Relationships between carboxylate-based nutrient-acquisition strategies, phosphorus-nutritional status and rare earth element accumulation in plants

Abstract 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.