Relationships between anatomical characteristics and ozone sensitivity of leaves of several herbaceous dicotyledonous plant species at Great Smoky Mountains National Park

Many plant species in the Great Smoky Mountains National Park have experienced cell death, visible leaf injury, and reductions in overall growth attributable to ambient ozone exposure levels. The overall objective of this research was to determine if ozone sensitivity of leaves of herbaceous dicotyledonous species was related to differences in leaf anatomical characteristics such as stomatal density, cross-sectional cell areas, percentage of intercellular spaces, number of layers of palisade parenchyma and thicknesses of epidermal and mesophyll tissues. Results demonstrate that three ozone sensitive species, Sassafras albidum, Rudbeckia lacimata, and Rubus canadensis had higher stomatal densities and more intercellular spaces among palisade cells compared with less sensitive species (Magnolia tripetela, Aster divaricatus, and Liquidamber styraciflua). There were no statistically significant relationships between ozone sensitivity and cross-sectional area of spongy mesophyll cells, number of palisade parenchyma cell layers or thicknesses of epidermal or mesophyll tissues. These data support the hypothesis that ozone sensitivity is associated with leaf characteristics that relate to the ability of ozone to diffuse into leaves (high stomatal densities) and the ability of ozone to diffuse among the target cells (high percentage of intercellular spaces among palisade parenchyma cells).