Sensitivity of different Lupinus species to calcium under a low phosphorus supply

To study mechanism underpinning the calcifuge habit of some Lupinus species, especially under low-phosphorus (P) conditions, Lupinus species that were likely to respond differently to calcium (Ca) availability were assembled, and the sensitivity to Ca under a low-P supply was assessed. Seven Lupinus species (9 genotypes, L. albus L. cv Kiev, L. albus L. P26766, L. angustifolius L. cv Mandelup, L. angustifolius L. P26723, L. luteus L. cv Pootalong, L. hispanicus ssp. bicolor Boiss. and Reut. P22999, L. pilosus Murr. P27440, L. cosentinii Guss. P27225, and L. atlanticus Gladst. P27219) were grown hydroponically at 10 or 6000 μM Ca. Leaf symptoms, gas exchange and biomass were recorded; leaf and root nutrient concentrations were analysed, and the leaf cell types in which Ca and P accumulated were determined using elemental X-ray microanalyses. Calcium toxicity was demonstrated for L. angustifolius P26723, L. hispanicus ssp. bicolor. P22999, and L. cosentinii P27225, whereas the other species were tolerant of a high Ca supply under low-P conditions. In addition, genotypic differences in Ca toxicity were found within L. angustifolius. Most Ca accumulated in the mesophyll cells in all species, whereas most P was located in epidermal cells.