The Role of Leaf Anatomy and Morphology in Determining Ozone Susceptibility in Cut-leaf Coneflower

Cutleaf coneflower (Rudbeckia laciniata var. digitata) is an ozone sensitive native wildflower growing within Great Smoky Mountains National Park (GRSM) where ozone pollution is often a problem. Individual coneflowers exhibit substantial variation in ozone sensitivity, yet the causes for this are not yet known. The purpose of my study was to evaluate whether differences in leaf anatomy and morphology between sensitive and tolerant individuals of coneflower were responsible for this variation in ozone susceptibility. I hypothesized that sensitive individuals would have thinner leaf and mesophyll layers, greater internal airspace, greater exposed cell surface, and thinner cell walls. Leaf samples were collected in June, July and August of 2004 from both sensitive and tolerant individuals for analysis. Micrographic measurements were made on thin prepared sections using light microscopy and included cuticle thickness, leaf and mesophyll thickness, internal airspace, exposed cell surface, cell area, live and dead cell number and cell wall thickness. There were few effects on any parameters related to sensitivity and the majority of differences found were related to season and habitat effects. Leaf anatomy and morphology did not differ between sensitive and tolerant plants, and therefore, these attributes do not appear to be the cause of sensitivity differences.