Ambient ozone effects on gas exchange and total non-structural carbohydrate levels in cutleaf coneflower (Rudbeckia laciniata L.) growing in Great Smoky Mountains National Park.

Ozone-sensitive and -tolerant individuals of cutleaf coneflower (Rudbeckia laciniata L.) were compared for their gas exchange characteristics and total non-structural carbohydrates at Purchase Knob, a high elevation site in Great Smoky Mountains National Park, USA. Photosynthesis and stomatal conductance decreased with increased foliar stipple. Sensitive plants had lower photosynthetic rates for all leaves, except the very youngest and oldest when compared to tolerant plants. Stomatal conductance decreased with increasing leaf age, but no ozone-sensitivity differences were found. Lower leaves had less starch than upper ones, while leaves on sensitive plants had less than those on tolerant plants. These results show that ambient levels of ozone in Great Smoky Mountains National Park can adversely affect gas exchange, water use efficiency and leaf starch content in sensitive coneflower plants. Persistence of sensitive genotypes in the Park may be due to physiological recovery in low ozone years.

Cutleaf coneflower (Rudbeckia laciniata L.) response to ozone and ethylenediurea (EDU).

Cutleaf coneflower (Rudbeckia laciniata L.) seedlings were placed into open-top chambers in May, 2004 and fumigated for 12 wks. Nine chambers were fumigated with either carbon-filtered air (CF), non-filtered air (NF) or twice-ambient (2x) ozone (O(3)). Ethylenediurea (EDU) was applied as a foliar spray weekly at 0 (control), 200, 400 or 600 ppm. Foliar injury occurred at ambient (30%) and elevated O(3) (100%). Elevated O(3) resulted in significant decreases in biomass and nutritive quality. Ethylenediurea reduced percent of leaves injured, but decreased root and total biomass. Foliar concentrations of cell-wall constituents were not affected by EDU alone; however, EDUxO(3) interactions were observed for total cell-wall constituents and lignocellulose fraction. Our results demonstrated that O(3) altered the physiology and productivity of cutleaf coneflower, and although reducing visible injury EDU may be phytotoxic at higher concentrations.

Use of ethylenediurea (EDU) to ameliorate ozone effects on purple coneflower (Echinacea purpurea).

Purple coneflower plants (Echinacea purpurea) were placed into open-top chambers (OTCs) for 6 and 12 weeks in 2003 and 2004, respectively, and exposed to charcoal-filtered air (CF) or twice-ambient (2x) ozone (O3) in 2003, and to CF, 2x or non-filtered (NF), ambient air in 2004. Plants were treated with ethylenediurea (EDU) weekly as a foliar spray. Foliar symptoms were observed in >95% of the plants in 2x-treated OTCs in both years. Above-ground biomass was not affected by 2x treatments in 2003, but root and total-plant biomass decreased in 2004. As a result of higher concentrations of select cell wall constituents (% ADF, NDF and lignin) nutritive quality was lower for plants exposed to 2x-O3 in 2003 and 2004 (26% and 17%, respectively). Significant EDU x O3 interactions for concentrations of cell wall constituents in 2003 indicated that EDU ameliorated O3 effects on nutritive quality. Interactions observed in 2004 were inconsistent.

Visible foliar injury caused by ozone alters the relationship between SPAD meter readings and chlorophyll concentrations in cutleaf coneflower.

The ability of the SPAD-502 chlorophyll meter to quantify chlorophyll amounts in ozone-affected leaves of cutleaf coneflower (Rudbeckia laciniata var. digitata) was assessed in this study. When relatively uninjured leaves were measured (percent leaf area affected by stipple less than 6%), SPAD meter readings were linearly related to total chlorophyll with an adjusted R (2) of 0.84. However, when leaves with foliar injury (characterized as a purple to brownish stipple on the upper leaf surface affecting more than 6% of the leaf area) were added, likelihood ratio tests showed that it was no longer possible to use the same equation to obtain chlorophyll estimations for both classes of leaves. Either an equation with a common slope or a common intercept was necessary. We suspect several factors are involved in altering the calibration of the SPAD meter for measuring chlorophyll amounts in visibly ozone-injured leaves, with the most likely being changes in either light absorption or scattering resulting from tissue necrosis.