Denitrification and Nitrous Oxide Production in Successional and Old-Growth Michigan Forests1
- G. Philip Robertson and
- James M. Tiedje2
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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