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or SO2 exposure causes a linear decline in soybean yield
Environmental Pollution (Series A) 34 (1984) 345-355
Low Level 0 3 and/or S O 2 Exposure Causes a Linear Decline in Soybean Yield P e t e r B. R e i c h & R o b e r t G. A m u n d s o n Department of Natural Resources and Boyce Thompson Institute, Cornell University, Ithaca, NY 14853, USA
ABSTRACT A field ./umigation system was modified from one described earlier (Reich et al., 1982) and used to expose unenclosed field-grown soybean plants Glycine max cv Hark to low levels of 0 3 and/or SO 2. A 3 x 3 Jactorial design was employed, allowing ./or analysis of individual effectsof and potential interactions between the two pollutants. During the experiment ambient 0 3 was significant, but low (mean concentration of 0"04 #l litre- 1), and ambient SO 2 were not detected. Plants were exposed to ambient air with or without additional pollutants for about 5 h per day on 16 days between 20 August and 12 September, 1980. Exposure to greater than ambient levels of O a (mean concentration 0./0.06 or 0.08 #l litre- 1) caused significant linear reductions 0./2-5 % in mass per seed and number oJ seeds per pod, 17-25 % in number of seeds and pods per plant and 10--25 ~ in seed yield (dry mass) per plant and per hectare. Exposure to greater than ambient levels of SO 2 (mean concentration oJ 0.06 or 0.11 #1 litre-1) caused significant linear reductions of 4-7 °fo in mass per seed. High S02 treatment (mean concentration of 0.11#l litre-1) also resulted in non-significant declines of 7-12% in yield per plant and per hectare. No significant interactions between the pollutants were observed and 0 3 had a several[old greater impact on soybean than SO 2 on either a concentration or a dose basis.
INTRODUCTION Past research has shown that the current United States National Ambient Air Quality Standards for vegetation do not protect all crop plants, and 345 Environ. Pollut. Set. A. 0143-1471/84/$03.00 © ElsevierApplied Science Publishers Ltd, England, 1984. Printed in Great Britain
346
Peter B. Reich, Robert G. Amundson
that 0 3 alone or in combination with other pollutants, including SO2, is responsible for up to 90 ~ of the crop losses in the United States due to air pollution (Heagle & Heck, 1980; Heck et al., 1982). Less clear, however, is the actual amount lost annually. Estimates range from $125 million to over $2 billion (Benedict et al., 1971 ; Heintz et al., 1976; Heagle & Heck, 1980; Heck et al., 1982). This large range of estimates is due to a lack of information concerning the effects of current ambient levels of pollution upon field grown crop plants. Recently, there have been a number of studies related to this subject, and most reports suggest that yields of soybean Glycine m a x L. and other crops are reduced linearly by increasing exposure to relatively low levels of 0 3 (Howell et al., 1979; Heagle & Heck, 1980; Heck et al., 1982; Reich et al., 1982). Also of concern are potential interactions between pollutants, since rarely does any air mass contain only one man-made contaminant at a time. The most common method of exposing plants in the field to gaseous pollutants is by use of open-top chambers (Mandl et al., 1973). Although this is the most thoroughly tested field exposure technique and has the capacity generally to control pollutant concentrations, it has a number of drawbacks. Among these are the artificial enclosure of plants and the relatively high cost of building and maintaining such a system. Other techniques which allow plants to grow unenclosed, where they are subject to ambient atmospheric conditions, have been more recently developed (Lee & Lewis, 1976; Reich et al., 1982). In 1979 we utilised a linear gradient exposure system (Reich et al., 1982) to fumigate unenclosed soybean plants in the field with low levels of 0 3 and SO2, and observed significant reductions in yield as a result. That gradient system used long, horizontal plastic tubes (plenums) to transport and release the pollutants into the crop stand. Thus, with fewer blowers and no chambers, the 'tubular release' system was much less expensive than one employing open-top chambers. One problem with the system as employed in 1979 was pollutant distribution. Since simultaneous linear gradients of both pollutants were produced in the same direction it was impossible to test for either individual or interactive pollutant effects. In 1980 we modified this technique and produced nine discrete, rather than graded, treatments. Consequently, by using a 3 x 3 factorial design we were able to make a complete analysis of main and interactive effects of exposure of young poplar plants to low levels of 0 3 and/or SO 2 (Reich et al., 1984). In this paper we describe the pollutant distribution characteristics of this chamberless system based on a field experiment and report the results of
Effects oJ ozone and sulphur dioxide on soybean
exposure soybean.
to SO 2
347
and O 3 upon yield and yield components in Hark
MATERIALS AND METHODS Soybeans (cv Hark) were planted in early June 1980 in the field near Ithaca, New York. Seeds were sown at a rate of approximately 30 seeds m - 1 within rows which were 61 cm apart. The soil was a Collamer silt loam (Cline & Bloom, 1965) fertilised with 350kgha -1 of 10-20-20NPK. Plants were exposed to pollutant treatments for about 5.25 h d a y (approximately 1030-1545 E D T ) o n 16 days between 20 August and 12 September 1980. Low (ambient), medium (ambient + approximately 0.02 #1 litre- ~ 0 3 or 0.05/~1 litre- 1 SO2) and high (ambient + approximately 0.04 pl litre- ~ 0 3 or 0.10 #1 litre- 1 SO2) treatments of pollutants were used in all nine combinations. The pollutants were delivered to the plants through two clear plastic plenums attached to a blower assembly. Ozone was generated by irradiating 0 2 with a UV light. Sulphur dioxide was supplied from a pressurised cylinder. Each pollutant was introduced into a separate plenum. Plenums were horizontal, straight, 20cm apart and positioned at mid-canopy height. Nine treatments were located along the plenums. Areas of elevated pollutant concentrations were produced by releasing the gases through holes in the plenums. Six such areas were used per plenum. At each area, holes were initially punched every 7.5 or 15 cm (for medium and high treatments, respectively), for a 1.5 m length of the plenum. These areas of pollutant discharge were separated by 4.0 or 9.5 m of plenum without pollutant release. Air quality in the experimental plot was monitored using 24 different Teflon sampling lines; three per treatment except for the ambient 'control' treatment. This treatment was only occasionally monitored since ambient levels of each pollutant were always similar in their three respective ambient treatments. Sampling probes were located at mid-canopy height. During exposures, air at each sampling point was monitored for 3 min in every 72-min cycle. Sulphur dioxide and ozone concentrations were measured by pulse fluorescent (TECO Monitor Series 43) and chemiluminescent (Monitor Labs Ozone Analyzer Model 8410E) detection devices, respectively, and were continuously recorded. Fumigations were not made on days when prevailing winds might be expected to cause pollutant concentrations in
348
Peter B. Reich, Robert G. Amundson
treatment areas to differ widely from designed levels. Since plants were unenclosed, pollutant concentrations in all treatments fluctuated due to wind. Also, since air movement differed with microsite, pollutant release was adjusted to produce and maintain consistent treatments as designed. After fumigations were ended on 12 September, plants were left in the field to dry and then the most central 80 plants within each treatment were harvested. The area occupied by each group of 80 plants was also measured. Number and dry mass of pods and beans from each plant were determined. Analysis of variance and linear regression analysis were used to test for significant main effects of and interactions between treatments. Treatment sums of squares (and degrees of freedom) were partitioned using orthogonal contrasts, and all possible single and interactive linear and quadratic effects of both main factors were tested by regression analysis. Then, after significant factors and levels were identified, appropriate dose and concentration response regression models were developed.
RESULTS
Air quality There is presently no standard method ofcharacterising plant exposure to either experimental or ambient air pollution. Thus, in an attempt at maximum clarity, and in order to allow comparison with other investigations, mean concentrations, total doses, and frequency distributions of concentrations are given in Table 1 and Fig. 1. Frequency distributions were obtained by averaging 3-min means for all monitoring sites within each pollutant treatment. The maximum 3-min concentrations of SO 2 (0.48 #1 litre - 1) and 0 3 (0.17 #1 litre- 1) observed in the high treatments were much greater than the respective mean concentrations (0.11 and 0-08~tl litre -1) in those treatments. Plants in the high 0 3 treatments were exposed for about 38 and 10h, respectively, to concentrations greater than 0.08 and 0-12#1 litre-1. Plants in the high SO 2 treatments were exposed for c. 36 and 15h, respectively, to concentrations greater than 0.10 and 0.20/A litre-1. Ambient SO 2 levels were undetectable, but ambient air often contained significant concentrations of 0 3. During daily pollutant exposures ambient 0 3 concentrations were between 0.04 and 0.09/~1 litre-1 for ¢. 70 ~ of the time.
Effects of ozone and sulphur dioxide on soybean
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Fig. 1. Frequency distribution of 03 and SO2 exposure concentrations at the three levels of each used in a 3 x 3 factorial design. Mean values were averaged over the 84 h of fumigation.
Plant response During the fumigation period no visible symptoms of leaf injury were observed on any plants. However, leaves which received elevated 0 3 treatments senesced earlier than leaves exposed to ambient air only. N o significant interactions in plant response were found between treatments. Thus, in analysing for main effects of each pollutant, data were pooled across all levels of the other pollutant. Yield and yield components were significantly decreased by 0 3 treatments, and the response was linear as a function of concentration or dose (Table 1). Reductions (below ambient treatments) due to elevated 0 3 treatments were 2 - 5 % in mass per seed and number of seeds per pod, 17-25 % in numbers of seed and pods per plant and 10-25 % in seed yield (dry mass) per plant and per hectare. The only significant effect of SO z was a 4 - 7 ~o decrease in mass per seed due to elevated S O / t r e a t m e n t s . However, high
Effects of ozone and sulphur dioxide on soybean
351
SEED MASS/PLANT lOO
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SO 2 treatment did result in non-significant decreases in seed yield per plant and per hectare of 7 and 12 %, respectively (Table 1). The response of soybean plants to greater than ambient levels of 0 3 or SO 2 is expressed as a percent of ambient-exposed plants in Figs 2 and 3 (yield of ambient plants is thus defined arbitrarily as 100 9/0). However, it should be noted that values for ambient plants differ between treatments (Table 1), since these were pooled across 0 3 treatments within ambient SO2 treatments, and vice versa. Differences in mean concentration and total dose between 0 3 treatments were less than half of such differences between SO 2 treatments (Table 1, Fig. 1). Consequently, although the observed reductions in yield per plant and per hectare due to 0 3 treatments were about 2 to 3 times greater than those due to SO 2 treatments, when these reductions are expressed in terms of an equivalent dose or concentration response, the effect of 0 3 is about 5 to 7 times greater than that of SO 2. Inasmuch as yield is the most important economic measure of plant response, and soybean yield had a significant response to 0 3 treatment, we developed a regression equation to describe yield response and a
352
Peter B. Reich, Robert G. Amundson
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model to predict percent reduction in yield due to elevations in ambient 0 3 concentrations (Table 2). The model predicts 22 and 47 ~ reductions in yield of Hark soybean plants (compared to plants exposed to an ambient concentration of 0.025/zl litre- 1) as a result of exposure to 0.06 and 0.10/~1 litre- 1 03 , respectively, for 5.25 h day- 1 on 16 days during podfill.
DISCUSSION Chronic exposure of Hark soybean plants to relatively low concentrations of 0 3 resulted in sizeable reductions in yield and yield components. The decreased number of pods per plant was responsible for most of the reduction in yield, but decreases in number of seeds per pod and in mass per seed also made significant contributions to the yield decline. In contrast to 03, SO 2 had much less effect on yield or its components. These results support the conclusions of an earlier study in which a linear gradient exposure system was used to expose Hark soybeans to both 0 3 and SO 2 (Reich et al., 1982). In field studies with other soybean cultivars,
354
Peter B. Reich, Robert G. Amundson
exposure to O s at less than 0.15 #1 litre- 1 also resulted in linearly declining yields (Heagle et al., 1974; Howell et al., 1979; Heck et al., 1982). Reductions in yields due to similar SO 2 concentrations have not been reported. Recent work in this laboratory found that net photosynthesis in soybean is reduced by chronic exposure to concentrations of O 3 similar to those used in this study. By comparing concentration response and yield reduction models with those for other soybean cultivars (Heck et al., 1982), we concluded that the response of Hark soybeans was fairly typical (Table 2). Also, the results obtained by using this 'tubular release' system were comparable with those obtained with open-top chambers in experiments where no chamber effects were found. Since chamber effects have been observed for soybeans and other crop species (Howell et al., 1979; Heck et al., 1982) it might be more appropriate in some cases to use a field fumigation system which allows crop stands to grow unenclosed.
CONCLUSIONS A fumigation system modified from one employed earlier (Reich et al., 1982) was used to expose field grown soybean plants to factorial treatments of 0 3 and SO 2. This system allowed plants to be unenclosed and thus subject to normal and fluctuating atmospheric factors. The technique proved to be an effective means of conducting dual pollutant experiments in the field, and offers promise for future studies. The sizeable reductions in yield observed as a result of exposure to relatively low pollutant concentrations and doses support contentions that ambient air quality, and in particular, elevated levels of 0 3, may be having significant deleterious effects on soybean and other crop species (see also Heagle et al., 1974; Howell et al., 1979; Heagle & Heck, 1980; Heck et al., 1982). This indicates the need for more research on the phytotoxic effects of air pollutants at typical ambient levels.
REFERENCES Benedict, H. M., Miller, C. J. & Olson, R. E. (1971). Economic impact of air pollutants on plants in the United States. New York, Coordinating Research Council.
Effects oj ozone and sulphur dioxide on soybean
355
Cline, M. G. & Bloom, A. L. (1965). Soil survey of Cornell University property and adjacent areas. Cornell Misc. Bull., 68. Ithaca, NY, NY State College of Agriculture, Corneil University. Heagle, A. S. & Heck, W. W. (1980). Field methods to assess crop losses due to oxidant air pollutants. In Crop loss assessment, ed. by P. S. Teng and S. V. Krupa. Proc. E. C. Stakman Commemorative Syrup., Misc. Publ., 7, 296-305. Agricultural Experimental Station, University of Minnesota. Heagle, A. S., Body, D. E. & Neeley, G. E. (1974). Injury and yield responses of soybean to chronic doses of ozone and sulfur dioxide in the field. Phytopathology, 64, 132-6. Heck, W. W., Taylor, O. C., Adams, R., Bingham, G., Miller, J., Preston, E. & Weinstein, L. (1982). Assessment of crop loss from ozone. J. Air Pollut. Control Ass., 32, 353-61. Heintz, H. T., Hershaft, A. & Horak, G. C. (1976). Nationaldamages ojair and water pollution. Final Report Contract 68-01-2821 for US Environmental Protection Agency by Environmental Control., Inc., Rockville, MD. Howell, R. K., Koch, E. J. & Rose, L. P., Jr (1979). Field assessment of air pollution-induced soybean yield losses. Agron. J., 71,285-8. Lee, J. J. & Lewis, R. A. (1976). Field experimental component: the bioenvironmental effects of sulfur dioxide. In The bioenvironmental impact oja coal-firedpowerplant, First Interim Report, ed. by R. A. Lewis and A. S. Lefohn, EPA-600/3-76-002. Mandl, R. H., Weinstein, L. H., McCune, D. C. & Keveny, M. (1973). A cylindrical, open top chamber for the exposure of plants to air pollutants in the field. J. environ. Qual., 2, 371-6. Reich, P. B., Amundson, R. G. & Lassoie, J. P. (1982). Reduction in soybean yield after exposure to ozone and sulfur dioxide using a linear gradient exposure technique. Water, Air and Soil Pollut., 17, 29-36. Reich, P. B., Lassoie, J. P. & Amundson, R. G. (1984). Reduction in growth of hybrid poplar following field exposure to low levels of 0 3 and/or SO 2. Can. J. Bot., in press.
Low Level 0 3 and/or S O 2 Exposure Causes a Linear Decline in Soybean Yield P e t e r B. R e i c h & R o b e r t G. A m u n d s o n Department of Natural Resources and Boyce Thompson Institute, Cornell University, Ithaca, NY 14853, USA
ABSTRACT A field ./umigation system was modified from one described earlier (Reich et al., 1982) and used to expose unenclosed field-grown soybean plants Glycine max cv Hark to low levels of 0 3 and/or SO 2. A 3 x 3 Jactorial design was employed, allowing ./or analysis of individual effectsof and potential interactions between the two pollutants. During the experiment ambient 0 3 was significant, but low (mean concentration of 0"04 #l litre- 1), and ambient SO 2 were not detected. Plants were exposed to ambient air with or without additional pollutants for about 5 h per day on 16 days between 20 August and 12 September, 1980. Exposure to greater than ambient levels of O a (mean concentration 0./0.06 or 0.08 #l litre- 1) caused significant linear reductions 0./2-5 % in mass per seed and number oJ seeds per pod, 17-25 % in number of seeds and pods per plant and 10--25 ~ in seed yield (dry mass) per plant and per hectare. Exposure to greater than ambient levels of SO 2 (mean concentration oJ 0.06 or 0.11 #1 litre-1) caused significant linear reductions of 4-7 °fo in mass per seed. High S02 treatment (mean concentration of 0.11#l litre-1) also resulted in non-significant declines of 7-12% in yield per plant and per hectare. No significant interactions between the pollutants were observed and 0 3 had a several[old greater impact on soybean than SO 2 on either a concentration or a dose basis.
INTRODUCTION Past research has shown that the current United States National Ambient Air Quality Standards for vegetation do not protect all crop plants, and 345 Environ. Pollut. Set. A. 0143-1471/84/$03.00 © ElsevierApplied Science Publishers Ltd, England, 1984. Printed in Great Britain
346
Peter B. Reich, Robert G. Amundson
that 0 3 alone or in combination with other pollutants, including SO2, is responsible for up to 90 ~ of the crop losses in the United States due to air pollution (Heagle & Heck, 1980; Heck et al., 1982). Less clear, however, is the actual amount lost annually. Estimates range from $125 million to over $2 billion (Benedict et al., 1971 ; Heintz et al., 1976; Heagle & Heck, 1980; Heck et al., 1982). This large range of estimates is due to a lack of information concerning the effects of current ambient levels of pollution upon field grown crop plants. Recently, there have been a number of studies related to this subject, and most reports suggest that yields of soybean Glycine m a x L. and other crops are reduced linearly by increasing exposure to relatively low levels of 0 3 (Howell et al., 1979; Heagle & Heck, 1980; Heck et al., 1982; Reich et al., 1982). Also of concern are potential interactions between pollutants, since rarely does any air mass contain only one man-made contaminant at a time. The most common method of exposing plants in the field to gaseous pollutants is by use of open-top chambers (Mandl et al., 1973). Although this is the most thoroughly tested field exposure technique and has the capacity generally to control pollutant concentrations, it has a number of drawbacks. Among these are the artificial enclosure of plants and the relatively high cost of building and maintaining such a system. Other techniques which allow plants to grow unenclosed, where they are subject to ambient atmospheric conditions, have been more recently developed (Lee & Lewis, 1976; Reich et al., 1982). In 1979 we utilised a linear gradient exposure system (Reich et al., 1982) to fumigate unenclosed soybean plants in the field with low levels of 0 3 and SO2, and observed significant reductions in yield as a result. That gradient system used long, horizontal plastic tubes (plenums) to transport and release the pollutants into the crop stand. Thus, with fewer blowers and no chambers, the 'tubular release' system was much less expensive than one employing open-top chambers. One problem with the system as employed in 1979 was pollutant distribution. Since simultaneous linear gradients of both pollutants were produced in the same direction it was impossible to test for either individual or interactive pollutant effects. In 1980 we modified this technique and produced nine discrete, rather than graded, treatments. Consequently, by using a 3 x 3 factorial design we were able to make a complete analysis of main and interactive effects of exposure of young poplar plants to low levels of 0 3 and/or SO 2 (Reich et al., 1984). In this paper we describe the pollutant distribution characteristics of this chamberless system based on a field experiment and report the results of
Effects oJ ozone and sulphur dioxide on soybean
exposure soybean.
to SO 2
347
and O 3 upon yield and yield components in Hark
MATERIALS AND METHODS Soybeans (cv Hark) were planted in early June 1980 in the field near Ithaca, New York. Seeds were sown at a rate of approximately 30 seeds m - 1 within rows which were 61 cm apart. The soil was a Collamer silt loam (Cline & Bloom, 1965) fertilised with 350kgha -1 of 10-20-20NPK. Plants were exposed to pollutant treatments for about 5.25 h d a y (approximately 1030-1545 E D T ) o n 16 days between 20 August and 12 September 1980. Low (ambient), medium (ambient + approximately 0.02 #1 litre- ~ 0 3 or 0.05/~1 litre- 1 SO2) and high (ambient + approximately 0.04 pl litre- ~ 0 3 or 0.10 #1 litre- 1 SO2) treatments of pollutants were used in all nine combinations. The pollutants were delivered to the plants through two clear plastic plenums attached to a blower assembly. Ozone was generated by irradiating 0 2 with a UV light. Sulphur dioxide was supplied from a pressurised cylinder. Each pollutant was introduced into a separate plenum. Plenums were horizontal, straight, 20cm apart and positioned at mid-canopy height. Nine treatments were located along the plenums. Areas of elevated pollutant concentrations were produced by releasing the gases through holes in the plenums. Six such areas were used per plenum. At each area, holes were initially punched every 7.5 or 15 cm (for medium and high treatments, respectively), for a 1.5 m length of the plenum. These areas of pollutant discharge were separated by 4.0 or 9.5 m of plenum without pollutant release. Air quality in the experimental plot was monitored using 24 different Teflon sampling lines; three per treatment except for the ambient 'control' treatment. This treatment was only occasionally monitored since ambient levels of each pollutant were always similar in their three respective ambient treatments. Sampling probes were located at mid-canopy height. During exposures, air at each sampling point was monitored for 3 min in every 72-min cycle. Sulphur dioxide and ozone concentrations were measured by pulse fluorescent (TECO Monitor Series 43) and chemiluminescent (Monitor Labs Ozone Analyzer Model 8410E) detection devices, respectively, and were continuously recorded. Fumigations were not made on days when prevailing winds might be expected to cause pollutant concentrations in
348
Peter B. Reich, Robert G. Amundson
treatment areas to differ widely from designed levels. Since plants were unenclosed, pollutant concentrations in all treatments fluctuated due to wind. Also, since air movement differed with microsite, pollutant release was adjusted to produce and maintain consistent treatments as designed. After fumigations were ended on 12 September, plants were left in the field to dry and then the most central 80 plants within each treatment were harvested. The area occupied by each group of 80 plants was also measured. Number and dry mass of pods and beans from each plant were determined. Analysis of variance and linear regression analysis were used to test for significant main effects of and interactions between treatments. Treatment sums of squares (and degrees of freedom) were partitioned using orthogonal contrasts, and all possible single and interactive linear and quadratic effects of both main factors were tested by regression analysis. Then, after significant factors and levels were identified, appropriate dose and concentration response regression models were developed.
RESULTS
Air quality There is presently no standard method ofcharacterising plant exposure to either experimental or ambient air pollution. Thus, in an attempt at maximum clarity, and in order to allow comparison with other investigations, mean concentrations, total doses, and frequency distributions of concentrations are given in Table 1 and Fig. 1. Frequency distributions were obtained by averaging 3-min means for all monitoring sites within each pollutant treatment. The maximum 3-min concentrations of SO 2 (0.48 #1 litre - 1) and 0 3 (0.17 #1 litre- 1) observed in the high treatments were much greater than the respective mean concentrations (0.11 and 0-08~tl litre -1) in those treatments. Plants in the high 0 3 treatments were exposed for about 38 and 10h, respectively, to concentrations greater than 0.08 and 0-12#1 litre-1. Plants in the high SO 2 treatments were exposed for c. 36 and 15h, respectively, to concentrations greater than 0.10 and 0.20/A litre-1. Ambient SO 2 levels were undetectable, but ambient air often contained significant concentrations of 0 3. During daily pollutant exposures ambient 0 3 concentrations were between 0.04 and 0.09/~1 litre-1 for ¢. 70 ~ of the time.
Effects of ozone and sulphur dioxide on soybean
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349
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Peter B. Reich, Robert G. Amundson
30
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•
.-=:-
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.24
.36 SO2
.48
Fig. 1. Frequency distribution of 03 and SO2 exposure concentrations at the three levels of each used in a 3 x 3 factorial design. Mean values were averaged over the 84 h of fumigation.
Plant response During the fumigation period no visible symptoms of leaf injury were observed on any plants. However, leaves which received elevated 0 3 treatments senesced earlier than leaves exposed to ambient air only. N o significant interactions in plant response were found between treatments. Thus, in analysing for main effects of each pollutant, data were pooled across all levels of the other pollutant. Yield and yield components were significantly decreased by 0 3 treatments, and the response was linear as a function of concentration or dose (Table 1). Reductions (below ambient treatments) due to elevated 0 3 treatments were 2 - 5 % in mass per seed and number of seeds per pod, 17-25 % in numbers of seed and pods per plant and 10-25 % in seed yield (dry mass) per plant and per hectare. The only significant effect of SO z was a 4 - 7 ~o decrease in mass per seed due to elevated S O / t r e a t m e n t s . However, high
Effects of ozone and sulphur dioxide on soybean
351
SEED MASS/PLANT lOO
9o
[, 80 a. 7o
m
S02J
L 03-1
L SO2/
L 03 J
LSO2J
L 03
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SO 2 treatment did result in non-significant decreases in seed yield per plant and per hectare of 7 and 12 %, respectively (Table 1). The response of soybean plants to greater than ambient levels of 0 3 or SO 2 is expressed as a percent of ambient-exposed plants in Figs 2 and 3 (yield of ambient plants is thus defined arbitrarily as 100 9/0). However, it should be noted that values for ambient plants differ between treatments (Table 1), since these were pooled across 0 3 treatments within ambient SO2 treatments, and vice versa. Differences in mean concentration and total dose between 0 3 treatments were less than half of such differences between SO 2 treatments (Table 1, Fig. 1). Consequently, although the observed reductions in yield per plant and per hectare due to 0 3 treatments were about 2 to 3 times greater than those due to SO 2 treatments, when these reductions are expressed in terms of an equivalent dose or concentration response, the effect of 0 3 is about 5 to 7 times greater than that of SO 2. Inasmuch as yield is the most important economic measure of plant response, and soybean yield had a significant response to 0 3 treatment, we developed a regression equation to describe yield response and a
352
Peter B. Reich, Robert G. Amundson
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Effects oJ ozone and sulphur dioxide on soybean
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L 03J
LSO2J LO3 J
Fig. 3. Number of seeds per pod, mass per seed and yield per hectare as per cent of ambient-exposed plants (A), for plants exposed to medium (M) and high (H) treatments of SO 2 and 03; values are means +__one standard error.
model to predict percent reduction in yield due to elevations in ambient 0 3 concentrations (Table 2). The model predicts 22 and 47 ~ reductions in yield of Hark soybean plants (compared to plants exposed to an ambient concentration of 0.025/zl litre- 1) as a result of exposure to 0.06 and 0.10/~1 litre- 1 03 , respectively, for 5.25 h day- 1 on 16 days during podfill.
DISCUSSION Chronic exposure of Hark soybean plants to relatively low concentrations of 0 3 resulted in sizeable reductions in yield and yield components. The decreased number of pods per plant was responsible for most of the reduction in yield, but decreases in number of seeds per pod and in mass per seed also made significant contributions to the yield decline. In contrast to 03, SO 2 had much less effect on yield or its components. These results support the conclusions of an earlier study in which a linear gradient exposure system was used to expose Hark soybeans to both 0 3 and SO 2 (Reich et al., 1982). In field studies with other soybean cultivars,
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Peter B. Reich, Robert G. Amundson
exposure to O s at less than 0.15 #1 litre- 1 also resulted in linearly declining yields (Heagle et al., 1974; Howell et al., 1979; Heck et al., 1982). Reductions in yields due to similar SO 2 concentrations have not been reported. Recent work in this laboratory found that net photosynthesis in soybean is reduced by chronic exposure to concentrations of O 3 similar to those used in this study. By comparing concentration response and yield reduction models with those for other soybean cultivars (Heck et al., 1982), we concluded that the response of Hark soybeans was fairly typical (Table 2). Also, the results obtained by using this 'tubular release' system were comparable with those obtained with open-top chambers in experiments where no chamber effects were found. Since chamber effects have been observed for soybeans and other crop species (Howell et al., 1979; Heck et al., 1982) it might be more appropriate in some cases to use a field fumigation system which allows crop stands to grow unenclosed.
CONCLUSIONS A fumigation system modified from one employed earlier (Reich et al., 1982) was used to expose field grown soybean plants to factorial treatments of 0 3 and SO 2. This system allowed plants to be unenclosed and thus subject to normal and fluctuating atmospheric factors. The technique proved to be an effective means of conducting dual pollutant experiments in the field, and offers promise for future studies. The sizeable reductions in yield observed as a result of exposure to relatively low pollutant concentrations and doses support contentions that ambient air quality, and in particular, elevated levels of 0 3, may be having significant deleterious effects on soybean and other crop species (see also Heagle et al., 1974; Howell et al., 1979; Heagle & Heck, 1980; Heck et al., 1982). This indicates the need for more research on the phytotoxic effects of air pollutants at typical ambient levels.
REFERENCES Benedict, H. M., Miller, C. J. & Olson, R. E. (1971). Economic impact of air pollutants on plants in the United States. New York, Coordinating Research Council.
Effects oj ozone and sulphur dioxide on soybean
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Cline, M. G. & Bloom, A. L. (1965). Soil survey of Cornell University property and adjacent areas. Cornell Misc. Bull., 68. Ithaca, NY, NY State College of Agriculture, Corneil University. Heagle, A. S. & Heck, W. W. (1980). Field methods to assess crop losses due to oxidant air pollutants. In Crop loss assessment, ed. by P. S. Teng and S. V. Krupa. Proc. E. C. Stakman Commemorative Syrup., Misc. Publ., 7, 296-305. Agricultural Experimental Station, University of Minnesota. Heagle, A. S., Body, D. E. & Neeley, G. E. (1974). Injury and yield responses of soybean to chronic doses of ozone and sulfur dioxide in the field. Phytopathology, 64, 132-6. Heck, W. W., Taylor, O. C., Adams, R., Bingham, G., Miller, J., Preston, E. & Weinstein, L. (1982). Assessment of crop loss from ozone. J. Air Pollut. Control Ass., 32, 353-61. Heintz, H. T., Hershaft, A. & Horak, G. C. (1976). Nationaldamages ojair and water pollution. Final Report Contract 68-01-2821 for US Environmental Protection Agency by Environmental Control., Inc., Rockville, MD. Howell, R. K., Koch, E. J. & Rose, L. P., Jr (1979). Field assessment of air pollution-induced soybean yield losses. Agron. J., 71,285-8. Lee, J. J. & Lewis, R. A. (1976). Field experimental component: the bioenvironmental effects of sulfur dioxide. In The bioenvironmental impact oja coal-firedpowerplant, First Interim Report, ed. by R. A. Lewis and A. S. Lefohn, EPA-600/3-76-002. Mandl, R. H., Weinstein, L. H., McCune, D. C. & Keveny, M. (1973). A cylindrical, open top chamber for the exposure of plants to air pollutants in the field. J. environ. Qual., 2, 371-6. Reich, P. B., Amundson, R. G. & Lassoie, J. P. (1982). Reduction in soybean yield after exposure to ozone and sulfur dioxide using a linear gradient exposure technique. Water, Air and Soil Pollut., 17, 29-36. Reich, P. B., Lassoie, J. P. & Amundson, R. G. (1984). Reduction in growth of hybrid poplar following field exposure to low levels of 0 3 and/or SO 2. Can. J. Bot., in press.