Ecology

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Science  30 Aug 2013:
Vol. 341, Issue 6149, pp. 938
DOI: 10.1126/science.341.6149.938-a
CREDIT: AP PHOTO/THE COLUMBIAN/TROY WAYRYNEN

Globally, forests and their soils account for about twice as much carbon as is present in the atmosphere, and hence the response of forests to increasing atmospheric CO2 is expected to be an important component of the global carbon cycle. However, compared to what is known from studies of small trees and herbaceous vegetation, in which elevated CO2 has been shown to have a fertilizing effect on growth, there has been relatively little experimental research on mature forest stands. Using a 45-m canopy crane in a 100-year-old mixed deciduous forest in Switzerland, Bader et al. exposed tree crowns to 550 ppm CO2 over 8 years and compared the ecosystem's response to that of control trees not exposed to elevated CO2. Key plant traits, including litter production, radial stem growth, leaf biomass, and foliar nitrogen, were unaffected. However, there were several indicators of altered below-ground processes, including enhanced nitrification and nitrate leaching and reduced water uptake by roots. Hence, it appears that—at least for the trees in this mature forest stand—elevated CO2 does not translate into increased carbon sequestration by the vegetation and that the consequences are more likely to manifest themselves in alterations in soil processes and nutrient cycling.

J. Ecol. 101, 10.1111/1365-2745.12149 (2013).

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