Examples of Belowground Mechanisms Enabling Legumes to Mitigate Phosphorus Deficiency

Legumes improve agricultural sustainability through symbiotic dinitrogen (N2) fixation which constitutes a major input into agroecosystems and may provide an ecologically acceptable complement or substitute for mineral nitrogen fertilizers. However, low soil nutrient availability, notably phosphorus (P), is among the most nutrient limitations for legumes whose sensitivity to P deficiency has been attributed to low soil P availability and higher P requirements during the symbiotic N2 fixation process. 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. This chapter reports numerous legume tolerance strategies to P deficiency that link morphological, physiological, and molecular responses. Stimulation of the root’s extracellular potentialities to improve solubilization and acquisition of the rhizosphere soil P as well as optimization of intracellular use efficiency and allocation of P has been described. Coincident with most knowledge on legume performance under P deficiency, exploration of biotic factors with synergistic and complementary interactions for the benefit of both plants and soil microorganisms is increasingly adopted. A holistic understanding of the key mechanisms underlying legume tolerance to abiotic constraints will be valuable for strategies to improve symbiotic N2 fixation and sustainable agriculture in a world of increasing population and declining renewable resources.