Decomposition of atmospheric hydrogen by soil microorganisms and soil enzymes

The decomposition of atmospheric hydrogen in different types of soil was measured. The decomposition of H₂ was apparently a first-order reaction. H₂ decomposition activity was proportional to the amount of soil with maximum activities at soil water contents of approx. 6–11% (w/w). The activity was lower under anaerobic conditions, but was constant between 1–20% O₂. It was destroyed by autoclaving and was partially inactivated by fumigation with NH₃, CHC1₃ or acetone, by u.v. irradiation and by treatment with NaCN or NaN₃, indicating that biological processes in the soil were responsible for the observed H₂ decomposition. Treatment of soil with toluene or CHCl₃ caused only a partial inactivation. Incubation of soil in the presence of streptomycin or actidione reduced H₂ decomposition by less than 50%, whereas CO consumption was abolished. The H₂ decomposition rates showed H₂ saturation curves with apparent Michaelis-Menten kinetics. Cooperative effects were not observed. V_max was reached at approx. 200 μl1^?1. The K_m values for H₂ were in the range of 30μl 1^?1, but increased to higher values, when the soil had been pretreated with high H₂ mixing ratios. Apparently, the observed H₂ decomposition by soil is not only due to the activity of viable microorganisms, but soil enzymes as well.