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

Abstract

Nitrogen-fixing root nodules in legumes release molecular hydrogen (H₂) into the rhizosphere, activating hydrogen-oxidizing bacteria (HOB) and influencing biogeochemical cycles. This study examined whether the legacy effect of HOB enrichment—established in soil microcosms previously exposed to elevated H₂ concentrations—affects biomass yield of common vetch (Vicia sativa), HOB population density, and rhizosphere microbial community composition. Soils differing by more than 60% in H₂ oxidation activity served as growth substrates. Bacterial 16S rRNA amplicon sequencing and droplet digital PCR targeting the hhyL gene (encoding the large subunit of group 1H/5 [NiFe]-hydrogenase) were employed. HOB abundance did not differ significantly between treatments, suggesting that soil nutrient levels and H₂ energy potential were insufficient to sustain HOB proliferation. Rhodanobacter spp. and Stenotrophomonas spp. were enriched during the elevated-H₂ activation phase but showed no persistent response after vetch cultivation. Root biomass and root-to-shoot ratios were lower in H₂-conditioned soils than in controls, consistent with reduced root proliferation driven by HOB-mediated nutrient promotion. Overall, the biofertilization effect of H₂ appears conditional rather than universal, requiring specific soil and microbial conditions not yet fully characterized.

Mechanism

H₂ released from nitrogen-fixing nodules activates soil HOB, which may promote nutrient availability and thereby reduce the need for root proliferation, resulting in lower root biomass and root-to-shoot ratios under elevated H₂ conditions.