Intercropping promotes maize growth by enhancing accumulation of specific metabolites in the rhizosphere and synergistic interaction between arbuscular mycorrhizal fungi and Bacillus

Abstract

Background and aims

Both arbuscular mycorrhizal (AM) fungi and Bacillus can be crucial for enhancing crop yield. However, their contribution to intercropping advantage remains unclear, and the underlying mechanisms require further investigation.

Methods

We evaluated the effects of inoculation with AM fungi and/or Bacillus on maize and soybean growth in intercropping systems under combined nitrogen (N) and phosphorus (P) stress conditions. Through integrated rhizosheath metabolomics and root transcriptomics analyses, we explored the underlying mechanisms by which root exudates contribute to the formation of intercropping advantage.

Results

Co-inoculation with AM fungi and Bacillus significantly increased plant dry weight and N and P contents of intercropped maize, but had less effects on intercropped soybean. Under co-inoculation, intercropping significantly increased not only plant growth and nutrient acquisition of maize, but also AM colonization and the abundance of Bacillus in the rhizosheath. Integrated root transcriptome and rhizosphere metabolome analyses revealed that intercropped maize accumulated more tryptophol and naringenin chalcone in the rhizosheath, and exhibited up-regulated expression of the genes involved in naringenin synthesis. Additionally, intercropped maize showed a greater accumulation of indole-3-acetic acid (IAA) in the rhizosheath and up-regulated expression of the genes involved in tryptophan metabolism and the IAA-signal-transduction pathway.

Conclusion

Both intercropping and co-inoculation contributed to growth promotion of intercropped maize. The specific metabolites likely promoted AM colonization and Bacillus growth, and impacted plant IAA levels, thereby enhancing growth of intercropped maize.