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Atmospheric CO2 Enrichment and Soil Nitrogen Availability in the Mojave Desert
Billings, S.A., Schaeffer, S.M., Zitzer, S., Charlet, T., Smith, S.D. and Evans, R.D.  2002.  Alterations of nitrogen dynamics under elevated carbon dioxide in an intact Mojave Desert ecosystem: evidence from nitrogen-15 natural abundance.  Oecologia 131: 463-467.

What was done
Naturally growing vegetation in the Mojave Desert of Nevada, USA, was enclosed within FACE plots receiving atmospheric CO2 concentrations of 350 and 550 ppm to study the effects of elevated CO2 on this desert community that is dominated by the perennial shrub Larrea tridentata.  In this particular paper, the authors report the results of measurements of plant nitrogen isotopic composition to determine if elevated CO2 affects nitrogen dynamics in this arid ecosystem.

What was learned
Over a seven-month sampling period, the amount of 15N within ambiently-grown and CO2-enriched vegetation increased by 34 and 58%, respectively.  The authors suggest that the larger CO2-induced enhancement of plant 15N concentration was due to atmospheric CO2 enrichment helping soil microbes to overcome soil carbon limitations, thus enabling microbial activity to increase and enhance the availability of soil nitrogen to plants.

What it means
In many desert areas, the productivity of natural ecosystems is limited by low soil carbon concentrations.  As the CO2 content of the atmosphere increases, however, greater inputs of carbon to soils via enhanced plant root exudation and litter production will likely stimulate soil microbial activities; and this enhanced microbial activity should increase the amount of soil nitrogen that is available to plants.  This phenomenon, in turn, should allow plants to produce even more biomass.  Hence, the productivity of carbon-limited ecosystems, such as deserts, will likely rise significantly as the CO2 concentration of the atmosphere continues its upward trajectory.

Reviewed 1 May 2002