Phosphorus (P)-deficiency symptoms are known for Lupinus species grown in calcareous soil, but we do not know if this is due to a high calcium (Ca) availability or a low P availability in the soil. To address this problem, we explored both the effects of Ca and its interactions with P on nutrient status and growth of three Lupinus species. Two Ca-sensitive genotypes (L. angustifolius L. P26723 and L. cosentinii Guss. P27225) and two Ca-tolerant genotypes (L. angustifolius L. cv Mandelup and L. pilosus Murr. P27440) were grown hydroponically at two P (0.1 and 10 μM) and three Ca (0.1, 0.6 and 6 mM) levels. Leaf symptoms and biomass were recorded, whole leaf and root nutrient concentrations were analysed, and leaf cellular P and Ca concentrations were determined. Phosphorus-deficiency symptoms were only observed in the Ca-sensitive genotypes. Among all the genotypes in this study, the Ca-tolerant L. pilosus showed an ability to maintain stable leaf Ca and P concentrations whereas the Ca-tolerant L. angustifolius cv Mandelup did not maintain a stable whole leaf Ca concentration, but maintained a low cytosolic Ca2+ concentration through effective Ca compartmentation. However, the two Ca-sensitive genotypes, L. angustifolius P26723 and L. cosentinii, did not exhibit an ability to maintain a stable whole leaf Ca concentration or effectively compartmentalise Ca. Therefore, having the capacity to maintain a stable whole leaf Ca concentration or effectively compartmentalising Ca in leaves are likely critical for Lupinus species to be Ca tolerant.
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