Strategies and adaptation mechanisms of legumes to low phosphorus availability in soils

Abstract

Legumes are well recognized for their impact in the sustainability of agricultural systems as well as for their nutritional and health benefits. Low availability of soil phosphorus (P) is one of the factors limiting the production of legumes, particularly in the Mediterranean and tropical areas. P-deficiency limits N₂ fixation, since it has been described to have a strong impact on the growth and survival of both rhizobia and host plant. This review describes the different processes (root changes, role of pH, organic anions, and enzymes) that affect the availability of P in the soils. In response to P-deficiency, plants use various adaptive strategies to improve soil P availability and their uptake efficiency, which involves modifications in nodulated-root architecture, rhizosphere acidification, and induction of genes involved in P use efficiency such as high-affinity P transporters and P-hydrolyzing phosphatases enzymes. Molecular, biochemical, physiological and morphological responses are triggered to stimulate soil Pi uptake or to optimize its intracellular use efficiency and allocation over all plant organs. A holistic understanding of the key mechanisms underlying legume tolerance to abiotic constraints will be valuable for strategies to improve sustainable agriculture in a world of increasing population and declining renewable resources.

Keywords: Legumes, root hairs, carboxylate, enzymes, phosphorus deficiency