Walz MINI-PAM-II, Manual, Page: 47 / 130

Saturation Pulse Analysis Chapter 5
41
•
ETR
max
, µmol electrons / (m
2
· s): Maximum electron
transport rate.
•
I
K
, µmol photons / (m
2
· s): Minimum saturating irradiance.
Evaluation of cardinal points requires WinControl-3. The software
uses two empirical functions to estimate these cardinal data: the
functions
REG1 and REG2 have been introduced by Platt et al.
(1980) and Jassby and Platt (1976), respectively, to describe
classical light response curves of photosynthesis.
REG1
In case of REG1, the cardinal point α results directly from fitting
the ETR below to experimental data.
mPot mPot
ETR
PAR
ETR
PAR
mPot
e e ETR ETR
⋅
−
⋅
−
⋅ − ⋅ =
β α
) 1 (
The latter equation considers photoinhibition of photosynthesis
by high light intensities. Therefore, the fitting procedure also
yields an
estimate for β, the “photoinhibition parameter“(Platt et
al. , 1980), and for ETR
mPot
, the maximum potential light-
saturated electron transport rate which would be observed if pho-
toinhibition was absent.
Platt
et al. (1980) have introduced the “Photoinhibition Index” (I
b
)
to quantify photoinhibition. The authors define I
b
as the PAR val-
ue required to photoinhibit ETR
mPot
by the factor of 1/e according
to:
β
mPot β
ETR I
=
With the results from curve fitting, WinControl-3 computes the
ETR
max
and I
K
according to:
α
β
β α
β
β α
α
) ( ) (
mαx
+
⋅
+
⋅ =
mPot
ETR ETR
and
α
m
K
ETR
I =
.