Phosphate form and neighbouring species determine interspecific interactions and maize root foraging behaviour for...

BACKGROUND: Root foraging is affected by fertilization and neighbouring plants, but how these two drivers affect interspecies interactions and regulate plant growth is poorly understood. The present study explores how phosphate type and neighbouring species influence maize root foraging behavior and phosphorus (P) acquisition. RESULTS: A pot experiment was conducted with three phosphate types [rock phosphate (RP), superphosphate (SSP) and potassium dihydrogen phosphate (KP)] and maize grown alone (single maize) or with maize (maize/maize), faba bean (maize/faba bean) or alfalfa (maize/alfalfa). Alfalfa improved maize P uptake and shoot biomass, with a pronounced facilitative effect in treatment with low-solubility P sources (RP, SSP), as evidenced by the positive relative interaction intensity (RII) values. By contrast, faba bean demonstrated competitive root interactions, especially under SSP supply, reducing the biomass of target maize. Lower biomass and P uptake, higher acid phosphatase activity and thin roots of alfalfa enhanced P mobilization, mitigating interspecific competition. Although faba bean secreted large amounts of carboxylates to the rhizosphere, its strong root growth and shoot biomass require large amounts of P, leading to competition with maize. Phosphate bioavailability further shaped interspecific dynamics, with RP and SSP promoting facilitation in maize/alfalfa and competition in maize/maize and maize/faba bean, whereas KP supply minimized competition across all mixtures. CONCLUSION: Strategic selection of neighbouring crops with appropriate P fertilizer can significantly enhance P-use efficiency while reducing interspecific competition. These findings highlight the importance of pairing poorly soluble P fertilizers with strategic crop combinations for sustainable agriculture.