| Soil salinization is one of the main limiting factors for forestry production and ecological protection of the environment.Excessive salinity can cause soil consolidation and reduced fertility,destroy the normal physiological functions of plants,and inhibit plant growth.Quercus nuttallii is a typical ectomycorrhizal mycorrhizal tree species,widely planted in the "Yangtze River Delta" and the eastern coast and other economically developed areas of China.Which has important economic and ecological value,with high ornamental value,high resistance and adaptability to environmental stress.However,the increasing soil salinization in coastal areas restricts the survival rate and productivity of Quercus nuttallii planting,therefore,improving the salt resistance of Quercus nuttallii has important guiding significance and practical application value for landscaping and ecological environment construction.In this study,Quercus nuttallii seedlings and three ectomycorrhizal fungi(EMF),Pisolithus tinctorius(Pt),Tuber(T)and Suillus grevillea(Sg),were selected as experimental materials.In this study,different EMF inoculations(inoculation with Pt,T and Sg,no inoculation as control)and salt stress(S0: no Na Cl added,S1:1‰ Na Cl added to the dry weight of the pot soil,S2: 2‰ Na Cl added to the dry weight of the pot soil,S3: 3‰ Na Cl added to the dry weight of the pot soil)treatments were used to study the effects of inoculation with different types of EMF at different salt stress levels on the growth and physiological characteristics of Quercus nuttallii seedlings.We investigated the effects of EMF inoculation on the growth and physiological characteristics of Quercus nuttallii seedlings under different levels of salt stress,explored the mechanism of EMF to alleviate the salt stress of Quercus nuttallii seedlings,screened out the best Quercus nuttallii-EMF combination under different levels of salt stress,and provided theoretical basis for ecological restoration of saline soils.The results of the study showed that:1、The EMF colonization rate of Quercus nuttallii seedlings with different inoculation treatments under different salt application treatments changed significantly.With the increase of salt stress level,the EMF colonization rate of seedlings inoculated with Pt and Sg showed an increasing and then decreasing trend,possessing a maximum at S1 level;the EMF colonization rate of seedlings inoculated with T and uninoculated decreased significantly(P<0.05).At the same salt stress level,the EMF colonization rate of seedlings inoculated with T was significantly higher(P<0.05)than the EMF colonization rate of seedlings under the other three inoculation treatments at the S0 level,and the EMF colonizationrate of seedlings inoculated with the treatment was significantly higher(P<0.05)than that of seedlings without the inoculation treatment at the S2 level.2、The three EMF inoculation treatments produced different effects on the inter-root soil properties of Quercus nuttallii seedlings at different salt application levels.With the increase of salt stress level,the content of C,N and P elements in the inter-root soil of Quercus nuttallii seedlings under each inoculation treatment decreased to different degrees.Soil total phosphorus content of Quercus nuttallii seedlings inoculated with T was significantly higher than other inoculation treatments at all salt application levels(P<0.05);soil ammonium nitrogen content was significantly increased by inoculation with T and Sg at S0,S1 and S2 levels(P<0.05);soil total carbon and nitrogen content of Quercus nuttallii seedlings inoculated with the three EMFs was significantly higher than that of the non-inoculated treatments at S3 level,and nitrate nitrogen content was significantly The soil total carbon and nitrogen contents of Quercus nuttallii seedlings inoculated with the three EMFs were significantly higher than those of the uninoculated treatment at S3 level,and the nitrate nitrogen content was significantly lower than that of the uninoculated treatment(P<0.05).3、With the increase of salt stress concentration,the growth indexes such as height,ground diameter and fresh weight of Quercus nuttallii seedlings under different inoculation treatments decreased significantly(P<0.05).Under the same salt stress treatment,inoculation with Pt significantly increased the height of Quercus nuttallii seedlings,inoculation with T and Sg significantly increased the seedling ground diameter,and all three inoculation treatments significantly increased the seedling root weight(P<0.05)compared to the uninoculated treatment at S1 level;inoculation with Sg significantly increased the seedling ground diameter compared to the uninoculated treatment at S2 level(P<0.05);at S3 level,the seedling diameter of all three inoculation treatments was significantly higher than that of the uninoculated treatment(P<0.05).Salt stress interfered with plant nutrient uptake and translocation,and inoculation with mycorrhizal fungi could promote the uptake of C,N,and P nutrients by the host plants.The total phosphorus content of leaves of seedlings inoculated with the three EMFs was higher than that of uninoculated treatments,among which,inoculation with Sg possessed significant changes(P<0.05);at S3 level,the total carbon and total nitrogen contents of leaves under the three inoculation treatments were higher than that of uninoculated treatments(P<0.05).With the increase of salt stress concentration,the net photosynthetic rate and transpiration rate of Quercus nuttallii seedlings under all inoculation treatments showed a trend of increasing and then decreasing,and had the maximum value at S1 level;the net photosynthetic rate,instantaneous carboxylation efficiency,stomatal limitation value and stomatal conductance of seedlings inoculated with T and Sg under the same salt stress concentration were higher than those of uninoculated treatments(P<0.05),and the transpiration rate and water use efficiency of seedlings inoculated with T and Sg were higher than those of uninoculated treatments(P<0.05).The transpiration rate and water use efficiency of seedlings in the inoculated treatment were higher than those in the uninoculated treatment(P<0.05).Inoculation of all three EMFs significantly increased the soluble sugar content and antioxidant enzyme activity of seedling leaves and decreased the malondialdehyde content in plants(P<0.05),with inoculation of Sg having the strongest effect on the regulation of antioxidant enzymes in seedlings,followed by inoculation of Pt.4、Principal component analysis showed that total chlorophyll content,ground diameter and stem fresh weight were more correlated with salt tolerance of Quercus nuttallii seedlings under each treatment.The subordinate function analysis showed that all three inoculation treatments improved the salt tolerance of seedlings.At S0,S2 and S3 salt stress levels,the salt tolerance of Quercus nuttallii seedlings was,in descending order,inoculated with Sg > inoculated with T >inoculated with Pt > uninoculated treatment,and at S1 salt stress level,the salt tolerance of Quercus nuttallii seedlings was,in descending order,inoculated with T > inoculated with Sg >inoculated with Pt > uninoculated treatment. |
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