Is genotypic variation of H⁺ efflux under P deficiency linked with nodulated-root respiration of N2 fixing common-bean (Phaseolus vulgaris L.)?

To examine genotypic variation of common bean in growth, phosphorus uptake, nodulated-root proton release, and nodule gas permeability, seven common bean recombinant inbred lines (RIL) from the cross of BAT477×DOR364 were inoculated by Rhizobium tropici CIAT 899 and grown in hydroaeroponic culture under glasshouse conditions. A positive correlation was observed between shoot and nodule biomass for most of the studied RILs. Under P deficiency, the tolerant common bean RILs acidified more of their rhizosphere than the sensitive ones. The proton release of the RILs 147, 124, 104, 75 and RIL34 was positively correlated with nodule O2 permeability. We conclude that nodulated common bean plants release a substantial amount of H⁺ into the rhizosphere that is linked to the symbiotic N2 fixation. It depends upon the nodule permeability to O2 diffusion, and varies with genotype.