Study On Characteristics Of Drought Tolerance During The Time Of Vegetation Resteration In Barren Land Of Xuyu

Two-year-old seedling of five tree species were potted and studied to test their characteristics of drought tolerance. The tree species include the followings:Pistacia chinensis Bunge,Dalbergia hupeana Hance,Celtis sinesis Pers.Quercus acutissima Carruth and Pinus elliotii.A drought simulating test was conducted and the specific method was.adapted from Hsiao(1973),in which four levels of gradient of water contents were set up such as:he check(ck)75%(percentage of Maximum water hold capacity of the soil); the slight stress(A)60%; moderate stress(B)45%and the severe stress(C)30%.Various morphological, physiological and chemical traits of all species were measured and tested. The total of four sets of data was taken with an interval of 10 days.The test results showed as followings:1.Under drought condition, the reduction of stomata conductance was not the only factor, which decreases the photosynthesis rate of seedlings. At the same time as the enhancing of drought intensity, the reduction of stomata5 conductance increases the stomata resistance, which resulted in casement of water loss from seedlings. This is favorite for seedlings to keep a good internal balance of water condition. Stomata inhibition delays the stress development and abates the stress intensity for photosynthesis organs on the one hand. And it also initiated the no-stomata inhibition caused by free radicals.2.As long as the increasing of stress intensity and lengthening of stress durations, the contents of Chla appeared an obvious declining trend with different degrees for all tree species. Considering the dynamic trends of Chlb and Chla, reduction of Chla contents also affects the changes of Chlb to certain degree.Under stress condition contents of carotenoid of all tree species apeared a declining trend with different degree for each species, among those the decline amounts of carotenoid of Pistacia chinensis is the least.This indicated that the more stable condition of carotenoid of Pistacia chinensis probably provide a function in drought to tolerance.3.The contents of proline, soluble sugar and soluble protein, which are related to osmotic adjustment ability, appeared different changes trend in different species. In the early stage, contents of those substances of more tolerant species appeared increasing trends; and those of most species appeared obvious declining trends at the late stage under light and moderate stress treatment. As the enhancing of stress intensity and the enhancing of stress duration the contents of proline showed significant increasing trends, this finding was coincidental with the results of some former researches that mean this index might be of great potential value in evaluating drought tolerant ability of tree species.4. Under drought stress condition, the activities of SOD of more tolerant tree species appeared an obvious enhancing trend at the early stage of stress treatment. Based on the changing interval, the more intensive of stress treatment, the more enhancing range will be. However as enlonging of treatment duration, those of less tolerant species firstly appeared a declining trend. 5.Basing on comprehensive analysis of survive rate and external performance of seedlings, the method of vague mathematical jurisdiction analysis was adopted and the relative drought tolerant ability of the 4 tree species was Pinus elliotii>Pistacia chinensis Bunge>Quercus acutissima Carruth>Dalbergia hupeana Hance>Celtis sinesis Pers.