Microbial activity and bacterial composition of H2-treated soils with net CO2 fixation

The effects of H2 gas treatment of an agricultural soil cultivated previously with a mixture of clover (Trifolium pratense) and alfalfa (Medicago sativa) on CO2 dynamics and microbial activity and composition were analyzed. The H2 emission rate of 250 nmol H2 g−1 soil h−1 was similar to the upper limit of estimated H2 amounts emitted from N2 fixing nodules into the surrounding soil ([Dong, Z., Layzell, D.B., 2001. H2 oxidation, O2 uptake and CO2 fixation in hydrogen treated soil. Plant and Soil 229, 1-12.]). After 1 week of H2 supply to soil samples simultaneously with H2 uptake net CO2 production declined continuously and this finally led to a net CO2 fixation rate in the H2-treated soil of 8 nmol CO2 g−1 soil h−1. The time course of H2 uptake and CO2 fixation in the soils corresponded with an increase in microbial activity and biomass of the H2-treated soil determined by microcalorimetric measurements, fluorescence in situ hybridization analysis (FISH) and DNA staining (DAPI). Shifts in the bacterial community structure caused by the supply of H2 were recorded. While the H2 treatment stimulated β-and γ-subclasses of Proteobacteria, it had no significant effect on α-Proteobacteria. In addition, FISH-detectable bacteria of the Cytophaga-Flavobacterium-Bacteroides phylum increased in numbers.