植物根际促生菌的筛选及其耐盐促生效果

Screening of plant growth-promoting rhizobacterium with salt tolerance from rhizosphere

摘要:

【目的】研究海水稻耐盐碱植物根际促生菌(plant growth-promoting rhizobacterium,PGPR)的耐盐促生机制及基于盐胁迫下陆地作物的促生效果。【方法】以分离自海水稻根际土壤的15株细菌为材料，进行盐耐受性、降碱能力和促生特性测定，筛选出互不拮抗的高活性菌株进行菌种鉴定和复合菌群的构建，并验证复合菌群对绿豆种子萌发的促生效果。【结果】筛选出的15株PGPR属于中度嗜盐菌，其中菌株SL-1属于极端嗜盐菌；4个菌株具有嗜盐耐碱兼降碱的特性，其中菌株SH-3的降碱能力最高(16.83%)。这4个嗜盐耐碱菌株的促生能力差别较大，均能够产生胞外聚合物(extracellular polymers,EPS)，其中菌株SH-3产EPS能力最高(0.47 g/g)；均具有产吲哚乙酸(indole-3-acetic acid,IAA)的能力，产量在0.70−1.48 mg/L之间。筛选出3个高活性菌株SL-1、SM-1和SH-3，分别隶属于芽孢杆菌属和肠杆菌属，可用于构建复合菌群。种子萌发实验表明，PGPR及其复合菌群在盐胁迫条件下对绿豆种子萌发具有促进作用，且复合菌群效果优于单一PGPR，与对照组相比，复合菌群在盐浓度为15 g/L时作用效果更显著，提高各项指标(根长、发芽率和简化活力指数)，相对盐害率从80.53%下降为18.95%，绿豆种子的耐盐阈值从10 g/L提高至15 g/L，说明复合菌群各菌株在促进绿豆种子发芽中具有协同作用；相关性分析发现，EPS和IAA活性之间呈较强的正相关关系，共同促进盐胁迫下绿豆种子的萌发和生长发育。【结论】菌株SL-1、SM-1和SH-3具有较强的嗜盐耐碱、降碱、产EPS、IAA和促进生长能力，为合理开发利用土壤微生物资源和改善盐碱土壤环境提供科学依据。

Abstract:

[Objective] To study the mechanism of plant growth-promoting rhizobacterium (PGPR) in the rhizosphere of sea rice and the effects of PGPR on the growth of terrestrial crops under salt stress. [Methods] The salt tolerance, alkali-reducing ability, and plant growth-promoting effect were determined for 15 bacterial strains isolated from the rhizosphere soil of sea rice. Highly active strains were selected for species identification and construction of a consortium. The effect of the consortium on the seed germination of mung bean was verified. [Results] The 15 strains of PGPR were moderately halophilic and strain SL-1 was an extreme halophile among them. Four halophilic strains had alkali tolerance and alkali-degrading effect, among which strain SH-3 had the highest alkali-degrading effect (16.83%). These four strains demonstrated different plant growth-promoting effects. All the strains could produce extracellular polymers (EPS), and strain SH-3 had the highest EPS production (0.47 g/g). The strains were capable of producing indole-3-acetic acid (IAA), with the yields between 0.70 mg/L and 1.48 mg/L. Three highly active strains SL-1, SM-1 and SH-3 belonging to Bacillus and Enterobacter were used to construct a consortium. Seed germination experiments showed that PGPR and the consortium promoted the seed germination of mung bean under salt stress. Moreover, the consortium showcased stronger promoting effect on seed germination than single PGPR. Compared with the control group, the consortium was more effective at the salt concentration of 15 g/L. Specifically, it improved the root length, germination rate, and simplified vitality index, while decreasing the relative salt injure rate from 80.53% to 18.95% and increasing the salt tolerance threshold of mung bean seeds from 10 g/L to 15 g/L. The data indicated that strains of the consortium coordinated to promote the seed germination of mung bean. The correlation analysis showed a strong positive correlation between EPS and IAA, both of which promoted the seed germination, growth, and development of mung bean under salt stress. [Conclusion] Strains SL-1, SM-1 and SH-3 had strong halophilicity, alkali tolerance, and abilities of degrading alkali, producing EPS and IAA, and promoting plant growth. The findings provide a scientific basis for the rational development and utilization of soil microbial resources and the improvement of saline-alkali soil environment.