This study presents how phosphate (P) availability and intercropping may influence the migration of rare earth elements (REEs) in legume–grass associations. In a replacement model, Hordeum vulgare was intercropped with 11% Lupinus albus and 11% Lupinus angustifolius. They were cultivated on two substrates, A (pH = 7.8) and B (pH = 6.6), and treated with 1.5 g P m−2 or 3 g P m−2. Simultaneously, a greenhouse experiment was conducted to quantify carboxylate release. There, one group of L. albus and L. angustifolius was supplied with either 200 µmol L-1 P or 20 µmol L-1 P. L. albus released higher amounts of carboxylates at low P supply than L. angustifolius, while L. angustifolius showed the opposite response. Plants cultivated on substrate B accumulated substantially higher amounts of nutrients and REE, compared to substrate A. Higher P supply did not influence the leaf and stem P concentrations of H. vulgare. Addition of P decreased REE accumulation in barley monocultures on alkaline soil A. However, when H. vulgare was cultivated in mixed culture with L. angustifolius on alkaline substrate A with high P supply, the accumulation of REE in H. vulgare significantly increased. Conversely, on acidic substrate B, intercropping with L. albus decreased REE accumulation in H. vulgare. Our findings suggest a predominant effect of soil properties on the soil–plant transfer of REEs. However, in plant communities and within a certain soil environment, interspecific root interactions determined by species-specific strategies related to P acquisition in concert with the plant’s nutrient supply impact REE fluxes between neighbouring plants.

Background and Aims A split-root approach was used to explore how phosphorus (P) nutrition in uences accumulation of rare earth elements (REE) in plant species with different P-acquisition strategies beyond the commonly explored REE-phosphate precipitation.Methods Six species (Triticum aestivum, Brassica napus, Pisum sativum, Cicer arietinum, Lupinus albus, and Lupinus cosentinii) were cultivated with a split-root system on two sand types. Phosphorus availability was controlled on one root side by watering the plants with different P-containing solutions (100 µM P, 0 µM P). Carboxylate release and changes in pH were measured on both sides. Concentrations of nutrients, cadmium (Cd), aluminium (Al), light REE (LREE: La-Eu), and heavy REE (HREE: Gd-Lu, including Y) in roots and shoots were analyzed by ICP-MS.Results Triticum aestivum, B. napus and C. arietinum did not respond to a low P supply with elevated carboxylate release. These species accumulated more REE when the P supply was low and higher REE concentrations were proportional to declining plant growth. However, P. sativum, L. albus and L. cosentiniiaccumulated less REE when Psupply was low. Plants that strongly acidi ed the rhizosphere and released low quantities of dicarboxylates accumulated more REE (with higher LREE/HREE ratios) than species that released tricarboxylates. ConclusionOur ndings suggest that REE accumulation strongly depended on rhizosphere acidi cation, in concert with the amount and composition of carboxylates determining the exclusion of REE-carboxylate complexes. Leaf REE signatures may be a promising indicator as a screen tool for carboxylate-based processes in the rhizosphere using an ionomic approach.

Background and Aims A split-root approach was used to explore how phosphorus (P) nutrition influences accumulation of rare earth elements (REE) in plant species with different P-acquisition strategies beyond the commonly explored REE-phosphate precipitation. Methods Six species (Triticum aestivum, Brassica napus, Pisum sativum, Cicer arietinum, Lupinus albus, and Lupinus cosentinii) were cultivated with a split-root system on two sand types. Phosphorus availability was controlled on one root side by watering the plants with different P-containing solutions (100 µM P, 0 µM P). Carboxylate release and changes in pH were measured on both sides. Concentrations of nutrients, cadmium (Cd), aluminium (Al), light REE (LREE: La–Eu), and heavy REE (HREE: Gd–Lu, including Y) in roots and shoots were analyzed by ICP-MS. Results Triticum aestivum, B. napus and C. arietinum did not respond to a low P supply with elevated carboxylate release. These species accumulated more REE when the P supply was low and higher REE concentrations were proportional to declining plant growth. However, P. sativum, L. albus and L. cosentiniiaccumulated less REE when P-supply was low. Plants that strongly acidified the rhizosphere and released low quantities of dicarboxylates accumulated more REE (with higher LREE/HREE ratios) than species that released tricarboxylates. Conclusion Our findings suggest that REE accumulation strongly depended on rhizosphere acidification, in concert with the amount and composition of carboxylates determining the exclusion of REE-carboxylate complexes. Leaf REE signatures may be a promising indicator as a screen tool for carboxylate-based processes in the rhizosphere using an ionomic approach.

This study presents how nutrient availability and intercropping may influence the migration of REE when cultivated under P-deficient conditions. In a replacement model, Hordeum vulgare was intercropped with 11% Lupinus albus cv. Feodora and 11% L. angustifolius cv. Sonate. They were cultivated on two substrates, A (pH = 7.8) and B (pH = 6.6). Two nutrient solutions were supplied, with N, K, Mg and high P-supply (P+), the other with N, K, Mg, and one-third of P-supply (P-, applied to L0 and Lan only). Simultaneously, a greenhouse experiment was conducted to quantify carboxylate release. There, one group of L. albus and L. angustifolius was supplied with 200 µM K2HPO4 (P+) together with the other nutrients while a second group received 20 µM P (P-). L. albus released higher carboxylates at low P-supply than L. angustifolius. Higher P-supply did not influence the P concentrations and contents of H. vulgare neither on substrate A nor on substrate B. However, addition of P decreased the concentrations of REEs, especially in plants cultivated on alkaline soil. Nutrient accumulation decreased in H. vulgare in intercropping with L. angustifolius when cultivated on the alkaline substrate A with high P-supply. In the same conditions, the accumulation of REE in H. vulgare significantly increased. Conversely, on the acidic substrate B intercropping with L. albus decreased REE contents and concentrations in H. vulgare. Intercropping with L. angustifolius opens an opportunity for enhanced phytomining and accumulation of REE. Furthermore, intercropping with L. albus on REE polluted soils may be utilized to restrict REE accumulation in crops used for food production.