Study On Drought Resistance Of Six Shrub Tree Species In Drought Area Of Lanzhou City

In the Lanzhou City—a city with shortage of water resources, the bush as the main tree species should be utilized to the rehabilitation and reconstruction in arid areas. In order to ensure the ecological restoration of vegetation effect, we must consider and study the resistance characteristics of the trees. Six shrub species: Caragana licentiana, Caragana roborovskyi, Ceratoides latens, Caryopteris mongolica Bunge, Zygophyllum xanthoxylum and Reaumuria soongorica were selected as experimental materials, in natural and man-made simulated drought conditions, the biological indicators were investigated among the six kinds of shrubs, and their growth and adaptability of drought-resistant physiology and ecology were compared.In addition, their cell membrane and chlorophyll thermal stability were studied with leaves of the six kinds of shrubs under different temperatures. Use of charts, correlation analysis, the method of subordinate function ,the method of level scoring of fuzzy mathematical theory and other statistical methods, the six kinds of shrubs'drought-resistant capacity were evaluated, and meanwhile seasonal changes of drought-resistant indicators evaluated by fuzzy comprehensive. Seasonal variations of drought-resistant capacity was discussed, with a view to the region's vegetation recovery and reconstruction process and provide a theoretical basis. Main results are as follows:1. The seasonal changes of leaves traits in summer and autumn were studied. Results showed that adaptive changes of leaves characters in season turnover reflected the differences of growth status and adaption mechanisms. Utilizing fuzzy math functions to calculate various indicators under the natural and man-made simulation drought conditions, the average attached value were used to determine strength or weakness of different species under the responding drought stress. The results showed that: under the natural conditions, the drought resistance of Reaumuria soongorica was the strongest, Zygophyllum xanthoxylum was second, followed by Caragana licentiana, Ceratoides latens and Caryopteris mongolica Bunge; Caragana roborovskyi was the weakest; while under the artificial simulation conditions, Zygophyllum xanthoxylum was the best, Caryopteris mongolica Bunge was second, followed by Reaumuria soongorica, Ceratoides latens, Caragana licentiana; Caragana roborovskyi was the weakest.2. According to the order of drought resistance under the two stress conditions.Using fuzzy math class the order was scored , the comprehensive score results showed that: drought-resistant of Zygophyllum xanthoxylum was the most capable, followed by Reaumuria soongorica, Caryopteris mongolica Bung, Caragana licentiana and Ceratoides latens tied for fourth, Caragana roborovskyi was the final, the drought-resistant was the worst.3. The seasonal changes of indicators under the function of natural and man-made simulated drought conditions was comprehensively evaluated with fuzzy math. Results showed that: the indicators there are differences in summer and autumn seasons, autumn shrubs overall capacity than the summer drought has weakened .4. With the same time on 45℃water bath, the harmness was calculated by the relative conductivity of leaves to judge the degree of thermal stability, and by comparing the cell membrane permeability changes, the cell membrane sensitivity to the high-temperature environment was evaluated. Results showed that: the cell membrane of Reaumuria soongorica, Ceratoides latens were the most sensitive to the heat stress, Caragana roborovskyi, Zygophyllum xanthoxylum were followed, Caryopteris mongolica Bung, Caragana licentiana were the least sensitive.performance of membrane from the high to low followed: Caragana licentiana, Caryopteris mongolica Bunge, Ceratoides latens, Caragana roborovskyi, Reaumuria soongorica, Zygophyllum xanthoxylum.5. With the same time on 56℃water bath, calculation of chlorophyll stability index accoring to leaves chlorophyll content determines the stability of different species, the results showed that: trends and changes of each component of chlorophyll are different, the order of chlorophyll thermal stability from high to low was as follow: Caragana licentiana, Caragana roborovskyi, Caryopteris mongolica Bung, Reaumuria soongorica, Ceratoides latens.6. Through in the arid areas of Lanzhou City the comprehensive analysis and evaluation of the six kinds of shrubs growth and physical resistance,it was suggested that in autumn--- the weaker growth period, it is better take effective protective measures to prevent the high temperature and drought.