Relationships between leaf anatomy and ozone sensitivity of Fraxinus pennsylvanica marsh. and Prunus serotina Ehrh.

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It is well known that there are genetic differences in sensitivity of broad-leaved tree species to ozone (O3). It would be helpful to know if individual trees in the field could be classified as sensitive or tolerant based on properties of sensitivity other than the presence/absence of foliar injury symptoms. We hypothesized that leaf anatomical characteristics allowing greater amounts of O3 inside the leaf would be found in the leaves of sensitive individuals compared to the leaves of tolerant individuals. Light microscopy was used to examine 11 anatomical characters of leaves of field-grown Fraxinus pennsylvanica Marsh. and Prunus serotina Ehrh. trees that differed in O3 sensitivity, as determined by injury symptoms. The characters were measured on uninjured areas of leaves collected in the field from trees classified as tolerant or sensitive. There were significant differences between sensitive and tolerant individuals of both species for several characters, including stomatal density, palisade mesophyll thickness and total mesophyll thickness, and the percentage of spongy mesophyll layer relative to total leaf mesophyll. Differences in stomatal density were inconsistent for the two species considered. The palisade mesophyll was significantly thinner by 27 and 17% in sensitive green ash and black cherry leaves compared to tolerant leaves, causing the percentage of spongy mesophyll layer relative to total leaf thickness to be 20-12% higher for sensitive compared to tolerant individuals. Consequently, the total leaf thickness was less for sensitive trees for both species. This aspect of leaf anatomy was consistent with shade leaf anatomy and may be associated with O3 sensitivity for these two broad-leaved species. © 1992.

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Environmental and Experimental Botany