Methane and nitrous oxide fluxes of soils in pure and mixed stands of European beech and Norway spruce

Summary Tree species can affect the sink and source strength of soils for atmospheric methane and nitrous oxide. Here we report soil methane (CH 4 ) and nitrous oxide (N 2 O) fluxes of adjacent pure and mixed stands of beech and spruce at Solling, Germany. Mean CH 4 uptake rates ranged between 18 and 48 μg C m −2 hour −1 during 2.5 years and were about twice as great in both mixed and the pure beech stand as in the pure spruce stand. CH 4 uptake was negatively correlated with the dry mass of the O horizon, suggesting that this diminishes the transport of atmospheric CH 4 into the mineral soil. Mean N 2 O emission was rather small, ranging between 6 and 16 μg N m −2 hour −1 in all stands. Forest type had a significant effect on N 2 O emission only in one mixed stand during the growing season. We removed the O horizon in additional plots to study its effect on gas fluxes over 1.5 years, but N 2 O emissions were not altered by this treatment. Surprisingly, CH 4 uptake decreased in both mixed and the pure beech stands following the removal of the O horizon. The decrease in CH 4 uptake coincided with an increase in the soil moisture content of the mineral soil. Hence, O horizons may maintain the gas diffusivity within the mineral soil by storing water which cannot penetrate into the mineral soil after rainfall. Our results indicate that conversion of beech forests to beech–spruce and pure spruce forests could decrease soil CH 4 uptake, while the long‐term effect on N 2 O emissions is expected to be rather small.