Study On Soil Microbial Community Structure Of Pyrus Betulifolia Plantation And The Mechanism Of Salt And Alkali Tolerance Of Arbuscular Mycorrhizal Pyrus Betulifolia Seedlings

Pyrus betulifolia Bunge is a deciduous tree of Rosaceae,which has the advantages of resisting adverse environments such as drought,cold,barren and saline-alkali,and has high economic development value in medicine,breeding,furniture and so on.It is an important pioneer tree species for afforestation,urban landscaping tree species and economic tree species in arid and barren mountainous areas of China.Arbuscular mycorrhizal fungi can extensively form symbiotic relationship with terrestrial plants,improve plant resistance and promote plant growth and development.At present,the understanding of the improvement of plant tolerance by inoculating AMF is still in the stage of rich and in-depth exploration.In this experiment,taking Pyrus betulifolia as the target material,the effect of Pyrus betulifolia on saline-alkali soil improvement was clarified by investigating the soil microorganisms of Pyrus betulifolia plantation in saline-alkali soil environment,and the native arbuscular mycorrhizal fungi were screened out in the rhizosphere soil of Pyrus betulifolia.Then,the pot experiment was conducted to explore the inoculation technical scheme of AMF infection to the root system of Pyrus betulifolia.Then,the physiological and ecological mechanism of improving saline-alkali stress tolerance of Pyrus betulifolia inoculated with AMF was studied.Finally,the effects of different inoculation concentrations on the infection of Pyrus betulifolia plantation in saline-alkali land were analyzed to determine whether the laboratory test can be extended to practical application.The results are as follows:（1）Cultivation of Pyrus betulifolia can effectively reduce the content of salt and alkali in soil and increase the content of nitrogen,carbon,phosphorus and other nutrient elements in soil.Cultivation of Pyrus betulifolia can promoting enrichment of beneficial bacteria such as Pseudomonas,Lysobacter,Mortierella and Guehomyces in rhizosphere soil.The cultivation of Pyrus betulifolia improves the complexity and stability of microbial network in rhizosphere soil,and has obvious positive effects on saline-alkali land improvement.A total of 14 species of arbuscular mycorrhizal fungi belonging to 4 orders,6 families and 10 genera were detected in the soil of Pyrus betulifolia plantation in the saline-alkali land of the Yellow River Delta.According to the conditions of high relative abundance and accurate identification,the AMF used in this experiment was selected as Rhizophora Rhizopus（RI）.（2）Through the effects of different saline-alkali stress on the seed germination of Pyrus betulifolia,it was clear that when the concentration of saline-alkali stress was lower than3.0‰,saline-alkali soil had little inhibitory effect on seed germination,seed vigor and bud growth,and even promoted it.However,when the concentration of saline-alkali was higher than that of 4.5‰,the seed germination,seed vigor and seedling growth of Pyrus betulifolia were inhibited.At the same time,it was determined that the seeds of Pyrus betulifolia had high tolerance to the saline-alkali composition in Binzhou area,which provided the data basis for the pot experiment.（3）Under pot conditions,through the effects of different inoculation methods on the root infection of Pyrus betulifolia,it was found that when the saline-alkali degree was 3.0‰,the saline-alkali stress had no significant effect on the root infection of Pyrus betulifolia,and the infection rate of hole application（82.06%-84.57%）was the highest,followed by that of drilling（78.43%-80.43%）.There was no significant difference between the two inoculation methods.But the infection rate of root dipping was significantly higher than that of root dipping（16.67%-19.33%）.Through hole application,3-month-old and 1-year-old seedlings of Pyrus betulifolia were inoculated with Ri under different saline-alkali concentrations in pot culture,and the infection rate was determined.When the concentration of saline-alkali stress is lower than 6.0‰,the influence of saline-alkali stress on the infection of Ri to the root system of Pyrus betulifolia is low.There is no significant difference in infection rates between the seed seedlings of Pyrus betulifolia and the one-year-old transplanted seedlings of Pyrus betulifolia,which are 79.35%-83.69%and 72.91%-74.07%,respectively.However,when the concentration of saline-alkali stress is higher than 6.0‰,the infection ability of Ri to the root system of Pyrus betulifolia increases with the deepening of saline-alkali stress.（4）Under pot conditions,the seedling height growth,aboveground and underground biomass,root structure of Pyrus betulifolia and ion distribution in vivo were compared under different concentrations of saline-alkali stress such as 0,1.5,3,4.5,6,7.5‰.The results showed that Ri inoculation could effectively promote the growth of Pyrus betulifolia seedlings,increase the biomass of each part of Pyrus betulifolia seedlings,and at the same time increase the surface area,volume and branch number of seedling roots.Ri inoculation can effectively reduce the absorption of Na+in soil,promote the absorption and utilization of K⁺and Ca²⁺,and improve K⁺/Na⁺and Ca²⁺/Na⁺,thus promoting the tolerance of Pyrus betulifolia to different saline-alkali stresses.（5）Under pot conditions,physiological indexes and photosynthetic indexes of seedlings of Pyrus betulifolia under different saline-alkali stress were analyzed.The results showed that Ri inoculation could effectively reduce the permeability of cell membrane,reduce the accumulation of MDA and Pro in leaves,and promote the accumulation of osmotic adjustment substances such as SS and SP in plants.Improve the activities of antioxidant enzymes such as SOD and POD in leaves,effectively relieve the damage of cell membrane in leaves,and eliminate the toxic effects of reactive oxygen species on the leaves of Pyrus betulifolia.It increased the accumulation of photosynthetic pigments such as Chla and Chlb in leaves,increased photosynthesis and stomatal opening,enhanced actual photochemical efficiency,improved photochemical quantum efficiency and electron transfer ability,improved photosynthesis,promoted the growth and development of Pyrus betulifolia and the accumulation of biomass,thus improving the tolerance of Pyrus betulifolia to saline-alkali stress.（6）Under field conditions,the root infection rate of Pyrus betulifolia plantation was compared after applying different concentrations of Ri.The results showed that in the actual saline-alkali environment,the inoculation of Ri could effectively infect the root system of Pyrus betulifolia,and the infection rate of 10g/pit（208g/m~3）could reach 70.45%,with no significant difference from that of 20g/pit（417g/m~3）（78.43%）.This shows that the results in the laboratory can be further applied in the actual environment,and the concentration of bacteria applied in the actual environment is determined.To sum up,Cultivation of Pyrus betulifolia can effectively improve the saline-alkali soil environment,and the improvement of saline-alkali tolerance of Pyrus betulifolia seedlings by inoculation with Ri may be to promote the absorption of mineral elements by improving the root configuration of Pyrus betulifolia under saline-alkali stress.It can inhibit the absorption of soil Na⁺by Pyrus betulifolia,promote the absorption of mineral elements such as Ca²⁺and K⁺,and regulate the distribution of mineral elements in Pyrus betulifolia.It can regulate the osmotic balance of cells,and further regulate the osmotic balance in plants by promoting the accumulation of osmotic adjustment substances,and alleviate the damage degree of saline-alkali stress to the cell membrane system of the leaves of Pyrus betulifolia.It can alleviate the damage of saline-alkali stress to the plants such as Pyrus betulifolia by enhancing the activity of antioxidant enzymes and promoting the reduction of reactive oxygen species.At the same time,inoculation with Ri can also promote the absorption and utilization of nutrients in Pyrus betulifolia,thus affecting the synthesis of photosynthetic pigments in Pyrus betulifolia leaves and promoting the ability of Pyrus betulifolia seedlings to absorb and utilize light energy.Finally,it will promote the growth and development of Pyrus betulifolia seedlings together,and improve the tolerance of Pyrus betulifolia seedlings to saline-alkali stress.