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Isotopic variability of N 2 O emissions from tropical forest soils
Author(s) -
Pérez T.,
Trumbore S. E.,
Tyler S. C.,
Davidson E. A.,
Keller M.,
Camargo P. B.
Publication year - 2000
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/1999gb001181
Subject(s) - soil water , ultisol , oxisol , inceptisol , environmental science , denitrification , tropics , rainforest , environmental chemistry , subtropics , fractionation , nitrogen , chemistry , ecology , soil science , biology , organic chemistry
We report measurements of the 15 N and 18 O signature of N 2 O emitted from tropical rain forest soils at the La Selva Biological station in Costa Rica and in the Fazenda Vitoria in the State of Pará, Brazil. The δ 15 N values ranged from −34 to 2‰ with respect to atmospheric N 2 , while δ 18 O values had a smaller range, from −4 to 18‰ with respect to atmospheric O 2 . We attribute these large variations to differences in microbial production, consumption, and transport of N 2 O. In general the δ 15 N of N 2 O emissions from an Oxisol soil in Brazil were consistently enriched by ∼20‰ in 15 N compared to those from Ultisol and Inceptisol soils in Costa Rica. Denitrification is the most likely source of N 2 O in both locations during the rainy season, and the 15 N of nitrate was similar in both locations. We attribute the overall variability in emitted 15 N to differences in the ratio of N 2 O:N 2 escaping from the soil to the atmosphere, with a larger fraction of the N 2 O reduced to N 2 at the Brazilian sites. We found light δ 15 N‐N 2 O values associated with high N 2 O emissions in a fertilized agricultural site in Costa Rica and in a “hot spot” of high emissions in the forest site in Brazil. This result suggests that the increase of substrate availability might increase the fractionation associated with N 2 O production. Overall, the Brazilian Oxisol soils had the most enriched δ 15 N‐N 2 O emissions yet measured from soils. If these are more representative of tropical soil emissions than the Costa Rica emissions, then the globally averaged δ 15 N‐N 2 O tropical rain forest soil source is more enriched than previously estimated. The large variations in isotopic signature for N 2 O emissions demonstrate the potential utility of stable isotopes as tools for understanding the processes of N 2 O production and consumption in soils.