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Photosynthetic Response of a Desert Plant to Elevated CO2
Hamerlynck, E.P., Huxman, T.E., Nowak, R.S., Redar, S., Loik, M.E., Jordan, D.N., Zitzer, S.F., Coleman, J.S., Seeman, J.R. and Smith, S.D.  2000.  Photosynthetic responses of Larrea tridentata to a step-increase in atmospheric CO2 at the Nevada Desert FACE Facility.  Journal of Arid Environments 44: 425-436.

What was done
A FACE experiment was begun in a Mojave Desert ecosystem located in Nevada, USA, in the spring of 1997 to determine the responses of native desert vegetation to atmospheric CO2 enrichment.  The dominant species present within the circular 25-m-diameter FACE plots was the evergreen perennial shrub known commonly as creosote (Larrea tridentata).  In this paper, the authors report on photosynthetic and other gas exchange data collected during wet and dry conditions that were experienced during the first six months of differential CO2 fumigation (360 and 550 ppm).

What was learned
Elevated CO2 positively impacted rates of net photosynthesis in this desert species throughout the growing season.  During wet and dry environmental conditions, for example, photosynthetic rates of CO2-enriched plants were about 100 and 80% greater, respectively, than those observed for ambiently-grown plants, due to the 53% increase in atmospheric CO2 concentration.  Because elevated CO2 did not significantly impact rates of stomatal conductance, the water-use efficiency of the CO2-enriched plants was also 100 and 80% greater than that of control plants during the same wet and dry periods.

What it means
As the CO2 content of the air continues to rise, it is likely that creosote shrubs will exhibit dramatically enhanced photosynthetic rates and increased biomass production throughout the entire year, as this woody perennial is highly responsive to atmospheric CO2 enrichment under both water-limiting and non-limiting conditions.  Thus, this ongoing phenomenon should contribute to an overall greening of the globe and perhaps to a more specific reduction in desertification, as these shrubs grow more robustly and use available soil moisture much more efficiently with more CO2 in the air.

Reviewed 22 November 2000