Is phosphorus efficiency low for symbiotic nitrogen fixation?

International audiencePhosphorus is the limiting nutrient for legume symbiotic nitrogen fixation in most soils of the planet. Thus the yield of legumes generally responds to phosphorus fertilization. The P requirement of legumes is generally higher when their growth depends upon atmospheric nitrogen than upon ammonium or nitrate. This communication will revise the metabolic and structural utilizations of P that may limit the P efficiency for N2 reduction in legume nodules and their genetic variation among legume species. The interaction with P metabolism will be illustrated with our results on nodule phytase activity (Araujo et al. 2008), and the tissue expression of the corresponding gene by in situ RT-PCR on nodule sections. The later will be compared with that of phosphoenol pyruvate phosphatase, and other candidate genes like trehalose 6-P phosphatase, that have been identified by deep super SAGE on nodule mRNA populations (Molina et al. 2011). The selection procedure of contrasting genotypes in P utilization for N2 fixation will be proposed to assess the functions involved in the adaptation of N2-fixing legumes in agro-ecosystems with low P soils, and to improve the yield of legumes and the sustainability of agricultural systemsdepending upon N2-fixation