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

from theses. The principal processes an d
subjects which will be covered in sequence are
(A) assimilation of CO 2 and respiration ,
(B) transpiration, water conduction, an d
water deficits, (C) translocation of photosynthates,
and (D) mineral nutrition . Stomatal
status and leaf resistance are considere d
in relation to various aspects of gas exchange .
Energy budgets, nutrient cycling, growth, and
modeling of processes are considered b y
other authors in this symposium, so are no t
emphasized in this paper .
Assimilation of CO 2
and Respiration
The principal emphasis in the IBP on assessment
and understanding of dry matter
production naturally focuses attention o n
photosynthesis and the conditions and factors
which influence its rate . Likewise the magnitude
of respiratory losses is of complementary
interest. Both short-term and long-term influences
on the rates of these processes are o f
importance in estimating seasonal and annual
totals . Further, both inter- and intra-specifi c
variability must be taken into account . Regardless
of the factor under study, methods of
individual measurement assume marked
importance, and carrying over these measurements
commonly made on portions of the
plant to the entire forest stand is even mor e
important. The latter aspect is considered i n
the papers of this symposium on terrestrial
modeling.
Measuremen t
The appearance in late 1971 of the detailed
and authoritative book, Plant Photosyntheti c
Production, Manual of Methods (Sestak,
6atsky, and Jarvis, eds .), makes a detailed
consideration of principles and techniques o f
measurement unnecessary here . Thus a general
consideration of methods and their applicability
in the Coniferous Biome wil l
suffice .
Many useful studies have been performe d
under controlled-environmental conditions ,
using assimilation chambers of various types
(Jarvis et al . 1971) . Such studies may be criticized
on the basis that plants grown or hel d
for study in controlled-environment rooms or
boxes may behave differently from materia l
growing under natural conditions . Thus a
number of studies have been devoted to ga s
exchange of conifers in the field (e .g., Botkin ,
Woodwell, and Tempel 1970 ; Gentle 1963 ;
Helms 1965, 1970 ; Hodges 1967 ; Hodges and
Scott 1968; Kunstle 1971; Ungerson and
Scherdin 1965; and Woodman 1971) . Also
the extensive unpublished studies on Picea
abies (L.) Karst of W . Koch' and of O . L .
Lange and E . -0. Schulze 2 should be mentioned.
To eliminate the influence of greenhouse
or controlled-environment on the
plants, several workers have used seedlings o r
saplings brought in from the field or garden ,
or made measurements on excised branches
from field growing trees (Brix and Ebell 1969 ;
Keller 1971 ; Parker 1963; Pisek, Larcher ,
Moser, and Pack 1969 ; Pisek and Kemnitzer
1968 ; and Poskuta 1968) .
All of the measurements in the studies
cited in the previous paragraph were made using
assimilation chambers of various kinds .
Difficulties and potential errors associate d
with use of such enclosures are well covere d
by Larcher (1969a) and Jarvis et al . (1971) .
The major concerns pertain to excessive
boundary layer resistances if stirring is inadequate,
to significant departures of irradiatio n
and energy balances from those of unenclose d
foliage, and to errors inherent in the measuring
itself .
Techniques other than those using assimilation
chambers are available (Larcher 1969a ,
Denmead and Mcllroy 1971) . Harvest techniques
give direct measurements of dry matte r
accumulation, but must pertain with conifer s
to time intervals of several weeks or months .
Thus they cannot give information on responses
to various controlling factors, nor d o
they give information on respiratory losses .
However, apart from their intrinsic value ,
they may serve as an independent check on
I Forest Botanical Institute, University of Munich ,
Germany .
2 Botanical Institute II, University of Wiirzburg ,
Germany .
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