| Seasonal drought of Karst region is one of the important limit factors of vegetation restoration of degraded land in rocky desertification. Using simulated Karst typical habitat and trying experiments under different water stress conditions, which was studied the physioecological characteristics of four kinds of typical tree species in Karst region, and discussed the drought adaptation mechanism of the typical tree species, experiment1is that the annual seedlings of Karst typical restoration tree species Delavaya toxocarpa, Cyclobalanopsis glauca and Acer cinnamomifolium were used as experimental materials. We simulated Karst "double layer" geological characteristics, applied the water supply layered simulation column of soil layer-rock layer-karst water layer, and conducted three water gradient treatments with80%,60%and40%field water capacity. The growth and physiological indexes of drought resistance were measured after15,30and45days treated with different water gradients. Experiment2is that the annual seedlings of Karst typical restoration tree species Alchornea trewioides was used as experimental material. Plants were potted in large and small flowerpot used Karst Brown lime soil(large volume is4.30m3and small volume is0.84m3). We conducted three water gradient treatments with80%,60%and40%field water capacity. The growth and physiological indexes and physicochemical properties of rhizosphere soil of drought resistance were measured after45days treated with different water gradients. The different water gradient treatment period of the two experiments were synchronised with the drought season in Guangxi Karst area. These experiments were conducted to study the effects of Karst habitat simulation on typical restoration species in growth physiology and explore their drought adaptation mechanism.The main results are as follows.1. The order of drought resistance of three Karst typical restoration tree species is Cyclobalanopsis glauca> Acer cinnamomifolium> Delavaya toxocarpa. Cyclobalanopsis glauca is suitable for growing in Karst habitat.At45days after treated with three different field capacities, with the increase of drought stress, the plant height increments, ground diameter increments, the relative growth rate of plant height and relative growth rate of ground diameter of Karst typical restoration tree species Delavaya toxocarpa, Cyclobalanopsis glauca and Acer cinnamomifolium were showed a decreasing tendency. The orders of relative growth rate of plant height and relative growth rate of ground diameter of three kinds of plants at the same field capacity were Cyclobalanopsis glauca> Acer cinnamomifolium> Delavaya toxocarpa. Leaf relative water content and malondialdehyde content of Cyclobalanopsis glauca were lower than these of Acer cinnamomifolium or Delavaya toxocarpa. And the chlorophyll content, soluble protein content and soluble sugar content of Cyclobalanopsis glauca are higher than these of Acer cinnamomifolium or Delavaya toxocarpa.2. Three kinds of plants had stronger water retaining capacity in Karst habitat, and plant secondary damage caused with membrane lipid peroxidation products was increased under different water stress. Protein metabolism and sugar metabolism in plants were changed. The osmotic adjustment substances soluble protein and soluble sugar were accumulated in plants, photosynthesis were decreased to adapt Karst habitat, so as to improve the drought resistance of plants.At15,30and45days after the same field water capacity treatment, with the increase of drought stress, leaf relative water content and chlorophyll content of three kinds of Karst typical restoration tree species were showed a decreasing tendency, the malondialdehyde content, soluble sugar content and soluble protein content in leaves were showed an increasing tendency.Under different field water capacity, with the extension of treatment time, the leaf relative water content of three kinds of Karst typical restoration tree species were showed a decreasing tendency, the malondialdehyde content, soluble sugar content were decreased, but the decline degree is not great. The chlorophyll content were decreased. The malondialdehyde content, soluble sugar content and soluble protein content in leaves were increased.3. Alchornea trewioides in severe drought were affected physicochemical characteristics of the rhizosphere soil to improve drought resistance throght plant metabolism and growth characteristics change.At45days after treated with different field capacity, with the increase of drought stress, Alchornea trewioides rhizosphere soil pH value, available phosphorus, available potassium and organic matter content showed an increasing tendency under large pot or small pot, while the total nitrogen content showed an decreasing tendency. The average plant height increment and relative growth rate of large or small potted Alchornea trewioides plants showed a significant decreasing tendency. The root to top ratio showed increasing tendency. At45days after treated with40%field capacity, the rhizosphere soil pH value, available phosphorus content, available potassium content and total nitrogen content in large pot were lower than those in small pot, and organic matter content in large pot was higher than that in small pot, the average plant height increment, relative growth rate and root to top ratio of large potted plants were higher than those of small potted plants. We considered that large potted Alchornea trewioides plants compared with small potted plants were beneficial for drought tolerance in plants.This research was explored the effect of water stress on physioecological characteristics of four kinds of typical Karst restoration tree species used simulation of typical Karst habitats. The research results will provide the scientific basis to improve the ecological environment in Southwest China Karst region, to develop vegetation restoration of degraded land in Karst rocky desertification, and to select and breed Karst typical recovery plants. |
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