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Saline-alkali stress is one of the main abiotic constraints limiting plant growth and development. Endophytic bacteria can enhance the stress tolerance of host plants by increasing osmotic adjustment substances and boosting antioxidant enzyme activities. [Objective] To isolate and identify saline-alkali tolerant endophytic bacteria from the roots of alfalfa grown in saline-alkali soil and evaluate them regarding the saline-alkali tolerance, plant growth-promoting traits, effects on alfalfa growth under saline-alkali stress, and colonization. [Methods] Saline-alkali tolerant endophytes were isolated by the tissue homogenization method from alfalfa roots. Strains were identified by morphological observation, 16S rRNA gene-based phylogenetic analysis, and physiological and biochemical assays. Multiple plant growth-promoting traits were assayed in vitro. A greenhouse pot experiment was conducted to assess the effect of the selected strain on alfalfa growth under saline-alkali conditions. Colonization of strain Z-1 in alfalfa roots was visualized by green fluorescent protein tagging and laser scanning confocal microscopy. [Results] Pseudomonas moraviensis Z-1 was successfully isolated from the roots of alfalfa growing in saline-alkali soil. The endophytic bacterial strain tolerated 4% NaCl and pH 9.0 and displayed the ability to produce 1-aminocyclopropane-l-carboxylate deaminase, siderophores, indole-3-acetic acid, and soluble phosphorus. Under saline-alkali conditions, inoculation with Z-1 significantly increased the dry weights of the aboveground parts, root vigor, and soluble protein content of alfalfa. Moreover, the strain significantly increased catalase, peroxidase, and superoxide dismutase activities and decreased the hydrogen peroxide, superoxide anion, and malondialdehyde content (P<0.05). Confocal microscopy confirmed successful colonization of Z-1 in alfalfa roots at 7.57×104 CFU/g. [Conclusion] The saline-alkali tolerant endophytic bacterium Z-1 plays a vital role in promoting alfalfa growth and enhancing its tolerance to saline-alkali stress. It represents a promising candidate for developing microbial preparations to ameliorate saline-alkali soil.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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