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Nitrogen loss from unpolluted South American forests mainly via dissolved organic compounds

An Addendum to this article was published on 08 August 2002


Conceptual1,2,3,4 and numerical5,6,7,8 models of nitrogen cycling in temperate forests assume that nitrogen is lost from these ecosystems predominantly by way of inorganic forms, such as nitrate and ammonium ions. Of these, nitrate is thought to be particularly mobile, being responsible for nitrogen loss to deep soil and stream waters. But human activities—such as fossil fuel combustion, fertilizer production and land-use change—have substantially altered the nitrogen cycle over large regions9, making it difficult to separate natural aspects of nitrogen cycling from those induced by human perturbations10. Here we report stream chemistry data from 100 unpolluted primary forests in temperate South America. Although the sites exhibit a broad range of environmental factors that influence ecosystem nutrient cycles11,12,13 (such as climate, parent material, time of ecosystem development, topography and biotic diversity), we observed a remarkably consistent pattern of nitrogen loss across all forests. In contrast to findings from forests in polluted regions, streamwater nitrate concentrations are exceedingly low, such that nitrate to ammonium ratios were less than unity, and dissolved organic nitrogen is responsible for the majority of nitrogen losses from these forests. We therefore suggest that organic nitrogen losses should be considered in models of forest nutrient cycling, which could help to explain observations of nutrient limitation in temperate forest ecosystems.

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Figure 1
Figure 2: Hydrologic nitrogen losses from temperate forest watersheds in 13 areas of South America and 3 areas of eastern North America.
Figure 3: Hydrologic losses of dissolved inorganic and organic nitrogen, DIN and DON, estimated across the range of precipitation inputs to unpolluted forests of South America.


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We thank S. Nodvin for sharing samples from CO and SF; M. Medina, B. Houlton, J. Armesto, C. Perez, G. Steinhart, J. O'Brien, G. Likens, J. Franklin, O. Sala, G. Lewis, T. Flum, J. Jamison, Corporación Nacional Forestal de Chile and Administración de Parque Nacionales de Argentina for site selection, field assistance and sample collection; M. Brown and K. Lohse for sample analysis; E. Boyer for cartography; and J. Compton, T. Fahey, R. Howarth, K. Lajtha, J. von Fischer, G. Lewis and P. Vitousek for comments on the manuscript. This work is a contribution to the Cordillera Piuchué Ecosystem Study and was supported by the Andrew W. Mellon Foundation, the NASA Earth Systems Science Fellowship Program and the US NSF.

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Perakis, S., Hedin, L. Nitrogen loss from unpolluted South American forests mainly via dissolved organic compounds. Nature 415, 416–419 (2002).

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