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• Decoding Soybean Root Secretions: By analyzing secretions within the soybean root secretome across three different soybean nodulation genotypes with the same background, we discovered that supernodulating soybeans secrete higher levels of fatty acids and carbohydrates. • Bacterial Communities Clarification: Investigating the rhizosphere bacterial communities of soybeans with varying nodulation patterns in central China, we identified Sphingomonadaceae as the predominant rhizosphere bacteria associated with soybean nodulation capacity. • Metabolites and Bacterial Attraction: The soybean root secretes a metabolite called cis -4-hydroxy-D-proline, which attracts the accumulation of Sphingomonadaceae species in the soybean rhizosphere. Furthermore, oleic acid and cis -4-hydroxy-D-proline provide essential carbon nutrients for the growth of Sphingomonadaceae species. • Promoting Oilseed Growth: Exogenous application of Sphingomonadaceae bacteria, either alone or in combination with rhizobia, can effectively promote subsequent rapeseed growth. • These findings elucidate the role of soybean nodulation in rhizosphere bacterial dynamics, highlighting its importance in sustainable agricultural practices. Crop rotation, a crucial agricultural practice that enhances soil health and crop productivity, is widely used in agriculture worldwide. Soybeans play a crucial role in crop rotation owing to their nitrogen-fixing ability, which is facilitated by symbiotic bacteria in their root systems. The soybean-rapeseed rotation is an effective agricultural practice in the Yangtze River Basin of China. However, the mechanism underlying the effectiveness of this system remains unknown. The aim of this study was to decipher the mechanisms by which previous soybean cultivation enhances the growth of subsequent rapeseed. Soybeans with three distinct nodulation genotypes were rotated with rapeseed, and the impact of previous soybean cultivation on subsequent rapeseed growth was evaluated by examining the soybean root secretome and soil rhizosphere microbiome. Soybean-rapeseed rotation significantly enhanced subsequent rapeseed growth and yield, especially when supernodulating soybean plants were used, which released the most nitrogen into the soil rhizosphere. The differences in soybean nodulation capability led to variations in root exudation, which in turn influenced the bacterial communities in the rhizosphere. Notably, the supernodulating soybean plants promoted Sphingomonadaceae family of bacteria growth by secreting oleic acid and cis -4-hydroxy-D-proline, and further attracted them through cis -4-hydroxy-D-proline. Furthermore, the exogenous application of Sphingomonadaceae bacteria, either alone or in combination with rhizobia, significantly enhanced the growth of rapeseed. Our data definitively demonstrated the crucial role of previous soybean cultivation in enhancing the yield of rapeseed, with the assistance of Sphingomonadaceae bacteria and rhizobia. This study elucidates the role of soybean nodulation in rhizosphere bacterial dynamics, highlighting its importance in sustainable agricultural practices.
Liu et al. (Thu,) studied this question.