Relationships between cellular injury, visible injury of leaves, and ozone exposure levels for several dicotyledonous plant species at Great Smoky Mountains National Park

Abstract

Ozone is a ubiquitous air pollutant in the troposphere that can significantly affect terrestrial vegetation. Great Smoky Mountains National Park (GRSM), in eastern Tennessee and in western North Carolina, is experiencing ozone concentrations that may be sufficient to injure vegetation. The purpose of this research was to determine (1) if the percentages of dead palisade parenchyma cells were correlated with the percentages of leaf area that exhibited stippling (necrosis) and (2) if percentages of dead palisade parenchyma cells were correlated with cumulative ozone exposure for leaves of native plants in field chamber ozone exposures at GRSM. Such relationships between cells and leaf injuries with cumulative ozone exposure level may eventually provide an understanding of the leaf anatomical parameters that confer sensitivity of foliage to ozone insult. Using linear regression models, percentages of dead palisade parenchyma cells were correlated positively with percentages of leaf areas with visible injuries for Sassafras albidum, Rudbeckia laciniata, and Rubus canadenis for two growing seasons. For each of the three species there were positive relationships with r 2 values between 0.52 and 0.90 with probability values below 0.001 in all cases. No statistically significant relationships for these parameters occurred for Aster divaricatus, Magnolia tripetela, Liquidamber styraciflua, Rhus copallina, and Platanus occidentalis. The lack of relationships for these five species between percentage of dead cells and percentage of leaf area with visible leaf injury was attributed to large percentages of palisade cell death with only small amounts of visible leaf injuries during fumigation. In addition to the above relationships, percentages of dead palisade parenchyma cells were positively correlated by linear regression with cumulative ozone exposure for S. albidum ( r 2=0.83) and R. canadensis ( r 2=0.64). Both had probability values below 0.001. The results are discussed with regard to the factors that may confer such levels of sensitivity which need to be tested quantitatively. To our knowledge this is the first report to demonstrate statistically significant quantitative relationships among percentage of dead palisade parenchyma cells, percentage of leaf area with visible injuries, and cumulative ozone exposure of foliage of broad-leaved plant species.