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Reduction of soil carbon formation by tropospheric ozone under increased carbon dioxide levels


In the Northern Hemisphere, ozone levels in the troposphere have increased by 35 per cent over the past century1, with detrimental impacts on forest2,3 and agricultural4 productivity, even when forest productivity has been stimulated by increased carbon dioxide levels5. In addition to reducing productivity, increased tropospheric ozone levels could alter terrestrial carbon cycling by lowering the quantity and quality of carbon inputs to soils. However, the influence of elevated ozone levels on soil carbon formation and decomposition are unknown. Here we examine the effects of elevated ozone levels on the formation rates of total and decay-resistant acid-insoluble soil carbon under conditions of elevated carbon dioxide levels in experimental aspen (Populus tremuloides) stands and mixed aspen–birch (Betula papyrifera) stands. With ambient concentrations of ozone and carbon dioxide both raised by 50 per cent, we find that the formation rates of total and acid-insoluble soil carbon are reduced by 50 per cent relative to the amounts entering the soil when the forests were exposed to increased carbon dioxide alone. Our results suggest that, in a world with elevated atmospheric carbon dioxide concentrations, global-scale reductions in plant productivity due to elevated ozone levels will also lower soil carbon formation rates significantly.

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Figure 1: Total carbon incorporated into soils during 4 yr of exposure to elevated O3 + CO2 and elevated CO2.
Figure 2: Carbon incorporated into the stable acid-insoluble fraction of soils during 4 yr of exposure to elevated O3 + CO2 and elevated CO2.


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This research was supported by the US Department of Energy's Office of Science (BER: Program for Ecosystem Research and National Institute for Global Environmental Change), the USDA Forest Service (Northern Global Change and North Central Research Station), the National Science Foundation (DEB, DBI/MRI), and the USDA Natural Research Initiatives Competitive Grants Program. G. Hendry, K. Lewin, J. Nagey, D. Karnosky and J. Sober have been instrumental in the successful implementation of this long-term field experiment.

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Correspondence to Wendy M. Loya.

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Loya, W., Pregitzer, K., Karberg, N. et al. Reduction of soil carbon formation by tropospheric ozone under increased carbon dioxide levels. Nature 425, 705–707 (2003).

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