An Apparatus for the Measurement of Carbon Dioxide
and Water Vapor Exchange of Attached
Sugarbeet Leaves
N.
TERRY,
L.
J.
WALDRON, AND
A..
CLRICH '
R ece ived for jJub licat ion July '3, 1971
Introduction
In order to investigate the eHects of mineral nu trient defi­
ciency and the toxic properties of air pollutants on the photo­
synthesis , respiration and diffusion resistances of sugarbeet
leaves, an apparatus was constructed to control the environment
of individual leaves and to simultaneousLY and continuously
measure leaf temperature, and carbon dioxide and water vapor
exchange. This was achieved by locating tbe leaf in a test cham­
ber and determining the differences in carbon dioxide and water
vapor concentration of th e a ir stream entering and leaving the
chamber. A detailed description of the apparatus employed is
presented in this paper. For convenience, the apparatus is con­
sidered to consist of three main functional parts, referred to as
modules: Module A is follow ed in sequ ence in the gas flow cir­
cuit by Module B, which includes the leaf chamber, and then
by Module C (see Figure 1). The apparatus ,vas also constructed
in this form to fac ilitate eas e of dismantling and re-erection and
to minimize the length of t he flow path to and from the leaf
chamber. Description of th e methods for the control and meas­
urement of leaf irradiance, for the measurement of air flow rate,
and for output h andling and display arc included in separate
sections.
Description
Nlodule A. AjJparatus for the control of air flow rate and inlet
carbon dioxide ' concentlCltion La the leaf chamb er.
Air from the laboratory air line was passed through a series
of filters to remove oil , liyuid water, and particulate matter (FI
and F2), water vapor (F3 and F6), and carbon dioxide (F4 and
F5) (Figure 1). The air flow was maintained at a constant rate
by using a pressure regulator (R2) which supplied air at a con­
stant pressure to a flow controller (FCr) which in turn
maintained a constant pressure difference across a needle
valve (V3) irrespective of variations in the downstream pressure.
1 Department of So ils and Plant N Ulrition , U niversity of California , Berkeley , California
94720.
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JOURNAL OF THE
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At this point carbon dioxide was introduced into the air stream
from a cylinder via a low flow controller (Fe2), flow meter
(FMI), and precision needle valve (V4). The air and carbon
dioxide were then mixed in <:in II-liter ballast tank (B). Thus,
by varying the carbon dioxide fiow rate through V4, air with
carbon dioxide concentrations ranging from 0 to 2500 p.I 1 I air
could be supplied to the leaf, the selected concentration varying
less than ± 0.5%.
t.fODlJ!..E A
MODULE B
Figure I.-Diagram of the gas flow circuit. B-ballast tank, II liter
capacity; El,2-heat exchanger, coils of copper tubing; Fl-filter, porous
stone and trap; F2-filter, charcoal; F3,S,7,8,9-filter, anhydrous magnesium
perchlorate; F4-filter, 40 % aqueous solution of potassium hydroxide;
F5-£ill~r, granular soda·lime; rCI-flow controller, Moore constant dif­
ferential Model 63 BD; FC2-£low controller, Moore constant <4£ferential
Model 63 BU·L; FMl-flow meter, CO 2 , low·flow, Wallace & Tiernan,
Varea·meter, series NA-16; FM2,3,4 - flow meter, differential pr,essure
across capillary constriction; HG-dew point hygrometer; IRGA-infra-red
CO 2 analy:uer, Beckman M o :iel 215A; LC-Ieaf chamber; MI ,2,3,4-pres­
sure gauge, mechanical; M 5,6,7-pressur,e gauge, manometric; P-water
pump; PS-psychrometer; D..l-regulator, air pressure 0·100 psi; R2­
regulator, air pressure, Moore Nullmatic 10·30; R3-regulator, two·stage
for CO 2 , Matheson 1'.'0. g·59<t; VI,3,5,6,7-valves; V2-valve, check; V4­
precision n.eedle valve, for regulating CO 2 flow; "VB1,2-water baths.
Module B. Apparatus for the control of leaf enviTonment.
The leaf to be investigated was placed in a Lucite leaf cham­
ber (see Figure 2) with internal dimensions of 28 x 21 x 3 cm.
The leaf was fixed horizontally in the median plane position by
VOL. 16, No.6,
Jury
1971
173
means of two 0.1 mm monofilament nylon grid supports, one
placed above (CS) and the other below the leaf (LS). The leaf
was sealed in the chamber by means of a small Lucite bracket
(PB) which was clamped on to the petiole using modeling clay,
and then slotted intu the wall of the leaf chamber. The upper
wall, which was in the form of a water jacket (''''J), was sealed
to the lower part of the chamber by a rubbeT gasket (G) and 6
brass clamps (C).
Figure 2.-Diagram of the leaf chamber (exploded view). C-clamp;
CF-chamber floor; C'V-chamber wall; G-gasket, rubber; }l\'I -inlet
manifold; LS---Iower leaf support; P-propeller; ~B-petiole bracket; s­
septum; THl,2-thermistors; VS-upper leaf support; WJ-water jacket.
Air entered the chamber through 28 one-half mm diameter
holes in a manifold which ran the length of the chamber, and
exited via a manifold with ] 4 one-mm diameter holes situated
on the opposite side of the chamber. Chamber air 'was moved
rapidly over the leaf and continually mixed by an electrically
driven propeller (P) mounted below the leaf, the blades of which
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were perpendi cular to the plane or rotation. In order to prevent
air from being circul ated m ainly in the plane of propeller r ota­
tion, a septum (S) was positioned across the cen ter of the cham­
ber so tha t air was force d to move up over the leaf.
The temperature oj' the irradiated leaf, w hich depended on
the amount of radi ant energy impinging on it and the extent
of dissipation of thi s energy by trans piration, convection and
re-radiation , co uld be maintained within ± O.SOC of the desired
leaf temperature by circul ating water of constant temperature
from vVBl through VV] (inside depth 2 cm). The water supply
to v\] was also introd uced via manifolds similar to those for
air but 'with 12 one-mm holes for entry and 6 two-mm holes for
exit. The incoming air to the leaf cham ber was also brought to
the tern perature of "VB 1 by passage throu gh a heat exchanger
(El ).
Two thermistors, TIl , (Yellow Springs Instruments Co.,
Precision Thermistor Probe, No. 44105) were mounted in sup­
porting steel conduits with th e th ermistor bead on a plastic·stiff­
ened wire protruding 4 mm from the end of the conduit. Each
conduit was inserted into the leaf chamb er through two rubber
O-rings inside the ball of a ball joint which permitted th e ther­
mistors to be inserted or withdrawn to a varying degTee and
rotated to the desired posi tio n. Leaf tempera ture was measured
by pressing the th ermistors at vari ous points again st the surface
of the leaf.
The accuracy of the two therm istors in determining leaf
tem perature was ch ecked by means of a Barnes infra-red field
thermometer (;-Jo . PRT-IOL). Measurem en ts by these two meth­
ods were esse ntiall y in agreement, g iven the precision of the
Barnes thermom eter (± 0.2 ' C). Temperature variations of up
to O.s oC were found at different points on the surface of the
leaf, and up to 0.2 ' (; differe nce between the upper and lower
surfaces of the leaf.
.
The ambi ent gas (i.e. carbon dioxide or water vapor) con­
centration in the leaf chamber was determined by the rate of air
flow throu gh the chamber, the gas concentrati on of the inlet air,
the extent of turbulent mixing of air 1vithin the chamber and
the gas exchange ac tivity of the leaf. Because of the vigorous
stirring o( the fan the gas, carbon dioxide or water vapor, con­
centrati on of the ou tlet air was assumed to be the ambient value.
The concen trati on of water vapor in th e inlet air was very low
sin ce the air was dried by passage throu gh F6 and F7 but by ad­
j usting the rate of flow of air through the leaf chamber it was
possible to maintain the ambient relative humidity at about 85 %
u sing the water vapor emiw~ d by the transpiring leaf.
VOL. 16, No.6,
JULY
1971
475
/vlodule C. Apparatus tor the meaS1lrf'ment of water vapo r pres­
sure and cm'bon dioxide concentration.
The water vapor pressure of the a ir entering the leaf cham­
ber, e" and leaving the cham ber, e y , was estimated using a Dew
Point Hygrometer, He;. (Cambridge Systems, Model No. 880) ,
and a psychrometer, PS, respectively. The latter was similar to
that described by Slatyer and Bierhuizen (3)", the difference being
in the use of thermistors as temperature sensors rather than ther­
mocouples. Part of the outlet air stream from the chamber 'was
passed through heat exchanger E2 in vVB2 to bring the air to
temperature, T, before entry into the psychrometer. Air flow
ra~e through the psychrome ter was usually maintained at 2 II
mIn.
Calculation of transpiration rate was carried out in the fol­
lowing way. The psychrometric equation can b e written as
e w - e = A(T - Tw)
[I]
where T is the temperature of the air entering the psychrometer
(equal to the \ 'VB2 temperature); T w , the wet bulb temperature;
e w , the saturation vapor pressure at T "' ; e, the vapor pressure at
TOC; and A, the psychrometric constant having the value of
0.5 mm of mercury per degree C. The wet bulb temperature
of the outlet air streams, T w , was obtained by direct measure­
ment (the psychrometer wet bulb tenperature range being 15­
40°C) while the saturation vapor pressure at T,<, i.e. e w , was
obtained from the Handbook of Chemistry and Physics (2) .
Rearranging equation [lJ and applying it to our system to ob­
tain the vapor pressure in the leaf chamber, we have
[2J
ey = (e w +- ATw) - AT
A graph of (e w +- A Tw) as a function of Tw was prepared so that
the calculation of e). from equation [2J could he expedited. The
vapor pressure of the inlet air stream, e" was obtained from
determination of the dew point, and ~e, i.e. e) - ex> determined.
Transpiration rate was therefore (~el eT) pF, where e'r" was the
saturation vapor pressure at T OC ; p, the density of water vapor
in saturated air at T ~ C; and F , the air flow rate through the
leaf chamber.
The two air streams leaving HG and PS passed through flow
meters FVI4 and F\1 3, respectively, and were dried by passage
through anhydrous magnesium perchlorate (F9 and F8) before
entry into the infra-red carbon dioxide analyzer, IRGA, for
determination of the difference in carbon dioxide concentra­
tions between the inlet and outlet airstreams. The analyzer de­
tected carbon dioxide differen tial concentrations in the range
o to 100 f.d 1-1 with an accuracy of == 1%. Calibration curves
'Numbers in parentheses refer to literatu re cited.
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JOURNAL OF THE
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for the analyzer were obtained from bottled air-C0 2 mixtures
of known concentration obtained from Matheson Chemical Co.
lVleasurem ent of air flow rate.
The flow meters used for the measurement of air flow rate
in Modules Band C determined the pressure drop (t..P ) across
a short length (about 1 cm) of capillary tubing. The flow meters
were calibrated 'with a Wet Test Meter (Precision Scientific Co .)
over a range of pressures at constant temperature. Flow rate
was related to the pressure drop across the capillary, but not
proportionall) so in the range ot flow rates used , a result prob­
ably indicating the transition from laminar to turbulent flow
through the capillaries.
At the flow rates used, the data were described by F =
C(t..P )~, where F is the flow rate (l/min at STP), t..P is the pres­
sure drop across the capillary constriction, and C is a constant
depending on the average pressure at the meter. Thus, logarith­
mic plots of F against t..P were linear and facilitated. interpola­
tion.
The flow meters 'w ere arranged in the gas circuit so that the
air flow through the leaf chamber was given by the difference
in flow rates measured by FM2 and FM4.
Control and measurement of inadiance.
The leaf was irrad.iated by means of a 1000-W quartz-iodine
incandescent lamp (Berkey Colortran No. LQKIO/DY) fitted
with a filter to reduce the infra-red heat load on the leaf. The
lamp was mounted on a frame which could be raised or lowered
in relation to the leaf surface to pro\ ide a range of irradiances.
The spectral intensity and the radiant flux density impinging
on the leaf in the chamber 'were measured using a spectroradio­
meter (Instrumentation Specialties Co. , Inc., "fodel SR) (Figure
3). The radiant flux density at the leaf surface was obtained
by integrating the area under the curves between 380 and 15:>0
m,u. and between 100 and 700 m,u., giving \alues of 32.7 and 23 .6
mWcm- 2 , respectivdy. The radiant flux density transmitted
through a sugar beet leaf placed between the radiometer and
the lamp under the same conditions was 4.22 mvVcrn- 2 (380-1550
m,u.), and 1.07 mWcm-2 (400-700 m,u.). The luminous flux den­
sity measured with a Weston cell at the position of the radio­
meter when the water-jacketed chamber cover was between the
lamp and the instrument was 6500 foot-candles. Thus, the rela­
tion between energy units and photometric units was
23.6 mvVcm-2
6.5 x 103 ft-c = 36.3 x 10- ' mvVcm-2 /ft-c
a ratio comparable to that given by Gaastra for combined fila­
ment high-pressure mercury vapor lamps (Gaastra (1), see Table
VOL. 16, No.6,
JULY
1971
IV, HPL and ML). The radiation spectrum should remain es­
sentially unchanged when the lamp is raised to decrease the
radiant flux density so that under such conditions photocell
measurements can be converted to radiant flux density by using
this factor.
1000
1200
14 00
Wo v e len g lh , >..(mll-)
Figure 3.-The relation of sp ectl'al intensity (HA) with wave-length
(A) of the light source obtained by placing a spectroradiometer in the
position of the leaf (solid line), and beneath the leaf (dotted line)_ The
leaf was normally positioned 50 em from the lamp with the glass heat
filter and water-filled chamber cover between the lamp and the leaf.
Output handling and display.
The outputs from the thermistors measuring the tempera­
tures of the leaf, vvater baths and psychrometer wet bulb, and
the output from the carbon dioxide analyzer were sequentially
displayed on a potentiometric recorder (IIeathkit Servo-recorder,
EUQ-20A) by means o[ a custom-built fully transistorised auto­
matic switch.
Summary
An apparatus is described which measures the rates of the
carbon dioxide and water vapor exchange of attached sugar­
beet leaves in a controlled environment. Leaves were enclosed
in a chamber and the gas exchange determined using an open
flow circuit. Carbon dioxide concentration was determined bv
infra-red gas analyzer, and water vapor concentration by dev;r
point hygrometer and thermistor psychrometer.
Acknowledgements
The authors gratefully acknowledge the suggestions and me­
ticulous technical assistance of Clyde Brown in the construction
of this apparatus . This work was supported by the Agricultural
Research Service, U .S. Department of Agriculture, under cooper­
ative agreement No. 12-14-100-9754 (34) administered by the
Plant Science Division, Beltsville, Ylaryland.
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JOURNAL OF THE
(I)
GAASTRA,
(2)
HODGMAN, (3) P.
1959.
S. S. B. T.
Literature Cited
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tcmpCLlture, and stomatal diffusion resist­
59
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]Vl. SELBY. 1962. Handbook of
Rubber
and
Ohio.
R. O. and J. F. BlERHCIZE!'I. 1964. Differential
for continuous measurements of transpiration. Plant
1051-1056.