| Soil salinization has serious adverse effects on agriculture and ecological environment.In our country,there are about 100 million hectares of saline-alkali land,and the coastal saline-alkali land is particularly difficult to treat because of reasons such as rising groundwater level and seawater backflow.Plant growth-promoting rhizobacteria(PGPR)can improve plant tolerance to adverse conditions through its own metabolism and interaction with plants,providing a new idea of the improvement in saline soil.In this study,the bacterium with good growth-promoting functions was isolated from the saline-alkali soil,and those strains were identified.Then,according to the growth-promoting effect of salt-tolerant growth-promoting bacterium on Brassica campestris,the compound bacterial agent was prepared,and its application potential was verified through the potted planting experiment,and the medium and fermentation conditions were optimized.In this study,574 strains of salt-tolerant bacteria were isolated from saline-alkali soil.Among these strains,125 strains have the function of dissolving phosphorus,147 strains have the function of dissolving inorganic phosphorus,177 strains have the function of dissolving silicate,and 128 strains have the function of producing IAA.According to the results of functional text of the strains,8 strains of excellent characters were selected for bacterial species identification.Combining the results of the colony and cell morphological characteristics,physiological and biochemical characteristics and 16S r DNA sequence analysis,it was determined that strain 1-39 is Priestia megaterium,strain 2-52 is Priestia aryabhattai,strain 2-175 is Bacillus zanthoxyli,strain 3-30 is Glutamicibacter endophyticus,strains 3-43 and 3-110are Brevibacterium frigoritolerans,strain 3-117 is Psychrobacter alimentarius,and strain 3-120 is Oceanobacillus profundus.According to the interbacterial antagonism experiment,Strain 3-110,which had a significant inhibition on strain 1-39,2-52,3-30 and 3-43,was excluded.So the other 7 strains were used in the potted planting experiment.And the results showed that under saline-alkali conditions,the application of a single bacteria treatment shown different degrees of promotion on the growth of plants.Among them,the above ground part wet weight of plants treated with strain 2-52 increased by 84.71%,and the root length of plants treated with strain 2-175increased by 91.74%compared with salt-alkali treatment.In terms of the effect of different treatments on soil enzyme activity,compared with salt-alkali treatment,strain 2-52 increased soil sucrase activity by 87.80%,and strain 1-39 increased urease activity by 41.66%in the soil treated.Under unfavorable conditions,the content of MDA and other peroxides in plants will increase significantly,and antioxidant enzymes can effectively reduce the damage of these substances to plants.The results showed that MDA content of Brassica campestris leaves treated with strain 3-117 was the lowest,which was decreased by 57.14%compared with saline-alkali treatment.And the effects of strain 1-39 on CAT and SOD activities in Brassica campestris were significantly and stably increased by 62.61%and 72.55%,respectively.According to the above experimental results,this study prepared F01,F02 and F03compound bacterial agents.Among them,compound bacterial agent F01 had the best growth promoting effect on Brassica campestris.And its effects on above ground part wet weight,total root length,soil urease and catalase activities and malondialdehyde content in leaves were better than other compound bacterial agents and single bacteria treatments.The above ground part wet weight and total root length of plants were 2.18 times and 2.11 times of that of saline-alkali treatment,respectively,and increased 36.67%and 14.98%compared with that of single bacteria treatment.In the plant pot soil treated with this compound bacterial agent,the activity of sucrase was increased by 99.05%and 34.50%compared with saline-alkali treatment and single bacteria 3-117 treatment,respectively.In addition,F01 treatment significantly increased the activity of antioxidant enzymes and decreased the content of MDA in Brassica campestris leaves.In order to make the compound bacterial agent better applied to the actual fermentation production,this study preliminarily optimized the culture medium and fermentation conditions of each single bacteria constituting the compound bacterial agent F01.The experimental results showed that the optimum medium for strain 1-39 is 30 g/L maltose,20 g/L peptone and 8 g/L Mg SO4,the optimum fermentation conditions are 37?,220 rpm,and the optimum p H is 6.5.The optimum medium for the strain 3-30 is 20 g/L glucose,20 g/L yeast powder and 6 g/L Mg SO4,the optimum fermentation conditions are 37°C,200 rpm,and the optimum p H is 8.5.The optimum medium for strain 3-117 is 30 g/L maltose,20 g/L yeast powder and 8 g/L Mg SO4,the optimum fermentation conditions are 37?,220 rpm,and the optimum p H is 8.5. |
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