How P-nutrition status and the presence of non-essential metals (Al, REE) affect root carboxylate release and shoot element accumulation in plants with different nutrition strategies

Rhizosphere processes related to nutrient acquisition and element exclusion overlap in time, space, and function depending on the composition of metal-chelating ligands released by plant roots in concert with rhizosphere pH. Thus, the presence of non-essential metals might influence the nutrient (phosphorus: P) acquisition in the rhizosphere, while processes related to nutrient acquisition might contribute to metal tolerance. However, until nowadays,  the interactions of essential and non-essential elements are poorly understood on a rhizosphere level. In the present study, we characterized the P-inefficient species Zea mays and Triticum aestivum with regard to their carboxylate release under conditions of P deficiency and compared the results with the P-efficient species Lupinus albus. In addition, we explored how the presence of microdoses of rare earth elements (REE) and aluminum (Al) alters carboxylate release and the shoot elemental composition of the plants. P deficiency increased carboxylate release in L. albus but not in T. aestivum. Lupinus albus released more carboxylates than T. aestivum did, regardless of the P-status. The exposure of plants to Al and REE in the early growth stage influenced biomass development, carboxylate release, and shoot elemental composition of mature plants. Notably, the effect of metal availability is clearly dependent on the plant species and the P status of the plants. The mechanisms remain poorly understood. However, these findings demonstrate that non-essential elements clearly shape chemical soil-plant interactions in the rhizosphere and have an impact on element acquisition.