Growth And Photosynthetic Physiological Characteristics Response Of Chionanthus Retusus Seedlings To Water And Salt Stress

Chionanthus retusus belongs to Chionanthus in Oleaceae family.It is a deciduous shrub or tree.It has a combination of economic,ornamental and medicinal values,and is a national rare native tree species.The characteristics of drought,flood and salt tolerance of Chionanthus retusus were studied to reveal the water and salt tolerance of Chionanthus retusus.Stress experiments were conducted with potted seedlings.It even provides reference for the application of Chionanthus retusus species resources in barren hill afforestation,bottomland and mild saline land restoration.In this experiment,the cuttings of three-year-old Chionanthus retusus were used as materials,and the water and salt stress tests were carried out with potted seedlings in greenhouse The growth morphological changes,gas exchange parameters,chlorophyll fluorescence characteristic parameters and physiological and biochemical indexes of Chionanthus retusus under stress were determined and the thresholds of drought,waterlogging and salt tolerance were calculated.The main results are as follows:1.Effects of water stress on Chionanthus retusus（1）In the continuous drought stress experiment,the drought lasted for 6d and caused the leaf drying and falling off,as well as the decline of photosynthetic and physiological and biochemical indexes.At 14d,a few groups in the test group experienced large-scale defoliation,and 23d,almost all the leaves of the experiment seedlings fell dead.The fitting curve of photosynthetic response showed that with the decrease of soil relative water content,P_nmaxand LSP were significantly decreased,while R_dwas significantly increased,until Relative water content of soil was reduced to 22.46%,and then decreased significantly.Through simulation calculation,the threshold value of soil relative water content that Chionanthus retusus could tolerate is RWC>34.63%.（2）In the gradient water stress experiment,with the increase of stress degree,the growth index（damage index）,C_i,F_oand MDA content were significantly increased,however,P_n,G_s,T_r,F_v’/F_m’,F_v/F_m,Φ_PSⅡ,q ^P,ETR,antioxidant enzymes such as SOD and POD and the content of proline Pro were gradually decline,which were significant differences.Among them,it was more suitable to grow under SD（RWC 55-60%）and WF（Waterlogging treatment）conditions and showed good adaptability.However,which showed intolerance under HD（RWC 30-35%）could still last for about 21d.The thresholds of drought tolerance was RWC 44.6%,and the thresholds of waterlogging tolerance was 20 d.2.The effect of salt stress on Chionanthus retusus（1）With the increase of NaCl concentration,the growth index（damage index）,C_i,F_oand MDA content were significantly increased,however,P_n,G_s,T_r,F_v’/F_m’,F_v/F_m,Φ_PSⅡ,q ^P,ETR,antioxidant enzymes such as SOD and POD and the content of proline content Pro were gradually decline,which were significant differences.Normal growth can be sustained for a period of time when the soil salt content is 0.4%.When NaCl≤0.4%,it was mainly restricted by stomatal factors,and the variation range of each index was small.When NaCl≥0.8%,it was mainly affected by non-stomatal limiting factors,and the variation range of each index increased significantly,indicating that the fringe tree may be seriously or even irreversible effects.Taking the Net Photosynthetic Rate（P_n）as the index,the threshold value of salt tolerance was determined to be 0.48%,which indicated that it had a strong salt tolerance.Therefore,it could be used as an excellent species for cultivation in saline soil area.