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Objective To screen indigenous rhizobia with high salt tolerance and plant growth-promoting traits from alfalfa nodules and clarify their phylogenetic status and functional potential, thereby providing strain resources and a theoretical basis for developing localized, efficient alfalfa symbiosis and further addressing the constraints of saline soil on alfalfa production in Inner Mongolia. Methods Indigenous alfalfa rhizobia were collected from six saline-alkali sites in Inner Mongolia via a trapping method. Following isolation and purification, the taxonomic status of the strains was determined by 16S rRNA gene sequencing. The plant growth-promoting functions were evaluated through nodulation tests, along with assays for nitrogen fixation, phosphorus solubilization, potassium solubilization, indole-3-acetic acid (IAA) production, and exopolysaccharide (EPS) content. Seed germination and pot experiments were carried out to evaluate the salt stress-alleviating effect of the target strain. Results A total of 250 strains were isolated, with Sinorhizobium meliloti being predominant (227 strains, 90.8%). Eight efficient nodulating strains (e.g., 1B1Y and 1B2Y) were screened out, all of which possessed nitrogen-fixing and potassium-solubilizing capabilities. Some strains (e.g., 2B3Y and 9B3Y) could solubilize organic phosphorus and produce siderophores. Strain 9B3Y secreted the highest amount of IAA (67.5 mg/L), while 16C1Y produced the highest EPS content (2.684 g/L). Under salt stress (0.4% NaCl), the aboveground fresh weight of alfalfa inoculated with strain 2B3Y increased by 29% compared with that of the saline control, and the strain significantly alleviated the inhibition on seed germination (notably increasing the root length). Conclusion The strains screened out, particularly strain 2B3Y, can effectively mitigate the inhibitory effects of salt stress on alfalfa through nitrogen fixation and the secretion of IAA and EPS. These strains show promise for application in alfalfa production and soil improvement in saline regions of Inner Mongolia.
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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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