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Effects of Elevated CO2 on Leaf Litter Quality in a Mojave Desert Ecosystem
Billings, S.A., Zitzer, S.F., Weatherly, H., Schaeffer, S.M., Charlet, T., Arnone III, J.A. and Evans, R.D.  2003.  Effects of elevated carbon dioxide on green leaf tissue and leaf litter quality in an intact Mojave Desert ecosystem.  Global Change Biology 9: 729-735.

What was done
The authors recount how Strain and Bazzaz (1983) "hypothesized that CO2 enrichment would lower plant N [nitrogen] content relative to C [carbon] content, slow litter decomposition, and thus reduce soil N availability," noting that the two scientists additionally suggested "this lower N availability would serve as a negative feedback to further plant productivity."  Hence, they tested this hypothesis in a study of green leaves and senesced leaf litter of four shrub species -- Larrea tridentata (DC.) Cov., Ambrosia dumosa (A. Gray) Payne, Lycium andersonii (A. Gray) and Lycium pallidum (Miers var. oligospermum C. Hitchc. -- exposed to an atmospheric CO2 concentration of 550 ppm for a period of three years at the Nevada Desert FACE facility, which is located 15 km north of Mercury, Nevada, USA in an intact Mojave Desert ecosystem.

What was learned
Green leaf N content was indeed reduced with respect to C content in some of the shrub species in some of the years of the study.  However, the authors report they "found no effect of CO2 on N or C content, C:N ratios, or lignin or cellulose concentrations in leaf litter of L. tridentata, L. pallidum, L. andersonii, or A. dumosa."

What it means
In the words of the authors, "the difference in effects of elevated CO2 on green leaf tissue and leaf litter presented in this study confirms that the litter quality hypothesis of Strain and Bazzaz (1983) may not be realized in a high CO2 atmosphere," as has also been noted by Norby et al. (2001).  Hence, they conclude that "potential increases in desert productivity with elevated CO2 thus may not be limited by reduced leaf litter quality."  This finding is extremely good news for the biosphere, for it means, as the authors also report, that "deserts are expected to be among the most responsive ecosystems to elevated CO2, with increases in productivity leading to potential increased C sequestration."

Norby, R.J., Cotrufo, M.F., Ineson, P., O'Neill, E.G. and Canadell, J.G.  2001.  Elevated CO2, litter chemistry, and decomposition: a synthesis.  Oecologia 127: 153-165.

Strain, B.R. and Bazzaz, F.A.  1983.  Terrestrial plant communities.  In: Lemon, E.R. (Ed.), CO2 and Plants, Westview Press, Boulder, CO, pp. 177-222.

Reviewed 23 July 2003