Drought Tolerance Mechanisms And Evaluation Of Zelkova Schnideriana,Quercus Virginiana And Ligustrum Lucidum

Based on the experiment of water stress in pots, two-year-old seedlings of three tree specieswhich were Zelkova schnideriana, Quercus virginiana and Ligustrum lucidum were subjected.Sixteen indicators which were drought damage symptoms, seedling height, ground diameter,chlorophyll a content, chlorophyll b content, total chlorophyll content, the ratio of chlorophyll aand b, net photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency,relative water content, relative conductivity, malondialdehyde content, peroxidase content,superoxide dismutase content and soluble sugar content were observed and measured. Theprincipal component analysis method and subordinate function method were used to evaluate thedrought resistance of each species.The results showed that:1. When stress level and stress time increased, the Stress symptoms of each tree speciebecame more serious. Three tree species declined with the increase of the degree ofdrought, under moderate and severe stress, the seedling height net growth and ground diameternet growth of Zelkova schnideriana and Ligustrum lucidum dropped significantly whencompared with contral trees. It showed that both the seedling height and ground diameter wererestrained under drought stress, comparing with contral trees of Quercus virginiana, only severestress dropped significantly.2. The chlorophyll a content，chlorophyll b content and the ratio of chlorophyll a and bshowed a downward trend after rising first over time under each processing of Three tree species,and total chlorophyll content always decreased with the loss of the soil moisture, compared withthe control treatment of Quercus virginiana and Ligustrum lucidum, mild stress of totalchlorophyll content fell23.37%and16.42%, meanwhile moderate and severe stress wererelatively stable, but under severe drought stress treatment, total chlorophyll content of Zelkovaschnideriana fell dramatically. The average total chlorophyll content of Quercus virginiana andLigustrum lucidum were higher than Zelkova schnideriana, the drought treatment reduced thephotosynthetic capacity of leaves.3. With the stress increased, the daily averages of net photosynthetic rate, transpiration rate,stomatal conductance and water use efficiency of the three tree species were reduced, the dailydata of water use efficiency of Zelkova schnideriana ranged from2.937~3.58μmol mmol-1,Ligustrum lucidum ranged from3.396~4.227μmol mmol-1, Quercus virginiana ranged from4.09~4.593μmol mmol-1. In the same soil water grade, the daily averages of the four indexes ofZelkova schnideriana were relatively small, followed by Ligustrum lucidum, whereas those ofQuercus virginiana were the largest.4. The relative water content of three tree species in different soil moisture conditionsdecreased along with time passed and stress level strengthened, indicating the content of free water and bound water. Under drought stress, relative electric conductivity of the trees showed arising trend, and it reached the maximum late at the last time which rose to89.16%,89.16%and58.26%Under severe stress respectively, comparing with the original data,it reached to148%,132%and141%respectively.5. With the extension of stress time, the malondialdehyde rised continuously, differentprocessing level three tree species have reached the maximum late at the last time. With theincrease of drought stress, the peroxidase increaed, superoxide dismutase content showed a trendof gradually declined, it was one of reactions three tree species adaptting to drought stress. Dueto an acute shortage of water in plant probably, and the enzyme activity was affected. As a kindof effective osmotic regulator, the soluble sugar content was on the rise with degree of stress, theplants was hurt under drought stress.6. Through a comprehensive evaluation of sixteen physiological and biochemical indexes inexperiments, using principal component analysis and the membership function method, the thesiscalculated the order of the three tree species of drought tolerance should be: Zelkovaschnideriana>Quercus virginiana>Ligustrum lucidum.