in this area.The results were as follows:1.The morphological index of two tree seedlings changed significantly under the drought stress.With the drought stress continuing,two tree seedlings' needle length,height and basal diameter showed a trend of decline,but the change of Larix principis-rupprechtii is greater than Pinus tabuliformis.The growth rate of primary root had a different trend that Larix principis-rupprechtii rising and Pinus tabuliformis decline after rising first during the whole drought stress.2.The water conditions of two tree seedlings changed significantly under the drought stress.As the drought stress time continuing,relative water content,stem hydraulic conductivity and root activity tended to decline,while water saturation deficit and leaf water retention a rising tendency,and the Larix principis-rupprechtii is greater than Pinus tabuliformis.3.The two tree seedlings' photosynthetic physiological indexes changed significantly under the drought stress.The contents of Chlorophyll a,chlorophyll b and chlorophyll(a+b)showed a trend of increase after falling and the value of chlorophyll(a/b)decreases of Larix principis-rupprechtii during whole drought stress.Pinus tabuliformis' content of chlorophyll a,chlorophyll b and chlorophyll(a+b)was continually slow down,and the value of the chlorophyll(a/b)is on a small scale fluctuations during whole drought stress.Meanwhile,with drought stress lasting,net photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO2 concentration(Ci)and transpiration rate(Tr)present the changing trend of falling after rising first,but the change amplitude and rate are obviously different,particularly on the transpiration rate.4.The two tree seedlings' Non-structural carbohydrates contents changed significantly under the drought stress.The change trend of soluble sugar(SS),starch(S)and soluble sugar and starch ratio is roughly same,but the total structural carbohydrate(NSC)showed a different rule.The Larix principis-rupprechtii expression was "down-up-down",Pinus tabuliformis performance for "the rise and fall".In addition,the change rule of organs' non-structural carbohydrates of The 2 trees was different.The rule of Larix principis-rupprechtii was:leaf>root>stem,and the change of different organs in Pinus tabuliformis was roughly the same.5.It is concluded that the drought resistance of Larix principis-rupprechtii were weaker than Pinus tabuliformis comprehensive evaluated by fuzzy function method.