Hans Wullaert, Edzo Veldkamp, Marife D. Corre:
Immediate Impact of Elevated Nitrogen Input on Trace Gases Emissions in an Old-Growth Lowland Forest in Panama

HANS WULLAERT¹, EDZO VELDKAMP², MARIFE D. CORRE^2
1University of Mainz, Geographic Institute, Germany
²Georg-August-Universität Göttingen, Institute for Soil Science and Forest Nutrition (IBW), Germany

In tropical areas, nitrogen (N) emission, transport and deposition are projected to increase rapidly in the next decades. In this study, the consequences of elevated N input on trace gases emissions from a tropical lowland forest soil were evaluated. The study site is located in Gigante Peninsula, Panama, which included control and N addition treatments each with four replicate plots. Urea-N was applied twice in 2006 (April 28 and June 6) at a rate of 31.25kg N ha^-1 each application. Nitrous oxide (N₂O), nitric oxide (NO), carbon dioxide (CO₂) and methane (CH₄) fluxes were intensively measured prior to and until one month after the second N application; this measurement period was within the beginning of the rainy season. We observed significantly higher NO emissions from the N-fertilised than the control plots, but N₂O, CO₂ and CH₄ fluxes did not differ. The increased NO fluxes were largely observed during the first week after the second fertilisation, when water-filled pore space (WFPS) has increased as the rainy season progressed. N₂O emissions could possibly increase with N addition when soil moisture further increase into the rainy season. The significant correlation between N₂O + NO fluxes and NH₄⁺ levels and the range of WFPS (40-60%) indicated that N trace gases were possibly predominantly produced by nitrification. The fertiliser- induced N oxide emission was 3% of the applied N. The CO₂ and CH₄ fluxes indicated that initial N addition did not bring detectable change in microbial decomposition and root respiration for CO₂ emissions and in CH₄ consumption and production for CH₄ fluxes, at least during the early rainy season covered in our measurement.

Keywords: Climate change, denitrification, N cycling, nitrification, tropical lowland forest

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Contact Address: Hans Wullaert, University of Mainz, Geographic InstituteMainz, Germany, e-mail: wullaertuni-mainz.de