Enhanced biological nitrogen fixation in alfalfa through the synergistic interactions between Sinorhizobium meliloti and Priestia aryabhattai

Nitrogen fertilizer is crucial for agricultural output. However, prolonged overuse has resulted in nitrate leaching, and potential soil acidification. Research on microbial fertilizers has become essential to enhance soil conditions and minimize nitrogen fertilizer usage. In alfalfa cultivation, research on efficient compound microbial agents remains limited, therefore, this study concentrates on the investigation of dual microbial combinations. In the screening process, black soil was utilized with alfalfa plants as samples to identify a strain of rhizobacteria, Sinorhizobium meliloti LMGL3-1 , exhibiting nitrogen-fixing capabilities, and Priestia aryabhattai ( Bacillus aryabhattai ) YJHT21, demonstrating phosphorus-solubilizing abilities. The S. meliloti strain demonstrated the ability to symbiotically associate with the alfalfa variety Longmu 806, resulting in the formation of effective nodules containing leghemoglobin, thereby enabling the plants to thrive in the absence of nitrogen fertilizer application. Here, we discovered that the addition of phosphorus-solubilizing P. aryabhattai enhanced plant growth and increased nitrogenase activity of S. meliloti . Moreover, the incorporation of P. aryabhattai resulted in a significant increase in flavonoid production within the root system of alfalfa plants. Consequently, under the influence of the inducer extracted from the root system of quantitatively analyzed plants, the rhizobacteria exhibited enhanced production of metabolites associated with the Nod factor cluster. The current experiment demonstrated that the interaction between the two bacteria significantly enhanced nitrogen fixation, effectively substituting nitrogen fertilizer in alfalfa cultivation with improved efficiency and offered theoretical support for the eco-friendly advancement of microbial compound fertilizers as a substitute for chemical fertilizers.