Effects Of Piriformis Indiana Inoculation On Physiological Characteristics Of Ulmus Pumila Under Different Water Stress

Ulmus pumila L.is one of the main tree species for shelterbelt and timber forest construction and afforestation in sandy wasteland and saline-alkali land in northern China,which has the characteristics of drought resistance,saline-alkali resistance and cold resistance.Water stress affects the growth and development of plants.Artificial inoculation of fungi can effectively alleviate the damage caused by water stress and improve their resistance to stress.In this study,two Ulmus pumila strains（Y9,Y65225）were used as experimental materials,and Piriformospora indica（PI）was inoculated.To explore the effects of inoculation on grafting growth,photosynthesis,chlorophyll fluorescence,chlorophyll content,antioxidant enzyme activity,osmoregulation substances and malondialdehyde content of two Ulmus pumila strains under four kinds of water stress（25%,50%,75%and 100%of field capacity28%）,and to clarify the effect of inoculation of PI on stress resistance of Ulmus pumila strains.It provides theoretical basis and technical reference for further enriching afforestation germplasm materials and supporting technologies and improving the quality of vegetation construction in arid areas.The results are as follows:（1）Inoculation of Pyriformis indiana could alleviate the effect of water stress on leaves and branches of Ulmus pumila.With the deepening of drought stress,the number of green leaves and the growth of lateral branches of Y9 and Y65225 Ulmus pumila decreased continuously,and water loss was reduced by reducing the number and area of leaves of both types of Ulmus pumila.Compared with CK,Inoculation of Pyriformis indiana can effectively alleviate the yellowing and litter of white elm leaves,and increase the growth of new branches.After inoculation,the Ulmus pumila strains could still grow normally under 25%water treatment,and the growth state was better than CK.（2）Inoculating Pyriformis indiana can improve the gas exchange parameters and light utilization efficiency of Ulmus pumila under water stress.With the decrease of water gradient,the Fv/Fm,Fv/F0 andΦPSⅡin Y9 and Y65225 showed a decreasing trend,while NPQ showed an increasing trend.Under the same water treatment,the values of Fv/Fm,Fv/F₀,ΦPSⅡand NPQ inoculated with PI were all higher than those of CK.PI inoculation could enhance the light energy utilization efficiency of Ulmus pumila by improving the opening degree of PSII reaction center.Under the same water treatment,the values of Pn,Tr,Ci and Gs inoculated with PI were higher than those of CK,and the values of Ls were lower than those of CK.Stomatal limiting factor was the main factor affecting the photosynthetic rate of Ulmus pumila.The inhibition of photosynthesis of the two species of Ulmus pumila was enhanced with the decrease of water treatment gradient.PI inoculation could reduce the chlorophyll decomposition rate of white elm,increase the contents of Chl,Chla and Chlb,and then improve the photosynthesis of Ulmus pumila,and alleviate the damage of Ulmus pumila under drought stress.（3）Inoculating Pyriformis indiana can improve the physiology of drought resistance of Ulmus pumila under water stress.With the decrease of water gradient,the MDA content,antioxidant enzyme activity and osmoregulatory substances of Y9 and Y65225 gradually increased on the whole.Under the same water treatment,the MDA content of Inoculating Pyriformis indiana was lower than that of CK,and the activities of SOD,POD and CAT were higher than that of CK.Compared with CK,the content of osmoregulatory substances of inoculation Pyriformis indiana could increased to a certain extent.Inoculation Pyriformis indiana can increased the activity of antioxidant enzymes,enhanced the antioxidant defense system,increased the content of osmotic regulating substances,decreased the content of malondialdehyde,and reduced the damage of membrane lipid peroxidation of Ulmus pumila.（4）Comprehensive evaluation and analysis.Correlation analysis was conducted between four water treatment gradients and 24 indexes of Ulmus pumila,and the membership function values of each index were calculated.The results were as follows:PI65225（0.6143）＞PI9（0.5548）＞CK65225（0.5415）＞CK9（0.4958）.The results indicated that PI inoculation could improve the drought tolerance of Ulmus pumila under stress,and the drought tolerance of Y65225 under PI inoculation and CK treatment was higher than that of Y9.CK9 and PI9 had the largest membership function value under 75%water treatment,and CK65225 and PI65225 had the largest membership function value under 100%water treatment.Under the same water treatment,the membership function values of PI inoculation and CK inoculation of two Ulmus pumila species were different,and the membership function value of PI9inoculation was the highest under 25%water treatment.The membership function of PI65225was the highest under 50%,75%and 100%water treatment.