H2 oxidation, O2 uptake and CO2 fixation in hydrogen treated soils

In many legume nodules, the H-2 produced as a byproduct of N-2 fixation diffuses out of the nodule and is consumed by the soil. To study the fate of this H-2 in soil, a H-2 treatment system was developed that provided a 300 cm(3) sample of a soil:silica sand (2:1) mixture with a H-2 exposure rate (147 nmol H-2 cm(-3)hr(-1)) similar to that calculated exist in soils located within 1-4 cm of nodules (30-254 nmol H-2 cm(-3)hr(-1)). After 3 weeks of H-2 pretreatment, the treated soils had a K-m and V-max for H-2 uptake (1028 ppm and 836 nmol cm(-3) hr(-1), respectively) much greater than that of control, air-treated soil (40.2 ppm and 4.35 nmol cm(-3) hr(-1), respectively). In the H-2 treated soils, O-2, CO2 and H-2 exchange rates were measured simultaneously in the presence of various pH(2). With increasing pH(2), a 5-fold increase was observed in O-2 uptake, and CO2 evolution declined such that net CO2 fixation was observed in treatments of 680 ppm H-2 or more. At the H-2 exposure rate used to pretreat the soil, 60% of the electrons from H-2 were passed to O-2, and 40% were used to support CO2 fixation. The effect of H-2 on the energy and C metabolism of soil may account for the well-known effect of legumes in promoting soil C deposition.