The potential biofertilization effect of H₂ is accompanied by a modest impact on the composition of microbial communities in the rhizosphere of common vetch

The abundance of HOB possessing group 1H/5 [NiFe]-hydrogenase was indistinguishable between the treatments, indicating that soil nutrient content (inorganic and organic carbon) and the energy potential of H₂ were insufficient to support their growth. <i>Aeromicrobium</i> spp. and <i>Ramlibacter</i> spp. were favored by eH₂ exposure at the activation stage, but their response was lost after vetch growth. The root biomass and the root/shoot ratio were reduced in soil conditioned with eH₂ compared to control soil exposed to ambient H₂, suggesting that the plant growth-promotion activity of HOB reduces root proliferation for nutrient prospection. These results provide new experimental evidence suggesting the biofertilization effect of H₂ is not universal and requires specific conditions that are yet to be identified.