Patrick M. McCool

Response of a white clover indicator system to tropospheric ozone at eight locations in the United States

A white clover (Trifolium repens L.) system using measured biomass to indicate effective concentrations of tropospheric ozone (O3) has been developed. The system utilizes the relative response of an O3-sensitive clone (NC-S) and an O3-resistant clone (NC-R) grown in 15-liter pots. Forage (leaves, stems and flowers) is cut, dried, and weighed at 28-day intervals. Forage dry weight ratios (NC-S/NC-R) for individual or multiple harvests indicate O3 concentrations during growth. In, 3 years of testing in open-top field chambers at Raleigh, North Carolina, O3 always decreased growth of NC-S more than that of NC-R and the NC-S/NC-R ratio routinely decreased as the O3 concentration increased. A national field test was performed in 1993 and 1994 to determine if the clover system can account for effects of climatic variables on clover growth per-se, and if climatic variables affect the relative response of the two clones to O3. Eight locations (Corvallis, Oregon; Kennedy Space Center, Florida; Delaware, Ohio; Amherst, Massachusetts; Blacksburg, Virginia; Raleigh, North Carolina; Riverside, California; San Bemardino mountains, California) provided large differences in O3 concentrations and climate. The NC-S/NC-R forage ratios for three consecutive 28-day growth periods for each year as related to the mean 12 hour per day O3 concentrations are presented in this manuscript. Ratios were generally highest where mean O3 concentrations were lowest (Oregon and Florida), lowest where mean O3 concentrations were highest (both California locations), and intermediate at other locations.

Ozone Descriptors for an Air Quality Standard to Protect Vegetation

Exposure of plants to ozone (O3) causes injury and reduced growth. Describing the form and function of the O3 exposure in relation to plant response is important in the regulatory process. Research has shown that plants show greater response to O3 as concentration increases. The duration of the O3 exposure is also important in the ability of vegetation to maintain O3 repair mechanisms. The O3 entering the leaf is important in plant response, thus O3 fluxes are more important than ambient concentrations. However, at this time an air quality standard useful for the regulatory process should be based on ambient O3 exposures. The selection of O3 exposure descriptors should incorporate factors pertinent to plant response. Research suggests that exposure descriptors which give greater weight to peak concentrations, and those which account for cumulative exposure, show the closest relationship to plant response. Ozone exposure summaries using concentration averages do not adequately relate plant response with am...

Selecting ozone exposure statistics for determining crop yield loss from air pollutants

Numerous ozone exposure statistics were calculated using hourly ozone data from crop yield loss experiments previously conducted for alfalfa, fresh market and processing tomatoes, cotton, and dry beans in an ambient ozone gradient near Los Angeles, California. Exposure statistics examined included peak (maximum daily hourly) and mean concentrations above specific threshold levels, and concentrations during specific time periods of the day. Peak and mean statistics weighted for ozone concentration and time period statistics weighted for hour of the day were also determined. Polynomial regression analysis was used to relate each of 163 ozone statistics to crop yield. Performance of the various statistics was rated by comparing residual mean square (RMS) values. The analyses demonstrated that no single statistic was best for all crop species. Ozone statistics with a threshold level performed well for most crops, but optimum threshold level was dependent upon crop species and varied with the particular statistics calculated. The data indicated that daily hours of exposure above a critical high-concentration threshold related well to crop yield for alfalfa, market tomatoes, and dry beans. The best statistic for cotton yield was an average of all daily peak ozone concentrations. Several different types of ozone statistics performed similarly for processing tomatoes. These analyses suggest that several ozone summary statistics should be examined in assessing the relationship of ambient ozone exposure to crop yield. Where no clear statistical preference is indicated among several statistics, those most biologically relevant should be selected.

Air pollutant yield-loss assessment for four vegetable crops

Abstract Crop loss was evaluated for leaf lettuce, green onion, turnip and beet in a field chamber system using a gradient of ambient pollutants. The nine-chamber gradient had air flows adjusted to filter pollutants to 100, 90, 80, 70, 60, 50, 35, 20 and 0% of ambient or ambient plus added ozone. Dose-response functions were calculated for the four crops using both a 12-h seasonal mean dose statistic and a 0.10 μl l −1 threshold dose summary. Yield-loss functions were generated from yield equations. Crop yield-loss functions for green onion, turnips and beets were significant with 12-h seasonal mean ozone dose. Yield-loss functions based on the 0.10 μl l −1 threshold were significant for onion, lettuce and beets. Multiple regression analysis using both dose summary statistics did not produce a better predictive model of yield loss for any of the four crops examined.

The use of transfer function models to describe the relationship between pollutant exposure and leaf stomatal opening

Abstract Gas flux into plant leaves is regulated, in part, by stomatal opening and closing. Research has shown that stomatal responses can be influenced by exposure to gaseous pollutants. Measurements of stomatal response at a few fixed times have been tabulated, but models of stomatal response to pollutants over time have not been fully developed. Box-Jenkins time series models may be useful in describing the relationship between pollutant flux and stomatal aperture over time. Transfer function models (multivariate time series) can be used to relate input time series (pollutant load) and output time series (stomatal response). A basic description of time series and transfer function analysis is presented. Experimental considerations are also discussed. An example is presented using transfer function models to relate ozone fumigation of sunflower to changes in leaf temperature, used as a surrogate for stomatal responses to ozone.

Response of kidney bean to sequential ozone exposures

Abstract Predisposition of plants to injury or growth effects from consecutive exposures is an important concept in that multiple exposures cannot be represented by simply adding a series of independent events. The independence of individual exposures in a sequence of exposures was investigated. Red kidney bean was exposed to 0.30 ppm (599 μg/m 3 ) ozone for 3 hr at 12 days of age. Subsequent second exposures of the same dose were applied at 13, 14, 15, 16, 17 or 18 days of age. Piecewise linear regressiion analysis indicated that plants became tolerant or desensitized to second fumigations if the exposures were closely spaced. After a discrete interval between exposures, plants again exhibited detrimental growth effects. In separate experiments, an interval of 3 or 5 days between exposures was necessary to detect a detrimental growth response in stem, leaf and total dry weight parameters. Leaf area did not exhibit consistent responses to a second ozone exposure in any treatment. Implications of the recovery period to plant response and experimental fumigation designs are discussed.

Statistical analysis of differences in response of beans to ozone

Abstract The shape of the frequency-distribution response curves of Phaseolus vulgaris L. ‘California Light Red Kidney’ beans exposed to three levels of ozone was examined. A non-parametric statistical test, the Kolmogorov-Smirnov (K-S) test, was useful in determining shape or distributional differences in response to ozone. The analysis indicated that significant differences existed in the distribution of oxidant stipple injury response at different ozone fumigation treatment levels. Significant non-normal response distributions, skewed and truncated toward zero injury, were evident at low ozone fumigation treatment levels. There were near-normal distributions of response to ozone at the higher fumigation treatment level that resulted in moderate injury. Variability in injury increased with higher treatment level. Data for growth parameters indicated normal distribution of response to treatment. Parametric tests showed few differences among chambers or among sections within chambers for the fumigation facility used in this experiment. The experiment demonstrates that parametric statistics may provide inaccurate analysis of injury data with some treatments showing little injury.