Nitrogen fixation, hydrogen production and N2O emissions

H-2 is a by-product of the nitrogenase reaction. Exposure to H-2 is linked to increased N2O production, increased CO2 fixation and plant growth promotion in soil. The effects of H-2 exposure on soil were observed using controlled H-2 gas treatments and field trials with legumes. In field trials, increased N2O production was observed in soil adjacent to legume nodules and inoculation of H-2-oxidizing isolates led to increased N2O emissions in corn fields. Many H-2-oxidizing isolates tested positive for key denitrification genes, indicating a connection between H-2 uptake and N2O emissions. H-2 treatment significantly increased copy number of the nitrite reductase (nirK) gene suggesting increased denitrification as the source of N2O. There was also a significant increase in copy number and expression of the RubisCO (cbbL) gene in soil. H-2-oxidizing bacterial isolates (JM63 and JM162a) were found to promote plant growth, increasing tiller number and yield in spring wheat and barley. Combined results of T-RFLP and 16S rDNA clone libraries analysis revealed bacterial community structure changes in response to H-2 treatment, primarily with increases to the Gammaproteobacteria and Betaproteobacteria groups. The results of these studies help provide a better understanding of the soil bacterial community's responses to H-2 exposure and may lead to the development of a commercially viable plant growth promoting inoculant.