PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest
PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest
PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest
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<strong>Experimental</strong> System<br />
Summer field trials for the cuvette wer e<br />
conducted at the Allen Thompson Researc h<br />
Center during 1971 . The open system (fig . 2)<br />
utilized included an air intake approximately<br />
25 m above the ground on a tower located<br />
3 m from that used as an access to study<br />
trees. Air was drawn to the ground, through a<br />
20-liter "mixing reservoir," to assure uniformity<br />
and prevent "noisy" carbon dioxid e<br />
analyzer output, and then passed through a<br />
manifold for distribution to two Model 506 R<br />
Reciprotor (Copenhagen) pumps . One of<br />
these pumped a comparison airstream to th e<br />
URAS II (Hartmann and Braun, Frankfurt )<br />
infrared gas analyzer housed 46 m away in th e<br />
permanent site building and the other move d<br />
air to the cuvette located at 17 .2 m, back to<br />
the ground, through a flow meter, and then t o<br />
the differential analyzer. The attenuating<br />
reservoir, manifold, pumps, and flow mete r<br />
were located in a shelter at the tower base a s<br />
was the power supply-temperature controllerfan<br />
controller. A Honeywell recorder and the<br />
URAS II, however, were located in the site<br />
building. Two 0 .004-inch copper-constanta n<br />
thermocouples were used for temperature<br />
sensing inside the cuvette and one 22-gage<br />
thermocouple was positioned in a shaded<br />
location outside .<br />
In addition to cuvette data, meteorologica l<br />
data were provided by instruments located o n<br />
the adjacent meteorological tower . Scholander<br />
bomb and pressure infiltrometer (Fry<br />
and Walker 1967) samples were routinel y<br />
taken to provide estimates of water potentia l<br />
and stomatal aperture. These data were correlated<br />
with cuvette and meteorological dat a<br />
collected during each trial . Sampling wa s<br />
carried out at cuvette level and illustrativ e<br />
values reported here represent averages-tw o<br />
to three twigs for Scholander pressures (Ps )<br />
and five to seven needles for stomatal infiltration<br />
pressure (Pstom) .<br />
During preliminary trials, the cuvette temperature<br />
was maintained within at least ±<br />
1 .5° C of ambient under conditions of high<br />
AI R<br />
INTAKE<br />
CUVETTE<br />
-1<br />
PUMPS<br />
MIXING --Lf<br />
RESERVOIR<br />
-r<br />
l~I<br />
_ 1<br />
FLO W<br />
METE R<br />
J 1<br />
1<br />
URASII<br />
FLO W<br />
METER<br />
MANIFOL D<br />
Figure 2 . <strong>Experimental</strong> system used during 1971 field trials .<br />
275