L. O. Hedin Steven S. Perakis 2002 <p><span>Conceptual</span>^{<a id="ref-link-section-d257630553e377" title="Likens, G. E. &amp; Bormann, F. H. Biogeochemistry of a Forested Ecosystem 2nd edn (Springer, New York, 1995)." href="https://www.nature.com/articles/415416a#ref-CR1" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 1" data-mce-href="https://www.nature.com/articles/415416a#ref-CR1">1</a>,<a id="ref-link-section-d257630553e380" title="Aber, J. et al. Nitrogen saturation in temperate forest ecosystems: Hypotheses revisited. BioScience 48, 921–34 (1998)." href="https://www.nature.com/articles/415416a#ref-CR2" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 2" data-mce-href="https://www.nature.com/articles/415416a#ref-CR2">2</a>,<a id="ref-link-section-d257630553e383" title="Tamm, C. O. Nitrogen in Terrestrial Ecosystems (Springer, Berlin, 1991)." href="https://www.nature.com/articles/415416a#ref-CR3" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 3" data-mce-href="https://www.nature.com/articles/415416a#ref-CR3">3</a>,<a id="ref-link-section-d257630553e386" title="Stoddard, J. L. in Environmental Chemistry of Lakes and Reservoirs (ed. Baker, L. A.) 223–284 (American Chemical Society, Washington DC, 1994)." href="https://www.nature.com/articles/415416a#ref-CR4" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 4" data-mce-href="https://www.nature.com/articles/415416a#ref-CR4">4</a>}<span>&nbsp;and numerical</span>^{<a id="ref-link-section-d257630553e390" title="Schimel, D. S., Braswell, B. H. &amp; Parton, W. J. Equilibration of the terrestrial water, nitrogen, and carbon cycles. Proc. Natl Acad. Sci. USA 94, 8280–8283 (1997)." href="https://www.nature.com/articles/415416a#ref-CR5" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 5" data-mce-href="https://www.nature.com/articles/415416a#ref-CR5">5</a>,<a id="ref-link-section-d257630553e393" title="Rastetter, E. B. et al. Resource optimization and symbiotic nitrogen fixation. Ecosystems 4, 369–388 (2001)." href="https://www.nature.com/articles/415416a#ref-CR6" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 6" data-mce-href="https://www.nature.com/articles/415416a#ref-CR6">6</a>,<a id="ref-link-section-d257630553e396" title="McGuire, A. D. et al. Equilibrium responses of global net primary production and carbon storage to doubled atmospheric carbon dioxide: sensitivity to changes in vegetation nitrogen concentration. Glob. Biogeochem. Cycles 11, 173–189 (1997)." href="https://www.nature.com/articles/415416a#ref-CR7" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 7" data-mce-href="https://www.nature.com/articles/415416a#ref-CR7">7</a>,<a id="ref-link-section-d257630553e399" title="McKane, R. B. et al. Climatic effects on tundra carbon storage inferred from experimental data and a model. Ecology 78, 1170–1187 (1997)." href="https://www.nature.com/articles/415416a#ref-CR8" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 8" data-mce-href="https://www.nature.com/articles/415416a#ref-CR8">8</a>}<span>&nbsp;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 regions</span>^{<a id="ref-link-section-d257630553e403" title="Vitousek, P. M. et al. Human alteration of the global nitrogen cycle: Sources and consequences. Ecol. Appl. 7, 737–750 (1997)." href="https://www.nature.com/articles/415416a#ref-CR9" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 9" data-mce-href="https://www.nature.com/articles/415416a#ref-CR9">9</a>}<span>, making it difficult to separate natural aspects of nitrogen cycling from those induced by human perturbations</span>^{<a id="ref-link-section-d257630553e407" title="Hedin, L. O., Armesto, J. J. &amp; Johnson, A. H. Patterns of nutrient loss from unpolluted, old-growth temperate forests: Evaluation of biogeochemical theory. Ecology 76, 493–509 (1995)." href="https://www.nature.com/articles/415416a#ref-CR10" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 10" data-mce-href="https://www.nature.com/articles/415416a#ref-CR10">10</a>}<span>. 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 cycles</span>^{<a id="ref-link-section-d257630553e411" title="Jenny, H. Factors of Soil Formation (McGraw-Hill, New York, 1941)." href="https://www.nature.com/articles/415416a#ref-CR11" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 11" data-mce-href="https://www.nature.com/articles/415416a#ref-CR11">11</a>,<a id="ref-link-section-d257630553e414" title="Gorham, E. Factors influencing supply of major ions to inland waters, with special reference to the atmosphere. Geol. Soc. Am. Bull. 72, 795–840 (1961)." href="https://www.nature.com/articles/415416a#ref-CR12" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 12" data-mce-href="https://www.nature.com/articles/415416a#ref-CR12">12</a>,<a id="ref-link-section-d257630553e417" title="Vitousek, P. M. &amp; Reiners, W. A. Ecosystem succession and nutrient retention: a hypothesis. BioScience 25, 376–381 (1975)." href="https://www.nature.com/articles/415416a#ref-CR13" data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref" aria-label="Reference 13" data-mce-href="https://www.nature.com/articles/415416a#ref-CR13">13</a>}<span>&nbsp;(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.</span></p> application/pdf 10.1038/415416a en Nature Publications Nitrogen loss from nonpolluted South American forests mainly via dissolved organic compounds article