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

The effects of H-2 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 H-2 emission rate of 250 nmol H-2 g(-1) soil h(-1) was similar to the upper limit of estimated H-2 amounts emitted from N-2 fixing nodules into the surrounding soil ([Dong, Z., Layzell, D.B., 2001. H-2 oxidation, OZ uptake and CO2 fixation in hydrogen treated soil. Plant and Soil 229, 1-12.]). After 1 week of H-2 supply to soil samples simultaneously with H-2 uptake net CO2 production declined continuously and this finally led to a net CO2 fixation rate in the H-2-treated soil of 8 nmol CO2 g(-1) soil h(-1). The time course of H-2 uptake and CO2 fixation in the soils corresponded with an increase in microbial activity and biomass of the H-2-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 H-2 treatment stimulated beta-and gamma-subclasses of Proteobacteria, it had no significant effect on alpha-Proteobacteria. In addition, FISH-detectable bacteria of the Cytophaga-Flavobacterium-Bacteroides phylum increased in numbers. (c) 2005 Elsevier Ltd. All rights reserved.