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Isotopic identification of global nitrogen hotspots across natural terrestrial ecosystems

Author(s): E. Bai | B. Z. Houlton | Y. Wang

Journal: Biogeosciences Discussions
ISSN 1810-6277

Volume: 8;
Issue: 6;
Start page: 12113;
Date: 2011;
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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's 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 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 unmanaged biosphere.
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