| In recent years,soil salinization caused by climate change is a major problem faced by natural and agricultural systems.This phenomenon seriously affects the physiology and development of plants,resulting in the normal growth of crops being hindered.At present,the use of microbes to improve plant tolerance to salt stress has attracted much attention.However,there are some problems in the routine inoculation process,such as a low survival rate and the application being blocked.Therefore,the focus of this study on soil microorganisms is to screen plant growth-promoting bacteria(PGPB)which can enhance the salt tolerance and growth-promoting ability of maize,and adopt microbial seed coating technology to help PGPB survive and colonize with biochar as a coating carrier.The purpose is to explore the mechanism of microbial coating regulating plant growth under salt stress,provide the theoretical basis for the popularization and application of PGPB under salt stress environment,and also provide a guarantee for the efficient utilization of saline-alkali land and agricultural production increase.The main results are as follows:(1)In this study,bacteria in rhizosphere soil and plants of sweet potato,corn and peanut were screened.And 27 strains with high salinity tolerance were selected after re-screening by increasing salt concentration.After qualitative determination of IAA,ACC deaminase,nitrogen fixation,phosphorus solubilization,and siderophore production of these strains and quantitative determination of their ability to produce IAA and inorganic phosphorus,4 strains were screened out for germination test.Then,2 strains(M4 and ZH3-2)were selected as the functional strains in this experiment.Both strains,identified as Serratia marcescens and Serratia nematodiphila,can survive in a 15% Na Cl concentration.In the growth promotion test,qualitative determination dominates,while in the quantitative test,IAA synthesis amounts of 27.95 and 26.19μg/L,as well as phosphorus solubilization amounts of 0.97 and 0.95 g/L,respectively,were observed.(2)In order to ensure that these strains can remain stable and multiply in the soil,biochar was used as the carrier and Arabic gum as an adhesive to coat the seeds and target strains and set the ratio of biochar to Arabic gum as 2:1,and the ratio of seed weight to biochar was 1:0.08,1:0.12,1:0.16,1:0.20 and 1:0.24.When the proportion of biochar is 1:0.16,compared with the control group,the index date is the best.The root length and bud length significantly increased by 58% and 73% compared with the control group,so the optimum ratio of biochar to seed weight was 1:0.16.The target strains M4 and ZH3-2 were used for coating,and the results of the germination test showed that the two strains could significantly promote seed germination and growth.(3)According to the results of the pot experiment,the coating treatment of strains M4 and ZH3-2 can improve the photosynthetic rate,transpiration rate,and stomatal conductance of leaves,and then improve the plant height and biomass of maize,such as BM4 group increased by 41%,40%,and 33% respectively compared with the control group.In addition,the coating treatment enhanced the nutrient content of maize plants by significantly enhancing the activities of photosynthetic enzyme PEPC(134%in the BM4 group and 194% in the BZH3-2 group),antioxidant enzymes SOD(75% in the BM4 group and 66% in the BZH3-2 group)and CAT(138% in the BM4 group and168% in the BZH3-2 group),and by reducing the MDA content(57% in the BM4 group and 64% in the BZH3-2 group).By increasing the contents of soluble sugar,soluble protein,and proline,this treatment can further promote the growth of maize,improve the vitality and growth ability of maize roots under salt stress,and increase the biomass of roots.The soluble protein and proline in the BM4 group increased by93% and 99% respectively.At the same time,it was found that the effect of symbiosis between different strains and plants was also different.Based on the study of colonization efficiency,it was known that the relative expression of direct inoculation strain M4 and coating inoculation strain ZH3-2 is significant,they are respectively 553 times and 357 times of the control group,which lays the foundation and basis for all the research results.Finally,it was found that this treatment can also increase the number of species in the rhizosphere soil of maize,and then increase the richness and diversity of bacterial communities in the rhizosphere soil.Among them,the number of species in the BM4 group and the BZH3-2 group increased by 77% and 94%,respectively compared with CK group.In conclusion,this study investigated the mechanism of action on maize growth under salt stress using two salt-tolerant and growth-promoting strains with suitable coating ratios,which can provide theoretical support for the cultivation of crops in saltstressed soils. |
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