United States Corvallis Environmental
Environmental Protection Research Laboratory
Agency Corvallis, Oregon 97330
ISOPRENE EMISSION RATES
FROM LIVE OAK
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ISOPRENE EMISSION RATES
FROM LIVE OAK
CERL-040
May 1978
by
David T. Tingey
Hilman C. Ratsch
Marybeth Manning
Louis C. Grothaus
Walter F. Burns
Ernest W. Peterson
Terrestrial Ecology Branch
Ecological Effects Research Division
Corvallis Environmental Research Laboratory
U. S. Environmental Protection Agency
Corvallis, Oregon 97330
and
Northrop Services, Inc.
200 SW 35th St.
Corvallis, Oregon 97330
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ISOPRENE EMISSION RATES FROM LIVE OAK
David T. Tingey, Hilman C. Ratsch, Marybeth Manning, Louis C. Grothaus
Walter F. Burns and Ernest W. Peterson
U.S. Environmental Protection Agency and Northrop Services Inc.
200 SW 35th St. Corvallis, OR 97330
ABSTRACT
There is growing awareness about the role of vegetation as a source of
reactive hydrocarbons that may serve as photochemical oxidant precursors. A
study was designed to assess the influence, independently, of variable light
and temperature on isoprene emissions from live oak ( Quercus virginiana,
Mill.). Plants were conditioned in a growth chamber, then transferred to an
environmentally controlled gas-exchange chamber. Samples of the chamber
atmosphere were collected, isoprene was concentrated cryogenically and meas-
ured by gas chromatography. The logistic function was used to model isoprene
emission rates. Under regimes of low temperature (20°C) or darkness, isoprene
emissions were lowest. With increasing light intensity or temperature the
concentration of isoprene increased, reaching maxima at 800 pEinsteins/m2/sec
and 40-44°C, respectively. Higher temperatures caused a large decrease in
emissions. Since the emission of isoprene is light saturated at moderate
intensities, temperature appears to be the main factor controlling emissions
during most of the day.
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INTRODUCTION
High levels of ozone have been measured in urban, rural and remote
locations well away from significant anthropogenic sources of oxidant pre-
curors. These elevated levels in rural and remote areas could result from
transport into these areas and/or the photooxidation of biogenic hydrocarbons.
It is unclear which process is more important, in part, because biogenic
emission rates of reactive hydrocarbons are not adequately known. Isoprene
(2-methyl-l,3-butadiene) has been identified as a volatile emission product
from at least 35 plant species representing 16 families (Table 1). The
biogenic production of isoprene is light dependent (Rasmussen and Jones 1973;
Sanadze and Kalandadze, 1966b; Sanadze and Kursanov, 1966) and increases with
light intensity until the process controlling emissions are light saturated
(Sanadze and Kalandadze, 1966a). The action spectra of isoprene production
exhibits a maximum in the red wavelengths (Rasmussen and Jones, 1973; Sandze
and Kalandadze, 1966b). The temperature coefficient (Qio) of isoprene produc-
tion varies between 2.8 and 3.6; emissions increase with temperature reaching
a maximum between 35 and 43°C and decreases sharply at temperatures above 40
to 43°C (Sanadze and Kalandadze, 1966a; Rasmussen and Jones, 1973).
Previous studies (i.e. Sanadze and Kalandadze, 1966a and 1966b; Rasmussen
and Jones, 1973) used detached leaves or leaf discs. The objectives of this
study were, (1) to determine isoprene emission rates from intact plants under
2
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carefully controlled environmental conditions, (2) to determine the indepen-
dent influence of light and temperature on emission rates, and (3) to estimate
algorithms for isoprene emissions which could be used to standardize emission
rates determined in the field.
UBMARY
U S Environmental Piotactloo Kyeoaf
Corvalli* Environmental RatMtch L»b
200 S W. 3Sth Stro*
CorraUi*. Oi*9ob 07330
3
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METHODS AND MATERIALS
PLANT CULTURE. Live oak ( Quercus virginiana, Mill.) plants were obtained
from the Division of Forestry, Florida Department of Agriculture and Consumer
Services as bare root seedlings and potted in 15-cm pots in a Jiffy-mix;
perlite* (1:2;V:V) mixture. After initial leaf drop and subsequent appearance
of new growth, the oak plants were cultured in a greenhouse at maximum day/
night temperatures of 23° and 18°C, respectively. Sunlight was supplemented
and the photoperiod extended to 16 hr per day with light from HID sodium
vapor lamps. The plants received 1/2 strength modified Hoaglund's nutrient
solution daily. At least 4 weeks before sampling, oak plants were placed in
a growth chamber and conditioned at maximum day/night temperatures of 27° and
18°C, respectively, with a 16 hr light period. When samples were taken, the
plants had both mature and young expanding leaves.
GAS-EXCHANGE SYSTEM. The gas-exchange system used to determine emission
rates (Figure 1) consisted of a 1) gas-exchange chamber that enclosed the
foliage, 2) an air flow system that controlled C02 concentration, dew point
and provided hydrocarbon-free air (pure air source) to the gas-exchange
* Mention of a trademark or proprietary product does not consitute a guarantee
or warranty of the product by the U.S. Environmental Protection Agency and
does not imply its approval to the exclusion of other products that may
also be suitable.
4
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chamber, and 3) a monitoring system that measured C02 concentration and
dewpoint of the atmosphere entering and exiting the plant chamber, light
intensity within the plant chamber, and air and leaf temperature.
GAS-EXCHANGE CHAMBER. The gas-exchange chamber was similar to one described
by Huang, et al. (1975) with the mixing characteristics of a constant-stirred-
tank reactor (Rogers, et al., 1977). The gas-exchange chamber (Figure
2) was designed for use in a controlled environment chamber which regulated
light and cooling. In each experiment the upper chamber was removed to
insert the pot-root mass into the lower chamber. The two halves of the 24 cm
diam disc with center cut out were fitted around the stem, set in place, and
sealed to the stem and chamber with modeling clay. The upper chamber was
placed over the plant without injuring leaves and sealed to the chamber base.
Both upper and lower chambers contained impellers with exterior motors and
the upper chamber contained 2.5 cm high baffles arranged equidistant around
the walls of the chamber to insure well mixed air. Heating element and
temperature sensor were connected to a Love model 48* temperature controller.
Within the upper chamber air temperature was monitored with a shielded
thermocouple, leaf temperature with a thermistor clipped to the undersurface
of the leaf and light (400 - 700 nm) with a Lambda Instruments model LI-190
SR Quantum Sensor.** Various light levels were obtained by a stepwise increase
in the number of incandescent and fluorescent lights in the controlled
environment chamber and the addition of a sodium vapor lamp.
5
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AIR FLOW SYSTEM. Air was pumped through an Aadco* pure air generator to
remove hydrocarbons, C02 and reduce the dew point (Figure 1). Carbon dioxide
and water vapor were then added back to the air stream to obtain desired
levels. The dew point of the air entering the gas-exchange chamber was held
constant during each experimental run. Inlet dew points ranged between -2
and 6°C and were obtained by mixing dry air from the pure air generator with
humidified air. The dewpoint of air exiting the chamber varied between 15
and 32°C depending on experimental conditions. Air flow into the inlet port
of the gas-exchange chamber was adjusted by a valve, monitored by a flowmeter
and ranged from 2 to 5 1/min depending on plant size and environmental condi-
tions. Air samples for C02 dew point and hydrocarbon analysis were taken
from sample ports at the chamber's inlet and outlet, respectively. Carbon
dioxide concentration and dew point of the air stream were monitored with a
infrared gas analyzer and dew point hygrometer, respectively. Inlet and
outlet C02 concentrations of the air stream ranged from 400 to 600 and 310 to
390 m1/1, respectively. Changes in C02 concentrations in the chamber were
not large enough to have any significant effect on isoprene emission (Jones
and Rasmussen, 1975).
HYDROCARBON SAMPLING AND ANALYSIS. Isoprene was separated using a 3 m x 3.2
mm 0D stainless steel column of Porasil E(80/100 mesh)/Alltech CS-10 (10%
stationary phase). Analyses were performed isothermally at 90°C using helium
(20 cm3/min) as a carrier gas and the isoprene measured with a flame ioniza-
tion detector (FID). Since a FID responds linearly to the mass of organic
carbon (David, 1974), a 1.01 pl/1 isooctane standard was used to calculate
the mass of organic carbon emitted as isoprene. Three to six 1 ml isooctane
6
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standards were taken each day with a reproducibility of ± 2%. A 99.9% pure
standard of isoprene was used to establish the isoprene retention time and
profile.
Twenty ml air samples were collected from the sample ports of the gas-
exchange chamber using a 100 ml Pressure LOC* syringe. The samples were
injected through a 6 port valve onto a stainless steel trap (61 cm x 0.25 mm
ID) immersed in liquid oxygen to concentrate the hydrocarbon sample (Rasmus-
sen, et ah, 1974). Following sample injection the stainless steel trap
remained in the cryogen for a 4 min period with a helium purge flow (13
cm3/min) through it. The concentrated sample was volatilized onto the column
by rapidly heating the trap in boiling water.
Positive identification of isoprene emissions from live oak was made by
a combination of gas chromatography and mass spectrometry. The isoprene mass
spectra were compared to the EPA Mass Spectral Search System (MSSS), Registry
of Mass Spectral Data (Stenhagen, et al_., 1974) and the 99.9% isoprene stan-
dard to confirm identification.
EXPERIMENTAL DESIGN. The influence of temperature on isoprene emissions at
various light levels was studied by increasing leaf temperature from 20 to
47°C in 4 to 6°C increments at each of 4 light levels (approximately 100,
200, 400, or 800 |jEinsteins/m2/sec). To measure the effect of light intensity
on isoprene emissions, light intensity was increased stepwise 0, 100, 200,
400 and 800 pEinsteins/m2/sec at each of 4 leaf temperatures (29, 35, 40, or
47°C). After each change of light or temperature a 60 min equilibration time
was observed before collecting 3 air samples for hydrocarbon analysis. A
7
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minimum of 3 plants was used to develop each temperature or light response
curve. After each experiment, leaves were removed from the live oak and dry
weight measured after the leaves dried at 70°C for 72 hr.
Isoprene emission rate (pg C/ g dry wt/hr) from the oak was calculated
using the following equation:
Isoprene emission rate - JAConc
W
J = air flow rate through the gas-exchange chamber (1/hr)
AConc = change in isoprene concentration of air as a result of passage
through the gas-exchange chamber (pg/1). There was no isoprene
in the air entering the chamber.
W = total leaf dry weight of the plant (g)
DATA ANALYSIS. The relationship between means and standard deviations of
samples taken at each light and/or temperature point indicated that the
isoprene emission rate was distributed log-normally. Therefore the emission
data were transformed to their respective natural logarithms for all statis-
tical analysis. Means of the 3 samples collected at each light and tempera-
ture combination were computed and used to estimate the isoprene response
curves.
Experimentation (Sanadze and Kalanadze, 1966a; Rasmussen and Jones,
1973) and biological theory suggested that the isoprene response curves
should approach asymptotically their maximum values. A 3rd order polynomial,
rational and logistic functions were considered as models for the response
curves. The logistic function was selected because it had good asymptotic
properties and best fit the data.
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The equation for the 4 parameter logistic function is:
F(x) = +D
1 + exp[-B(x-C)]
A = the difference between the minimum and maximum
B = shape parameter which determines how quickly the function goes from its
minimum to maximum
C = location parameter which determines the point along the X axis where
the curve is centered
D = minimum value of function
Since the logistic function is nonlinear in its parameters, a non
linear least squares procedure was used to estimate the parameters for the
response curves. The algorithm used was Marquardt's (1970) as implemented in
a subroutine written by Dr. Larry Male at EPA-CERL Corvallis. The choice of
initial parameter estimates, critical in nonlinear estimation, was made by
trying various parameter values until plots showed that the resulting curves
fit the data reasonably well. Means of isoprene emissions above 44°C were
not used to estimate temperature response curves because isoprene production
dropped off rapidly at higher temperatures and no longer followed the logistic
curve.
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RESULTS
Increasing the light at all temperatures increased significantly isoprene
emission rates until maxima were reached (Figure 3). The parameter estimates
for the logistic curves illustrated in Figure 3 are listed in Table 2. In
the dark at all temperatures isoprene emissions were low (0.5 pg C/g dry
wt/hr or less). As light intensity increased isoprene emission increased
significantly to about 75 pg C/g dry wt/hr at 40°C and 800 pEinsteins/m2/sec.
However, at 47°C increasing light elicited only a slight increase in isoprene
emission (2 pg C/g dry wt/hr). As the light intensity increased, light
saturation of isoprene emission process was approached (within 5%) or reached.
Light intensities above the saturating light level would not significantly
increase isoprene emission rates.
Increasing temperature increased isoprene emission rates at the four
light levels (Figure 4). The parameter estimates for the logistic curves
illustrated in Figure 4 are listed in Table 3. Isoprene emissions increased
with temperature at each light level but the increases were greater at the
higher light intensities. Maximum isoprene emissions occurred between 40 and
44°C with the largest emission (about 120 pg C/g dry wt/hr) at the high light
level and 44°C. At higher temperatures (above 44°C) for all light levels
there was a sharp decline in isoprene emission to 2 pg C/g dry wt/hr or less.
When the higher temperatures persisted for several hours, marginal leaf
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necrosis developed. No emission data were collected below 27°C at the high
light intensity because the gas-exchange chamber could not be cooled to lower
temperatures under this radiant-energy load.
To determine if isoprene emission rates varied significantly over time
for plants held under constant environmental conditions, emission rates were
measured over a 5 to 6 hr period (Table 4). The flux estimates varied ± 4
and ± 2 pg C/g dry wt/hr about the means for plants 1 and 2, respectively.
These variations in emission rates are essentially insignificant compared to
the changes caused by altering the environment.
To illustrate the magnitude of plant-to-plant variability, emission
rates were measured for 18 different plants under 3 different light levels at
a leaf temperature of 35°C (Table 5). At each light intensity most emission
rate estimates were close to the mean; only a few plants deviated substan-
tially. Based on this limited sampling, plant variability appeared to range
between 20 and 45%.
Despite plant-to-plant variability, the logistic response curves fit the
data closely (Figures 5 and 6) and this is supported by the multiple correla-
tion coefficients (R2) listed in Tables 2 and 3 which are generally 0.85 or
greater. Each graph illustrates the logistic response curve and the means
used to estimate that curve. Comparisons of the estimated response curves to
the data illustrate the generally good agreement. Only at 47° (Figure 5) was
there a poor fit of the data to the response curve. This occurred under
conditions of very low emissions and unusually high temperatures.
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DISCUSSION
The light dependency of isoprene emissions and the light saturation re-
sponse of live oak were similar to other plant species (Sanadze and Kalan-
dadze, 1966a; Rasmussen and Jones, 1973). Because the isoprene emission
process was light saturated at relatively low light intensities (approximately
800 |jEinstiens/m2/sec) many leaves of a canopy would be light saturated for
most of the day. The primary importance of light to isoprene emission is to
provide the photochemical energy to drive the biosynthetic pathways of iso-
prene formation. The small amounts of isoprene emitted during dark hours
have been previously reported (Rasmussen and Jones, 1973). It is not known
if these emissions result from isoprene produced in the dark or if they are
residual from the preceding day.
The temperature influence of isoprene emissions from live oak was similar
to responses reported for other species (Sanadze and Kalandadze, 1966a;
Rasmussen and Jones, 1973). Leaves which are strongly sunlit can be consider-
ably warmer than air temperature, while leaves within the canopy may be
cooler than air temperature. The high leaf temperatures (greater than 44°C)
associated with decreased emissions could occur under field conditions on
leaves in full sun. The high temperature (above 44°C) decrease in isoprene
emissions may be associated with the temperature inactivation of the metabolic
processes that form isoprene.
12
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To model typical diurnal isoprene emission patterns the environmental
conditions for an average of summer days in Tampa, Florida and the estimated
isoprene emission rates interpolated from the light intensity and temperature
response curves (Figures 3 and 4) were used. Climatic summaries (e.g. Visher,
1954; NOAA, 1974) indicated an average daily solar radiation of approximately
500 Langleys and average maximum and minimum air temperatures of 32 and 20°C,
respectively, during the summer. The hourly values for the solar radiation
flux were estimated by assuming that the flux varied sinusoidally with a
maximum (1.1 Langley/min) at local noon and zero at 0600 and 1800 hr. The
average hourly air temperature was inferred from the observed average maximum
and minimum temperatures and what is known about typical diurnal temperature
cycles. Empirical results in our laboratory indicated that the temperature
of sunlit leaves was related to the air temperature by T-| = 1.25 (T + 0.9)
where T, is leaf temperature and T is air temperature (both in °C). The
I a
leaf temperature for shaded leaves was assumed to be 1°C less than air tem-
perature.
Estimated hourly emission rates of isoprene for oak trees in the vicinity
of Tampa, Florida are shown in Figure 7. As expected, the predicted maximum
emission rates occurred, during midday. During early morning and late after-
noon hours when temperatures are moderate and leaves are not light saturated,
light is the main factor controlling emission rates. However, during most of
the day, the leaves of the outer canopy are light saturated and varying air
temperature controls emission rates. In contrast, for heavily shaded leaves
(not light saturated) the light intensity is important throughout the day.
More than 80% of the daily isoprene emissions from oak trees is expected
13
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to occur after 1000 hours. The isoprene emissions estimated from the model
and reported in Figures 3, 4, 5 and 6 were similar to emission rates measured
on oak in the Tampa, Florida, area (P.R. Zimmerman, personal communication).
The estimated emission rates in Figure 7 could be altered by assuming dif-
ferent environmental conditions at the leaf or by changing the proportions of
leaves that are sunlight to shaded leaves.
14
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LITERATURE CITED
David D.J., 1974. Gas Chromatography Detectors, Wiley and Son, New York.
293 pp.
Huang, C-Y, J.S. Boyer and L.N. Vanderhoef. 1975. Acetylene reduction
(nitrogen fixation) and metabolic activities of soybean having various
leaf and nodule water potentials. Plant Physiol. 56:222-227.
Jones, C.A. and R.A. Rasmussen 1975. Production of isoprene by leaf tissue.
Plant Physiol. 55:982-987.
Marquardt, D.W. 1970. Generalized inverses, ridge regression, biased linear
estimation, and nonlinear estimation. Technometrics 12: 591-612
NOAA, 1974. Climates of the States, Vol 1 Water Information Center, Port
Washington, New York. 480 pp.
Rasmussen, R.A. 1970. Isoprene: Identified as a forest-type emission to the
atmosphere. Environ. Sci. Technol. 4:667-671.
Rasmussen, R.A. 1972. What do the hydrocarbons from trees contribute to air
pollution. S. Air Pollut. Contr. Assoc. 22:537-543.
Rasmussen, R.A. and C.A. Jones. 1973. Emission isoprene from leaf discs of
Hamamelis. Phytochemistry 12:15-19.
Rasmussen, R.A., H.H. Westburg and M. Holdren. 1974. Need for standard
reference G.C. methods in atmospheric hydrocarbon analysis. Chromatogr.
Sci. 12:80-84.
15
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Rogers, H.H., H.E. Jeffries, E.P. Stahel, W.W. Heck, L.A. Ripperton and A.M.
Witherspoon. 1977. Measuring air pollutant uptake by plants: A
direct kinetic technique. J. Air Pollut. Control Assoc. 27:1192-1197.
Sanadze, G.A. 1961. Absorption of molecular hydrogen by illuminated leaves.
Sov. Plant Physiol. 8:443-446.
Sanadze, G.A. 1969. Light-dependent excretion of molecular isoprene.
Progress in Photosynthesis Research 2:701-706.
Sanadze, G.A. and G.M. Dolidze. 1961. Mass-spectrographic identification of
compounds of C5H8 (isoprene) type in volatile emissions from the leaves
of plants. Soobshch. Akad. Nauk Gruz. SSR 27:747-50.
Sanadze, G.A. and A.N. Kalandadze. 1966a. Light and temperature curves of
the evolution of C5H8. Sov. Plant Physiol. 13:411-413.
Sanadze, G.A. and A.N. Kalandadze. 1966b. Evolution of the diene C5H8 by
poplar leaves under various conditions of illumination. Dokl. Bot.Sci.
168: 95-97.
Sanadze, G.A. and A.L. Kursanov. 1966. On certain conditions of evolution
of the diene C5H8 from poplar leaves. Sov. Plant Physiol. 13:184-189.
Stenhagen, E., S. Abrahamsson and F.W. McLafferty. 1974. Registry of Mass
Spectral Data, Wiley, New York. 3358 pp.
Visher, S. S. 1954. Climatic Atlas of the United States, Harvard University
Press, Cambridge. 403 pp.
16
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TABLE I: PLANT SPECIES IN WHICH ISOPRENE HAS BEEN REPORTED
SCIENTIFIC NAME
COMMON NAME
REFERENCE
Robinia paeudoacacia L.
Black Locust
Sanadze, 1961
Cladraetie lutea (Michx) Koch
Yellow wood
Rasmussen, 1972
Amorpha Pruticoaa L.
False indigo
Sanadze, 1969
Inga apeatabilia (Vahl) Wild.
Rasmussen, 1970
Rhamrtus sp.
Buckthorn
Rasmussen, 1972
Morus sp.
Paper Mulberry
Rasmussen, 1972
Fieoua coataricana (Liebn) Mig.
Higo Fig
Rasmussen, 1970
Plantanua occidentalia L.
Sycamore
Rasmussen, 1972
Populua balsamifera L.
Balsam poplar
Rasmussen, 1972
PopuluB deltoid.ee Bartr.
Eastern Cottonwood
Rasmussen, 1970
Populua nigra L.
Black Poplar
Sanadze and Kalandadze, 1966a
Populu8 Simonii Carr.
Simon Aspen
Sanadze, 1961
Populue sp.
Aspen
Rasmussen, 1970
Salix alba L.
White Willow
Sanadze, 1961
Salix babylonica
Weeping Willow
Rasmussen, 1970
Onerous borealis Michx.
Northern Red Oak
Jones and Rasmussen, 1975
Qucpoub iberica B1eb.
Iberian oak
Danadze, and Dilidze, 1961
QuercitB rubra L.
Red Oak
Rasmussen, 1970
Hamamelie virginiana L.
Witchhazel
Jones and Rasmussen, 1975
Liquidambar etyraaiflua, L.
Sweetgum
Rasmussen, 1970
Picea engetmannii Parry
Engelmann Spruce
Rasmussen, 1972
Pioea glauca (Moench) Voss
White spruce
Rasmussen, 1970
Picea mariana (Mill) B.S.P.
Black spruce
Rasmussen, 1970
Picea pungerw Engl.
Blue Spruce
Rasmussen, 1970
Picea sitchenaia (Bong.) Carr.
Sitka Spruce
Rasmussen, 1972
Mangifera indica L.
Mango
Rasmussen, 1970
Bums eempervirene L.
Common Boxwood
Sanadze, 1969
Eucalyptus camaldulenaie L.
Australian river red gum
Rasmussen, 1970
Eucalptus Gunnii Montana Rook.
Cider gum
Rasmussen, and Jones, 1973
Carludovica inaignie Duch.
Panama hat palm
Rasmussen, 1970
Banibuaa sp.
Bamboo
Rasmussen, 1970
Coco8 nicifera L.
Coconut palm
Rasmussen, 1970
Mahonia aquifolia (Pursh) Nutt.
Oregon grape
Rasmussen, 1972
Liriodendron tulipifera L.
Yellow Poplar
Rasmussen, 1972
17
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TABLE 2. PARAMETER ESTIMATES FOR THE LOGISTIC CURVES
DETERMINED WITH VARYING LIGHT INTENSITIES*.
Parameter Estimates
'C
A
B
C
D
R2
29
8.63
0.00691
54.26
- 4.75
0.91
35
19.12
0.00838
-108.55
-15.12
0.96
40
21.38
0.00570
-207.44
-17.03
0.92
47
9.62
0.00969
-178.08
- 8.93
0.23
Ln (Isoprene) = + D
1 + exp [-B (x-C)]
x = Light Intensity yE/m2/Sec
TABLE 3. PARAMETER ESTIMATES FOR THE LOGISTIC CURVES
DETERMINED WITH VARYING TEMPERATURES*.
Light Intensity
Parameter Estimates
yE/M2/sec
A
BCD
R*
100
1.55
0.20
25.17
0.16
0.85
200
1.58
0.79
32.97
1.60
0.90
400
1.87
0.35
30.27
1.86
0.88
800
4.88
0.18
25.26
0.11
0.68
* Ln (Isoprene) = + D
1 + exp [-B (x - C)J
x = leaf Temperature °C
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TABLE 4. ISOPRENE PRODUCTION (yg C/g dry w/hr) UNDER CONSTANT
ENVIRONMENTAL CONDITIONS *
Hours+ Plant 1 Plant 2
3
24.5
—
4
32.9
32.9
5
26.4
34.4
6
26.2
34.7
7
27.1
32.5
8
29.5
34.1
9
31.0
35.9
I
28.2
34.1
* The plants were held at constant environmental conditions (leaf temperature,
35°C; light intensity, 400 yE/m2/sec) and triplicate samples were
collected hourly and mean emission rates determined.
+ Hours after the lights were turned on in the controlled environment chamber.
19
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TABLE 5. COMPARISONS OF ISOPRENE EMISSIONS
(ug C/g dry wt/hr) FROM PLANTS
AT SEVERAL LIGHT INTENSITIES*
^200
Light Intensity (uE/m2/sec)
^00
^800
18.8
51.8
46.4
16.6
31.8
108.9
7.1
33.7
67.4
24.1
39.3
73.7
19.2
31.6
60.3
24.3
44.1
64.1
18.4
38.7
70.1
Leaf temperature ranged between 33 and 37°C, triplicate samples
were collected from each plant and a emission rate determined.
Each emission rate estimate was from a different plant.
20
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co2
Scrubber
Bypass
t
Humidifier
i
yr
-^H8)—
Metering
Valves
CO,
Controlled Environment Chamber!
L
Gas-Exchange
Chamber
Flowmeter
Sample
Port
/
\
Infra red
Analyzer
Recorder
Flowmeter
Pump
Drierite
Dew
Point
Sensor
Recorder
Figure 1. Air flow pattern through the gas exchange chamber and arrangement of instrumental
on.
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1. OUTLET PORT
2. LEAF TEMPERATURE SENSOR
3. EXHAUST PORT
4. TEMPERATURE SENSOR
5. FAN
6. HEATING ELEMENT
7. LIGHT SENSOR
8. PRESSURE GAUGE PORT
9. THERMOCOUPLE WIRES
10. INLET PORT
TEMPERATURE CONTROLLERS
Figure 2. Plant gas-exchange chamber with the major components Illustrated.
The volumes of the upper and lower chambers were 44.2 and 11.3
liters, respectively.
22
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100
200
400
600
800
Figure 3.
LIGHT INTENSITY-/i.E/m/sec
The influence of varying light intensity on isoprene emission rate
at various leaf temperatures. The figure is a consolidation of
the curves in Figure 5.
23
-------
200
5
>»
-o
o>
O
o>
I
Ld
H
<
cr
CO
CO
UJ
u
z
Ld
oc
Q_
O
CO
100
~400*
30 35 40
LEAF TEMPERATURE -C
Figure 4. The influence of varying temperature on isoprene emission rate at
various light levels. The figure is a consolidation of the curves
in Figure 6.
24
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100
50
5
> 10
10 5
o»
LlI
< 0.1
en 100
? 50
CO
CO
10
5
LlI
LlI
I
0.5
o—
0
200
400
600
800 0
200
400
600
800
LIGHT INTENSITY - /xEinstein / m2/sec
Figure 5. Changes in isoprene emission rates as a function of varying light intensity at 4 leaf
temperatures. The data points shown on the graphs are means of triplicate samples.
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-too
b 200
iLl
LlI
z
LlI
tt:
CL
o
CO
10
5
1
~400
1 1
-
o
o
O ("Q
° o°
—
_o
i
i i
20 25 30 35 40 45 20 25 30
LEAF TEMPERATURE - °C
Figure 6. Changes in isoprene emission rates as a function of varying leaf temperature at 4 light
intensities. The data points shown on the graphs are means of triplicate samples.
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W 50
/
/
/
/
? 20
600
900 1200
TIME OF DAY
1500
1800
Figure 7.
Estimated isoprene emission rates for oak leaves in Tampa Florida
for an average of summer days. A—sunlit leaves (assumed leaves
hotter than air temperature); B—shaded leaves (assumed leaves 1°C
less than air temperature and radiation intensity equal to one-half
ambient sunlight); C—shaded leaves (assumed leaves 1°C less than
air temperature and radiation intensity equal to 1/4 ambient sun-
light. 800 yE/m2/sec equals approximately 0.5 Langley/min.
27
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