Abstract
Arising from: F. Magnani et al. Nature 447, 849–851 (2007)10.1038/nature05847; Magnani et al. reply
Magnani et al.1 found that net carbon (C) sequestration of temperate and boreal forests is clearly driven by nitrogen (N) deposition. From the positive relationship between average net ecosystem production (NEP) and wet N deposition, the authors further conclude that “no signs of N saturation were apparent” in the studied forests and that this is “casting doubts on the risk of widespread ecosystem nitrogen saturation”. Nitrogen additions can clearly alter net ecosystem production, but net ecosystem production cannot be used as an indicator of N saturation.
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Nitrogen saturation implies a change in N cycling from a closed internal cycle to an open cycle2 where excess N is leached and/or emitted from the forest ecosystem. These changes in forest ecosystem functioning have been extensively documented3,4. Examples from literature lead us to suggest that some of the forest ecosystems discussed in the concerned article might be N saturated, irrespective of the increased net ecosystem production. Evidence for N saturation has been observed in forest ecosystems subject to N deposition levels similar to the relatively low deposition range reported in the concerned article1 (that is, less than 10 kg N ha-1 yr-1 wet deposition), including considerable nitrate loss (up to 10 kg N ha-1 yr-1) through runoff or seepage water5,6,7 and elevated emissions of NO and N2O8. Because Magnani et al.1 did not measure any of these pathways of N loss, they cannot rule out N saturation in the studied forest ecosystems.
The demonstrated relationship between N deposition and C sequestration is an important finding, consistent with other literature9. In our opinion, however, Magnani et al.1 demonstrate an incorrect view on the phenomenon of N saturation and, in doing so, greatly ignore the effect of N deposition and saturation on soil acidification, groundwater and surface water quality, biodiversity, and ecosystem services other than C sequestration. Because the data presented by Magnani et al.1 do not allow an evaluation of the N saturation status of the studied forests, the expressed “doubts on the risk of widespread ecosystem nitrogen saturation” are not substantiated. At the moment, N saturation of forest ecosystems is probably not yet a widespread problem on a global scale, but it is surely a widespread problem in densely populated and more industrialized regions4,7. From the Europe-covering IFEF (Indicators of Forest Ecosystem Functioning) and Level-II (UN-ECE/EC intensive monitoring plots) databases10,11, it can be deduced that more than 25% of the European forests included in these databases are N saturated (considering the nitrate seepage flux as indicator and 5 kg (357 mol) N ha-1 yr-1 as a threshold value of N saturation). Furthermore, from a large number of sites in the northeastern United States4, N saturation was indicated as a frequently occurring phenomenon. As substantial increases in global N emissions are predicted for the coming 50 yr12, the potential risk of widespread N saturation of forest ecosystems in the long term cannot be denied.
References
Magnani, F. et al. The human footprint in the carbon cycle of temperate and boreal forests. Nature 447, 848–850 (2007)
Matson, P., Lohse, K. A. & Hall, S. J. The globalization of nitrogen deposition: Consequences for terrestrial ecosystems. Ambio 31, 113–119 (2002)
Aber, J. D. et al. Nitrogen saturation in temperate forest ecosystems—Hypotheses revisited. Bioscience 48, 921–934 (1998)
Aber, J. D. et al. Is nitrogen deposition altering the nitrogen status of northeastern forests? Bioscience 53, 375–389 (2003)
Dise, N. B., Matzner, E. & Gundersen, P. Synthesis of nitrogen pools and fluxes from European forest ecosystems. Wat. Air Soil Pollut. 105, 143–154 (1998)
Macdonald, J. A. et al. Nitrogen input together with ecosystem nitrogen enrichment predict nitrate leaching from European forests. Glob. Change Biol. 8, 1028–1033 (2002)
Gundersen, P. K., Schmidt, I. K. & Raulund-Rasmussen, K. Leaching of nitrate from temperate forests—effects of air pollution and forest management. Environ. Rev. 14, 1–57 (2006)
Pilegaard, K. et al. Factors controlling regional differences in forest soil emission of nitrogen oxides (NO and N2O). Biogeosciences 3, 651–661 (2006)
Karjalainen, T. et al. Causes and Consequences of Forest Growth Trends in Europe—Results of the RECOGNITION Project. European Forest Institute Research Report (Brill, Leiden, in the press).
Lorenz, M. et al. Nitrogen retention and release in European forests: Deriving indicators from large databases. In Forest Condition in Europe: 2005 Technical Report (Federal Research Centre for Forestry and Forest Products (BFH), UNECE Geneva, 2005)
Van der Salm, C., de Vries, W., Reinds, G. J. & Dise, N. B. N leaching across European forests: Derivation and validation of empirical relationships using data from intensive monitoring plots. For. Ecol. Manage. 238, 81–91 (2007)
Galloway, J. N. et al. Nitrogen cycles: past, present, and future. Biogeochemistry 70, 153–226 (2004)
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De Schrijver, A., Verheyen, K., Mertens, J. et al. Nitrogen saturation and net ecosystem production. Nature 451, E1 (2008). https://doi.org/10.1038/nature06578
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DOI: https://doi.org/10.1038/nature06578
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