Ozone injury on cutleaf coneflower (Rudbeckia laciniata) and crown-beard (Verbesina occidentalis) in Great Smoky Mountains National Park

Incidence and severity of visible foliar ozone injury on cutleaf coneflower (Rudbeckia laciniata L.) and crown-beard (Verbesina occidentalis Walt.) were determined along selected trails at three locations in Great Smoky Mountains National Park during the summers of 2000 and 2001: Clingmans Dome, Cherokee Orchard Road and Purchase Knob. Cutleaf coneflower exhibited a greater amount of foliar injury than crown-beard each year of the 2-year study. Incidence and severity of injury was significantly greater for cutleaf coneflower growing near the edge of the Clingmans Dome trail than in the interior of the stand. Injury was greater at Clingmans Dome than Purchase Knob (70% vs. 40% ozone-injured plants, respectively), coincident with greater ozone exposures. In contrast to Clingmans Dome, there were no differences in injury between plants growing near- and off-trail at Purchase Knob. Differences in sensitivity to ozone were not observed for crown-beard growing near the edge compared with the interior of the stand adjacent to the Cherokee Orchard Road Loop. Ozone injury was greatest on the lower leaves for both species sampled with over 95% of the injured leaves occurring on the lower 50% of the plant. This is the first report of foliar ozone injury on these plant species in situ, in the Park, illustrating the great variability in symptom expression with time, and within and between populations.     

Seasonal profiles of leaf ascorbic acid content and redox state in ozone-sensitive wildflowers

Cutleaf coneflower (Rudbeckia laciniata L.), crown-beard (Verbesina occidentalis Walt.), and tall milkweed (Asclepias exaltata L.) are wildflower species native to Great Smoky Mountains National Park (U.S.A.). Natural populations of each species were analyzed for leaf ascorbic acid (AA) and dehydroascorbic acid (DHA) to assess the role of ascorbate in protecting the plants from ozone stress. Tall milkweed contained greater quantities of AA (7-10 micromol g(-1) fresh weight) than crown-beard (2-4 micromol g(-1) fresh weight) or cutleaf coneflower (0.5-2 micromol g(-1) fresh weight). DHA was elevated in crown-beard and cutleaf coneflower relative to tall milkweed suggesting a diminished capacity for converting DHA into AA. Tall milkweed accumulated AA in the leaf apoplast (30-100 nmol g(-1) fresh weight) with individuals expressing ozone foliar injury symptoms late in the season having less apoplast AA. In contrast, AA was not present in the leaf apoplast of either crown-beard or cutleaf coneflower. Unidentified antioxidant compounds were present in the leaf apoplast of all three species. Overall, distinct differences in antioxidant metabolism were found in the wildflower species that corresponded with differences in ozone sensitivity.     

Concentrations of mercury in otters (Lutra lutra L.) in Scotland in relation to rainfall

The incidence and severity of visible foliar ozone injury on black cherry (Prunus serotina) seedlings and saplings and tall milkweed (Asclepias exaltata) plants in Great Smoky Mountains National Park (GRSM) were determined by surveys along selected trails conducted during late summer 1992. The incidence (% injured plants) of ozone injury on black cherry was 47% and the percent injured leaves/injured plant and average leaf area injured were 43 and 6%, respectively. Maximum severity (avg. leaf area of the most severely injured leaf) was 12%. Black cherry seedlings and saplings exhibiting ozone injury were taller than non-injured plants. When insect feeding was present, it occurred 96% of the time on plants with ozone injury. Significantly more injury (p=0.007) on black cherry (% injured leaves/injured black cherry) occurred in the NW section of GRSM compared with the other Park sections. Regression analyses showed no relationships in ozone injury with respect to aspect, slope or elevation. Tall milkweed was evaluated twice during August for ozone injury. The incidence (% injured plants) of ozone injury was 74 and 79% for the first and second survey, respectively. The percentage of injured leaves per plant from the first to second survey was 63 to 79%, respectively. Tall milkweeds showing ozone injury were taller than the non-injured plants. The percentage of insect-damaged plants was 50% among plants without ozone injury and 60% among ozone-injured plants. Non-injured tall milkweed had fewer flowers and/or pods than the injured plants. Mean leaf area injured increased over time, and mean maximum leaf area injured increased from 8 to 11% during the same period. Regression analyses showed no differences in ozone injury regarding aspect, slope or elevation. Our findings indicate that ozone injury is widespread throughout the Park on sensitive vegetation.     

Interpreting spatial variation in ozone symptoms shown by cutleaf cone flower,Rudbeckia laciniata L

Visible injury caused by ozone is recorded every year in native plant species growing in Great Smoky Mountains National Park (USA). One of the most sensitive species, cutleaf coneflower (Rudbeckia laciniata L.), shows great variation in symptoms between and within populations but the causes of this variation and its ecological significance are currently unknown. This paper presents data relating to genetic variation, ozone concentrations, stomatal conductance and light (PAR) within populations. The data show that populations differ in genetic diversity, one consisting of only three genets while another was very diverse. In the former population, symptoms varied greatly within a single genet, pointing to a large micro-environmental influence. Measurements of ozone, stomatal conductance and PAR within plant canopies suggest that variation in symptom expression is unlikely to be due to differences in ozone flux and more likely to be due to variation in light. The variation in visible symptoms raises the question of what bioindicators actually indicate, and it suggests that symptoms should be interpreted with great caution until the underlying causes of that variation are fully understood.     

Seasonal development of ozone-induced foliar injury on tall milkweed (Asclepias exaltata) in Great Smoky Mountains National Park

The goals of this study were to document the development of ozone-induced foliar injury, on a leaf-by-leaf basis, and to develop ozone exposure relationships for leaf cohorts and individual tall milkweeds (Asclepias exaltata L.) in Great Smoky Mountains National Park. Plants were classified as either ozone-sensitive or insensitive based on the amount of foliar injury. Sensitive plants developed injury earlier in the season and to a greater extent than insensitive plants. Older leaf cohorts were more likely to belong to high injury classes by the end of each of the two growing seasons. In addition, leaf loss was more likely for older cohorts (2000) and lower leaf positions (2001) than younger cohorts and upper leaves, respectively. Most leaves abscised without prior ozone-like stippling or chlorosis. Failure to take this into account can result in underestimation of the effects of ozone on these plants.     

Sub-canopy deposition of ozone in a stand of cutleaf coneflower

Although there has been a great deal of research on ozone, interest in exposure of native, herbaceous species is relatively recent and it is still not clear what role the pollutant has in their ecological fitness. The ozone exposure of a plant is usually expressed in terms of the concentration above the canopy or as a time-weighted index. However, to understand the physiological effects of ozone it is necessary to quantify the ozone flux to individual leaves as they develop, which requires knowing the deposition velocity and concentration of the pollutant as a function of height throughout the plant canopy. We used a high-order closure model of sub-canopy turbulence to estimate ozone profiles in stands of cutleaf coneflower (Rudbeckia laciniata L.) located in the Great Smoky Mountains National Park, USA. The model was run for periods coinciding with a short field study, during which we measured vertical concentration profiles of ozone along with measurements of atmospheric turbulence and other meteorological and plant variables. Predictions of ozone profiles by the model are compared with observations throughout the canopy.     

Assessing the risk of foliar injury from ozone on vegetation in parks in the U.S. National Park Service's Vital Signs Network

The risk of ozone injury to plants was assessed in support of the National Park Service's Vital Signs Monitoring Network program. The assessment examined bioindicator species, evaluated levels of ozone exposure, and investigated soil moisture conditions during periods of exposure for a 5-year period in each park. The assessment assigned each park a risk rating of high, moderate, or low. For the 244 parks for which assessments were conducted, the risk of foliar injury was high in 65 parks, moderate in 46 parks, and low in 131 parks. Among the well-known parks with a high risk of ozone injury are Gettysburg, Valley Forge, Delaware Water Gap, Cape Cod, Fire Island, Antietam, Harpers Ferry, Manassas, Wolf Trap Farm Park, Mammoth Cave, Shiloh, Sleeping Bear Dunes, Great Smoky Mountains, Joshua Tree, Sequoia and Kings Canyon, and Yosemite.     

Seedling insensitivity to ozone for three conifer species native to Great Smoky Mountains National Park

Field symptoms typical of ozone injury have been observed on several conifer species in Great Smoky Mountains National Park, and tropospheric ozone levels in the Park can be high, suggesting that ozone may be causing growth impairment of these plants. The objective of this research was to test the ozone sensitivity of selected conifer species under controlled exposure conditions. Seedlings of three species of conifers, Table Mountain pine (Pinus pungens), Virginia pine (Pinus virginiana), and eastern hemlock (Tsuga canadensis), were exposed to various levels of ozone in open-top chambers for one to three seasons in Great Smoky Mountains National Park in Tennessee, USA. A combination of episodic profiles (1988) and modified ambient exposure regimes (1989-92) were used. Episodic profiles simulated an average 7-day period from a monitoring station in the Park. Treatments used in 1988 were: charcoal-filtered (CF), 1.0x ambient, 2.0x ambient, and ambient air-no chamber (AA). In 1989 a 1.5x ambient treatment was added, and in 1990, additional chambers were made available, allowing a 0.5x ambient treatment to be added. Height, diameter, and foliar injury were measured most years. Exposures were 3 years for Table Mountain pine (1988-90), 3 years for hemlock (1989-91), and 1 and 2 years for three different sets of Virginia pine (1990, 1990-91, and 1992). There were no significant (p<0.05) effects of ozone on any biomass fraction for any of the species, except for older needles in Table Mountain and Virginia pine, which decreased with ozone exposure. There were also no changes in biomass allocation patterns among species due to ozone exposure, except for Virginia pine in 1990, which showed an increase in the root:shoot ratio. There was foliar injury (chlorotic mottling) in the higher two treatments (1.0x and 2.0x for Table Mountain and 2.0x for Virginia pine), but high plant-to-plant variability obscured formal statistical significance in many cases. We conclude, at least for growth in the short-term, that seedlings of these three conifer species are insensitive to ambient and elevated levels of ozone, and that current levels of ozone in the Park are probably having minimal impacts on these particular species.     

Atmospheric mercury in the Great Smoky Mountains compared to regional and global levels

Improvements in measurement technology are permitting development of a more detailed scientific understanding of the cycling of mercury in the global atmospheric environment. Critical to advancing the state of knowledge is the acquisition of accurate measurement of speciated mercury (gaseous and particulate) at ground research stations in a variety of settings located around the globe. This paper describes one such research effort conducted at TVA's Look Rock air quality monitoring site in Tennessee—a mountain top site (813 m elevation) just west of the Great Smoky Mountains National Park. The Great Smoky Mountains National Park is the largest National Park in the eastern US and it receives environmental protection under a variety of US statutes. Gaseous and particle mercury species along with some additional trace gases were measured at Look Rock during two field studies totaling 84 days in the spring and summer of 2004. Average results for the entire sampling period are: gaseous elemental mercury Hg(0): 1.65 ng m⁻³, reactive gaseous mercury RGM: 0.005 ng m⁻³, particulate mercury Hg(p): 0.007 ng m⁻³. Literature review indicates that these levels are within the range found for other rural/remote sites in North America and worldwide. Reactive and particulate mercury comprised together less than 1%, on average, of total airborne mercury at Look Rock. When compared to the global background mercury literature, the Look Rock measurements demonstrate that the atmospheric mercury levels in the vicinity of the Great Smoky Mountains National Park are clearly dominated by the global atmospheric pool, not by local or regional sources.     

Temporal patterns of foliar ozone symptoms on tall milkweed (Asclepias exaltata L.) in Great Smoky Mountains National Park

Incidence and severity of ozone-induced foliar symptoms on tall milkweed (Asclepias exaltata L.) along selected trails in Great Smoky Mountains National Park (GRSM) were determined by two surveys/season conducted from 1992 through 1996. Overall incidence was 73%, and was 84%, 44%, 90%, 58%, and 82% for 1992-1996, respectively for the same clusters. Average incidence was 61% and 84% for the 1st and 2nd surveys, respectively. Seasonal comparisons showed two distinct injury groupings regarding incidence and severity of injury: 1992, 1994 and 1996 (high injury); 1993 and 1995 (low injury). No discernible patterns were observed between symptomatic and asymptomatic plants regarding height, herbivory or flowering. Regression analyses indicated no differentiation in foliar symptoms regarding topographic position, aspect, slope or elevation over the 5-year study period. Our findings indicate other micro-site or genetic factors may control ozone sensitivity of tall milkweed in GRSM.     

Size-mediated foliar response to ozone in black cherry trees

Local ozone concentration and visible foliar injury were measured over the 1994 growing season on open-grown black cherry (Prunus serotina Ehrh.) trees of varying size (age) within forest stands and adjacent openings at a site in north-central Pennsylvania. Relationships were determined between visible ozone injury and ozone exposure, as well as calculated between injury and ozone uptake expressed as the product of stomatal conductance and ozone concentration. In addition, simultaneous measurements of visible symptoms and leaf gas exchange were also conducted to determine the correlation between visible and physiological injury and ozone exposure. By September, the amount of leaf area affected by visible foliar ozone injury was greatest for seedlings (46%), followed by canopy trees (20%) and saplings (15%). A large amount of variability in foliar ozone symptom expression was observed among trees within a size class. Sum40 and Sum60 (ozone concentration > 40 and > 60 nl liter(-1)) cumulative exposure statistics were the most meaningful indices for interpretation of foliar injury response. Seedlings were apparently more sensitive to ozone injury than larger trees because their higher rates of stomatal conductance resulted in higher rates of ozone uptake. Seedlings also had higher rates of early leaf abscission than larger trees with an average of nearly 30% of the leaves on a shoot abscised by 1 September compared to approximately 5% for larger trees. However, per unit ozone uptake into the leaf, larger trees exhibited larger amounts of foliar injury. The amount of visible foliar injury was negatively correlated (r(2) = 0.82) with net photosynthetic rates, but was not related to stomatal conductance. Net photosynthesis and stomatal conductance thus became uncoupled at high levels of visible foliar injury.     

Methane emissions from wastewater management

Gas exchange and ozone-induced foliar injury were intensively measured during a 6-day period in mid-August 1998 on leaves of Acer pseudoplatanus, Betula pendula, Corylus avellana, Fagus sylvatica, Fraxinus excelsior, Morus nigra, Prunus avium, Prunus serotina, Rhamnus cathartica, and Viburnum lantana at a forest nursery site in Canton Ticino, Switzerland. Plants were grown in four open plots (AA), four open-top chambers receiving carbon-filtered (CF) air, and four receiving non-filtered (NF) air. Significant variation in gas exchange (F > 12.7, P < 0.001) was detected among species with average net photosynthesis and average stomatal conductance differing by a factor of two. Species also varied significantly in foliar injury for those leaves for which we measured gas exchange (F = 39.6, P < 0.001). Fraxinus excelsior, M. nigra, P. avium, P. serotina, R. cathartica, and V. lantana showed more injury than A. pseudoplatanus, B. pendula, C. avellana, and Fagus sylvatica. Plants grown in CF chambers had significantly higher net photosynthesis (A) and stomatal conductance to water vapor (gwv), and lower foliar injury than plants grown in NF chambers and AA plots; interactions between species and ozone treatments were significant for all variables (F > or = 2.2, P < 0.05) except gwv (F = 0.7, P > 0.1). Although A and gwv decreased and foliar injury increased with leaf age, the magnitude of these changes was lower for plants grown in CF chambers than for plants grown in NF chambers and AA plots. Neither ozone uptake threshold (r = 0.26, P > 0.20) nor whole-plant injury (r = -0.15, P > 0.41) was significantly correlated with stomatal conductance across these species. It appears that the relationships between stomatal conductance and foliar injury are species-specific and interactions between physiology and environments and leaf biochemical processes must be considered in determining species sensitivity to ambient ozone exposures.     

Seasonal trends in reduced leaf gas exchange and ozone-induced foliar injury in three ozone sensitive woody plant species

Seasonal trends in leaf gas exchange and ozone-induced visible foliar injury were investigated for three ozone sensitive woody plant species. Seedlings of Populus nigra L., Viburnum lantana L., and Fraxinus excelsior L. were grown in charcoal-filtered chambers, non-filtered chambers and open plots. Injury assessments and leaf gas exchange measurements were conducted from June to October during 2002. All species developed typical ozone-induced foliar injury. For plants exposed to non-filtered air as compared to the charcoal-filtered air, mean net photosynthesis was reduced by 25%, 21%, and 18% and mean stomatal conductance was reduced by 25%, 16%, and 8% for P. nigra, V. lantana, and F. excelsior, respectively. The timing and severity of the reductions in leaf gas exchange were species specific and corresponded to the onset of visible foliar injury.     

Physiological and foliar symptom response in the crowns of Prunus serotina, Fraxinus americana and Acer rubrum canopy trees to ambient ozone under forest conditions

The crowns of five canopy dominant black cherry (Prunus serotina Ehrh.), five white ash (Fraxinus americana L.), and six red maple (Acer rubrum L.) trees on naturally differing environmental conditions were accessed with scaffold towers within a mixed hardwood forest stand in central Pennsylvania. Ambient ozone concentrations, meteorological parameters, leaf gas exchange and leaf water potential were measured at the sites during the growing seasons of 1998 and 1999. Visible ozone-induced foliar injury was assessed on leaves within the upper and lower crown branches of each tree. Ambient ozone exposures were sufficient to induce typical symptoms on cherry (0-5% total affected leaf area, LAA), whereas foliar injury was not observed on ash or maple. There was a positive correlation between increasing cumulative ozone uptake (U) and increasing percent of LAA for cherry grown under drier site conditions. The lower crown leaves of cherry showed more severe foliar injury than the upper crown leaves. No significant differences in predawn leaf water potential (psi(L)) were detected for all three species indicating no differing soil moisture conditions across the sites. Significant variation in stomatal conductance for water vapor (g(wv)) was found among species, soil moisture, time of day and sample date. When comparing cumulative ozone uptake and decreased photosynthetic activity (P(n)), red maple was the only species to show higher gas exchange under mesic vs. drier soil conditions (P < 0.05). The inconsistent differences in gas exchange response within the same crowns of ash and the uncoupling relationship between g(wv) and P(n) demonstrate the strong influence of heterogeneous environmental conditions within forest canopies.     

Aerosol light scattering measurements as a function of relative humidity: a comparison between measurements made at three different sites

The water uptake by fine aerosol particles in the atmosphere has been investigated at three rural National Parks in the United States (Great Smoky Mountains, Grand Canyon and Big Bend National Parks). The relative humidity (RH) of sample aerosols was varied from less than 20% to greater than 90% using Perma Pure drying tubes as the scattering coefficient of the aerosol was measured with a Radiance Research M903 nephelometer. Data from these studies show that growth curves at all the three sites are similar in shape but the magnitude of growth can vary considerably from day to day. The growth curves from Great Smoky Mountains show smooth continuous growth over the entire range of RH, while the growth curves from the Grand Canyon and Big Bend show smooth and continuous growth on some days and deliquescence on other days. Comparing 12-h filter samples of chemical composition data with the aerosol growth curves, we find that higher fractions of soluble inorganic compounds (sulfate and nitrate) produce growth curves of greater magnitude than do higher concentrations of either organic carbon or soil material.     

Estimates of particle hygroscopicity during the Southeastern Aerosol and Visibility Study

Aerosol water content was determined from relative humidity controlled optical particle counter (ASASP-X) size distribution measurements made during the Southeastern Aerosol and Visibility Study (SEAVS) in the Great Smoky Mountains National Park during summer 1995. Since the scattering response function of the ASASP-X is sensitive to particle refractive index, a technique for calibrating the ASASP-X for any real refractive index was developed. A new iterative process was employed to calculate water mass concentration and wet refractive index as functions of relative humidity. Experimental water mass concentrations were compared to theoretically predicted values assuming only ammonium sulfate compounds were hygroscopic. These comparisons agreed within experimental uncertainty. Estimates of particle hygroscopicity using a rural aerosol model of refractive index as a function of relative humidity demonstrated no significant differences from those made with daily varying refractive index estimates. Although aerosol size parameters were affected by the assumed chemical composition, forming ratios of these parameters nearly canceled these effects.     

Estimates of Particle Hygroscopicity during the Southeastern Aerosol and Visibility Study

ABSTRACT

Aerosol water content was determined from relative humidity controlled optical particle counter (ASASP-X) size distribution measurements made during the Southeastern Aerosol and Visibility Study (SEAVS) in the Great Smoky Mountains National Park during summer 1995. Since the scattering response function of the ASASP-X is sensitive to particle refractive index, a technique for calibrating the ASASP-X for any real refractive index was developed. A new iterative process was employed to calculate water mass concentration and wet refractive index as functions of relative humidity. Experimental water mass concentrations were compared to theoretically predicted values assuming only ammonium sulfate compounds were hygroscopic. These comparisons agreed within experimental uncertainty. Estimates of particle hygroscopicity using a rural aerosol model of refractive index as a function of relative humidity demonstrated no significant differences from those made with daily varying refractive index estimates. Although aerosol size parameters were affected by the assumed chemical composition, forming ratios of these parameters nearly canceled these effects.     

Response to ambient ozone of two white clover (Trifolium repens L.cv. "Regal") clones, one resistant and one sensitive, grown in a Mediterranean environment

Two clones of white clover (Trifolium repens L.) differing in ozone tolerance were grown in southern Italy during 1997 and 1998 to study the effects of ambient ozone exposure on yield, leaf morphology and water use. Ambient ozone levels were high in both years with values exceeding the threshold for leaf injury reported in the literature. In both years ozone injury was observed on the sensitive clone (NC-S) but not on the resistant one (NC-R), and leaf and stolon dry matter production was significantly lower in NC-S than in NC-R. However, it cannot be excluded that other factors, such as high temperature, interacted with the effect of ozone on biomass production. The clones differed in morphological characteristics. Lower total leaf area in NC-S plants was due to a smaller number of leaves per plant, but the average area per leaf was higher in NC-S. Specific leaf weight and net assimilation rate were higher in the more productive clone (NC-R). Cumulative plant water use was higher in NC-R in each growth period because of the larger leaf area; by contrast, water use per unit leaf area was higher in NC-S, indicating higher leaf conductance to water vapour. The results suggest that ozone significantly reduces the yield of sensitive white clover plants under well-watered conditions, and that the difference in ozone tolerance between clover clones is related to differences in leaf morphology and water use.     

Effects of ozone impact on the gas exchange and chlorophyll fluorescence of juvenile birch stems (Betula pendula Roth.)

Effects of ozone impact on gas exchange and chlorophyll fluorescence of juvenile birch (Betula pendula) stems and leaves were investigated. Significant differences in the response of leaves and stems to ozone were found. In leaves, O3 exposure led to a significant decline in photosynthetic rates, whereas stems revealed an increased dark respiration and a concomitant increase in corticular photosynthesis. In contrast to birch leaves, corticular photosynthesis appeared to support the carbon balance of stems or even of the whole-tree under O3 stress. The differences in the ozone-response between leaves and stems were found to be related to ozone uptake rates, and thus to inherent differences in leaf and stem O3 conductance.     

Additive and antagonistic effects of ozone and salinity on the growth, ion contents and gas exchange of five varieties of rice (Oryza sativa L.)

Five varieties of rice (Oryza sativa L.) of varying salinity resistance were grown in non-saline and in saline conditions, with and without a repeated exposure to ozone at a concentration of 83 nmol mol(-1) giving an AOT40 (cumulative exposure above 40 nmol mol(-1)) of 3600 nmol mol(-1) h. Salinity caused a substantial reduction in shoot and root dry weight in all varieties, but the effect on root growth was proportionately less than on shoot growth. Ozone reduced root dry weight but the treatment used did not significantly affect shoot dry weight. Both salinity and ozone reduced plant height. The potassium concentration in the leaves of all five varieties was reduced by salinity, and by ozone in both saline and non-saline treatments. Ozone reduced the sodium concentration in plants grown at 50 mM NaCl but had no effect upon the chloride concentration. Carbon dioxide assimilation, transpiration and stomatal conductance were all reduced by salinity and by ozone and there was close quantitative similarity between the effects of ozone and/or salinity upon assimilation, stomatal conductance and transpiration. There were some antagonistic effects but there were additive effects of salinity and of ozone on root dry weight, plant height, shoot potassium concentration, photosynthesis, transpiration and stomatal conductance. The possible basis of the additive effects of salinity and ozone on gas exchange and mineral uptake are discussed.