Nitrogen fixation, hydrogen production and N₂O emissions

Flynn, B., Scott, N. and Dong, Z. 2014. Nitrogen fixation, hydrogen production and N 2 O emissions. Can. J. Plant Sci. 94: 1037–1041. H 2 is a by-product of the nitrogenase reaction. Exposure to H 2 is linked to increased N 2 O production, increased CO 2 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 N 2 O production was observed in soil adjacent to legume nodules and inoculation of H 2 -oxidizing isolates led to increased N 2 O emissions in corn fields. Many H 2 -oxidizing isolates tested positive for key denitrification genes, indicating a connection between H 2 uptake and N 2 O emissions. H 2 treatment significantly increased copy number of the nitrite reductase (nirK) gene suggesting increased denitrification as the source of N 2 O. 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.