ABSTRACT
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.
ABSTRACT
Lupines (Lupinus species; Fabaceae) are an ancient crop with great potential to be developed further for high-protein feed and food, cover crops, and phytoremediation. Being legumes, they are capable of symbiotically fixing atmospheric nitrogen. However, Lupinus species appear to be nonmycorrhizal or weakly mycorrhizal at most; instead some produce cluster roots, which release vast amounts of phosphate-mobilizing carboxylates (inorganic anions). Other lupines produce cluster-like roots, which function in a similar manner, and some release large amounts of carboxylates without specialized roots. These traits associated with nutrient acquisition make lupines ideally suited for either impoverished soils or soils with large amounts of phosphorus that is poorly available for most plants, e.g., acidic or alkaline soils. Here we explore how common the nonmycorrhizal phosphorus-acquisition strategy based on exudation of carboxylates is in the genus Lupinus, concluding it is very likely more widespread than generally acknowledged. This trait may partly account for the role of lupines as pioneers or invasive species, but also makes them suitable crop plants while we reach "peak phosphorus".
