PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

Proceedings-Research on Coniferous Forest Ecosystems-A symposium .
Bellingham, Washington-March 23-24, 197 2
Development and testing of a n
inexpensive thermoelectrically
cooled cuvette
David J . Salo, Department of Botan y
John A . Ringo, Department of Electrical Engineerin g
James H . Nishitani, Department of Botany
an d
Richard B . Walker, Department of Botany
University of Washingto n
Seattle, Washingto n
Abstract
An economical temperature-controlled cuvette system has been developed to monitor CO 2 assimilation an d
dark respiration in the crowns of mature Douglas-fir (Pseudotsuga menziesii) trees at the Cedar River Thompso n
site. Temperatures in the Plexiglas assimilation chambers are controlled with thermoelectric coolers, and CO 2
concentration changes are measured with a differential infrared gas analyzer. Preliminary field data sugges t
cuvette temperatures can be maintained within ±1 °C of ambient even under high insolation conditions .
Introduction
The "cuvette technique" has been used fo r
field assessment of carbon dioxide assimilation
since the 1930's (Bosian 1933), but the
findings of these studies have often bee n
criticized. These criticisms of cuvette methods
have usually resulted from the difficulties of
maintaining a plant-chamber environmen t
closely approximating that outside the en -
closure .
Cuvette Problems
Problems encountered have included th e
development of "deep" boundary layers alon g
leaf surfaces with the concomitant establishment
of abnormal C0 2 , vapor pressure, an d
temperature gradients . Additionally, CO 2
concentrations deviating markedly fro m
ambient levels have frequently occurred an d
water condensation in chambers and in ai r
conducting lines has been of particular con -
cern at night, during cold weather periods ,
and during periods of intense thermoelectri c
cooling of cuvette bases . But probably th e
most difficult problem to overcome has bee n
that of chamber heating during periods o f
high insolation . In efforts to achieve temperature
control under these conditions, a variet y
of chamber designs, fabrication procedure s
and materials, and cooling techniques have
been utilized .
A common practice employed by many investigators
has been the use of various thin
plastic film "skins" to cover cuvette frames .
Bourdeau and Woodwell (1965) used 8 mi l
polyvinyl chloride (PVC), Ritchie (1969) use d
2 mil PVC, and Hodges (1965) used 5 mil
polypropylene . These efforts have met with
varying degrees of success because plastics
differ markedly in CO 2 permeability, as well as
infrared and visible light transmittance . As an
example, though the IR transmissivity o f
polyethylene is relatively good its visible light
transmittance is less than that of either Plexiglas
(methyl methacrylate) or PVC . It is also
273