Effect of variable phosphorus availability on root mechanisms involved in mobilization of the soil P in three lupine species.

Improving the soil phosphorus (P) acquisition efficiency by plants is one of the most important challenges for modern agriculture. Only 15-20% of this nutrient applied to the soil with fertilisers is used by plants, with the majority being converted to less available forms. Lupine species are a great genetic model system with significant potential to provide novel information. Here we present an investigation into the effects of variable availability in the rhizosphere on P-mobilising mechanisms and photosynthetic activity, studied in 12 varieties of three lupine species. P uptake was significantly stimulated by low molecular weight organic acid (OA) exudation and H-ATPase-mediated proton transport in roots. The predominant mechanism in white lupine was the H release into the rhizosphere, OA exudation predominated in yellow lupine, while narrow-leaved lupine varieties used both strategies effectively. Three lupine species showed significant differences in the quantitative and qualitative composition of carboxylic acids in root exudates. The variable P availability in soil solution significantly affected the photosynthetic performance of the plants studied. At the same time, the activity of the photosynthetic electron transport chain and photosynthetic CO assimilation was a key factor determining activity of the mechanisms involved in P mobilisation. We discuss the implications of these contrasting strategies for our understanding of tolerance to low P and in relation to breeding plants with higher P acquisition efficiency.