β-Elemonic acid mediated enrichment of Paenibacillus to help Salvia miltiorrhiza Bunge alleviate drought stress

Microorganisms can improve the adaptability of crops to drought and high-temperature stress. However, the changes of rhizosphere microbial communities under climate stress and the potential mechanisms driving microbial changes remain poorly understood. In this study, the medicinal plant Salvia miltiorrhiza was used as the research object. ITS, 16S rRNA amplicon sequencing, and liquid chromatography-mass spectrometry-based metabolomics were integrated to investigate its physiological and biochemical responses to drought, high-temperature, and combined drought-high temperature under greenhouse. Additionally, we determined the seedling weight, leaf water content, active ingredient content of underground part, and the content of chlorophyll, leaf nitrogen, phosphorus, and potassium. The results demonstrated that microorganisms can alleviate stress by enhancing the water retention capacity of S. miltiorrhiza leaves; TD group increased by about 13%, promoting nutrient absorption; and the chlorophyll content of group D increased by about 78%, boosting photosynthetic efficiency and increasing the levels of stress-resistant compounds. We found that bacteria exhibited greater sensitivity to climatic stress factors, with Paenibacillus being significantly enriched only in the stress-treated group. Moreover, the synthetic community comprising Paenibacillus was confirmed to help S. miltiorrhiza alleviate drought stress. We further found that β-elemonic acid, a triterpene acid secreted by plant roots, specifically enriched Paenibacillus under drought stress. In addition, β-elemonic acid significantly promoted the growth of S. miltiorrhiza in the presence of Paenibacillus under drought stress. Our findings suggest that S. miltiorrhiza enrich beneficial Paenibacillus to combat drought stress through the secretion of the key metabolite β-elemonic acid. Video Abstract.