Leaf size and surface characteristics of Betula papyrifera exposed to elevated CO2 and O3.

Betula papyrifera trees were exposed to elevated concentrations of CO(2) (1.4 x ambient), O(3) (1.2 x ambient) or CO(2) + O(3) at the Aspen Free-air CO(2) Enrichment Experiment. The treatment effects on leaf surface characteristics were studied after nine years of tree exposure. CO(2) and O(3) increased epidermal cell size and reduced epidermal cell density but leaf size was not altered. Stomatal density remained unaffected, but stomatal index increased under elevated CO(2). Cuticular ridges and epicuticular wax crystallites were less evident under CO(2) and CO(2) + O(3). The increase in amorphous deposits, particularly under CO(2) + O(3,) was associated with the appearance of elongated plate crystallites in stomatal chambers. Increased proportions of alkyl esters resulted from increased esterification of fatty acids and alcohols under elevated CO(2) + O(3). The combination of elevated CO(2) and O(3) resulted in different responses than expected under exposure to CO(2) or O(3) alone.