Fulvic acid (FA) promotes symbiosis between legumes and rhizobia. To elucidate from the aspect of symbiosis, the effects of root irrigation of water-soluble humic materials (WSHM) or foliar spraying of its highly active component, FA, on soybean root exudates and on rhizosphere microorganisms were investigated. As a result, WSHM/FA treatments significantly altered root exudate metabolite composition, and isoflavonoids were identified as key contributors in both treatments compared to the control. Increased expression of genes related to the isoflavonoid biosynthesis were validated by RT-qPCR in both treatments, which notably elevated the synthesis of symbiotic signals genistein, daidzin, coumestrol, and biochanin A. Moreover, the WSHM/FA treatments induced a change in rhizosphere microbial community, coupled with an increase in the relative abundance of rhizobia. Our findings showed that WSHM/FA promotes symbiosis by stimulating the endogenous flavonoid synthesis and leads to rhizobia accumulation in the rhizosphere. This study provides new insights into mechanisms underlying the FA-mediated promotion of symbiosis.

中文翻译：

---

黄腐酸通过刺激内源类黄酮合成和分泌促进豆科植物-根瘤菌共生

黄腐酸（FA）促进豆科植物和根瘤菌之间的共生。为了从共生的角度阐明大豆根系分泌物和根际微生物的影响，研究了水溶性腐殖质（WSHM）灌根或叶面喷施其高活性成分FA对大豆根系分泌物和根际微生物的影响。结果，WSHM/FA 处理显着改变了根分泌物代谢物的组成，并且与对照相比，异黄酮类化合物被认为是这两种处理的关键贡献者。在两种处理中，通过 RT-qPCR 验证了与异黄酮类生物合成相关的基因表达增加，显着提高了共生信号金雀异黄素、大豆苷、香豆雌酚和生物鸡宁 A 的合成。此外，WSHM/FA 处理诱导了根际微生物的变化。群落，加上根瘤菌相对丰度的增加。我们的研究结果表明，WSHM/FA 通过刺激内源类黄酮合成促进共生，并导致根瘤菌在根际积累。这项研究为 FA 介导的共生促进机制提供了新的见解。