内蒙古地区苜蓿耐盐促生根瘤菌的筛选及盆栽验证

Screening of salt-tolerant and plant growth-promoting rhizobia from alfalfa in Inner Mongolia and verification through pot experiments

摘要:

目的 针对内蒙古盐渍化土壤制约苜蓿生产的问题，从该地区苜蓿根瘤中筛选耐盐能力强、促生效果优的根瘤菌，明确其系统发育地位与功能潜力，为开发本地化苜蓿高效共生结瘤的根瘤菌菌剂提供菌种资源和理论依据。方法 在内蒙古自治区采集6个不同盐碱区域的土壤，通过捕获法获取土著苜蓿根瘤菌，分离纯化后采用16S rRNA基因序列分析鉴定菌株分类地位；通过结瘤试验、固氮/解磷/解钾能力测定、产吲哚-3-乙酸(indole-3-acetic acid, IAA)与胞外多糖含量检测等评价促生功能；结合种子萌发试验与耐盐盆栽试验测定菌株缓解盐胁迫的效果。结果 共分离出250株菌株，其中苜蓿根瘤菌(Sinorhizobium meliloti)占90.8% (227株)；筛选出8株高效结瘤菌株(1B1Y、1B2Y等)，均具备固氮与解钾能力，部分菌株(如2B3Y、9B3Y)可解有机磷、产铁载体；9B3Y的IAA分泌量最高(67.5 mg/L)，16C1Y的胞外多糖含量最高(2.684 g/L)；在盐胁迫(0.4% NaCl)条件下，2B3Y处理组苜蓿地上部鲜重较盐水对照组增长29%，且显著缓解种子萌发抑制(根长提升明显)。结论 筛选获得的菌株(尤其是2B3Y)能通过固氮、分泌IAA与胞外多糖等机制有效缓解盐胁迫对苜蓿的抑制作用，有望应用于内蒙古盐渍化土壤的苜蓿生产与土壤改良。

Abstract:

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.