Potential for N2O production from beech (Fagus silvaticus) forest soils with varying pH

This study was made to quantify the gas emission from denitrification and determine the environmental regulation of these processes in forest soils. The objective was to examine the importance of substrates for denitrification in four beech (Fagus silvaticus) forest soils with pH values from 7.2 to 4.3. This study was carried out to determine the effect of acetate, nitrate and soil water content on nitrous oxide (N2O) production. Measurements were made in the field using a simple soil cover and in the laboratory with soil water slurries. The slurries were amended with nitrate and acetate; acetylene (C2H2) was added as inhibitor. Low activities were found in the field with no seasonal variation observed. Increased water content occasionally stimulated N2O production but acetylene inhibition was not observed. Annual figures for N2O production in the field were estimated to range from 0.6 to 2.2 kg N2O-N ha-1 yr-1 and increased to 0.6-4.5 kg when water was added. The treatments resulted in considerable increases in activity in the slurries but were greatest when all treatments were combined; the daily rate of N2O production increased from 3 to 15 times following C2H2, acetate and nitrate addition, highest in the neutral soil. The soil profile study showed decrease of activity with depth, with most of the N2O production taking place in the upper 7 cm. A comparison between in situ and laboratory measurements of N2O production is difficult since one assumes that the two sets of results would be parallel, and that they will respond to treatments in the same way. In the soil slurry experiments, N2O production was relatively uniform at different soil pH values but total denitrification increased at higher soil pH. All substrate additions resulted in increased N2O production, demonstrating a high potential for denitrification, i.e. a denitrifier population depleted of substrates and responding rapidly to the addition of nitrate as well as acetate.