Abstract
Ozone is a major air pollutant in many parts of the world. In the Lower Mainland of British Columbia, occurrences of levels exceeding the B.C. Level A hourly objective of 50 ppb (parts per billion; nl L⁻¹)are frequent in suburban and rural areas. Growth and yield responses of numerous crop and tree species to ozone at daytime hourly average concentrations up to or exceeding 200 ppb have been described by others. However, this information has largely come from studies using open-top field chambers and using experimental protocols involving the enrichment of the ambient air with ozone that do not simulate true field conditions. The present studies used an open-field zonal air pollution system (ZAPS) to examine the effects of low levels of ozone on the yield and growth dynamics of locally important cultivars of pea (Pisum sativum L. cv. Puget), potato (Solanum tuberosum L. cv. Russet Burbank), bean (Phaseolus vulgaris L. cv. Galamore) and radish (Raphanus sativus L. cvs. Cherry Belle and French Breakfast), and of young Douglas-fir saplings (Pseudotsuga menziesii (Mirb.) Franco), under true field conditions. The experiments were conducted in 1986 and 1988-1990, and involved exposures to 12 randomly assigned treatments characterized by stochastically varying degrees of enrichment of the ambient ozone levels, together with ambient air control plots. In each year, the treatments obtained in the ZAPS had unimodal concentration distributions that fitted the Weibull distribution, and typical season-long diurnal average concentration profiles with mid-afternoon maxima. Since the enrichment levels were proportional to the ambient ozone level, the ranges of concentrations achieved in the treatments varied from day to day and from year to year. For each species and season, the exposure treatments were summarized in terms of seasonal daytime means and various cumulative exposure indices. However, comparisons of linear regressions of different growth variables with different indices led to standardization on the use of the D50 index, defined as the number of days per season or per harvest interval in which an hourly mean ozone concentration of 50 ppb was exceeded in any hour between 0900 and 2100 (PDT). Significant (p <0.05) negative linear regressions of yield with increasing D50 exposure were found for all crops. The effects on final yield were reflected in significant decreases in the dry weights of the total plant, stems and leaves, and in leaf areas, by the time of final harvest. However, during the earlier stages of growth, the effects were less marked and the regressions failed to reach significance, even at p <0.10. Three experiments with radish in 1989 revealed pronounced differences in response, depending on time of year. No significant effects of ozone were observed on either Cherry Belle or French Breakfast cvs. in the first experiment in June, but significant growth reductions were observed in the July-August and August-September plantings. The second planting experienced the highest exposures, but since the exposures during the first and third experiments were comparable, the different responses observed suggest the influence of other environmental factors related to time of year. In general the dynamics of crop growth were adversely affected by increased exposure, reaching significance at the later harvest intervals. Absolute growth rates of all crops and cultivars were significantly reduced (p <0.05), but relative growth rates were more variable and their reductions only reached significance at p <0.10, although in several cases significant increases were observed in the early stages of growth. Overall, adverse effects on the growth of all of the crops were observed even though the daytime hourly average ozone concentrations rarely exceeded 120 ppb. Differences between the responses of the radish cultivars indicated that cv. Cherry Belle is more sensitive than cv. French Breakfast. No consistent significant effects of ozone on the growth of Douglas-fir saplings occurred until the end of the second season of exposure (1989). By then, reductions in second flush growth were observed. These effects were carried over into the following year, as revealed by reduced leader growth in early 1990. Although Douglas-fir has been described as relatively insensitive to ozone, these results suggest that long-term detrimental effects on growth may occur. In all species the relationships between many growth variables and exposure appeared to be non linear. However, although there were several cases in which non-linear Weibull or gamma functions provided improvements in fit compared to simple linear regressions, there was no consistent pattern of improvement. Since indices such as D50 merely define exposure and do not necessarily reflect uptake of ozone by foliage, estimates of ozone flux were made during the experiments with radish and Douglas-fir. Whole plant porometry was used at intervals to determine water vapour conductances, which were then used to estimate ozone fluxes over the preceding time period. With radish, linear regressions of various growth measures using estimated flux (FLUXSUMC) as the dependent variable generally showed poorer fits than regressions based on the D5 0 index. However, with second flush growth of Douglas-fir, better fits were obtained with FLUXSUMC than D50, reaching significance for weight and leaf area at the final harvest in 1989. To avoid the assumption that measured conductances accurately reflected conductances during the preceding interval of days, estimates of ozone flux were also calculated based on multiple linear regressions of conductance and several environmental variables. These estimates of flux (FLUXSUMM) employed the meteorological variables and ozone levels recorded throughout the exposure seasons. Although 75 percent of the comparisons with linear regressions based on the D50 index showed better fits with FLUXSUMM, only the regression for second flush weight at harvest 5 was significant. The present study therefore provides only limited support for the view that the use of flux estimates rather than exposure indices results in improvements in describing growth responses to ozone.
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Claims 20
Claim · model-written summary
The exposure treatments had unimodal concentrations fitting a Weibull distribution and diurnal profiles with mid-afternoon maxima.
Not reportedTaxon
Verbatim
e0“the treatments obtained in the ZAPS had unimodal concentration distributions that fitted the Weibull distribution, and typical season-long diurnal average concentration profiles with mid-afternoon maxima.”
Claim · model-written summary
pea yield had a significant negative linear relationship with increasing D50 ozone exposure.
- Taxon
- pea
Lathyrus oleraceust0 - Treatment
- increasing D50 exposuree0
- Outcome
- yielde0
- Direction
- negativee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Significant (p <0.05) negative linear regressions of yield with increasing D50 exposure were found for all crops.”
t0“cultivars of pea (Pisum sativum L. cv. Puget)”
Claim · model-written summary
potato yield had a significant negative linear relationship with increasing D50 ozone exposure.
- Taxon
- potato
Solanum tuberosumt0 - Treatment
- increasing D50 exposuree0
- Outcome
- yielde0
- Direction
- negativee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Significant (p <0.05) negative linear regressions of yield with increasing D50 exposure were found for all crops.”
t0“potato”
Claim · model-written summary
bean yield had a significant negative linear relationship with increasing D50 ozone exposure.
Verbatim
e0“Significant (p <0.05) negative linear regressions of yield with increasing D50 exposure were found for all crops.”
t0“bean”
Claim · model-written summary
radish yield had a significant negative linear relationship with increasing D50 ozone exposure.
- Taxon
- radish
Raphanus sativust0 - Treatment
- increasing D50 exposuree0
- Outcome
- yielde0
- Direction
- negativee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Significant (p <0.05) negative linear regressions of yield with increasing D50 exposure were found for all crops.”
t0“and radish (Raphanus sativus L. cvs. Cherry Belle and French Breakfast)”
Claim · model-written summary
Final harvest total-plant, stem and leaf dry weights and leaf area decreased significantly under ozone exposure.
Verbatim
e0“significant decreases in the dry weights of the total plant, stems and leaves, and in leaf areas, by the time of final harvest.”
t0“ozone on the yield and growth dynamics of locally important cultivars of pea”
e1“yield with increasing D50 exposure were found for all crops.”
Claim · model-written summary
Early-growth regressions did not reach significance even at p <0.10.
Not reportedDirection
Verbatim
e0“during the earlier stages of growth, the effects were less marked and the regressions failed to reach significance, even at p <0.10.”
t0“ozone on the yield and growth dynamics of locally important cultivars of pea”
e1“yield with increasing D50 exposure were found for all crops.”
Claim · model-written summary
Neither radish cultivar had significant ozone effects in the June experiment.
- Taxon
- radishRaphanus sativust0
- Material
- Cherry Belle or French Breakfaste0
- Treatment
- ozonee0
- Outcome
- effectse0
- Setting
- Junee0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“No significant effects of ozone were observed on either Cherry Belle or French Breakfast cvs. in the first experiment in June”
t0“and radish (Raphanus sativus L. cvs. Cherry Belle and French Breakfast)”
Claim · model-written summary
Radish growth was significantly reduced in the July–August and August–September plantings.
- Taxon
- radishRaphanus sativust0
- Outcome
- growthe0
- Direction
- reductionse0
- Setting
- July-August and August-September plantingse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“significant growth reductions were observed in the July-August and August-September plantings.”
t0“and radish (Raphanus sativus L. cvs. Cherry Belle and French Breakfast)”
Claim · model-written summary
Absolute growth rates of all crops and cultivars declined significantly.
Verbatim
e0“Absolute growth rates of all crops and cultivars were significantly reduced (p <0.05)”
t0“effects of low levels of ozone on the yield”
Claim · model-written summary
Relative growth rates had variable responses, with reductions significant only at p <0.10.
Verbatim
e0“relative growth rates were more variable and their reductions only reached significance at p <0.10”
t0“ozone on the yield and growth dynamics of locally important cultivars of pea”
e1“yield with increasing D50 exposure were found for all crops.”
Claim · model-written summary
Several crops had increased relative growth rates early in growth.
Verbatim
e0“in several cases significant increases were observed in the early stages of growth.”
t0“relative growth rates were more variable and their reductions only reached significance at p <0.10”
t1“effects of low levels of ozone on the yield”
e1“yield with increasing D50 exposure were found for all crops.”
Claim · model-written summary
Cherry Belle radish was more ozone-sensitive than French Breakfast.
- Taxon
- radishRaphanus sativust0
- Material
- cv. Cherry Bellee0
- Outcome
- more sensitivee0
- Direction
- more sensitivee0
- Comparator
- cv. French Breakfaste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“cv. Cherry Belle is more sensitive than cv. French Breakfast.”
t0“and radish (Raphanus sativus L. cvs. Cherry Belle and French Breakfast)”
Claim · model-written summary
Douglas-fir second flush growth declined by the end of the second exposure season.
- Taxon
- Douglas-fir
Pseudotsuga menziesiit0 - Treatment
- ozonet0
- Outcome
- second flush growthe0
- Direction
- reductionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“reductions in second flush growth were observed.”
t0“ozone on the growth of Douglas-fir saplings”
Claim · model-written summary
Douglas-fir leader growth was reduced in early 1990.
- Taxon
- Douglas-firPseudotsuga menziesiit0
- Treatment
- ozonet0
- Outcome
- leader growthe0
- Direction
- reducede0
- Setting
- early 1990e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“reduced leader growth in early 1990.”
t0“ozone on the growth of Douglas-fir saplings”
Claim · model-written summary
Nonlinear Weibull or gamma fits sometimes improved on linear regression but showed no consistent improvement.
Verbatim
e0“several cases in which non-linear Weibull or gamma functions provided improvements in fit compared to simple linear regressions, there was no consistent pattern of improvement.”
t0“In all species”
Claim · model-written summary
Estimated flux gave poorer fits than D50 for radish growth measures.
- Taxon
- radishRaphanus sativuse0
- Outcome
- poorer fitse0
- Direction
- poorere0
- Comparator
- regressions based on the D5 0 indexe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“With radish, linear regressions of various growth measures using estimated flux (FLUXSUMC) as the dependent variable generally showed poorer fits than regressions based on the D5 0 index.”
Claim · model-written summary
Estimated flux improved Douglas-fir second flush growth fits over D50, with significant weight and leaf-area fits at final harvest in 1989.
- Taxon
- Douglas-firPseudotsuga menziesiie0
- Organ / stage
- second flush growthe0
- Outcome
- better fitse0
- Direction
- bettere0
- Comparator
- D50e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“with second flush growth of Douglas-fir, better fits were obtained with FLUXSUMC than D50, reaching significance for weight and leaf area at the final harvest in 1989.”
Claim · model-written summary
FLUXSUMM fit better than D50 in 75 percent of comparisons, but only second flush weight at harvest 5 was significant.
- Taxon
- Douglas-firPseudotsuga menziesiit0
- Outcome
- better fits with FLUXSUMMe0
- Value
- 75 percente0
- Qualifier
- only the regression for second flush weight at harvest 5 was significante0
- Comparator
- D50 indexe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“75 percent of the comparisons with linear regressions based on the D50 index showed better fits with FLUXSUMM, only the regression for second flush weight at harvest 5 was significant.”
t0“of young Douglas-fir saplings”
Claim · model-written summary
The authors found limited support that flux estimates improve descriptions of growth responses over exposure indices.
Verbatim
e0“The present study therefore provides only limited support for the view that the use of flux estimates rather than exposure indices results in improvements in describing growth responses to ozone.”
t0“plant growth”