Denitrification and Nitrous Oxide Production in Successional and Old-Growth Michigan Forests
1984
Robertson, G. P. | Tiedje, James M.
Soils from 12 successional and old-growth forests in Michigan were examined for N₂O production under each of three incubation conditions: without amendment, in a 20% (vol/vol) acetylene atmosphere, and in an acetylene-amended atmosphere after a simulated rainfall. Intact cores were taken during the growing season and incubated in the laboratory for 90 to 180 min in a porespace-recirculation system that sampled for N₂O and CO₂ at 10-min intervals. Measurable rates of N₂O production occurred in cores from all sites and under all incubation conditions; in general but not always, rates were higher in the presence of C₂H₂ than in its absence, and increased upon simulated rainfall. Under acetylene- and water-amended conditions, mean production was highest in an old-growth and a late-successional hardwood site and in a recent clearcut (30 to 80 mg N₂O-N m⁻² d⁻¹); intermediate rates (2 to 3 mg N₂O-N m⁻² d⁻¹) were observed in soils from a midsuccessional hardwood stand and from two old-field communities, and low rates (<0.6 mg N₂O-N m⁻² d⁻¹) occurred in soils from a young sand dune community, from a midsuccessional and a late-successional hardwood stand, and from a managed, a midsuccessional, and an old-growth conifer community. Nitrate production, CO₂ production and water content could explain 65% of the variation in rates of N₂O production among sites under acetylene-amended conditions. Nitrate pool sizes and pH differed substantially among sites but were not well correlated with N₂O production. The presence of a class of cores that produced N₂O only in the absence of acetylene suggests that sources of N₂O other than denitrifiers may be important in some sites.
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