Study On Response Characteristics Of Six Tree Species To Drought Stress

The potted one-year-old seedlings of six economic tree species were tested to study their characteristics of response to drought stress. Two methods that continuous drought stress and gradient water control method were taken to measure the growth, physiological and biochemical indices of these seedlings, on which basis evaluation indices system of drought resistance was established to provide scientific and theoretic basis for selection of tree species for afforestation in arid mountain areas. The test results are as the followings. The height growth of seedling was inhibited under two water-controlling conditions, and the enhancement of drought stress intensity increased degree of inhibition. The biomass production of seedlings appeared a decreasing trend with the declining of content of soil water. The ratio of root to stem was increasing obviously with the enhancement of drought stress intensity. The stomatal inhibition was the major limiting factor of photosynthesis of Castanea mollissima BL., Juglans regia L. and Armeniaca vulgaris Lam under slight water stress condition and the limiting factor was then changed to be non-stomatal inhibition under the moderate and severe drought stress conditions. The major limiting factor of photosynthesis of Zanthoxylum bungeanum Maxim was stomatal inhibition under water stress. The photosynthesis reduction of Diospyros kaki L.f. and Gleditsia sinensis Lam was caused by stomatal inhibition factors under the slight and moderate drought stress conditions, and then changed into non-stomatal inhibition under severe stress condition. These phenomena show that stomatal inhibition of photosynthesis generally occurred under slight water stress condition. However, as the intensity of drought stress was enhanced, the non-stomatal inhibition of photosynthesis becomed the major factor. The changing trends in the contents of chlorophyll, carotenoids and the ratio of chlorophylla over chlorophyllb appeared similar under these two stress treatment conditions. Drought stress inhibited the composition of chlorophyll of Juglans regia L, and on the contrary, it enhanced the chlorophyll composition of Castanea mollissima BL and other four tree species. Drought stress enhanced the production of carotenoids. Chla was more sensitive to drought than that of chlb. As the intensity of drought stress was enhanced, the contents of proline of all seedlings were increased significantly. More contents of proline in seedlings of Gleditsia sinensis Lam, Zanthoxylum bungeanum Maxim and Armeniaca vulgaris Lam were accumulated under both stress treatment conditions. Under the continuous drought condition, the contents of soluble sugar of all seedlings were obviously increased as the intensity of drought stress was enhanced. Under the gradient water control condition, the contents of soluble sugar were basically higher than that of the check group. Under the same water gradient and as the lengthening of stress time, the increasement of soluble sugar played certain role of osmosis. The contents of soluble protein of Juglans regia L and Gleditsia sinensis Lam appeared a declining trend as the treatment duration was lengthened under continuous drought stress. That of Castanea mollissima BL, Zanthoxylum bungeanum Maxim, Diospyros kaki L.f. and Armeniaca vulgaris Lam appeared an increasing first and then decreasing trends as the treatment duration was lengthened. A similar changing trends of soluble protein contents of all six tree seedlings of the same gradient level were appeared under gradient water control condition, that meaned a decreasing and then increasing trend. The cell membrane conductance, MDA content and generating rate of of the seedlings appeared an increasing trend as the intensity of stress was enhanced under two water-controlling conditions. This meaned that the membrane system of seedlings were all damaged. And this damage probably was closely related with the extra oxidation of membrane grease. The four protective enzymes, SOD, POD, CAT and APX integrated cooperately to eliminate the extra free radical, and hence increaed the seedling adaptibility to drought stress. The generating rate of was increased greatly at the late stage of treatment, and this indicated the productive ability of free radical elminating function was already weakened. It was conferred that the production rate of extra free radical beyond the eliminating capacity of protective system. The adaptability and production capacity of six tree seedlings were compared by subordination function method of vague mathematics and transpiration rate, water-absorbing ability, osmotic adjustment, anti-oxidant system, net photosynthesis rate, water utilization efficiency, biomass production were selected as evaluation index in the drought-resistant assessment of six tree species. The ability of drought resistant of the six tree species were in descending order as following: Zanthoxylum bungeanum...