Effects Of Mycorrhizal Fungi On The Growth And Physiological Characteristics Of Walnut Seedlings Under Salt Stress

The land in the coastal areas is vast,but the soil salinization is serious,and NaCl-based salt stress restricts production and ecological environment construction of agricultural and forestry.Using biological measures to improve saline-alkali land is the most sustainable and efficient way to restore ecological environment and develop economy.With the development of walnut industry,coastal saline-alkali areas also began to develop walnut industry,but the growth and production of walnut is easy to be inhibited due to high soil salinity.However,inoculation of mycorrhizal fungi can alleviate salt stress and improve the effectiveness of production.Therefore,we inoculated Piriformospora indica(P fungi)and Suillus tomentosus(S fungi)into walnut seedlings respectively to explore the effects of mycorrhizal fungi on growth,biomass,photosynthesis,chlorophyll fluorescence and contents of walnut seedlings under salt stress and to analyze the salt tolerance of walnut seedlings inoculated with mycorrhizal fungi.We expect to provide a theoretical basis for expanding the planting area in salinized land and enriching the economic forest species in saline-alkali areas.The research results are as follows:(1)With the increase of salt concentration,the control treatments and walnut seedlings inoculated P and S growth index,plant height,ground diameter,number of leaves,number of side branches,fresh weight and dry weight of roots,stems,leaves,shows a decreasing trend.Compared with the CK,inoculating P or S can effectively accumulate the growth and biomass accumulation of walnut seedlings,and improve the salt tolerance of walnut seedlings.In the production practice,P fungi and S fungi can be used to inoculate walnuts to improve salt tolerance.After the two mycorrhiza and the walnut seedlings were symbiotic,they could grow normally at a salt concentration of 75 mmol/L.(2)Under the same salt stress,the actual photochemical efficiency of walnut seedlings inoculated with P and S fungi was significantly higher than that of CK treatment.The variation of inoculation treatment was lower than that of CK treatment.Inoculation of P and S fungi enhances the light energy utilization efficiency of walnut seedlings by increasing the openness of the PSII reaction center.The Pn,Tr,WUE and CUE values of the leaves of walnut seedlings inoculated with P and S fungi under the same treatment were higher than those of CK treatment,and the variation of the gas exchange parameters after inoculation was smaller than that of the control.The limiting factors affecting the photosynthesis rate of Pfungi and CK treatment were changed from stomatal limitation to non-stomatal limitation,and the photosynthetic limiting factor of S-inoculation was non-stomatal limitation.(3)Under the same salt stress,the indexes of Chl,Chl a and Chl a/b in the leaves of walnut seedlings after inoculation with P and S were higher than those treated with CK,and the change range was smaller than that of CK treatment.Inoculation treatment effectively increased the chlorophyll content in the leaves of walnut seedlings,increased their photosynthesis and promoted the growth of plants.The content of malondialdehyde treated by CK treatment at the same salt concentration was significantly higher than that of inoculation treatment.The activity of SOD after treatment with P and S fungi was significantly higher than that of CK treatment at the same treatment time,and the change of MDA and SOD was lower than that of CK treatment.Inoculation of P fungi and S fungi significantly increased the SOD activity in the leaves of walnut seedlings,enhanced the antioxidant defense system,reduced the content of malondialdehyde,reduced the peroxidative damage of membrane lipids,and reduced the content of reactive oxygen species.