Stomatal behavior of ozone-sensitive and -insensitive coneflowers (Rudbeckia laciniata var. digitata) in Great Smoky Mountains National Park

Morphological and physiological attributes were assessed to elucidate the underlying mechanisms of ozone (O-3) sensitivity in a highly sensitive species, cutleaf coneflower (Rudbeckia laciniata var. digitata). Foliage at the same height in the canopy on paired O-3-sensitive and -insensitive cutleaf coneflowers was assessed for level of foliar symptoms, stomatal density, stomatal responsiveness to dynamic changes in light and leaf-to-air vapor pressure deficit (VPD), steady-state responses to light and CO2, intrinsic transpirational efficiency, and plant water balance. There were no morphological differences between the sensitivity types that might have contributed to greater O-3 uptake in sensitive individuals. Stomata of sensitive plants were less responsive than those of insensitive plants to experimentally increased and decreased light intensities, and to increased VPD. O-3-insensitive plants had greater intrinsic transpirational efficiencies, greater maximum assimilation rates under saturating CO2 and light, and greater carboxylation rates. Different physiological attributes vary independently within an individual plant, which collectively confer sensitivity or insensitivity to O-3 injury.