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Effects of O3 and acidic rain on photosynthesis and growth in sugar maple and northern red oak seedlings
Environmental Pollution (Series A) 40 (1986) 1-15
Effects of 0 3 and Acidic Rain on Photosynthesis and Growth in Sugar Maple and Northern Red Oak Seedlings
Peter B. Reich, Anna W. Schoettle & Robert G. Amundson Boyce Thompson Institute, Cornell University, Ithaca, New York 14853, USA
ABSTRACT Two-year-oM sugar maple Acer saccharum and northern red oak Quercus rubra seedlings were exposed to all combinations of several levels each of ozone (03) and simulated acidic rain. Deposition rates and amounts of simulated rain were normal for eastern North America (12"5mm of rain twice per week) and levels of acidity in the various treatments ranged between p H 5"6 and 3"0. Plants were exposed to 0 3for 7h per day on 5 d per week. Concentrations of 0 3 were constant and ranged between 0.02 and O"12 #1 litre- 1 in the various treatments. Ozone treatments caused significant declines in net photosynthesis in both species, with the largest reductions observed (30 % in maple and 20 % in oak) after two months in the highest 0 3 treatment (0"121~1 litre-l). Reductions in growth as a result of 0 3 treatments occurred in sugar maple, but apparently due to the relatively short duration of the pollution treatments, growth reductions were not observed in red oak. Chlorophyll contents in sugar maple leaves increased as a result of 0 3 exposure. Simulated acidic rain treatments had no effect on either net photosynthesis or growth in either species and no interactive effects of the two pollutants were observed. The results of this study suggest that sugar maple and red oak are relatively insensitive to acidic rain over the course of a single growing season, but potential long-term effects are unknown. These two species were sensitive to relatively low concentrations of 0 3, and ambient levels of 0 3 in eastern North America could be having significant deleterious effects on sugar maple and red oak in the field. 1
Environ. Pollut. Set. A. 0143-1471/86/$03-50 © Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain
2
Peter B. Reich, Anna 14I. Schoettle, Robert G. Amundson
INTRODUCTION In eastern North America acidic precipitation and low-level ozone (03) pollution occur frequently and over a widespread area (National Academy of Sciences, 1977; Likens & Butler, 1981). Forests in this region may be currently undergoing widespread decline (Burgess, 1984), and there has been much speculation concerning the potential role of air pollution in such an occurrence (Johnson & Siccama, 1983). A worse situation exists in European forests (Anon., 1982). Unfortunately, little is known about the response of forest trees to either acidic rain or ambient (low-level) O 3 pollution, and information regarding potential interactions between these two pollutants is almost nonexistent at this time. One important area of concern involves the potential direct effects of these pollutants upon photosynthesis and growth in tree species. Reductions in net photosynthesis (Pn) as a result of exposure to low levels of O a (
Effects o f ozone and acid rain on trees
3
MATERIALS A N D M E T H O D S
Sugar maple Several hundred genetically diverse two-year-old sugar maple A c e r s a c c h a r u m L. seedlings were obtained from the Musser Forest Nursery in Indiana, PA. The seedlings were lifted from the nursery in March 1982 and shipped to Ithaca, NY, where they were kept in cold storage (3-4 °C) in the dark. The seedlings were planted in 3.5-1itre pots on 22 June 1982 and grown in a shaded glasshouse at the Boyce Thompson Institute, Ithaca, NY. Seedlings were grown in a 1 : 1 : 1 mixture (v:v) of peat, perlite and soil, and were kept well watered throughout the experiment. Bud break and leaf emergence began within a week of planting (some plants later had a second flush). A 4 x 3 factorial design was used in which plants were exposed to all combinations of four levels of 0 3 and three of acidic rain. On 6 July, 45 randomly selected plants (15 per rain treatment) were placed in each of four controlled environment 0 3 fumigation chambers (Western Environmental, Napa, CA). Chamber conditions included 16 h photoperiods with day/night temperatures and relative humidities of 22/17 _+ 1 °C and 50/60 _+ 5 ~ , respectively. Photosynthetically active radiation at the top of the plant canopy was about 750 ttmol m - 2 s - 1, but was halved during the first and last half hour of each photoperiod. Light was provided by a 1:1 mixture of mercury multi-vapour and highpressure sodium lamps (General Electric, Cleveland, OH). Beginning on 6 July, plants were exposed to constant concentrations of 0.03, 0.06, 0-09 or 0.12 #1 litre - 1 03 for about 7 h per day on five days per week. The 0"03/~1 litre -1 treatment was chosen as representative of ambient air in an unpolluted environment (Heck et al., 1982). No zero 0 3 treatment was used since plants never experience such a condition in nature. Beginning on 10 July, plants were transferred twice weekly to a glasshouse equipped to apply treatments with simulated acidic rain. Exposure was for 1.25 h each time, with a weekly deposition rate of 25mm. Rain treatments were applied at either pH 5-6, 4-0 or 3-0. To test for direct effects on foliage the soil was shielded from the simulated rain by plastic covers, which were placed over the tops of the pots. The covers were removed after each rain event. The 0.03 #1 litre- 1 03 treatment was obtained by partial filtration of ambient air. Additional 0 3 was generated
4
Peter B. Reich, Anna IV. Schoettle, Robert G. Amundson
by passing 0 2 by a UV source (Ozone Research Equipment Corp., Phoenix, AZ) and was 'bled' through micrometer valves into the air stream entering each chamber. The 0 3 concentration in the chamber atmosphere was measured with a chemiluminescent 0 3 monitor (Model 8410E, Monitor Labs, San Diego, CA), which was periodically calibrated with a Dasibi Ozone Monitor (Model 1003-PC, Dasibi Environmental Corp., Glendale, CA). A solenoid-valve switching system was used to sample the air sequentially in each chamber twice an hour. To avoid chamber or position effects, treatments were rotated weekly from chamber to chamber, and within each treatment the position of plants within a chamber was randomly varied during the weekly chamber rotation. Simulated rain was administered with a hydraulic spray nozzle (Type RA-2, Delavan Corp., West Des Moines, IA, USA) situated 3 m above a 1 m diameter turntable. The deposition rate of the nozzles was 10 m m h - 1 at 20 psi, with a mass medium droplet diameter of 0.33 mm. Solutions were acidified with a mixture of sulphuric and nitric acid at a sulphate (SO 2-) to nitrate (NO3) ratio of 2:1 on a weight basis. Acidity for each rain event was determined with a pH meter (Orion Research, Model 901A, Cambridge, MA). The seedlings were divided into three groups that were sequentially harvested after six, eight and ten weeks of pollutant treatments. Five plants in each of the twelve pollutant treatments were placed in each harvest group. At every harvest all plants were measured for height, stem diameter, number of leaves, leaf area (LI-COR Model LI-3000, Lincoln, NB) and leaf, shoot and root dry mass. Prior to the experiment, stem diameter and height were measured for all plants for later use in analyses of covariance. Net photosynthetic rates for intact, individual leaves were assessed in the growth chambers with either of two portable thermoelectrically cooled and heated cuvettes (Reich, 1983). Growth chamber air was passed through the cuvette, the air flow rate was monitored, and the difference in the CO 2 concentrations between the air stream entering and leaving the cuvette was continuously measured by an IR CO 2 analyser (ANARAD Model AR-600R) and recorded. The cuvette atmosphere was mixed constantly by a fan and tests of either CO 2 or O 3 concentrations found no gradients within the cuvette. The C 0 2 analyser was calibrated daily in the differential mode using certified CO2 standard gases (Scott Specialty Gases, Plumsteadville, PA). During measurements of CO 2 exchange, air
Effects o f ozone and acid rain on trees
5
temperature in the cuvette was 22 + 1 °C and CO 2 concentration ranged between 330 and 340 #1 litre-'. Areas of paper replicas of sample leaves were measured using the leaf area meter and net photosynthetic rates were calculated on a leaf area basis. Measurements of Pn were made between 1100 and 1600h, using fully expanded leaves from the first flush only. Analyses of variance and covariance (stem diameter and height prior to treatment were the covariants) were used to test for individual and interactive effects upon growth and net photosynthesis. Treatment sums of squares (and degrees of freedom) were partitioned using orthogonal contrasts, and linear, quadratic and, where applicable, cubic effects of the pollutants were tested by regression analysis. Once these had been determined, linear regression was used to describe the relationship between 0 3 exposure concentration and Pn. Northern red oak
Methods and procedures used for studying northern red oak in the laboratory were similar to those described above for sugar maple, except as detailed below. The seedlings were lifted in autumn 1982 and stored at 3-4 °C until January 1983. On 18 January, the seedlings were planted in pots in the glasshouse in either of two forest soils collected in Dryden, NY. Seedlings remained dormant for several weeks, but stems began to turn green in early February, and bud break and leaf emergence occurred in most seedlings in late February. A 2 x 3 x 3 factorial design was used in which plants were grown in either of the two soils and treated to all combinations of three levels each of 0 3 and acidic rain. Prior to the beginning of pollutant treatments, plants in each soil were classified into six groups by size (height, stem diameter, number of leaves) and by date of emergence, and one plant was assigned randomly from within each 'size class' to each of the nine combined pollutant treatments. On 9 March these seedlings were transferred (by 0 3 treatment) into three controlled environment fumigation chambers. Chamber conditions were as for sugar maple except that day/night temperatures were 25/20 + 1 °C and the photoperiod was 15 h long. Plants were exposed to constant concentrations (0.02, 0.07 or 0.12 #1 litre- ') of 0 3 for about 7 h per day on 5 days per week and were treated for 1.25 h (1.25 cm) with simulated rain of pH 5.0, 4-0 or 3.0 on each of 2 days per week. Plants were grown in either Mardin soil collected from
6
Peter B. Reich, Anna W. Schoettle, Robert G. Amundson
the Cornell University Mt Pleasant Research Area (approximately 2.4 km southeast of Etna, NY) or in Phelps soil from private property near Fall Creek (approximately 1.6 km northeast of Etna, NY). Both soils were developed under forest vegetation (Neeley, 1965). Mardin is a moderately well-drained, medium-textured channery silt loam. It is a strongly acidic soil (pH 4.1) formed from low lime, acidic glacial till. Very thin O and A horizons (total of 5-7 cm deep) lie atop a B horizon which extends from about 5 to 40 cm in depth. Soil was collected from approximately the top 20 cm of the profile. Mardin soil is low in Ca, P, K and Mg and high in AI (Table 1). Phelps is a deep, moderately well-drained, medium-textured gravelly silt loam (pH 6.3) formed in layered water-laid deposits of sand, silt and gravel. The A horizon extends to a depth of about 40 cm. The soil used in this study was largely from this horizon. Phelps soil is low in P, with average levels of other nutrients (Table 1). Soil analysis was done by the Cornell University Agronomy Analytical Laboratory and Morgan's extract solution was used. For the field study, approximately 125 red oak seedlings were planted in Mardin soil in 3.5-1itre pots in early summer 1983. These seedlings had been kept at 3-4 °C in the dark since autumn 1982 and were from the same group of seedlings used in the laboratory experiment. The plants were grown and fumigated daily with three 0 3 treatments in open-top chambers (Heagle et al., 1973; Mandl et al., 1973) in a field near Ithaca, NY. The three 0 3 treatments were charcoal-filtered air (CF--mean concentration of 0.024/A litre-1), nonfiltered air (NF--mean concentration of 0-044/A litre -1) and nonfiltered air, to which 0 3 was added ( + O3--mean concentration of 0.079 #1 litre - 1). The levels of O 3 in the NF treatment were always similar to ambient levels and the treatments were designed to be 0.5 (CF), 1.0 (NF) and 1.5 ( + 03) times the ambient concentration. A proportional controller directed by an ambient 0 3 TABLE 1
Soil Test Results for Mardin (pH 4.1) and Phelps (pH 6.3) Soils l~g g-m Soil
Mardin Phelps
P
1.8 0.4
K
8-5 17.0
Mg
3.8 26.0
Ca
10.0 285.0
Mn
4.3 2.6
Fe
31.0 2.8
AI
82-7 13.7
N
N
(NO3)
(NH3)
2.3 3-3
0.5 0.3
Zn
0.5 0.1
Effects o f ozone and acid rain on trees
7
monitor was used to make the daily 0 3 additions for 7 h (1000 to 1700 h EDT) except when precluded by rain or technical difficulties. Since 03 treatments were designed to be in fixed relation to the ambient 0 3 concentration, treatment concentrations varied daily in a pattern typical of ambient air (concentrations increased during the morning and decreased during the afternoon). In all treatments, the average daily 1 h maximum concentration was between 0.01 to 0.02 #1 litre- 1 higher than the mean 7 h daily concentrations and the maximum 7 h concentration observed during the experiment was about 2-5 times greater than the mean 7 h concentration. The 0 3 generation, distribution and monitoring systems were described previously (Kohut, 1981). Measurements of P~ in the field were made using the same portable instrumentation as indoors and two of the three 0 3 treatments were compared after four, seven and nine weeks of treatment. A t-test was used to determine significant differences between treatments. Plants in all three treatments were harvested after nine weeks of 0 3 exposure.
RESULTS
Growth of sugar maple seedlings There were no significant interactions between the pollutant treatments or between the pollutant treatments and the sequential harvests. Hence, growth data presented in Table 2 were pooled from all treatments and harvests. Acidic rain treatments had no significant effects on any growth variables. Ozone treatments caused a significant decline in height and stem diameter (quadratic and linear, respectively, in relation to 0 3 concentration), and there was a trend towards a negative effect for the other variables (p < 0-10). For instance, plant dry weight and leaf area decreased by 9 and 1 3 ~ , respectively, as 0 3 treatment mean concentrations increased from 0.03 to 0.12 #1 litre -1. Foliage was not visibly damaged by pollutant treatments.
Net photosynthesis of sugar maple seedlings Acidic rain treatments had no effect on Pn and did not interact with 0 3 treatments (Table 2). In contrast, Pn declined linearly in response to O 3 (Fig. l and Table 2) and a decrease of 30 ~o was observed between the
Ozone Acidic rain Ozone x acidic rain
Significance
Range o f standard error
5-6 4"0 3'0
Acidic rain (pH)
0'03 0'06 0-09 0.12
Treatment Ozone (Id litre - 1)
* ns ns
ns
0"8-1.0
35.0 38-2 35.6
36" 1 37.2 36.9 33"9
Height (cm)
ns ns
1 "4-1 "7
28"6 29.7 27"8
29.6 28-6 29' 1 27.5
Number o f leaves
ns
* ns
0-01-0-02
0-67 0"67 0"66
0"68 0"69 0.66 0.64
Stem diameter (cm)
ns
ns ns
31-36
582 654 591
636 623 621 554
(cm 2)
Leaf area
ns
ns ns
0-45-0.52
11 '29 11-68 10"76
11-53 11 '25 11'30 10-59
Total dry weight (g)
ns
* ns
0-204).26
6'68 6"57 6-98
6-24 6'40 7-45 6"88
Chlorophyll A + B contents (mg dm- 2)
ns
** ns
0.24-0.63
6' 12 5'80 5'92
7'03 6-12 5'72 5'06
Net photosynthetic rate (mg dm 2 h-1)
TABLE 2 Growth, Chlorophyll A + B Contents, and Net Photosynthesis of Sugar Maple Seedlings Treated with 0 3 o r Simulated Acidic Rain. Values for Growth Variables and Chlorophyll Contents are Means Pooled from Three Replicate Harvests After Six, Eight and Ten Weeks of Treatments (n = 45 for 03, 60 for Rain Treatments, Respectively). Values for Net Photosynthesis are Means Pooled from the Entire Experiment (Mean n = 35 for 0 3, 47 for Rain Treatments, Respectively). Significance of Treatments is Indicated by * (p < 0-05) or ** (p < 0.01)
2
a,
Effects o f ozone and acid rain on trees
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.c 8 "0 M
E "-"6 kJ Z I-4 >.
m 0
Pn " ?.6 - 20. :~ ( 0 3 )
p. ,I
.03
I
.06
I
i
.09
.12
03 CONC. (ppm) Fig. 1. Mean net photosynthesis ( + SE) of sugar maple seedlings in four O3 treatments. The significant regression equation for net photosynthesis as a function of 0 3 exposure concentration (#1 litre-1) is also shown.
lowest (0.03#1 litre -1) and highest (0-12pl litre -1) 0 3 treatments. Although leaf age (which increased during the experiment) was significantly related to Pn, it did not affect the relative photosynthetic response to 03; a regression equation developed using leaf age as a covariant did not differ significantly from the equation given in Fig. 1.
Chlorophyll contents in sugar maple seedlings Acidic rain treatments had no effect on Chl contents in sugar maple leaves, while 0 3 treatments had a significant (p < 0.05) impact on Chl a, Chlb and Chla + b contents (Table 2; only Chla + b shown). Chl contents increased slightly between the 0-03 and 0.06/4 litre -1 treatments, rose substantially between 0.06 and 0-09#1 litre -1 and declined modestly between 0.09 and 0.12 #1 litre-1. Also, Chl contents declined from 7.2 to 6.6 to 6-5 mg d m - 2 as leaves aged from six to eight to ten weeks, respectively. Such a change with increasing leaf age is typical of trends observed in poplar and soybean (Reich, 1983; Reich et al., in press a); however, in these species chlorophyll contents decreased as a result of 0 3 exposure.
Soil Ozone Acidic rain Interactions
Significance
Range of standard error
5-0 4-0 3.0
Acidic rain pH
0"02 0"07 0.12
Ozone (~tl litre- x)
Mardin Phelps
Treatment Soil
** ns ns ns
1" 1-2.0
20.6 21.4 20.6
20.1 21 '6 20-8
22.0 19.7
Number of leaves
**
ns ns ns
ns
O'Olq)'02
0"85 0'83 0-88
0"85 0-86 0"85
0.87 0.84
Stem diameter (cm)
ns ns ns
1-0 1-7
50.6 51'0 50-6
50.5 50-8 51"0
51.5 50.0
Height (cm)
ns ns ns
**
74-140
1 118 1156 1 141
1 104 1 200 1 112
1 252 1 025
(cm 2)
Leaf area
ns ns ns
*
1-1-3'8
41-9 42"2 43"7
41"7 43"8 42'2
43.6 41-5
Total dry weight (g)
* ns ns
*
0"17q).34
7"10 6"84 7"27
7'82 7.04 6-98
7.43 6.76
Net photosynthetic rate (rag dm -2 h -1)
TABLE 3 G r o w t h and Net Photosynthesis of Red Oak Seedlings Treated in the L a b o r a t o r y with 0 3 or Simulated Acidic Rain. Sample Sizes for G r o w t h Variables were 54 for Soil T r e a t m e n t a n d 36 for b o t h 0 3 a n d R a i n T r e a t m e n t s , While for N e t Photosynthesis they were 105 for Soil T r e a t m e n t a n d 70 for b o t h Pollutants. Significance of T r e a t m e n t s is Indicated by * ( p < 0.05) or ** ( p < 0.01)
~-
Effects of ozone and acid rain on trees
11
Growth of northern red oak seedlings Soil w a s the o n l y t r e a t m e n t to h a v e a significant effect o n g r o w t h o f red o a k seedlings in the c h a m b e r s t u d y a n d n o i n t e r a c t i o n s b e t w e e n t r e a t m e n t s w e r e o b s e r v e d ( T a b l e 3). Seedlings g r o w n in M a r d i n soil h a d o v e r 20 ~ g r e a t e r l e a f a r e a t h a n t h o s e in P h e l p s soil a n d h a d a b o u t 5 - 1 0 ~o g r e a t e r s t e m d i a m e t e r , n u m b e r o f leaves a n d t o t a l d r y weights t h a n t h o s e in Phelps soil. T h e r e w a s n o effect o f 0 3 t r e a t m e n t s o n g r o w t h o f o a k seedlings in the field s t u d y ( T a b l e 4). N o visible p o l l u t a n t injury w a s o b s e r v e d in a n y t r e a t m e n t in either o f the t w o o a k studies.
Net photosynthesis of northern red oak seedlings I n the l a b o r a t o r y study, soil a n d 0 3 t r e a t m e n t s h a d significant effects o n Pn, b u t acidic r a i n did n o t a n d n o i n t e r a c t i o n s b e t w e e n t r e a t m e n t s were
TABLE 4 Mean Net Photosynthesis after Four, Seven or Nine Weeks of 0 3 Exposure and Total Dry Weight at Harvest (after Nine Weeks of 0 3 Exposure) of Red Oak Seedlings Exposed in Open-top Chambers to Charcoal-filtered, Nonfiltered, or Nonfiltered + 0 3 Treatments. Significant Difference Between 0 3 Treatments is Indicated by a * (p < 0.05) Mean net photosynthetic rate (mg dm -2 h -1) No. of weeks of 0 3 exposure
Total plant dry weight (g)
4
7
9
Charcoal-filtered (mean concentration =0.024/21 litre -1)
8.59 + 0-98
8.30 +__1-05
--
(n= 17)
(n= 12)
Nonfiltered (mean concentration = 0.044#1 litre- 1)
--
--
Nonfiltered + 0 3 (mean concentration =0'079#1 litre -1)
8.99 + 1.07
0 3 Treatment
Significance
48.1 + 3-0 (n = 21)
8.47 + 2.01
49.4 + 2.6
(n = 8)
(n = 21)
5-23 + 0.51
5.48 + 0.66
48"6 + 4.1
(n= 17)
(n= 12)
(n=8)
(n = 21)
ns
*
*
ns
12
Peter B. Reich, Anna W. Schoettle, Robert G. Amundson
observed (Table 3). Rates of Pn were roughly 10 ~ greater in Mardin than in Phelps soil in all 0 3 treatments, while plants exposed to either 0.07 or 0.12#1 litre-1 03 had P n 10 ~o lower (when averaged over the whole experiment) than those in the 0.02 #1 litre - 1 treatment. The effect of 0 3 on P n w a s linear in relation to concentration with a trend towards a quadratic effect. Chronic exposure to 0 3 had a gradually increasing impact on Pn (Fig. 2). The difference in Pn between 0 3 treatments was minimal after two weeks of exposure, and grew larger by weeks 4-6 and 9-11. At the latter time, Pn in the 0.07 and 0.12 ~1 litre- 1 treatments was 17 and 22 ~ , respectively, lower than in the 0.02 pl litre - 1 treatment. Furthermore, the net increases in Pn between the second and tenth weeks were 2-7, 1.8 and 0-7mg dm -2 h -1 in the 0.02, 0.07 and 0-12~1 litre -1 treatments, respectively. In the field study, the effects of 0 3 treatments o n Pn were similar to those observed in the chamber study. After four weeks of 0 3 exposure, no difference in P~ was observed between the charcoal-filtered
"7,
10
E u
E
8
U) Ld 5. ).,. Z ).. I/)
oj,..
G
o z
Q. i,.. z 4
'i
i 2
,L
4 W E E K S OF
I
03
i
G 8 EXPOSURE
i
0
Mean net photosynthesis ( + S E ) of northern red oak seedlings in three 0 3 treatments in relation to number of weeks of 0 3 exposure. Mean 0 3 exposure concentrations (pl litre-i) are given in the Figure. Fig. 2.
Effects of ozone and acid rain on trees
13
(mean=0.024/~l litre -1) and the nonfiltered plus 0 3 t r e a t m e n t (mean =0.079/~1 litre -1) (Table 4). However, after seven weeks of exposure, plants in the latter treatment had significantly lower Pn than those in the former. Also, after nine weeks of exposure, plants in the nonfiltered plus 0 3 treatment (mean = 0.079/~1 litre- 1) had lower Pn than seedlings in the nonfiltered treatment (mean = 0.044 pl litre- 1). DISCUSSION Two-year-old sugar maple and red oak seedlings were negatively affected by frequent exposure to low levels of 03, while simulated acidic rain had no effect and no interactions between the pollutants were observed. Pollutant treatments in this study extended for 2-3 months and the effects of low-level pollution over several years could be much greater (FreerSmith, 1984; Garsed & Rutter, 1984). Moreover, only fully expanded leaves from previously untreated plants were exposed to the pollutant treatments, and foliage may be more sensitive to pollution during expansion, or in the year following pollutant exposure. Thus, while the results of this investigation suggest that 0 3 and acidic rain have moderate and minimal effects, respectively, on sugar maple and red oak over a single growing season, greater effects may occur gradually over several years either via direct action on the plants or, indirectly, through effects on the soil or the soil microbial community (Reich et al., in press b). Ozone treatments caused significant declines in Pn in both species, but in red oak this occurred only after plants were exposed to 0 3 for five weeks. Since oaks in the field retain their foliage for approximately 20 weeks, low-level 0 3 pollution probably has an increasingly large impact on daily Pn in the latter portion of the growing season. Chronic 0 3 pollution may stimulate leaf senescence in both species, as has been shown for hybrid poplar (Reich et al., 1984; Reich & Lassoie, 1985). In both oak and maple, the impact of 0 3 on growth was less than on pn. Several factors contribute to this observation. First, differences in dry matter accumulation per plant caused by 0 3 treatments would be small in comparison to the previous dry weight plus current accumulation of seedlings. Second, because two-year-old plants were used, there was considerable variability in initial plant size. The analysis of covariance using stem diameter prior to the experiment as the covariant removed some of the variation due to initial seedling size, but knowledge of each plant's initial dry weight would have been a more powerful covariant.
14
Peter B. Reich, Anna W. Schoettle, Robert G. Amundson
Third, measurements of Pn for individual leaves were made under relatively high light conditions for the chamber (about ¼ of full sunlight) and these might slightly overestimate the percent reduction due to 0 3 for all the leaves of a plant as a whole; in hybrid poplar and soybean, leaves receiving lower levels of light had smaller percent reductions in P~ due to 0 3 than when at higher light levels (Reich, 1983; Reich et al., in press a). However, our results do not suggest that reductions in Pn are unimportant to growth: one must remember that trees in eastern North America are exposed, year after year, to 0 3 pollution for much of the growing season. Thus, if levels of 03 are great enough to cause reduced Pn, the reduction in assimilation will be compounded annually, and even slight reductions could contribute significantly to long-term declines in growth. In summary, acidic rain treatments in this study had no detectable effects on tree seedlings and 0 3 treatments caused moderate declines in photosynthesis and growth. These results cannot be directly extrapolated to the field situation, but help lay a foundation for long-term ecological studies which are needed to define accurately the effects of atmospheric deposition on growth and performance of forest trees. REFERENCES Anon. (1982). Forest damage from air pollution. (Translation of Waldschaden dutch Luftverunreinigung.) Publication series of the German Federal Ministry of Nutrition, Agriculture, and Forests, Series A. Applied Science, 273, Agriculture Publishers Munster-Hiltrup. Burgess, R. L. (ed.) (1984). Effects of acidic deposition on forest ecosystems in the Northeastern United States: An evaluation of current evidence. Publication ESF84-016 of the State University of New York, College of Environmental Science and Forestry. Duchelle, S. F., Skelly, J. M. & Chevone, B. I. (1982). Oxidant effects on forest tree seedling growth in the Appalachian Mountains. Water, Air and Soil Pollut., 18, 363-73. Freer-Smith, P. H. (1984). The response of six broad-leaved trees during longterm exposure to SO2 and NO 2. New Phytol., 97, 49-61. Garsed, S. G. & Rutter, A. J. (1984). The effects of fluctuating concentrations of sulphur dioxide on the growth of Pinus sylvestris L. and Picea sitchensis (Bong.) Carr. New Phytol., 97, 175-95. Heagle, A. S., Body, D. E. & Heck, W. W. (1973). An open-top field chamber to assess the impact of air pollution on plants. J. environ. Qual., 2, 365-8. 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.
Effects of ozone and acid rain on trees
15
Johnson, A. H. & Siccama, T. G. (1983). Acid deposition and forest decline. Environ. Sci. Technol., 17, 294-305. Kohut, R.J. ('1981). Northeast Regional Crop Loss Assessment Program Report. In National Crop Loss Assessment Network (NCLAN) 1980 Annual Report. Corvallis, OR, Environmental Protection Agency. Kress, L. W. & Skelly, J. M. (1982). Response of several eastern forest tree species to chronic dose of ozone and nitrogen dioxide. Plant Disease, 66, 1149-52. Lee, J. J. & Weber, D. E. (1979). The effect of simulated acid rain on seedling emergence and growth of eleven woody species. For. Sci., 25, 393-8. Likens, G. E. & Butler, T.J. (1981). Recent acidification of precipitation in North America. Atmos. Environ., 15, 1103 9. Mandl, R. H., Weinstein, L. H., McCune, D. D. & 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. Miller, P. R., Parmeter, J. R., Jr, Flick, B. H. & Martinez, C. W. (1969). Ozone dosage response of ponderosa pine seedlings. J. Air Pollut. ControlAss., 19, 435-8. National Academy of Sciences (1977). Ozone and other photochemical oxidants. Washington, DC. Neeley, J. A. (1965). Soil survey of Tompkins County, New York, Washington, DC, USDA. Reich, P. B. (1983). Effects of low concentrations of 0 3 on net photosynthesis, dark respiration, and chlorophyll contents in aging hybrid poplar leaves. PI. Physiol., Lancaster, 73, 291-6. Reich, P. B. & Lassoie, J. P. (1985). Influence of low concentrations of ozone on growth, biomass partitioning, and leaf senescence in young hybrid poplar plants. Environ. Pollut., Ser. A, 39, 39-51. 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., 62, 2835~41. Reich, P. B., Schoettle, A. W., Raba, R. & Amundson, R. G. (in press a). Low concentrations of 0 3 reduce leaf and whole plant net photosynthesis and chlorophyll contents of soybean. J. environ. Qual. Reich, P. B., Schoettle, A. W., Stroo, H. F., Troiano, J. & Amundson, R. G. (in press b). Effects of 0 3, SO 2 and acidic rain on mycorrhizal infection in northern red oak seedlings. Can. J. Bot. Tveite, B. (1980). Effects of acid precipitation on soil and forest. A. Tree growth in field experiments. In Ecological impact of acid precipitation, ed. by D. Drablos and A. Tollan, 206-7. Oslo, SNSF Project. Wood, T. & Bormann, F. H. (1977). Short-term effects of a simulated acid rain upon the growth and nutrient relations of Pinus strobus L. Water, Air & Soil Pollut., 7, 479-88. Yang, Y., Skelly, J. M., Chevone, B. I. & Birch, J. B. (1983). Effects of long-term ozone exposure on photosynthesis and dark respiration of eastern white pine. Environ. Sci. Technol., 17, 371-3.
Effects of 0 3 and Acidic Rain on Photosynthesis and Growth in Sugar Maple and Northern Red Oak Seedlings
Peter B. Reich, Anna W. Schoettle & Robert G. Amundson Boyce Thompson Institute, Cornell University, Ithaca, New York 14853, USA
ABSTRACT Two-year-oM sugar maple Acer saccharum and northern red oak Quercus rubra seedlings were exposed to all combinations of several levels each of ozone (03) and simulated acidic rain. Deposition rates and amounts of simulated rain were normal for eastern North America (12"5mm of rain twice per week) and levels of acidity in the various treatments ranged between p H 5"6 and 3"0. Plants were exposed to 0 3for 7h per day on 5 d per week. Concentrations of 0 3 were constant and ranged between 0.02 and O"12 #1 litre- 1 in the various treatments. Ozone treatments caused significant declines in net photosynthesis in both species, with the largest reductions observed (30 % in maple and 20 % in oak) after two months in the highest 0 3 treatment (0"121~1 litre-l). Reductions in growth as a result of 0 3 treatments occurred in sugar maple, but apparently due to the relatively short duration of the pollution treatments, growth reductions were not observed in red oak. Chlorophyll contents in sugar maple leaves increased as a result of 0 3 exposure. Simulated acidic rain treatments had no effect on either net photosynthesis or growth in either species and no interactive effects of the two pollutants were observed. The results of this study suggest that sugar maple and red oak are relatively insensitive to acidic rain over the course of a single growing season, but potential long-term effects are unknown. These two species were sensitive to relatively low concentrations of 0 3, and ambient levels of 0 3 in eastern North America could be having significant deleterious effects on sugar maple and red oak in the field. 1
Environ. Pollut. Set. A. 0143-1471/86/$03-50 © Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain
2
Peter B. Reich, Anna 14I. Schoettle, Robert G. Amundson
INTRODUCTION In eastern North America acidic precipitation and low-level ozone (03) pollution occur frequently and over a widespread area (National Academy of Sciences, 1977; Likens & Butler, 1981). Forests in this region may be currently undergoing widespread decline (Burgess, 1984), and there has been much speculation concerning the potential role of air pollution in such an occurrence (Johnson & Siccama, 1983). A worse situation exists in European forests (Anon., 1982). Unfortunately, little is known about the response of forest trees to either acidic rain or ambient (low-level) O 3 pollution, and information regarding potential interactions between these two pollutants is almost nonexistent at this time. One important area of concern involves the potential direct effects of these pollutants upon photosynthesis and growth in tree species. Reductions in net photosynthesis (Pn) as a result of exposure to low levels of O a (
Effects o f ozone and acid rain on trees
3
MATERIALS A N D M E T H O D S
Sugar maple Several hundred genetically diverse two-year-old sugar maple A c e r s a c c h a r u m L. seedlings were obtained from the Musser Forest Nursery in Indiana, PA. The seedlings were lifted from the nursery in March 1982 and shipped to Ithaca, NY, where they were kept in cold storage (3-4 °C) in the dark. The seedlings were planted in 3.5-1itre pots on 22 June 1982 and grown in a shaded glasshouse at the Boyce Thompson Institute, Ithaca, NY. Seedlings were grown in a 1 : 1 : 1 mixture (v:v) of peat, perlite and soil, and were kept well watered throughout the experiment. Bud break and leaf emergence began within a week of planting (some plants later had a second flush). A 4 x 3 factorial design was used in which plants were exposed to all combinations of four levels of 0 3 and three of acidic rain. On 6 July, 45 randomly selected plants (15 per rain treatment) were placed in each of four controlled environment 0 3 fumigation chambers (Western Environmental, Napa, CA). Chamber conditions included 16 h photoperiods with day/night temperatures and relative humidities of 22/17 _+ 1 °C and 50/60 _+ 5 ~ , respectively. Photosynthetically active radiation at the top of the plant canopy was about 750 ttmol m - 2 s - 1, but was halved during the first and last half hour of each photoperiod. Light was provided by a 1:1 mixture of mercury multi-vapour and highpressure sodium lamps (General Electric, Cleveland, OH). Beginning on 6 July, plants were exposed to constant concentrations of 0.03, 0.06, 0-09 or 0.12 #1 litre - 1 03 for about 7 h per day on five days per week. The 0"03/~1 litre -1 treatment was chosen as representative of ambient air in an unpolluted environment (Heck et al., 1982). No zero 0 3 treatment was used since plants never experience such a condition in nature. Beginning on 10 July, plants were transferred twice weekly to a glasshouse equipped to apply treatments with simulated acidic rain. Exposure was for 1.25 h each time, with a weekly deposition rate of 25mm. Rain treatments were applied at either pH 5-6, 4-0 or 3-0. To test for direct effects on foliage the soil was shielded from the simulated rain by plastic covers, which were placed over the tops of the pots. The covers were removed after each rain event. The 0.03 #1 litre- 1 03 treatment was obtained by partial filtration of ambient air. Additional 0 3 was generated
4
Peter B. Reich, Anna IV. Schoettle, Robert G. Amundson
by passing 0 2 by a UV source (Ozone Research Equipment Corp., Phoenix, AZ) and was 'bled' through micrometer valves into the air stream entering each chamber. The 0 3 concentration in the chamber atmosphere was measured with a chemiluminescent 0 3 monitor (Model 8410E, Monitor Labs, San Diego, CA), which was periodically calibrated with a Dasibi Ozone Monitor (Model 1003-PC, Dasibi Environmental Corp., Glendale, CA). A solenoid-valve switching system was used to sample the air sequentially in each chamber twice an hour. To avoid chamber or position effects, treatments were rotated weekly from chamber to chamber, and within each treatment the position of plants within a chamber was randomly varied during the weekly chamber rotation. Simulated rain was administered with a hydraulic spray nozzle (Type RA-2, Delavan Corp., West Des Moines, IA, USA) situated 3 m above a 1 m diameter turntable. The deposition rate of the nozzles was 10 m m h - 1 at 20 psi, with a mass medium droplet diameter of 0.33 mm. Solutions were acidified with a mixture of sulphuric and nitric acid at a sulphate (SO 2-) to nitrate (NO3) ratio of 2:1 on a weight basis. Acidity for each rain event was determined with a pH meter (Orion Research, Model 901A, Cambridge, MA). The seedlings were divided into three groups that were sequentially harvested after six, eight and ten weeks of pollutant treatments. Five plants in each of the twelve pollutant treatments were placed in each harvest group. At every harvest all plants were measured for height, stem diameter, number of leaves, leaf area (LI-COR Model LI-3000, Lincoln, NB) and leaf, shoot and root dry mass. Prior to the experiment, stem diameter and height were measured for all plants for later use in analyses of covariance. Net photosynthetic rates for intact, individual leaves were assessed in the growth chambers with either of two portable thermoelectrically cooled and heated cuvettes (Reich, 1983). Growth chamber air was passed through the cuvette, the air flow rate was monitored, and the difference in the CO 2 concentrations between the air stream entering and leaving the cuvette was continuously measured by an IR CO 2 analyser (ANARAD Model AR-600R) and recorded. The cuvette atmosphere was mixed constantly by a fan and tests of either CO 2 or O 3 concentrations found no gradients within the cuvette. The C 0 2 analyser was calibrated daily in the differential mode using certified CO2 standard gases (Scott Specialty Gases, Plumsteadville, PA). During measurements of CO 2 exchange, air
Effects o f ozone and acid rain on trees
5
temperature in the cuvette was 22 + 1 °C and CO 2 concentration ranged between 330 and 340 #1 litre-'. Areas of paper replicas of sample leaves were measured using the leaf area meter and net photosynthetic rates were calculated on a leaf area basis. Measurements of Pn were made between 1100 and 1600h, using fully expanded leaves from the first flush only. Analyses of variance and covariance (stem diameter and height prior to treatment were the covariants) were used to test for individual and interactive effects upon growth and net photosynthesis. Treatment sums of squares (and degrees of freedom) were partitioned using orthogonal contrasts, and linear, quadratic and, where applicable, cubic effects of the pollutants were tested by regression analysis. Once these had been determined, linear regression was used to describe the relationship between 0 3 exposure concentration and Pn. Northern red oak
Methods and procedures used for studying northern red oak in the laboratory were similar to those described above for sugar maple, except as detailed below. The seedlings were lifted in autumn 1982 and stored at 3-4 °C until January 1983. On 18 January, the seedlings were planted in pots in the glasshouse in either of two forest soils collected in Dryden, NY. Seedlings remained dormant for several weeks, but stems began to turn green in early February, and bud break and leaf emergence occurred in most seedlings in late February. A 2 x 3 x 3 factorial design was used in which plants were grown in either of the two soils and treated to all combinations of three levels each of 0 3 and acidic rain. Prior to the beginning of pollutant treatments, plants in each soil were classified into six groups by size (height, stem diameter, number of leaves) and by date of emergence, and one plant was assigned randomly from within each 'size class' to each of the nine combined pollutant treatments. On 9 March these seedlings were transferred (by 0 3 treatment) into three controlled environment fumigation chambers. Chamber conditions were as for sugar maple except that day/night temperatures were 25/20 + 1 °C and the photoperiod was 15 h long. Plants were exposed to constant concentrations (0.02, 0.07 or 0.12 #1 litre- ') of 0 3 for about 7 h per day on 5 days per week and were treated for 1.25 h (1.25 cm) with simulated rain of pH 5.0, 4-0 or 3.0 on each of 2 days per week. Plants were grown in either Mardin soil collected from
6
Peter B. Reich, Anna W. Schoettle, Robert G. Amundson
the Cornell University Mt Pleasant Research Area (approximately 2.4 km southeast of Etna, NY) or in Phelps soil from private property near Fall Creek (approximately 1.6 km northeast of Etna, NY). Both soils were developed under forest vegetation (Neeley, 1965). Mardin is a moderately well-drained, medium-textured channery silt loam. It is a strongly acidic soil (pH 4.1) formed from low lime, acidic glacial till. Very thin O and A horizons (total of 5-7 cm deep) lie atop a B horizon which extends from about 5 to 40 cm in depth. Soil was collected from approximately the top 20 cm of the profile. Mardin soil is low in Ca, P, K and Mg and high in AI (Table 1). Phelps is a deep, moderately well-drained, medium-textured gravelly silt loam (pH 6.3) formed in layered water-laid deposits of sand, silt and gravel. The A horizon extends to a depth of about 40 cm. The soil used in this study was largely from this horizon. Phelps soil is low in P, with average levels of other nutrients (Table 1). Soil analysis was done by the Cornell University Agronomy Analytical Laboratory and Morgan's extract solution was used. For the field study, approximately 125 red oak seedlings were planted in Mardin soil in 3.5-1itre pots in early summer 1983. These seedlings had been kept at 3-4 °C in the dark since autumn 1982 and were from the same group of seedlings used in the laboratory experiment. The plants were grown and fumigated daily with three 0 3 treatments in open-top chambers (Heagle et al., 1973; Mandl et al., 1973) in a field near Ithaca, NY. The three 0 3 treatments were charcoal-filtered air (CF--mean concentration of 0.024/A litre-1), nonfiltered air (NF--mean concentration of 0-044/A litre -1) and nonfiltered air, to which 0 3 was added ( + O3--mean concentration of 0.079 #1 litre - 1). The levels of O 3 in the NF treatment were always similar to ambient levels and the treatments were designed to be 0.5 (CF), 1.0 (NF) and 1.5 ( + 03) times the ambient concentration. A proportional controller directed by an ambient 0 3 TABLE 1
Soil Test Results for Mardin (pH 4.1) and Phelps (pH 6.3) Soils l~g g-m Soil
Mardin Phelps
P
1.8 0.4
K
8-5 17.0
Mg
3.8 26.0
Ca
10.0 285.0
Mn
4.3 2.6
Fe
31.0 2.8
AI
82-7 13.7
N
N
(NO3)
(NH3)
2.3 3-3
0.5 0.3
Zn
0.5 0.1
Effects o f ozone and acid rain on trees
7
monitor was used to make the daily 0 3 additions for 7 h (1000 to 1700 h EDT) except when precluded by rain or technical difficulties. Since 03 treatments were designed to be in fixed relation to the ambient 0 3 concentration, treatment concentrations varied daily in a pattern typical of ambient air (concentrations increased during the morning and decreased during the afternoon). In all treatments, the average daily 1 h maximum concentration was between 0.01 to 0.02 #1 litre- 1 higher than the mean 7 h daily concentrations and the maximum 7 h concentration observed during the experiment was about 2-5 times greater than the mean 7 h concentration. The 0 3 generation, distribution and monitoring systems were described previously (Kohut, 1981). Measurements of P~ in the field were made using the same portable instrumentation as indoors and two of the three 0 3 treatments were compared after four, seven and nine weeks of treatment. A t-test was used to determine significant differences between treatments. Plants in all three treatments were harvested after nine weeks of 0 3 exposure.
RESULTS
Growth of sugar maple seedlings There were no significant interactions between the pollutant treatments or between the pollutant treatments and the sequential harvests. Hence, growth data presented in Table 2 were pooled from all treatments and harvests. Acidic rain treatments had no significant effects on any growth variables. Ozone treatments caused a significant decline in height and stem diameter (quadratic and linear, respectively, in relation to 0 3 concentration), and there was a trend towards a negative effect for the other variables (p < 0-10). For instance, plant dry weight and leaf area decreased by 9 and 1 3 ~ , respectively, as 0 3 treatment mean concentrations increased from 0.03 to 0.12 #1 litre -1. Foliage was not visibly damaged by pollutant treatments.
Net photosynthesis of sugar maple seedlings Acidic rain treatments had no effect on Pn and did not interact with 0 3 treatments (Table 2). In contrast, Pn declined linearly in response to O 3 (Fig. l and Table 2) and a decrease of 30 ~o was observed between the
Ozone Acidic rain Ozone x acidic rain
Significance
Range o f standard error
5-6 4"0 3'0
Acidic rain (pH)
0'03 0'06 0-09 0.12
Treatment Ozone (Id litre - 1)
* ns ns
ns
0"8-1.0
35.0 38-2 35.6
36" 1 37.2 36.9 33"9
Height (cm)
ns ns
1 "4-1 "7
28"6 29.7 27"8
29.6 28-6 29' 1 27.5
Number o f leaves
ns
* ns
0-01-0-02
0-67 0"67 0"66
0"68 0"69 0.66 0.64
Stem diameter (cm)
ns
ns ns
31-36
582 654 591
636 623 621 554
(cm 2)
Leaf area
ns
ns ns
0-45-0.52
11 '29 11-68 10"76
11-53 11 '25 11'30 10-59
Total dry weight (g)
ns
* ns
0-204).26
6'68 6"57 6-98
6-24 6'40 7-45 6"88
Chlorophyll A + B contents (mg dm- 2)
ns
** ns
0.24-0.63
6' 12 5'80 5'92
7'03 6-12 5'72 5'06
Net photosynthetic rate (mg dm 2 h-1)
TABLE 2 Growth, Chlorophyll A + B Contents, and Net Photosynthesis of Sugar Maple Seedlings Treated with 0 3 o r Simulated Acidic Rain. Values for Growth Variables and Chlorophyll Contents are Means Pooled from Three Replicate Harvests After Six, Eight and Ten Weeks of Treatments (n = 45 for 03, 60 for Rain Treatments, Respectively). Values for Net Photosynthesis are Means Pooled from the Entire Experiment (Mean n = 35 for 0 3, 47 for Rain Treatments, Respectively). Significance of Treatments is Indicated by * (p < 0-05) or ** (p < 0.01)
2
a,
Effects o f ozone and acid rain on trees
9
.c 8 "0 M
E "-"6 kJ Z I-4 >.
m 0
Pn " ?.6 - 20. :~ ( 0 3 )
p. ,I
.03
I
.06
I
i
.09
.12
03 CONC. (ppm) Fig. 1. Mean net photosynthesis ( + SE) of sugar maple seedlings in four O3 treatments. The significant regression equation for net photosynthesis as a function of 0 3 exposure concentration (#1 litre-1) is also shown.
lowest (0.03#1 litre -1) and highest (0-12pl litre -1) 0 3 treatments. Although leaf age (which increased during the experiment) was significantly related to Pn, it did not affect the relative photosynthetic response to 03; a regression equation developed using leaf age as a covariant did not differ significantly from the equation given in Fig. 1.
Chlorophyll contents in sugar maple seedlings Acidic rain treatments had no effect on Chl contents in sugar maple leaves, while 0 3 treatments had a significant (p < 0.05) impact on Chl a, Chlb and Chla + b contents (Table 2; only Chla + b shown). Chl contents increased slightly between the 0-03 and 0.06/4 litre -1 treatments, rose substantially between 0.06 and 0-09#1 litre -1 and declined modestly between 0.09 and 0.12 #1 litre-1. Also, Chl contents declined from 7.2 to 6.6 to 6-5 mg d m - 2 as leaves aged from six to eight to ten weeks, respectively. Such a change with increasing leaf age is typical of trends observed in poplar and soybean (Reich, 1983; Reich et al., in press a); however, in these species chlorophyll contents decreased as a result of 0 3 exposure.
Soil Ozone Acidic rain Interactions
Significance
Range of standard error
5-0 4-0 3.0
Acidic rain pH
0"02 0"07 0.12
Ozone (~tl litre- x)
Mardin Phelps
Treatment Soil
** ns ns ns
1" 1-2.0
20.6 21.4 20.6
20.1 21 '6 20-8
22.0 19.7
Number of leaves
**
ns ns ns
ns
O'Olq)'02
0"85 0'83 0-88
0"85 0-86 0"85
0.87 0.84
Stem diameter (cm)
ns ns ns
1-0 1-7
50.6 51'0 50-6
50.5 50-8 51"0
51.5 50.0
Height (cm)
ns ns ns
**
74-140
1 118 1156 1 141
1 104 1 200 1 112
1 252 1 025
(cm 2)
Leaf area
ns ns ns
*
1-1-3'8
41-9 42"2 43"7
41"7 43"8 42'2
43.6 41-5
Total dry weight (g)
* ns ns
*
0"17q).34
7"10 6"84 7"27
7'82 7.04 6-98
7.43 6.76
Net photosynthetic rate (rag dm -2 h -1)
TABLE 3 G r o w t h and Net Photosynthesis of Red Oak Seedlings Treated in the L a b o r a t o r y with 0 3 or Simulated Acidic Rain. Sample Sizes for G r o w t h Variables were 54 for Soil T r e a t m e n t a n d 36 for b o t h 0 3 a n d R a i n T r e a t m e n t s , While for N e t Photosynthesis they were 105 for Soil T r e a t m e n t a n d 70 for b o t h Pollutants. Significance of T r e a t m e n t s is Indicated by * ( p < 0.05) or ** ( p < 0.01)
~-
Effects of ozone and acid rain on trees
11
Growth of northern red oak seedlings Soil w a s the o n l y t r e a t m e n t to h a v e a significant effect o n g r o w t h o f red o a k seedlings in the c h a m b e r s t u d y a n d n o i n t e r a c t i o n s b e t w e e n t r e a t m e n t s w e r e o b s e r v e d ( T a b l e 3). Seedlings g r o w n in M a r d i n soil h a d o v e r 20 ~ g r e a t e r l e a f a r e a t h a n t h o s e in P h e l p s soil a n d h a d a b o u t 5 - 1 0 ~o g r e a t e r s t e m d i a m e t e r , n u m b e r o f leaves a n d t o t a l d r y weights t h a n t h o s e in Phelps soil. T h e r e w a s n o effect o f 0 3 t r e a t m e n t s o n g r o w t h o f o a k seedlings in the field s t u d y ( T a b l e 4). N o visible p o l l u t a n t injury w a s o b s e r v e d in a n y t r e a t m e n t in either o f the t w o o a k studies.
Net photosynthesis of northern red oak seedlings I n the l a b o r a t o r y study, soil a n d 0 3 t r e a t m e n t s h a d significant effects o n Pn, b u t acidic r a i n did n o t a n d n o i n t e r a c t i o n s b e t w e e n t r e a t m e n t s were
TABLE 4 Mean Net Photosynthesis after Four, Seven or Nine Weeks of 0 3 Exposure and Total Dry Weight at Harvest (after Nine Weeks of 0 3 Exposure) of Red Oak Seedlings Exposed in Open-top Chambers to Charcoal-filtered, Nonfiltered, or Nonfiltered + 0 3 Treatments. Significant Difference Between 0 3 Treatments is Indicated by a * (p < 0.05) Mean net photosynthetic rate (mg dm -2 h -1) No. of weeks of 0 3 exposure
Total plant dry weight (g)
4
7
9
Charcoal-filtered (mean concentration =0.024/21 litre -1)
8.59 + 0-98
8.30 +__1-05
--
(n= 17)
(n= 12)
Nonfiltered (mean concentration = 0.044#1 litre- 1)
--
--
Nonfiltered + 0 3 (mean concentration =0'079#1 litre -1)
8.99 + 1.07
0 3 Treatment
Significance
48.1 + 3-0 (n = 21)
8.47 + 2.01
49.4 + 2.6
(n = 8)
(n = 21)
5-23 + 0.51
5.48 + 0.66
48"6 + 4.1
(n= 17)
(n= 12)
(n=8)
(n = 21)
ns
*
*
ns
12
Peter B. Reich, Anna W. Schoettle, Robert G. Amundson
observed (Table 3). Rates of Pn were roughly 10 ~ greater in Mardin than in Phelps soil in all 0 3 treatments, while plants exposed to either 0.07 or 0.12#1 litre-1 03 had P n 10 ~o lower (when averaged over the whole experiment) than those in the 0.02 #1 litre - 1 treatment. The effect of 0 3 on P n w a s linear in relation to concentration with a trend towards a quadratic effect. Chronic exposure to 0 3 had a gradually increasing impact on Pn (Fig. 2). The difference in Pn between 0 3 treatments was minimal after two weeks of exposure, and grew larger by weeks 4-6 and 9-11. At the latter time, Pn in the 0.07 and 0.12 ~1 litre- 1 treatments was 17 and 22 ~ , respectively, lower than in the 0.02 pl litre - 1 treatment. Furthermore, the net increases in Pn between the second and tenth weeks were 2-7, 1.8 and 0-7mg dm -2 h -1 in the 0.02, 0.07 and 0-12~1 litre -1 treatments, respectively. In the field study, the effects of 0 3 treatments o n Pn were similar to those observed in the chamber study. After four weeks of 0 3 exposure, no difference in P~ was observed between the charcoal-filtered
"7,
10
E u
E
8
U) Ld 5. ).,. Z ).. I/)
oj,..
G
o z
Q. i,.. z 4
'i
i 2
,L
4 W E E K S OF
I
03
i
G 8 EXPOSURE
i
0
Mean net photosynthesis ( + S E ) of northern red oak seedlings in three 0 3 treatments in relation to number of weeks of 0 3 exposure. Mean 0 3 exposure concentrations (pl litre-i) are given in the Figure. Fig. 2.
Effects of ozone and acid rain on trees
13
(mean=0.024/~l litre -1) and the nonfiltered plus 0 3 t r e a t m e n t (mean =0.079/~1 litre -1) (Table 4). However, after seven weeks of exposure, plants in the latter treatment had significantly lower Pn than those in the former. Also, after nine weeks of exposure, plants in the nonfiltered plus 0 3 treatment (mean = 0.079/~1 litre- 1) had lower Pn than seedlings in the nonfiltered treatment (mean = 0.044 pl litre- 1). DISCUSSION Two-year-old sugar maple and red oak seedlings were negatively affected by frequent exposure to low levels of 03, while simulated acidic rain had no effect and no interactions between the pollutants were observed. Pollutant treatments in this study extended for 2-3 months and the effects of low-level pollution over several years could be much greater (FreerSmith, 1984; Garsed & Rutter, 1984). Moreover, only fully expanded leaves from previously untreated plants were exposed to the pollutant treatments, and foliage may be more sensitive to pollution during expansion, or in the year following pollutant exposure. Thus, while the results of this investigation suggest that 0 3 and acidic rain have moderate and minimal effects, respectively, on sugar maple and red oak over a single growing season, greater effects may occur gradually over several years either via direct action on the plants or, indirectly, through effects on the soil or the soil microbial community (Reich et al., in press b). Ozone treatments caused significant declines in Pn in both species, but in red oak this occurred only after plants were exposed to 0 3 for five weeks. Since oaks in the field retain their foliage for approximately 20 weeks, low-level 0 3 pollution probably has an increasingly large impact on daily Pn in the latter portion of the growing season. Chronic 0 3 pollution may stimulate leaf senescence in both species, as has been shown for hybrid poplar (Reich et al., 1984; Reich & Lassoie, 1985). In both oak and maple, the impact of 0 3 on growth was less than on pn. Several factors contribute to this observation. First, differences in dry matter accumulation per plant caused by 0 3 treatments would be small in comparison to the previous dry weight plus current accumulation of seedlings. Second, because two-year-old plants were used, there was considerable variability in initial plant size. The analysis of covariance using stem diameter prior to the experiment as the covariant removed some of the variation due to initial seedling size, but knowledge of each plant's initial dry weight would have been a more powerful covariant.
14
Peter B. Reich, Anna W. Schoettle, Robert G. Amundson
Third, measurements of Pn for individual leaves were made under relatively high light conditions for the chamber (about ¼ of full sunlight) and these might slightly overestimate the percent reduction due to 0 3 for all the leaves of a plant as a whole; in hybrid poplar and soybean, leaves receiving lower levels of light had smaller percent reductions in P~ due to 0 3 than when at higher light levels (Reich, 1983; Reich et al., in press a). However, our results do not suggest that reductions in Pn are unimportant to growth: one must remember that trees in eastern North America are exposed, year after year, to 0 3 pollution for much of the growing season. Thus, if levels of 03 are great enough to cause reduced Pn, the reduction in assimilation will be compounded annually, and even slight reductions could contribute significantly to long-term declines in growth. In summary, acidic rain treatments in this study had no detectable effects on tree seedlings and 0 3 treatments caused moderate declines in photosynthesis and growth. These results cannot be directly extrapolated to the field situation, but help lay a foundation for long-term ecological studies which are needed to define accurately the effects of atmospheric deposition on growth and performance of forest trees. REFERENCES Anon. (1982). Forest damage from air pollution. (Translation of Waldschaden dutch Luftverunreinigung.) Publication series of the German Federal Ministry of Nutrition, Agriculture, and Forests, Series A. Applied Science, 273, Agriculture Publishers Munster-Hiltrup. Burgess, R. L. (ed.) (1984). Effects of acidic deposition on forest ecosystems in the Northeastern United States: An evaluation of current evidence. Publication ESF84-016 of the State University of New York, College of Environmental Science and Forestry. Duchelle, S. F., Skelly, J. M. & Chevone, B. I. (1982). Oxidant effects on forest tree seedling growth in the Appalachian Mountains. Water, Air and Soil Pollut., 18, 363-73. Freer-Smith, P. H. (1984). The response of six broad-leaved trees during longterm exposure to SO2 and NO 2. New Phytol., 97, 49-61. Garsed, S. G. & Rutter, A. J. (1984). The effects of fluctuating concentrations of sulphur dioxide on the growth of Pinus sylvestris L. and Picea sitchensis (Bong.) Carr. New Phytol., 97, 175-95. Heagle, A. S., Body, D. E. & Heck, W. W. (1973). An open-top field chamber to assess the impact of air pollution on plants. J. environ. Qual., 2, 365-8. 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.
Effects of ozone and acid rain on trees
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Johnson, A. H. & Siccama, T. G. (1983). Acid deposition and forest decline. Environ. Sci. Technol., 17, 294-305. Kohut, R.J. ('1981). Northeast Regional Crop Loss Assessment Program Report. In National Crop Loss Assessment Network (NCLAN) 1980 Annual Report. Corvallis, OR, Environmental Protection Agency. Kress, L. W. & Skelly, J. M. (1982). Response of several eastern forest tree species to chronic dose of ozone and nitrogen dioxide. Plant Disease, 66, 1149-52. Lee, J. J. & Weber, D. E. (1979). The effect of simulated acid rain on seedling emergence and growth of eleven woody species. For. Sci., 25, 393-8. Likens, G. E. & Butler, T.J. (1981). Recent acidification of precipitation in North America. Atmos. Environ., 15, 1103 9. Mandl, R. H., Weinstein, L. H., McCune, D. D. & 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. Miller, P. R., Parmeter, J. R., Jr, Flick, B. H. & Martinez, C. W. (1969). Ozone dosage response of ponderosa pine seedlings. J. Air Pollut. ControlAss., 19, 435-8. National Academy of Sciences (1977). Ozone and other photochemical oxidants. Washington, DC. Neeley, J. A. (1965). Soil survey of Tompkins County, New York, Washington, DC, USDA. Reich, P. B. (1983). Effects of low concentrations of 0 3 on net photosynthesis, dark respiration, and chlorophyll contents in aging hybrid poplar leaves. PI. Physiol., Lancaster, 73, 291-6. Reich, P. B. & Lassoie, J. P. (1985). Influence of low concentrations of ozone on growth, biomass partitioning, and leaf senescence in young hybrid poplar plants. Environ. Pollut., Ser. A, 39, 39-51. 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., 62, 2835~41. Reich, P. B., Schoettle, A. W., Raba, R. & Amundson, R. G. (in press a). Low concentrations of 0 3 reduce leaf and whole plant net photosynthesis and chlorophyll contents of soybean. J. environ. Qual. Reich, P. B., Schoettle, A. W., Stroo, H. F., Troiano, J. & Amundson, R. G. (in press b). Effects of 0 3, SO 2 and acidic rain on mycorrhizal infection in northern red oak seedlings. Can. J. Bot. Tveite, B. (1980). Effects of acid precipitation on soil and forest. A. Tree growth in field experiments. In Ecological impact of acid precipitation, ed. by D. Drablos and A. Tollan, 206-7. Oslo, SNSF Project. Wood, T. & Bormann, F. H. (1977). Short-term effects of a simulated acid rain upon the growth and nutrient relations of Pinus strobus L. Water, Air & Soil Pollut., 7, 479-88. Yang, Y., Skelly, J. M., Chevone, B. I. & Birch, J. B. (1983). Effects of long-term ozone exposure on photosynthesis and dark respiration of eastern white pine. Environ. Sci. Technol., 17, 371-3.