Oxidation of ethylene and methane in forest soils -: effect of CO2 and mineral nitrogen

The influence of inorganic nitrogen and CO2 on microbial C2H4 and CH4 consumption was evaluated in two forest soils (montane spruce forest and colline deciduous forest) under laboratory conditions at 25 degrees C. The soils were adjusted to a water tension of - 30 kPa. Nitrogen was added as KNO3 or (NH4)(2)SO4, while CO2 enrichment ranged from 1-20%. At 0, 24, and 96 h, the amounts of CH4 and C2H4 consumed were determined. In both soils, we observed a parallel response of C2H4 and CH4 to all kinds and concentrations of amendments, plausibly due to co-metabolism of C2H4 by either methanotrophs or nitrifiers. Ammonium-N inhibited hydrocarbon oxidation in the deciduous forest soil, but promoted it in the acidic spruce forest soil. Ammonium addition narrowed the C:N ratio of the spruce forest soil which was characterized by low pH but high humus content. Therefore, the general living conditions for microorganisms might have been improved. Conversely, NO3- inhibited hydrocarbon oxidation in both soils, here a non-specific ion toxicity ('salt-effect') is discussed. CO2 also had an inhibitory effect on hydrocarbon microbial uptake at high concentrations, with its production increasing at elevated CO2 levels. We conclude that the impact of nitrogen inputs and of enhanced CO2 on the sink strength for hydrocarbons depends on the amount and the kind of addition as well as on soil type. (C) 1999 Elsevier Science B.V. All rights reserved.