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Tomato response to concurrent and sequential NO2 and O3 exposures
428
Poster session summaries
Acknowledgement This work was conducted while the author was a Research Assistant in the Department of Crop Science, North Carolina State University, and was supported by the USDA-ARS/NSCU cooperative Air Quality Program.
Tomato Response to Concurrent and Sequential NO 2 and 03 Exposures S. N. Goodyear and D. P. Ormrod University of Guelph, Guelph, Ontario, Canada
Air quality standards/objectives were established using studies which assess the effects of single pollutants on plant processes. The typical ambient diurnal pattern for N O 2 is to peak in the morning and evening, while 03 levels peak at midday to late afternoon, coincidental with maximum solar radiation, allowing both concurrent and sequential exposures of the environment to the two gases. The objective of this study was to consider the effect of NO 2 and 03 singly, in combination and sequentially on the growth of the tomato plant. The levels chosen were the maximum acceptable 1 h standard for single pollutants, as recommended by the Canadian National Ambient Air Quality objectives. Although this level is a primary standard, it was chosen as a level that should not adversely affect plant growth. Tomato plants (Lycopersicon esculentum Mill cv New Yorker Special) were grown in a controlled environment to the four to six leaf stage and then exposed to NO2 and 03, singly and in combination, at pollutant concentrations equal to the chosen levels for a 1 h average 0-21ppm (400pgm -3) and 0.08ppm (160 #g m - 3). The two experiments were concurrent exposure: control (charcoal filtered air), NO/, 03, and concurrent N O z - b O 3 , and sequential exposure: control, N O 2 - O 3 , 03 - NO 2 (gas 1 for 1 h followed by gas 2 for 1 h). The plants were harvested 3 days after exposure. The concurrent NOz + 03 treatment significantly reduced stem fresh weight (SFW) and leaf fresh weight (LFW) relative to control (Table 1). These reductions were not detected in the single pollutant treatments, indicating the response of those growth parameters to the pollutant combination was coalitive. In the sequential study, significant effects were detected for the exposure of tomato to 03 for 1 h followed by N O 2 for 1 h (03 - N O / ) (Table 2). The 0 3 - NO2 treatment significantly reduced leaf area (LA), LFW and SFW relative to control, whereas the NO2 - 03 did not significantly affect any parameter relative to control (Table 2). The coalitive
429
Poster session summaries
TABLE 1 Response of Tomato to 03 and NO2, Singly and in Combination, at the Four to Six Leaf Stage* Response variable
Leaf area (cm z) Leaf fresh weight (g) Stem fresh weight (g)
Treatment Control
NO 2
03
NO2 + 03
539ab** 16'62b 5-39b
555b 16"80b 5"36b
54lab 16-3lab 5"43b
513a 15.44a 5-00a
* Responses measured on a per plant basis. Each entry is the geometric mean of five replications, with six sub-samples (plants) per replication. ** Values in each row followed by the same letter are not significantly different according to least significant difference tests (p = 0'05).
TABLE 2 Response of Tomato to Sequential Exposures to NO2 and 03* Response variables
Treatment Control
Leaf area (cm 2) Leaf fresh weight (g) Stem fresh weight (g)
454b** 13-49b 3.98b
NO2
-- 0 3
439ab 12"96ab 3'89b
0 3 -- NO2
428a 12"62a 3"63a
*, ** for explanation see Table 1.
response and the sequential effect of the pollutants at levels within the air quality criteria suggest that research is needed that reflects ambient occurrence of sequential and concurrent exposures to pollutant episodes which, when tested singly, do not cause injury. Criteria based on single pollutant experiments may not be adequate to establish air quality objectives for pollutants occurring together, either sequentially or concurrently.
Poster session summaries
Acknowledgement This work was conducted while the author was a Research Assistant in the Department of Crop Science, North Carolina State University, and was supported by the USDA-ARS/NSCU cooperative Air Quality Program.
Tomato Response to Concurrent and Sequential NO 2 and 03 Exposures S. N. Goodyear and D. P. Ormrod University of Guelph, Guelph, Ontario, Canada
Air quality standards/objectives were established using studies which assess the effects of single pollutants on plant processes. The typical ambient diurnal pattern for N O 2 is to peak in the morning and evening, while 03 levels peak at midday to late afternoon, coincidental with maximum solar radiation, allowing both concurrent and sequential exposures of the environment to the two gases. The objective of this study was to consider the effect of NO 2 and 03 singly, in combination and sequentially on the growth of the tomato plant. The levels chosen were the maximum acceptable 1 h standard for single pollutants, as recommended by the Canadian National Ambient Air Quality objectives. Although this level is a primary standard, it was chosen as a level that should not adversely affect plant growth. Tomato plants (Lycopersicon esculentum Mill cv New Yorker Special) were grown in a controlled environment to the four to six leaf stage and then exposed to NO2 and 03, singly and in combination, at pollutant concentrations equal to the chosen levels for a 1 h average 0-21ppm (400pgm -3) and 0.08ppm (160 #g m - 3). The two experiments were concurrent exposure: control (charcoal filtered air), NO/, 03, and concurrent N O z - b O 3 , and sequential exposure: control, N O 2 - O 3 , 03 - NO 2 (gas 1 for 1 h followed by gas 2 for 1 h). The plants were harvested 3 days after exposure. The concurrent NOz + 03 treatment significantly reduced stem fresh weight (SFW) and leaf fresh weight (LFW) relative to control (Table 1). These reductions were not detected in the single pollutant treatments, indicating the response of those growth parameters to the pollutant combination was coalitive. In the sequential study, significant effects were detected for the exposure of tomato to 03 for 1 h followed by N O 2 for 1 h (03 - N O / ) (Table 2). The 0 3 - NO2 treatment significantly reduced leaf area (LA), LFW and SFW relative to control, whereas the NO2 - 03 did not significantly affect any parameter relative to control (Table 2). The coalitive
429
Poster session summaries
TABLE 1 Response of Tomato to 03 and NO2, Singly and in Combination, at the Four to Six Leaf Stage* Response variable
Leaf area (cm z) Leaf fresh weight (g) Stem fresh weight (g)
Treatment Control
NO 2
03
NO2 + 03
539ab** 16'62b 5-39b
555b 16"80b 5"36b
54lab 16-3lab 5"43b
513a 15.44a 5-00a
* Responses measured on a per plant basis. Each entry is the geometric mean of five replications, with six sub-samples (plants) per replication. ** Values in each row followed by the same letter are not significantly different according to least significant difference tests (p = 0'05).
TABLE 2 Response of Tomato to Sequential Exposures to NO2 and 03* Response variables
Treatment Control
Leaf area (cm 2) Leaf fresh weight (g) Stem fresh weight (g)
454b** 13-49b 3.98b
NO2
-- 0 3
439ab 12"96ab 3'89b
0 3 -- NO2
428a 12"62a 3"63a
*, ** for explanation see Table 1.
response and the sequential effect of the pollutants at levels within the air quality criteria suggest that research is needed that reflects ambient occurrence of sequential and concurrent exposures to pollutant episodes which, when tested singly, do not cause injury. Criteria based on single pollutant experiments may not be adequate to establish air quality objectives for pollutants occurring together, either sequentially or concurrently.