Study On The Construction Of Alfalfa Growth Promoting Functional Synthetic Communities And Its Application Effects In Saline Alkali Soil

Alfalfa is a kind of leguminous forage widely planted in northern China.The development of alfalfa planting industry is seriously restricted by the salinization of soil and the large area distribution of saline-alkali soil.Plant rhizosphere growth promoters(PGPR)can not only improve the salt tolerance of plants to adapt to saline-alkali environment,but also improve saline-alkali soil by interacting with host plants to adapt to the growth of more plants.In this study,four kinds of synthetic bacteria with stable growth promotion ability of alfalfa were constructed by isolating and combining saline-alkali tolerant functional bacteria from alfalfa rhizosphere soil,and their application effects in saline-alkali soil were investigated.Key findings were as follows:1.Twenty-two strains of inorganic phosphorus solubilizing bacteria were qualitatively screened from alfalfa rhizosphere soil using PKO inorganic phosphorus medium,thirteen strains of organic phosphorus solubilizing bacteria were screened using Monghina organic phosphorus medium,and eight strains of potassium solubilizing bacteria were screened using potassium solubilizing medium.Rescreening according to strain function,two strains of WJL-7(Acinetobacter calcoaceticus)and WJL-8(Paenibacillus lautus)with highly inorganic phosphorus solubilization ability,two strains of YJL-9(Pseudomonas koreensis)and YJL-11(Priestia aryabhattai B8W22)with highly organic phosphorus solubilization ability,and the two strains of J-1(Pseudomonas reidholzensis)and J-4(Pantoea pleuroti)with highly potassium solubilization ability,two strains of WJL-18(Klebsiella pneumoniae)and YJL-13(Arthrobacter pascens)with highly IAA production ability,and one strain of YJL-12(Paenibacillus polymyxa)with cellulose degradation ability.2.The above nine strains were used to construct the synthetic communities.Antagonism experiments showed that strain YJL-12 had antagonistic effects with strains YJL-11 and YJL-13,respectively.Eleven kinds of synthetic communities were constructed by functional superposition and no antagonistic effects,and their effects on the growth promotion of alfalfa under salt and alkali stresses were investigated.The pot experiment showed that the group of SC 6,SC 7,SC 8 and SC 10 had stable growth promotion ability on alfalfa under salt or alkali stress conditions.(3)Pot experiments were conducted to explore the application effects of the above four synthetic communities in saline alkali soil,and all of them could promote the growth of alfalfa.The total nitrogen content of plants in the group SC 7 treatment was significantly higher than that of other treatments.The contents of soil available phosphorus and available potassium and the total phosphorus content of alfalfa in the group SC 8 treatment were higher than those in other treatments.The analysis of bacterial community diversity in alfalfa rhizosphere soil showed that the group of SC 8 increased bacterial diversity,while the diversity of group SC 6and SC 7 were decreased.In addition,specific microorganisms were enriched in the alfalfa rhizosphere soil after the group of SC 6,SC 7,SC 8 and SC 10 treatment,and different microbial communities were formed in the alfalfa rhizosphere.In summary,the synthetic communities constructed in this study,which were composed of growth promoting bacterium isolated from alfalfa rhizosphere soil,promoted the growth of alfalfa in saline soil by forming specific microbial community in alfalfa rhizosphere soil,increasing nutrient content in soil and increasing nutrient absorption of alfalfa.In addition,The combination of SC8 treatment is superior to other treatments in improving soil microbial diversity and nutrient content,making it suitable for the improvement of saline alkali soil..Our results provided a feasible reference and idea for improving the yield of alfalfa in saline soil and the development and utilization of saline soil.In summary,the synthetic communities composed of saline-alkali tolerant PGPR constructed in this study promoted the growth of alfalfa in saline alkali soil by shaping specific microbial communities in alfalfa rhizosphere soil,increasing nutrient content in soil and increasing nutrient uptake by alfalfa.Among them,group SC 8 was better than other treatments in improving soil microbial diversity and nutrient content,which was suitable for saline-alkali soil improvement.The growth promotion effects of group SC 10 treatment was better than other treatments,which was suitable for improving the growth of alfalfa in salinealkali soil.Our results provided a feasible reference and idea for improving the yield of alfalfa in saline soil and the development and utilization of saline alkali soil.