Ozone sensitivity of 28 plant selections exposed to ozone under controlled conditions

Ambient, ground-level ozone is the most important air pollutant affecting vegetation in the US. However, ozone-sensitive bioindicators need to be identified for use in field surveys to detect ozone-induced symptoms. To identify such bioindicators, 28 plant selections were exposed to ozone within greenhouse chambers during 2003 and 2004. Plants most sensitive to ozone included Asclepias incarnata (swamp milkweed), Asclepias syriaca (common milkweed), Cephalanthus occidentalis (buttonbush), Platanus occidentalis (American sycamore), Salix x cotteti (Bankers dwarf willow), Salix lucida (shining willow), Salix nigra (black willow), Salix sericea (silky willow), and Symphoricarpos albus (snowberry). Plants moderately sensitive included Aster novae-angliae (New England aster), Monarda didyma (bee-balm), Rhus aromatica (aromatic sumac), Salix discolor (pussy willow), Salix exigua (sandbar willow), Salix purpurea (basket willow), Sambucus ebulus (European dwarf elderberry), and Symphoricarpos spp. (mixture of "snowberries"). Plants more tolerant to ozone included Aster macrophyllus (bigleaf aster), Aster novi-belgii (New York aster), Cercis canadensis (redbud), Populus maximowizii x trichocarpa (hybrid poplar), Rudbeckia laciniata (cutleaf, or tall green-headed coneflower), Salix amygdaloides (peach-leaved willow), Salix eriocephala (diamond willow), Sambucus canadensis (American elder), Sambucus nigra (European elder), Symphoricarpos orbiculatus (coralberry), and Viburnum trilobum (highbush-cranberry). The incidence and severity of ozone-induced symptoms varied with species, ozone concentration, and length of exposure. Pigmented adaxial leaf surface stipple, bifacial necrosis, and premature defoliation were common foliar symptoms induced by ozone; leaf reddening, bronzing, and chlorosis occurred less frequently. Species that produced classic ozone-induced stipple in this study may serve as useful bioindicators in field surveys to confirm that ozone injury occurs in many parts of the country. Such findings may have a positive impact on establishing more stringent air-quality standards to protect vegetation and the environment.