Modifications of the leaf surface structures of Quercus ilex L in open, naturally CO2-enriched environments

Two Italian CO2 springs allowed us to study the long-term effect of a 350-2 600 mu mol mol(-1) increase in CO2 concentrations on the surface structures of leaves of Quercus ilex L. Carbon dioxide increased the quantity of cuti cular waxes, above an apparent threshold of 750 mu mol mol(-1) CO2. Leaf we ttability was not modified by CO2 concentrations. Reduction in stomatal fre quency was observable up to 750 mu mol mol(-1) CO2, the slope being almost the same as that estimated for the increase in CO2 concentration from prein dustrial times to the present. At higher concentrations, CO2 seemed to exer t no more impact on stomatal frequency.