Methane oxidation in soil profiles of Dutch and Finnish coniferous forests with different soil texture and atmospheric nitrogen deposition

We studied methane oxidation capacity in soil profiles of Dutch and Finnish coniferous forests. The Finnish sites (n = 9) had nitrogen depositions from 3 to 36 kg N ha⁻¹ a⁻¹. The deposition of N on the Dutch sites (n = 13) was higher ranging from 50 to 92 kg N ha⁻¹ a⁻¹. The Dutch sites had also limed counterparts. Methane oxidation rates were determined by incubating soil samples in the laboratory at +15°C with 10 µl CH₄1⁻¹ (10 ppmv CH₄). In general, CH₄ oxidation rates were highest in the uppermost mineral layers. The average CH₄ oxidation rate in the Finnish mineral soils was three times higher than that in the Dutch soils. The litter layers did not oxidize CH₄. In the Netherlands all organic horizons had a negligible capacity to oxidize CH₄. However, some Finnish organic horizons showed high CH₄ oxidation capacity. In the Netherlands, in contrast to Finland, there were some soil profiles lacking CH₄ oxidation. Higher contents of nitrate and ammonium, as well as greater production of nitrous oxide (N₂0) and lower production of carbon dioxide in the Dutch than in the Finnish forest soils reflected the high N deposition rate in the Netherlands. Not only the N deposition, but also the highly sorted soil texture (fine sand) with low amounts of both coarse and fine particles is an important reason for the low CH₄ oxidation in the Dutch soils. The proportions of fine and coarse particles, both well represented in moraine soils typical in northern Europe, correlated positively with the CH₄ oxidation. Fine particles provide a good surface for microbial growth. Coarse particles, on the other hand, enhance diflusion of CH₄ and oxygen into the soil. Methane oxidation in the Dutch mineral soils was slightly enhanced by liming