Isotopic identification of nitrogen hotspots across natural terrestrial ecosystems

• Published in: Biogeosciences Vol. 9; no. 8; pp. 3287 - 3304
• Main Authors: Bai, E, Houlton, B. Z, Wang, Y. P
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 23.08.2012; Copernicus Publications
• Subjects: Analysis; Denitrification; Terrestrial ecosystems
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-9-3287-2012

Nitrogen (N) influences local biological processes, ecosystem productivity, the composition of the atmospheric-climate system, and the human endeavour as a whole. Here we use natural variations in N isotopes, coupled with two models, to trace global pathways of N loss from the land to the water and atmosphere. We show that denitrification accounts for approximately 35 % of total N losses from the natural soil, with NO, N2O, and N2 fluxes equal to 15.7 ± 4.7 Tg N yr−1, 10.2 ± 3.0 Tg N yr−1, and 21.0 ± 6.1 Tg N yr−1, respectively. Our analysis points to tropical regions as the major "hotspot" of nitrogen export from the terrestrial biosphere, accounting for 71 % of global N losses from the natural land surface. The poorly studied Congo Basin is further identified as one of the major natural sources of atmospheric N2O. Extra-tropical areas, by contrast, lose a greater fraction of N via leaching pathways (~77 % of total N losses) than do tropical biomes, likely contributing to N limitations of CO2 uptake at higher latitudes. Our results provide an independent constraint on global models of the N cycle among different regions of the unfertilized biosphere.