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

Von Bertalanffy (1969) calls nonsummative
systems Gestalten ; for example, the nonadditivity
of mixing equal volumes of concentrated
sulfuric acid and water. Von Bertalanffy
provides another simple example where he
points out that the voltage of three isolated
conductors would be different from that i f
they were interconnected . Biological quantities
often act very much like the charge i n
von Bertalanffy's example in that their values
in concert are different from their isolated
values . Thus, it is essential for a biological re -
searcher to understand the distinction between
summative systems and Gestalten . It is
advisable to consider a biological system to b e
a Gestalt unless it can be proved otherwise .
We do not believe that the concepts of systems
can be overemphasized . It is not necessary
for each researcher to be adept at formulating
systems models, but he should be awar e
that few things in a biological system operat e
independently, and that it is difficult if no t
impossible to understand biological phenomena
if we simply take the one factor-on e
response approach. As a result, in modelin g
biological systems, the single most importan t
concept is that the model must be a syste m
model, consistent with the concepts of
systems theory .
Theoretical Validit y
We view a model as a tool to aid in under -
standing and prediction . Because there are, i n
theory at least, an infinite number of model s
that can apply to a given system, we must
select that model which provides the greatest
understanding and predictive power withi n
certain limitations . If our system of interest
can best be explained by physical principles ,
then the model should have physical validity ,
but there are systems which are not explain -
able from the physical paradigm, for example ,
animal behavior . In other cases, the physica l
theory is inadequate and the approach may b e
fruitless .
Given a physical-chemical system, like
photosynthesis, a physically valid model is usu -
ally a good choice . As an almost trivial example,
photosynthesis, P, has been expressed b y
Chartier (1966) as a function of light :
P 1 bL (3 )
where a/b is P at light saturation, and a is the
slope of the curve (fig . 1) at zero light since
a = dP/dL(1 + bL) . Lommen and coworkers
(1971) express the same phenomenon as :
PmL
P m
(L) = 1 + K L /L
where PmL is photosynthesis at light and C O 2
saturation and KL is that light intensity at
which Pm(L) = 1/2 PmL (fig. 2) .
a/s
P
Figure 1 . Photosynthesis as a function of light . From
Chartier (1966) A = slope of line O,X . Descriptio n
in text .
PM (L)
PML
------------------ -
K
(4)
Figure 2 . Photosynthesis as a function of light . Fro m
Lommen et al.(1971) . Description in text .
L
L
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