/@ 

United States 

I Department of 

Agriculture 

Effect of Acid Mist and Air Pollutants 

Forest Service on Yellow-Poplar Seedling Height 

Northeastern Forest 

Experiment Station 

and Leaf Growth 

Research Paper 

N E-572 Leon S. Dochinger 

1985 Keith F. Jensen 
The Authors 

Leon S. Dochinger received a B.S. degree in 1950 and a Ph.D. degree in 

1956 from Rutgers University, and an MS. degree in 1952 from Cornell 

University. In 1956, he joined the Central States Forest Experiment Station 

as a plant pathologist. Since 1970 he has been the Project Leader of the 

Northeastern Forest Experiment Station's air pollution unit in Delaware, 

Ohio, where he is currently conducting research on the impact of 

atmospheric deposition in eastern forests. 

Keith F. Jensen, plant physiologist, holds B.S. and Ph.D. degrees from 

Iowa State University. He joined the Northeastern Forest Experiment 

Station in 1963 and is now at the Station's laboratory in Delaware, Ohio, 

conducting research on the effects of atmospheric deposition on vegetation. 

Manuscript received for publication 14 May 1985 

Abstract 

One-year-old yellow-poplar seedlings were treated with acid mist at pH 

2.5, 3.5, 4.5, and 5.5 either alone or in combination with 0.1 ppm 03, S02, 

and N02, or NO2 plus S02. After 4 and 8 weeks of treatment, height, leaf 

area, and leaf and new shoot weight were determined and growth analysis 

variables calculated. Height, leaf area, and dry weight decreased with 

increasing acidity in seedlings treated with acid mist alone. Similar, but 

smaller reductions occurred in seedlings treated with SO2 and acid mist, 

but no differences were found in seedlings fumigated with NO2, NO2 plus 

SO?, or ozone and acid mist. Further studies using different combinations 

of pollutants and acid mist must be conducted before their apparent interactions can be more accuratelv assessed. 
Materials and Methods 

The Eastern United States has experienced 

i sublethal doses of atmospheric deposition over long 

periods of time as regional industrialization and urbanization have intensified. Forests are a dominant 

i ecosystem throughout the Northeast and numerous 

environmental stresses, including air pollution, have 

determined species succession, establishment, andF 

productivity. Documentation of these atmospheric 

impacts is limited since the consequences of pollution 

are usually chronic and subtle, but over time these 

simple changes are detrimental to forest growth 

(Dochinger and Calvert 1978). 

Yellow-poplar (Liriodendron tulipifera L.) is a 

primary species in 4 forest cover types and a secondary component in 12 other forest communities throughout most of the Eastern United States (Vick 1973). This 

species is sensitive to photochemical oxidants (ozone) 

which can effect foliage mottling, premature leaf loss, 

and reduced growth (Dochinger 1974, Duchelle et al. 

1982). Additional biomass responses can also result 

from ozone fumigation including decreases in leaf-area 

ratio, net assimilation rateiand shoot height growth 

rate (Jensen 1973, 1981). 

I Although no information is available on the interI action of acid rain and gaseous pollutants on yellowpoplar, limited study has yielded some research data 

t on the gaseous precursors of acid precipitation, sulfur 

dioxide, and nitrogen oxides, in various combinations 

1 with ozone. SO2 and ozone alone did not suppress total 

I shoot elongation of yellow-poplar after a 5-week fumigation period, whereas the combinations of 03 + S02, 

SO2 + Not, or the three gases significantly inhibited 

total shoot height and dry weight. Of the pollutant 

combinations, SO2 + NO2 most severely curtailed the 

I rate of height growth (Mahoney et al. 1983). Conversely, 

treatment with concentrations of 03 stimulated growth 

of yellow-poplar seedlings, whereas treatment with 

ambient levels had no adverse effect (Kress and Skelly 

1982). In areas around urban centers and in the vicinity 

of industrial sites, dominant or codominant yellow-poptar, growing in ambient air composed periodically of 

elevated concentrations of oxides of nitrogen and sulfur dioxide, produced less radial increment growth during periods of high pollutant concentrations (Stone and 

Skelly 1974). - 

This study was designed to quantify the nature 

and extent of ambient concentrations of N02, S02, and 

03 in conjunction with acid mist on shoot growth and 

leaf biomass of yellow-poplar seedlings. 

Twenty combinations of acid mist and air pollutant 

treatments were used in this study. As only four treatment chambers were available, five separate experiments were required. In the first experiment, the seedlings were treated with acid mist alone with pH of 

either 2.5, 3.5, 4.5, or 5.5. In the second experiment, the 

seedlings were treated with acid mist solution plus 0.1 

ppm S02; in the third experiment, acid mist solution 

and 0.1 ppm N02; in the fourth experiment, acid mist 

and 0.1 ppm 03; and in the fifth experiment, acid mist 

and 0.1 ppm SO2 plus 0.1 ppm N02. 

The fumigation chambers were similar to those 

described by Heck and others (1968). The Mylarcovered1 chambers had a single-pass air system and 

were located in an environmentally controlled room. 

The average daily temperature was 25"C, and average 

night temperature was 20°C. Light intensity during the 

16-hour photoperiod was approximately 250 pEm-2sec-1 

The air pollutants were added to the charcoal-filtered 

air stream and were sampled automatically in each 

chamber at 20-minute intervals. Ozone was sampled 

with a Dasibi Model 1003-AH03 monitor, SO2 with a 

Beckman Model 90 A SO2 monitor, and NO2 with a 

Monitor Labs Nitrogen Oxides Analyzer Model 8840. 

The seedlings were fumigated 4 hours each morning 

for 5 days a week, and the monitors were calibrated 

each day the seedlings were fumigated. 

The acidified mist solutions were prepared by adding sulfuric acid to distilled water. The final pH of the 

four solutions was 2.5, 3.5, 4.5, and 5.5. The solutions 

were applied to the chamber atmospheres with Northern cold water humidifiers (Model 77). Approximately 

1,500 ml of solution were added to each chamber 

during the 4-hour afternoon treatment period, and mist 

was applied 7 days a week. 

The 1-year-old yellow-poplar seedlings in each 

experiment were selected for uniformity and potted in 

15-cm plastic pots in a bog soil-sand mixture. They 

were immediately placed on benches in the environmentally controlled room that contained the fumigation 

chambers. When 80 seedling had broken dormancy, 20 

seedlings were randomly assigned to each treatment in 

' The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. 

Such use does not constitute an official endorsement or 

approval by the US. Department of Agriculture or the Forest 

Service of any product or service to the exclusion of others 

that may be suitable. 
the experiment and treatments started. The seedlings 

were watered as required and fertilized every 2 weeks 

with 100 ml of a general purpose fertilizer (Peters 

soluble fertilizer 20-20-20). 

Four weeks after the treatments were started, 10 

randomly selected seedlings from each treatment were 

harvested. The height, number of leaves, midrib length, 

and new stem and leaf dry weight of each seedling 

were measured. Dry weight of the leaves and stems 

was determined by drying them to constant weight at 

100°C. Leaf area was calculated from a quadratic 

equation relating midrib length to area. The remaining 

10 seedlings in each treatment were harvested after 8 

weeks of fumigation. 

After the final harvest, all the data were averaged 

by harvest date, and the growth analysis variables 

calculated. The variables calculated were relative 

growth rate (I~(WZIWI)I(TZ-T~)), relative leaf-area growth 

rate (ln(Az/A~)l(T~-TI)), specific leaf area (AIL), leaf-area 

ratio (AIW), and net assimilation rate 

((WZ - Wl)l(A2 - AI)) * (ln(A21Al)l(T~ - TI)) where W = 

total new growth weight, A = leaf area, and L = leaf 

weight (Hunt 1982). The data from the 8-week harvest 

within each experiment were also analyzed using a 

one-way ANOVA. No statistical comparisons were 

made between experiments because the means and 

variances were nonhomogeneous. 

Results and Discussion 

When the seedlings were treated only with acid 

mist, height growth after 8 weeks significantly 

decreased with a lowering in pH from 5.5 to 2.5 (Table 

1). Leaf weight and new stem weight of these seedlings did not significantly change in pH from 5.5 to 3.5 

but decreased significantly when the pH decreased 

from 3.5 to 2.5. Leaf area was also significantly 

decreased with a reduction in pH from 3.5 to 2.5. 

These differences are also reflected in the growth 

analysis variables (Table 2). Relative growth rate (RGR), 

net assimilation rate (NAR), and relative leaf-area 

growth rate (RLAGR) all decreased with an increase in 

acidity. A small drop in the variables was observed as 

the pH went from 5.5 to 3.5, but sharper decreases 

were found as the pH was lowered from 3.5 to 2.5. 

The mechanism by which seedling growth was 

reduced by the acid mist cannot be explained from this 

experiment. But by examining the growth analysis 

variables, some possibilities are suggested. The first 

suggestion is that acid mist reduced leaf growth rate. 

As leaf area is one of the controlling factors that determines the amount of photosynthate available for 

growth, this physiological relationship may then be 

responsible for the diminished growth of plant dry 

weight. This supposition is supported by the RLAGR 

data, which show that the seedlings in the pH 2.5 treatment were only adding new leaf area at a rate of oneseventh that of the seedlings in the pH 5.5 or 4.5 treatment. Even through the RLAGR was considerably lower 

for the seedlings in the pH 2.5 treatment, the amount 

of dry-weight movement into the leaves was nearly 

constant in all four treatments. Leaf-weight ratio (LW) 

ranged from 0.76 gmlgm for the seedlings treated with 

pH 2.5 and 4.5 mist to 0.81 gmlgm for the seedlings 

treated with pH 3.5 mist. The acid mist may have 

directly reduced the leaf expansion rate by interfering 

with the rate of cell enlargement during the growth 

process or cell division in the meristematic regions. 

The acid mist apparently reduced the treatment 

growth rates by indirectly inhibiting the photosynthetic 

rate. NAR for the seedlings treated with pH 2.5 mist 

was less than zero. This response implies that more 

carbohydrate was being used in respiration or repair of 

injured tissue than was being produced. 

This reduction in growth or dry weight production 

with a decrease in pH is partially supported by other 

researchers. Irving (1983) reviewed the current literature 

and concluded that the effects of acidified precipitation on crops seem to be minimal and responses may 

be either positive or negative. Wedding and others 

(1979) treated soybean plants with sulfuric-acid mist 

droplets. They found no visible toxicity symptoms on 

the plants, and tissue examined with the scanning 

electron microscope showed no apparent damage due 

to the mist. 

When the seedlings were fumigated with SOn in 

the morning before being treated with acid mist in the 

afternoon, similar growth patterns to those obtained 

with acid mist alone were observed, but only leaf area 

was significantly affected. Height of the seedling 

decreased with an increase in acidity, while acidity had 

no affect on leaf dry weight and new stem dry weight 

until the pH dropped below 3.5. RGR, NAR, LAR, SLA, 

and RLAGR decreased with increasing acidity with 

losses in LAR and SLA being greater than those 

observed with mist alone. 
Table 1.-Height, leaf dry weight, new stem dry weight, and leaf 

area of yellow-poplar seedlings treated with acid mist and1 

or air pollutants for 8 weeks (mean of 10 seedlings) 

Leaf New Stem 

Pollutant Mist Height Dry Wt Dry Wt Leaf Area 

pH 

None 5.5 

4.5 

3.5 

2.5 

SO2 5.5 

4.5 

3.5 

2.5 

NO2 5.5 

4.5 

3.5 

2.5 

SO2 + NO2 5.5 

4.5 

3.5 

2.5 

0 3 5.5 

4.5 

3.5 

2.5 

crn 

l98a 

21 5a 

186a 

50b 

274a 

293a 

202ab 

78b 

608 

553 

656 

51 3 

52 1 

493 

277 

31 5 

292 

231 

416 

302 

Values in the same column for each pollutant followed by the same letter are not 

significantly different at the 0.05 percent level. (Duncans Multiple Range Test) 

1 Table 2.-Growth analysis variables of yellow-poplar seedlings treated with acid mist and air pollutants 

RG R NAR LA R SLA RLAGR 

Pollutant Mist (gm gm-I wk-') (gm ~m-~ wk-') (cm2 gm-') (cm2 gm-') (cm2 cm-' wk-') 

pH 

None 5.5 

4.5 

3.5 

2.5 

SO2 5.5 

4.5 

3.5 

2.5 

NO2 5.5 

4.5 

3.5 

2.5 

SO2 + NO2 5.5 

4.5 

3.5 

2.5 

0 3 5.5 

4.5 

3.5 

2.5 
When the seedlings were fumigated with NO2 

alone or with SO2 before the acid mist treatments, no 

significant differences,were observed in any of the four 

variables measured with a change in pH. Similar 

results were observed with ozone. The growth analysis 

variables calculated for the NO2, NO2 + SO2, and 03 

treated plants were variable and showed no consistent 

trends. For example, whereas RGR and RLAGR tended 

to increase with acidity in the NO2 treated seedlings, 

no distinct trends were observed on the NO2 plus SO2 

or 03 fumigated seedlings. 

The process by which the air pollutants altered the 

impact of acid mist observed in the first study is uncertain but may have been partially due to their nutritional 

contributions. Although no statistical test can be made 

to compare the seedlings treated wth NO2 or NO2 plus 

SO2 with the seedlings that did not receive any fumigation, an examination of the data in Table 1 indicates 

that the seedlings in these treatments had more than 

twice the leaf area, twice the new stem and leaf dry 

weight, and were twice as tall as the seedlings that 

were not fumigated. Even though soluble fertilizer 

treatment can improve the growth of healthy seedlings, 

the NO2 treatment and related gaseous pollutants may 

have further stimulated growth that could mask the 

harmful effect of the acid mist. 

The results of these studies suggest that yellowpoplar growth decreased with increasing acidity 

whereas the addition of one or more gaseous pollutants of ozone, nitrogen dioxide, and sulfur dioxide did 

not cause significant growth reductions with increasing acidity.-In an experiment designed to determine if 

the inclusion of ozone modified the effects of acidity 

of simulated rain on yield of soybean, Troiano et al. 

(1983) concluded that soybean mass was only slightly 

curtailed with increasing acidity in filtered air. 

However, with unfiltered air (ozone), vegetative mass 

decreased with increasing acidity. These findings are 

not in total agreement with our data which indicate 

that yellow-poplar seedlings receiving ozone and acid 

mist were not affected whereas seedlings growth was 

reduced with increasing acidity. Although the procedure and methodology of applying acid rain may be primarily responsible for the experimental discrepancy in 

growth responses, other environmental and plant 

characteristics such as dose response, genetical tolerance of host, stages of physiological development, and 

plantlsoil nutrient status may also contribute. 

The conclusions of these studies are representative of a laboratory experiment using low gaseous 

pollutants and acidity dosages to observe their effects 

on yellow-poplar seedlings. Such extrapolation to 

forests may be questionable because of probable 

differences in responses of mature trees subject to 

variable environmental conditions. Nevertheless, our 

results indicate that yellow-poplar growth is affected 

and that the potential for change in forest structure 

and function may exist. Further study coupling acidity 

and gaseous pollutant dosages with soil chemistry 

under field conditions must be conducted to more 

accurately assess the consequences of atmospheric 

deposition on early and subsequent growth of forest 

trees. 

Literature Cited 

Dochinger, L. S. An assessment of air pollution injury 

to American forests. Sylwan 118:63-68; 1974. 

Dochinger, L. S.; Calvert, J. G. Air pollution sources: 

General effects and trends. Soil Conservation Society of America Proceedings. 33:187-193; 1978. 

Duchelle, S. F.; Skelly, J. M.; Chevone, 6. I. Oxidant 

effects on forest tree seedling growth in the Appala. 

chian Mountains. Water Air Soil Pollution. 

12:363-373; 1982. 

Heck, W. W.; Dunning, J. A.; Johnson, H. Design of a 

simple plant exposure chamber. Cincinnati, OH: National Center for Air Pollution Control; 1968; Publ. 

APTD-68-6. 

Hunt, R. Plant growth curves. Baltimore, MD: University Park Press; 1982. 

Irving, P. M. Acidic precipitation effects on crops: A 

review and analysis of research. Journal of Environmental Quality. 12:442-453; 1983. 

Jensen, K. F. Response of nine forest tree species to 

chronic ozone fumigation. Plant Disease Reporter. 

57:914-917; 1973. 

Jensen, K. F. Air pollutants affect the relative growth 

rate of hardwood seedlings. Res. Pap. NE-470. 

Broomall, PA: U.S. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station; 

1981. 5p. 

Kress, L. W.; Skelly, J. M. Response of several eastern 

forest tree species to chronic doses of ozone and 

nitrogen dioxide. Plant Disease. 66:1149-1152; 1982. 

Mahoney, M. J.; Skelly, J. M.; Chevone, B. I.; Moore, 

L. D. Response of yellow poplar (Liriodendron tulipifera L.) seedlings shoot-growth to low concentrations 

of 03, SO*, and NOz. Canadian Journal of Research. 

14:150-153; 1983. 

Stone, L. L.; Skelly, J. M. The growth of two forest tree 

species adjacent to a periodic source of air pollution. 

Phytopathology. 64:773-778; 1974. 

Troiano, J.; Colavito, L.; Heller, L; McCune, D. C.; 

Jacobson,. J. S. Effects of acidity of simulated rain 

and its joint action with ambient ozone on measures 

of biomass and yield in soybean. Environmental 

Experimental Botany. 23:113-119; 1983. 

Vick, Charles B. Yellow-poplar. FS-272. Washington, 

DC: U.S. Department of Agriculture, Forest Service; 

1973. 

Wedding, J. B.; Ligotke; M.; Hess, F. D. Effects of 

sulfuric mist on plant canopies. Environmental 

Science Technology. 13:875-878; 1979. 
Dochinger, Leon S.; Jensen, Keith F. Effect of acid mist and air pollutants 

on yellow-poplar seedling height and leaf growth. Res. Pap. NE-572. 

Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station; 1985. 4 p. 

One-year-old yellow-poplar seedlings were treated with acid mist at pH 2.5, 

3.5, 4.5, and 5.5 either alone or in combination with 0.1 ppm 03, S02, and 

NO2 or NO2 plus S02. After 4 and 8 weeks of treatment, height, leaf area, 

and leaf and new shoot weight were determined and growth analysis variables calculated. Height, leaf area, and dry weight decreased with increasing acidity in seedlings treated with acid mist alone. Similar, but smaller 

reductions occurred in seedlings treated with SO2 and acid mist, but no differences were found in seedlings fumigated with NO?, NO2 plus SO2, or 

ozone and acid mist. Further studies using different combinations of pollutants and acid mist must be conducted before their apparent interactions 

can be more accurately assessed. 

ODC: 425.1: 11 1.78: 423 Liriodendron tulipifera L. 

1 Keywords: Acid deposition; yellow-poplar seedlings 

*U.S. GOVERNMENT PRINTING OFFICE:1985-505-028:20032 
Headquarters of the Northeastern Forest Experiment Station are in 

Broomall, Pa. Field laboratories are maintained at: 

Amherst, Massachusetts, in cooperation with the University of 

Massachusetts. 

0 Berea, Kentucky, in cooperation with Berea College. 

Burlington, Vermont, in cooperation with the University of 

Vermont. 

Delaware, Ohio. 

0 Durham, New Hampshire, in cooperation with the University of 

New Hampshire. 

0 Hamden, Connecticut, in cooperation with Yale University. 

@ Morgantown, West Virginia, in cooperation with West Virginia 

University, Morgantown. 

0 Orono, Maine, in cooperation with the University of Maine, 

Orono. 

Parsons, West Virginia. 

Princeton, West Virginia. 

Syracuse, New York, in cooperation with the State University of 

New York College of Environmental Sciences and Forestry at 

Syracuse University, Syracuse. 

University Park, Pennsylvania, in cooperation with the 

Pennsylvania State University. 

Warren, Pennsylvania.