Mycorrhizal colonization decreases respiration of common bean nodulated root in hydroaeroponic culture

The bean-rhizobia symbiosis allows atmospheric nitrogen fixation through nodule formation. Nevertheless, nodule establishment in Mediterranean areas is subjected to various biotic and abiotic constraints such as phosphorus soils deficiency. This study compares plant-growth response to moderate (75 μmol KH₂PO₄ plant^?1 week^?1) versus severe phosphorus deficiency (30 μmol KH₂PO₄ plant^?1 week^?1) after inoculation with Rhizobium tropici CIAT 899 and Glomus intraradices of four Phaseolus vulgaris lines contrasting in P use efficiency (PUE) for their symbiotic nitrogen fixation (SNF) in hydroaeroponic culture. After 5 weeks of growth under glasshouse conditions, the oxygen consumption related to nitrogen fixation was measured on intact nodulated roots. The obtained results revealed that mycorrhizal colonization decreased the nodulated-roots O₂ consumption of P. vulgaris under both P deficiencies although it increased the growth of all plant organs and the nodulation with a large genotypic variability. Moreover, mycorrhizal colonization was higher under severe P deficiency than under moderate one. In conclusion, the tripartite inoculation improved growth parameters under severe P-deficiency with a decrease in nodulated root O₂ consumption.