HR: 1330h
AN: B32B-0389    [PDF]
TI: Global Patterns in Dissimilatory Nitrate Reduction: A Latitudinal Gradient in Nitrogen Retention and Loss
AU: * Silver, W L
EM: wsilver@nature.berkeley.edu
AF: Ecosystem Sciences, Department of Environmental Science Policy and Management, 151 Hilgard Hall #3110, University of California, Berkeley, CA 94720 United States
AU: Thompson, A W
EM: awt@nature.berkeley.edu
AF: Ecosystem Sciences, Department of Environmental Science Policy and Management, 151 Hilgard Hall #3110, University of California, Berkeley, CA 94720 United States
AU: Bradbury, D
EM: bradbury@nature.berkeley.edu
AF: Ecosystem Sciences, Department of Environmental Science Policy and Management, 151 Hilgard Hall #3110, University of California, Berkeley, CA 94720 United States
AU: Chapin, F S
EM: fffsc@aurora.uaf.edu
AF: Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775 United States
AU: Ewel, J J
EM: jackewel@gte.net
AF: Institute of Pacific Islands Forestry, USDA Forest Service, Pacific Southwest Research Station, 1151 Punchbowl St. Rm 323, Honolulu, HI 96813 United States
AU: Firestone, M K
EM: mkfstone@nature.berkeley.edu
AF: Ecosystem Sciences, Department of Environmental Science Policy and Management, 151 Hilgard Hall #3110, University of California, Berkeley, CA 94720 United States
AB: Increased nitrogen (N) deposition in humid environments has the potential to significantly increase nitrous oxide (N$_{2}$O) emissions via nitrification and denitrification. This potential N loss may be significantly offset by N retention from dissimilatory nitrate reduction to ammonium (DNRA). In this study, we report on rates of dissimilatory nitrate reduction to N$_{2}$O and ammonium along a latitudinal gradient from the tropics to the boreal forest. We conducted laboratory experiments with forest soils from Costa Rica, Puerto Rico, California, and Alaska to determine maximum potential rates of DNRA and N$_{2}$O production. We also conducted field experiments in Costa Rica, Puerto Rico, and Alaska to estimate in situ rates. Maximum potential rates of DNRA ranged from 10 ug/g/d in fertilized poplar forests in Alaska to 0.3 ug/g/d in unfertilized polyculture plantations in Costa Rica. At all sites, rates of DNRA appeared to be nitrate limited. On average, temperate and boreal forests had greater potential rates of DNRA (5 $\pm$ 1 ug/g/d) than tropical forests (3 $\pm$ 1 ug/g/d). Nitrogen fertilization significantly increased rates of DNRA in Alaska. Rates of maximum potential N$_{2}$O flux were generally lower than DNRA rates (0.16 to 4 ug/g/d). In field experiments, rates of DNRA were greatest in tropical rain forests in Puerto Rico, followed by wet forests in Costa Rica, and black spruce forests in Alaska. Although field DNRA rates were low in Alaska, they accounted for up to 13 % of gross mineralization and 24 % of gross nitrification. At all sites, rates of N$_{2}$O flux via denitrification and nitrification were significantly lower than N retention via DNRA. Our results suggest that this previously unmeasured N cycling pathway effectively competes with processes resulting in N-trace gas loss from a range of forested ecosystems.
DE: 0315 Biosphere/atmosphere interactions
DE: 1615 Biogeochemical processes (4805)
DE: 1890 Wetlands
SC: Biogeosciences [B]
MN: 2003 Fall Meeting