EFFECTS OF NITRATE AND LABILE CARBON ON DENITRIFICATION OF SOUTHERN TEMPERATE FOREST SOILS

The pressure for anthropogenic land use changes and logging of temperate forests in southern Chile is rapidly increasing, with its potentially high impacts on the capacity of soils to retain important limiting elements. We tested the hypotheses that logging increases the denitrification rates and nitrate and C limitation of denitrifiers activity would be higher in soils of unlogged, old-growth forests than in soils of logged forests. Potential denitrification rates were estimated by the acetylene inhibition assay in intact soil cores in laboratory short-term aerobic incubations using the following treatments: 0.7 mmol NO3-N addition, the same nitrate addition plus 23.3 mmol C-glucose, and controls (no additions) with and without 10% v/v acetylene. Forest logging did not significantly change soil nitrate content and C lability (e. g. soil C/N ratio). A nested two-factor ANOVA for repeated measures showed that denitrification was enhanced by nitrate plus labile C additions in both forests, suggesting that in both logged and unlogged forests labile C and nitrate limit denitrifiers activity. Increases were up to one order of magnitude when glucose was added to nitrate treated soils; from 373 +/- 113 to 3 353 +/- 451 mu g N2O-N m(-2) d(-1) in the unlogged, old-growth forest and from 1 369 +/- 941 to 12 192 +/- 7 474 mu g N2O-N m(-2) d(-1) in the logged forest. We conclude that, denitrification would be enhanced in logged forests in the longer term due to a greater nitrate and labile C availability of both in disturbed soils.