Effects Of Drought Stress On Growth And Physiological Characteristics Of Tabebuia Imprtiginosa Seedlings

The experimental material for this study were the annual Tabebuia impetiginosa seedlings.Using water gradient method to set five water gradients(100%,80%,60%,40%,20%of soil water holding capacity)for this drought stress test.The drought stress test was carried out to investigate the effects of drought stress on the growth and physiological indicator of Tabebuia impetiginosa seedlings.,and summarize the water conditions that are conducive to the growth of Tabebuia impetiginosa seedlings.And analyze its physiological response mechanism under drought stress,it provides a theoretical basis for the cultivation and promotion of Tabebuia impetiginosa in different environments..The main findings are as follows:(1)The height increment,diameter increment,SLA and biomass of Tabebuia impetiginosa seedlings decreased with the increase of water.Compared with 100%and 60%soil field water holding capacity,80%is more conducive to the growth of Tabebuia impetiginosa seedlings,40%and 20%significantly inhibited the growth of seedlings,and its leaf area is reduced,the accumulation of biomass is inhibited.(2)The treatment of 100%and 80%soil water holding capacity maintains a low content of soluble sugar,soluble protein and free proline during the test period.And the treatment of 60%,40%and 20%soil water holding capacity maintains a high content of soluble sugar,soluble protein and free proline during the test period.However,the soluble sugar content decreased in the later stage of the experiment,which may be related to the long-term high water shortage,and the soluble sugar hydrolysis or its synthesis hindered.(3)The treatment of 100%and 80%soil water holding capacity maintains low antioxidase activity during the test period.And the treatment of 60%,40%and 20%soil water holding capacity maintains high antioxidase activity.However,with the prolongation of drought stress,the antioxidase activity of the same water gradient increased first and then decreased.This change in the 40%and 20%soil field water holding capacity is most prominent,which indicates that the dynamic balance of reactive oxygen is destroyed under long-term drought stress.(4)Chlorophyll a,chlorophyll b and carotenoids showed a decreasing trend with the prolongation of stress time and soil water loss,and the photosynthetic pigments of 40%and 20%soil water holding capacity decreased significantly.lt indicates that the photosynthetic pigment is decomposed.The net photosynthetic rate,stomatal conductance and transpiration rate showed a decreasing trend with the deepening of drought stress.The intercellular carbon dioxide concentration increases with the decrease of soil moisture,it reached a minimum in the 60%soil field,and then showed an increasing trend.This indicates that the reason for the decrease in photosynthetic rate of 60%soil water holding capacity is the stomatal factor,and 40%and 20%are non-stomatal factors.The initial fluorescence increases with the degree of stress;Maximum fluorescence,variable fluorescence,light energy conversion efficiency(Fv/Fm)and potential activity(Fv/Fo)gradually decrease after 80%of the soil water holding capacity reaches its maximum value.(5)Through the analysis of seedling quality(QI)and membership function,it is concluded that 80%of soil water holding capacity is most conducive to the growth of Tabebuia impetiginosa seedlings.According to the analysis of membership function,the drought resistance of S.sinense seedlings is moderately resistant.From the plasticity analysis,growth and photosynthetic indicators are more sensitive to drought stress.