Study On Leaf Characteristics,Drought Resistance Physiology And Adaptation Strategies Of Several Of Alpine Malus Plants In Western Sichuan Plateau

In the plateau of western Sichuan,where water resources are scarce and conditions of afforestation are poor,the selection of suitable drought-resistant tree is of great significance for vegetation restoration and ecological construction in the area.In this study,five species of Malus plant（Malus toringoides（Rehd.）Hughes,Malus pumila Mill,Malus transitoria（Batal.）Schneid,Malus baccata（L.）Borkh）and Malus hupehensis（Pamp.）Rehd)were the subjects of the study,25 indicators related to their leaf characteristics and photosynthetic physiology were analyzed and determined,and they were selected by principal component analysis.11 indicators of drought-resistance were comprehensively evaluated by the fuzzy membership function method,and the different response strategies adopted by five plants to adapt to arid environment were summarized.The main conclusions are as follows:（1）In order to adapt to the droughty environment,there are differences in the leaf characteristics of the five species of plants:leaf area,thickness and petiole length are6.566cm²,0.233cm,and 2.674cm,respectively,the leaf area is the smallest;the leaf area and the width of Malus baccata is the smallest,only 77.995 and 2.732cm;the petiole of Malus transitoria is the shortest,only 2.532cm;the Malus pumila is mainly expressed in the leaf thickness is relatively large,reaching 0.257cm;the indicators of Malus hupehensis are not good.（2）In order to adapt to the droughty environment,there were significant differences in water and nutrients in the leaves of five plants:the leaf dry matter content of Malus transitoria was the highest,reaching 0.507;the moisture content of Malus baccata was55.000%,which was the highest in five plant species;The relative water content of Malus hupehensis is the highest,which is 87.300%,and its water saturation loss is 12.712%,which is the smallest among the 5 plants;the water content and leaf nitrogen content of Malus pumila are the largest,reaching 58.076%and 10.180g/kg;All indicators of Malus transitoria performed well.（3）The photosynthetic characteristics of the five species of plants were significantly different:the maximum net photosynthetic rate of Malus toringoides was 14.825 umolm^-2s^-1,and the light saturation point was about 1700 umolm^-2 s^-1;the highest net photosynthetic rate and the highest apparent quantum efficiency of Malus transitoria esculenta were15.294μmol m^-2s^-1 and 0.0420,respectively.The light compensation point of Malus baccata was the highest in the 5 plants,which was 87.851 umolm^-2 s^-1.The water use efficiency of Malus pumila and Malus toringoides is higher.（4）In order to adapt to the droughty environment,there were significant differences in water and nutrients in the leaves of five plants:POD content,soluble protein content,and Pro content of Malus toringoides were 4074.971u/（g*min）,6.724mg/g,and386.801ug/g,respectively,which is the highest among 5 species of Malus,the lowest content of MDA was 2.519umol/g,and the highest initial fluorescence of Malus baccata was186.213u/（g*FW）and 1026.399 which are the highest levels in the 5 plants.The soluble sugar content of Malus hupehensis was 0.832umol/g,which was the highest in the 5plants;the initial fluorescence of Malus pumila under dark adaptation was the highest,reaching 4210.103;and the indicators of Malus transitoria showed good performance.（5）Principal components analysis was performed on 25 indicators of 5 plants.11indicators were selected as indices to evaluate drought resistance of plants.They were:leaf area and leaf thick in leaf phenotypic indicators;Leaf moisture content and nutrient indicators of leaf dry matter content,water content,water saturation loss and leaf thick;leaf photosynthetic physiological indicators of chlorophyll content,soluble protein content,MDA content,Fo and Fm.（6）The membership function values of 11 indicators of 5 plants were calculated and averaged,then the drought resistance of 5 species of Malus plants was ranked according to the average value of the membership functions of each index.The higher the membership function value,the stronger the drought resistance.Therefore,the order of the drought resistance of several plants is as follows:Malus toringoides>Malus baccata>Malus pumila>Malus hupehensis>Malus transitoria.Through comprehensive evaluation,the species of the most drought-resistant tree in 5 species of Malus plants in the western Sichuan Plateau is Malus toringoides.