22.01.2014 Views

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

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

<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

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!