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Long-Term Effects of Elevated CO2 on Woody-Shrub Water Relations
Reference
Tognetti, R., Minnocci, A., Penuelas, J., Rashi, A. and Jones, M.B.  2000.  Comparative field water relations of three Mediterranean shrub species co-occurring at a natural CO2 vent.  Journal of Experimental Botany 51: 1135-1146.

What was done
The authors studied the long-term effects of atmospheric CO2 enrichment on water relations in three woody shrubs (Erica arborea L., Myrtus communis L., and Juniperus communis L.) growing naturally near CO2-emitting springs in Pisa, Italy.  Based on distances from the CO2 springs, physiological measurements were made on shrubs that had experienced atmospheric CO2 concentrations of about 360 and 700 ppm for their entire lifetimes.

What was learned
The effects of elevated CO2 on plant water relations varied according to shrub species and time of measurement (seasonal differences) over a 12-month monitoring period.  However, two common responses were evident in all shrubs; elevated CO2 reduced leaf stomatal conductances and increased leaf water potentials.

What it means
As the air's CO2 content rises, it is likely these Mediterranean shrubs will exhibit species-specific and season-specific changes in their water relations.  Specifically, all three of them will likely experience decreases in water loss though CO2-induced reductions in leaf stomatal conductance.  In addition, enhanced rates of photosynthesis will likely lead to greater carbohydrate synthesis and the accumulation of osmotically-active solutes in leaves, which would increase leaf water potentials and consequently provide plants with a more favorable water status.  Thus, CO2-induced enhancements of these drought-tolerating strategies, in the words of the authors, "may allow plants to endure severe periodic drought."


Reviewed 6 February 2002