SENFT, W. HERBERT. Dependence of light

Limnol.
Oceanogr.,
23(4), 1978, 709-718
@ 1978, by the American
Society of Limnology
and Oceanography,
Dependence
of light-saturated
on intracellular
concentrations
W. Herbert
Department
Inc.
rates of algal photosynthesis
of phosphorus
Senftl
of Ecology
and Behavioral
Biology,
University
of Minnesota,
Minneapolis
55455
Abstract
Specific rates of photosynthesis
at saturating irradiances (PO,J by laboratory populations
of
Chlorella
and Anabaena depend on intracellular
phosphorus (Q). A hyperbolic
model of the
is used to describe this relationship
for three measurements
of
form Popt = PoptR (1 -&/Q)
biomass (cell number, cell volume, and chlorophyll
a). Chlorophyll
a provides the most
adequate fit to the model. When chlorophyll
a is used as the measure of population size, both
the maximal specific rate of photosynthesis
(PO,:) and the subsistence cell quota (Ka) for
Anabaena are much larger than for Chlorella.
The model provides a conceptual
basis for
understanding
the relationship
between rates of photosynthesis
and intracellular
nutrients in
populations
of planktonic
algae.
difficult to measure (Jassby and Goldman
I975), even though they may be important in determining
species dominance
and succession
(Porter 1973; O’Brien
1974). This means that the relationship
of
growth to cellular nutrients must be reexamined in terms of a fundamental
process that can be measured in situ in order
to analyze the effects of nutrients on natural populations.
It seems highly probable that the dependence of growth rates on intracellular
nutrients
in laboratory
populations
reflects a more fundamental dependence of
photosynthesis
on intracellular
nutrients.
A decrease
in photosynthesis
corresponding to a lowered growth rate associated with nutrient deficiency has been
described by Healey (1973), Eppley and
Renger (1974), and Pickett (1975). Since
photosynthesis
supplies the energy stores
and carbon skeletons used in growth, it
is important to examine the relationship
between photosynthesis
and cellular nutrients. Because rates of photosynthesis
are easily measured in the field, these relationships,
unlike those for growth, can
then be applied to natural populations.
I have investigated
the photosynthetic
characteristics
of a blue-green
and a
green alga in response to changes in intracellular
phosphorus
and have found
major differences
in the photosynthetic
responses of these algae to a fixed nutritional status.
Ball
I thank R. Megard for advice and en709
Laboratory investigations
have shown
that growth rates of algal populations
depend on cellular levels of limiting
nutrients. Mackereth (1953) observed that
the growth rate of the freshwater diatom
Asterionella
.formosa is related to its intracellular
phosphorus
level. Caperon
(1968) showed that the growth rate of the
marine alga lsochrysis galbana could be
hyperbolically
related to the inferred cellular nitrate pool size, and Droop (1968)
observed a similar hyperbolic
relationship between the growth rate of Monochrysis Zutheri and intracellular
concentrations
of vitamin
Bj2. Fuhs (1969)
proposed an exponential equation for the
relationship
that he found between
growth rates of Cyclotella nana and Thalassiosira $uviatilis
and cellular
phosphorus concentrations.
The relationships
between growth rate and intracellular
nutrient
concentrations
have also been
described by hyperbolic functions (Droop
1973; Rhee 1973; Tilman and Kilham
1976).
These relationships
were discerned by
analyzing
growth rates of algal populations in batch, continuous, or semicontinuous culture. Growth is a net process involving both production
and loss terms,
Under laboratory conditions,
population
losses are well controlled. A lake, in contrast, often has large loss factors that are
’ Present address: Department
State University,
Muncie, Indiana
of Biology,
47306.
710
Senft
couragement. E. Gorham, J. Shapiro, D.
Tilman, and three anonymous reviewers
criticized
the manuscript,
J. Settles, J,
Balogh, and M. Balogh helped with laboratory work. R. Thrift developed
the
simplex portion of the computer program.
J. Wood and the Freshwater
Biological
Research Foundation
provided
laboratory space, computer facilities, and financial support. A portion of this work was
also supported
by ERDA
contract
E( 1 l-1)-1820 to R. Megard.
Theory
is the highest possible rate that a population could attain; as the physiology
of
the population
approaches
an “ideal”
state, Popt -+ PoptS.(In a similar manner,
P max + Pmax” as the algal cells become
nutrient saturated.) Both Popt and PoptSare
measured, short term, specific rates of
photosynthesis
obtained under constant
illumination
at a specified temperature.
It was assumed that the relationship
between measured specific rates of photosynthesis at saturating irradiances (Popt)
and intracellular
concentrations
(Q) of
nutrients is analogous to the relationship
between growth and cellular nutrients.
As intracellular
concentrations
of the limiting nutrient increase, the rate of photosynthesis approaches the nutrient-saturated rate (Popts). Furthermore,
the
intracellular
nutrient concentration
must
exceed a subsistence level (Ka) in order
for photosynthesis
to occur. The KQ value
for gross photosynthesis
does not equal
the KQ value for growth since at zero
growth rate gross photosynthesis
(equal
to at least respiration)
still occurs. Two
equations relating light-saturated
rates of
photosynthesis
and levels of intracellular
nutrients, based on two previously
published models of growth (Fuhs 1969;
Droop 1968), are proposed:
The specific rate of photosynthesis
at
saturating light is an important physiological measure of the photosynthetic
capability of phytoplankton.
It is referred
to as the maximal rate of photosynthesis,
P max, in mathematical
equations used to
describe and predict the photosynthesislight relationships
of algae (Smith 1936;
Steele 1962; Vollenweider
1965; Jassby
and Platt 1976). In those equations which
incorporate photoinhibition,
the value of
P max is usually much larger than the measured light-saturated
rate of photosynthesis because of the way in which photoinhibition
is built into the mathematical
expression. Vollenweider
(1965) and Fee
(1969) introduced the term P,,t, the optipopt = &,,9[1 _ 2-I(O-W&1],
cal rate of photosynthesis,
to differentiate
(1)
the measured light-saturated
rate of phoand
tosynthesis from the theoretical light-saturated rate, Pm,,. Popt and P,,, become
f’wt = po,,“(1 - f&/Q).
(2)
synonymous
in those equations that do
not incorporate
photoinhibition
(Smith
These equations represent the first for1936; Jassby and Platt 1976).
mulations
of the relationship
of photoThese definitions
of PoPt and Pm,, do
synthesis to cellular nutrient levels.
not imply any knowledge
about the nutritional
state of the algal population.
Methods
When dealing with the effects of nutrient
Axenic cultures of Anabaena cf. wislimitation
on the magnitude of light-satconsinense Prescott Univ. Nebraska colurated rates of photosynthesis,
we need
lection NU No. 41,~ md Chlorella
pyrmore precise terminology
and I have
enoidosa
Chick (’ i-th Carolina
Biol.
used the following
definitions
here. The
Supply Co. No. 15-L 470) were cultivated
optimal specific rate of photosynthesis,
,dla (Stanier et al.
in modified BGll
attained
P Ogt,is the rate of photosynthesis
1971). Stock culture
were kept under
under saturating light conditions. It varfluorest :nt lighting
(0.30
ies according to the physiological
state of continuous
Ein. rnA2. h-l) in 250-ml flasks containing
the algal population,
The nutrient-saturated specific rate of photosynthesis,
Pop?, BGll with a 1.6 PM ?-PO4 concentration
E
Intracellular
and used to inoculate glass carboys containing 9 liters of 6.5 pM P-PO4 BGll
medium adjusted to pH 7.2. These batch
cultures were stirred with a magnetic
stirrer and bubbled with sterile air at a
flow rate of -0.1 liter.minBi
under continuous white fluorescent
light (==0.43
Ein. rno2. h-l) at a temperature
of 23” rt
1°C. The cultures were harvested 48-192
h after inoculation
and checked for contamination
by plating onto a bacto-agar
medium. By choosing the time of harvest,
algal cells with various levels of cellular
phosphorus could be obtained, since the
population was required to share a finite,
and eventually
limiting,
supply of P04.
All other nutrients
were present in excess.
Rates of photosynthesis
and respiration
were estimated from changes in concentrations of oxygen in transparent
and
opaque BOD bottles (300-ml capacity).
Replicate transparent and opaque bottles
were exposed to a range of light intensities in an incubator similar to that described by Fee (1973). In initial experiments,
four
600-W
quartz-iodide
photoflood
lamps were used as a light
source; in later experiments
two of the
quartz-iodide
lamps were replaced by
750-W self-ballasted
mercury
vapor
lamps. Both light sources provided
a
range of light intensities great enough to
produce a complete photosynthesis-light
(P vs. I) relationship.
Spectral changes
associated with the different light sources
do not significantly
alter the photosynthetic response of these algae (Senft et al.
in prep.). Incubation
lasted for about 2 h
at 23” -r- 1°C. 0 xygen in the BOD bottles
was determined
titrimetrically
by the
azide modification
of the Winkler procedure (Am. Public Health Assoc. 1971).
Irradiance was measured with an underwater quantum sensor (Lambda Instr.
Co.) fitted with a specially
designed
spherical
collector
developed
by W.
Combs. In general, the light intensity received by any bottle in the incubator varied by no more than 10% as it rotated
through the light field.
Concentrations
of chlorophyll
a were
determined
from the SCORKJNESCO
phosphorus
711
equations
of Strickland
and Parsons
(1965). Samples were filtered onto 0.45-p
glass-fiber filters, ground in 90% acetone,
and extracted for 10 min. Subsamples of
algae were preserved with Lugol’s solution and counted on an inverted microscope.
Concentrations
of phosphorus were determined
on filtered (0.45-p pore size)
samples (Am. Public Health Assoc. 1971)
with ascorbic acid as the reducing agent.
Four analytical fractions of cellular phosphorus were separated. Total cellular
phosphorus was assumed to equal particulate P, which was measured after digestion with K2S208 in an autoclave for 45
min (Menzel and Corwin 1965). Surplus
P, a measure of luxury phosphorus stored
as cellular polyphosphates,
was extracted
according
to Fitzgerald
and Nelson
(1966) with 0.05 M Tris buffer (pH 7.7).
The acid-soluble
phosphorus
fraction,
which contains acid-soluble
7-min polyphosphates, ortho P, nucleotidic
labile P,
and polyphosphate
A, was extracted with
10% TCA at 4°C for 45 min (Kanai et al.
1965); the supernatant was then digested
as in particulate P. Free inorganic phosphorus in the cells-cellular-ortho
Pwas measured by adding acid-washed,
activated charcoal to the supernatant obtained from TCA-treated
samples and assaying immediately
for PO4 (Terry and
Hooper 1970).
Rem1 ts
Relationships
between gross photosynthesis and light for batch cultures of Anabaena and Chlorella
are illustrated
in
Fig. 1. Both species show large variations
in photosynthesis-light
curves as a function of cellular phosphorus. Phosphorus
nutrition
influences
the rates of photosynthesis
at saturating
irradiances.
In
Chlorella, the highest light-saturated
rate
measured is more than twice the lowest;
the highest light-saturated
rate in Anabaena is more than three times the lowest. The range of light saturation
for
Chlorella
is wide, 0.75-6.0 Ein. rne2. h-l,
much narrower (0.75-1.75 Ein. rnw2. h-‘)
for Anabaena.
Photosynthesis
in Ana-
712
Senft
plied by the user. The error function chosen here was a least-squares fit of the
form
ANABAENA
9 (Y
t=1
‘k
%
5
I
$
I
I
I
I
I
1
1
a.7
k
P
s. 0.6
CHLORELLA
-
W-J
Li
Lu
EO’
Q=135
Q=74
z
>
x
“0
6
2
0.2
Q=15
Q=3
F-1
0
1
LIGHT
Ii
2
3
INTENSITY
I
4
I
5
( Einrteinr-
I
I
I
J
6
7
8
9
m-‘-h
-’ I
Fig. 1. Photosynthesis-light
curves for batch
cultures of Anabaena and Chlorella
with different
cellular phosphorus levels, Q (nmoles P*pg Chl-‘),
Vertical bars represent 95% confidence limits calculated from pooled variance of light and dark bottles. Curves are hand drawn.
baena is inhibited
at high illumination,
decreasing
to only 60% of the lightsaturated rate at intensities
of 6.0 Ein.
m-2. h-1
Equations 1 and 2 were evaluated by
using the photosynthetic
responses of
Anabaena and ChZoreZZa to various levels
of intracellular
phosphorus. Popt was chosen as the highest rate of gross photosynthesis measured in a P vs. I curve, since
the curves from the photosynthesis
incubator always included
at least one
point in the light-saturated
region. Bestfit values for the two parameters (Pop? and
KQ) of both models were found with a
computer program incorporating
a simplex optimization
procedure. This method simultaneously
optimizes values for
the parameters of a theoretical
relationship by minimizing
an error function sup-
-
YtJ2,
(3)
where the differences
between experimental (y) and predicted (yt) points are
squared and summed for all points (n).
Values of yt less than zero were set equal
to zero, since rates of gross photosynthesis, unlike rates of growth, can never be
negative. If values of yt are allowed to be
negative, the theoretical
curve is forced
through the datum point with the lowest
cell quota (QmJ since yt + --OOif KQ >
of simQ min. Theoretical considerations
plex optimization
are detailed elsewhere
(Spendley et al. 1962; Nelder and Mead
1965; Deming and Morgan 1973; Morgan
and Deming 1974; King et al. 1975). On
the basis of two criteria (visual comparison and the magnitude of the error function, Eq. 3), the hyperbolic model (Eq. 2)
provides a better fit for all the observed
relationships.
Further discussion here is
limited to this model.
Three measurements
of biomass (cell
number, cell volume, and chlorophyll
a)
were used to estimate population
levels
in the cultures. Cell number (identified
by asterisks) and cell volume (identified
by primes) were chosen because they are
widely used estimates of algal densities
in laboratory populations.
Chlorophyll
a
was chosen for two reasons: it is an important photosynthetic
pigment, and it is
a practical measure of biomass for natural
phytoplankton
populations.
The conceptual model (Eq. 2) was tested separately
using each of these parameters.
Optimal rates of gross photosynthesis
and cellular phosphorus levels per individual alga are shown in Fig. 2. Both the
minimal
cell quota, &*(lO+
pmoles
Pm individual-l)
and the maximum rate of
photosynthesis,
Pop:*( low7 pmoles 0,.
individual-l
- h-l) for Anabaena are much
larger than the values for Chlorella.
This might be expected since an individual Anabaena
is composed of several cells (i.e. a filament) as opposed to
the single-celled
Chlorella . The experi-
.
Intracellular
0
ANABAENA
-
713
phosphorus
ANABAENA
PS
ap,* = 2.37
2.90 -
K&= 0.68
CHLORELLA
PS *
op,
K;=
l
q
0.97
0.07
l
0
KQ=
I
1.2
0
I
Q*
(IO-B
individual
-1
mental results for either species, however, do not provide a close fit to the
model.
The relationship
is different if cell volume is used as the estimate of population
size (Fig. 3). In this case, the maximal
ANABAENA
I
PARTICULATE
)
Fig. 2. Light-saturated
rates of gross photosynthesis vs. particulate phosphorus for Anabaena and
Chlorella.
Values of P,Pc* and KQ* are best-fit results from simplex optimization
of hyperbolic
model.
19.4c
Fig. 4.
0
1.2
2.4
PARTICULATE
Fig. 3.
Q’
3.6
( lo-”
gmoles
As Fig. 2, for P&’
= 20.6
4.8
P. pmm3 )
and I&‘.
6.0
6”
(nmolesP
I
200
Kg-Chl-’
I
)
As Fig. 2, for Pop? and KQ.
rate of gross photosynthesis,
Pop:’ (lo-l1
pmoles Oz. prnm3* h-l), is lower for Anabaena than for ChZoreZZa. Minimal
cell
quotas, I&‘( lo-l1 flmoles P~prn-~), are
similar in the two species.
The clearest expression of the relationship defined by Eq. 2 is provided when
chlorophyll
a is used to measure population size (Fig. 4). This can be seen by
performing a linear transformation
of the
model. Equation 2 can be rewritten
in
the form
p
P&(
I
150
I
0
4.8
pmoles P.
I
II
I
1
3.6
2.4
PARTICULATE
2.9
opt
=
POPtS
-
(PoPtK2wQ).
(4)
Plotting Popt vs. l/Q yields a straight line
with y-intercept
PoptS and x-intercept
l/&. Estimates of Pop? and Ke obtained
in this manner are only marginally
different from those of simplex optimization. Values of the correlation coefficient,
r, for Anabaena from the regression using
cell number, cell volume, and chlorophyll a as the measure of population size
are 0.66, 0.71, and 0.86. Chlorophyll
a
also provides
a better correlation
for
Chlorella
(r = 0.73) than either cell volume (r = 6.71) or cell number (r = 0.56).
714
0.70
Senft
ANABAENA
t
0”
9
CHLORELLA
0
$0.70
-
l
P&,
= 0.36
K0 = 1.5
I
20
0
SURPLUS
Fig. 5.
I
40
Q
I
60
( nmobs
I
80
P pg-Chl-’
100
l
)
I0
As Fig. 4, but vs. surplus phosphorus.
I
50
PARTICULATE
The estimates of Pop: (kmoles 02*pg
Chl-l-h-l)
and KQ (nmoles P*pg Chl-l)
show large differences between species
(Fig. 4). Anabaena
has a much higher
maximal rate of gross photosynthesis
than
Chlorella. The minimal particulate P cell
quota for Chlorella
is much lower than
that for Anabaena.
Values of Pop{ and KQ for these two species show the same relationship
when
0 35
-I
‘6
?
CELLULAR-ORTHO
Q
( nmoks
P-pg Chl“
1
0”
s
~070^a
op
035
.
.
k=
I
I
20
ACID-SOLUBLE
Fig. 6.
lular-ortho
I
40
2.0
I
80
I
60
Q
( nm&s
Pepg Chl-’
As Fig. 4, but vs. acid-soluble
phosphorus for Chlorella.
100
)
and cel-
I
100
I
150
Q
i nmoler
I
200
P.pg
Chl-’
)
Fig. 7. Respiration
rates as a function of particulate phosphorus for Anabaena and ChZoreZZu.
fractions of the total particulate pool are
examined. For surplus P (Fig. 5), Anabaena has a higher maximal rate of photosynthesis
and a higher minimal
cell
quota than Chlorella.
In Chlorella,
the
estimates of the photosynthetic
parameters for acid-soluble
P compounds
and
cellular-ortho
P (Fig. 6) are almost identical with the estimates for surplus P
compounds (Fig. 5). This is not surprising since the analytical
separations
of
these fractions are not physiologically
precise. In theory, the estimates of Popt
for a species obtained from plots of POPt
vs. different phosphorus fractions should
be identical. The estimates of Pop: from
Figs. 4, 5, and 6 agree reasonably well
within both species. Although
the data
for surplus, acid-soluble,
and cellular-ortho P show a much closer agreement to
the theoretical model, values of particulate P seem to provide an adequate measure of the nutritional
condition of these
algae.
Rates of respiration
by the two algal
species show different
relationships
to
intracellular
levels of phosphorus
(Fig.
7). Specific rates of respiration
(pmoles
02- pg Chl-l. h-l) of ChZoreZZa are unre-
Intracellular
phosphorus
715
ADP, and to a lesser extent AMP, also
stimulate O2 evolution when added to the
chloroplasts. The increase in oxygen evolution from the pea chloroplasts is a hyperbolic function of the amount of ATP
Discussion
added.
For the work reported here, the comThese results show that photosynthesis
responses dein algal populations
is a function of cel- parison of photosynthetic
pends on the unit used to measure poplular phosphorus
nutrition.
The hypera is used
bolic form of this relationship,
similar to ulation size. When chlorophyll
that of growth to cellular nutrition,
is not as a biomass estimate, Anabaena shows
a foregone conclusion because there are a much higher specific rate of gross phomany metabolic
processes involved
in tosynthesis and a much higher minimal
concentration
of cellular
phosphorus
growth other than photosynthesis
(respiIf, however, cell volume
ration, cell division, etc.). A limiting
nu- than Chlorella.
is used as the biomass estimate, the optrient may control a process such as cell
posite situation holds. Since the amount
division and so control the rate of growth.
of chlorophyll
per unit biomass can flucThese other processes may in turn regulate the photosynthetic
rate by some tuate widely
(Steele and Baird 1961,
feedback mechanism.
Nor need an in- 1962; Kuenzler and Ketchum 1962; Epcreased rate of photosynthesis
induce a pley and Renger 1974), rates of photosynparallel
increase in growth rate. End
thesis are very dependent
on the chloproducts of photosynthesis
may simply
rophyll:biomass
ratio, Variations in this
accumulate or leak out of the cell if the ratio can obscure the functional
depenproper nutrients
for protein synthesis,
dency of photosynthesis
on intracellular
DNA replication,
or cell wall synthesis
concentrations
of nutrients.
are lacking. We need to know more about
Comparisons of photosynthetic
values
the relationship
of cellular growth to cel- P opt ’ and KQ) with corresponding
growth
lular photosynthesis
in laboratory
culparameters (j.~,,, an d KJ are not easily
tures.
made. Several broad conclusions can be
The mechanism responsible for the ob- reached, however. Regardless of the bioserved photosynthetic
responses of cells
mass measure used, the responses ofAnto increased phosphorus
levels is un- abaena and Chlorella
to a fixed level of
known. One plausible
mechanism
may cellular phosphorus do differ dramaticalbe a precursor-product
reaction. Phos- ly. This suggests that each algal species
phorus-containing
precursors
can be may have a characteristic Popt and KQ valmaintained
at higher levels (yielding
ue, analogous to Rhee’s (1973) concept of
faster reaction rates) when Q is large;
specific values for growth parameters.
such precursors might include the nu- Whether this difference is characteristic
cleotides, ATP, ADP, and AMP, and in- of green and blue-green algae remains to
organic polyphosphates.
Miyachi
et al. be seen. If such differences are the rule
(1964) have suggested that under photoin natural systems, they would lend supsynthetic conditions polyphosphates
“C”
port to the ideas of Grenney et al. (1974)
and “A” serve as intermediates
in the and Tilman (1977) that the outcome of
transfer of phosphate to the phosphatecompetition
between
two species decontaining
compounds
synthesized.
At- pends on rates of both nutrient uptake
kinson (1968) proposed that the levels of and nutrient utilization.
AMP and ADP can influence the rate of
The relationship
of gross photosynthereactions involving
ATP synthesis. Rob- sis and cellular phosphorus shown here
inson and Wiskich (1976) have shown
provides a basis for understanding
the
that the oxygen evolution of isolated pea role that nutrients play in the growth and
cholorplasts
is stimulated
from two to maintenance
of phytoplankton
populatwelve times by the addition
of ATP.
tions. Previous studies on the constancy
lated to cellular phosphorus. The regression of respiration on cellular phosphorus
in Anabaena is significant, however.
716
Senft
Cpl 10.71
KQ-
E”
k4
0
0
5
10
( mg C ‘mg
cl-’
i
0
200
400
Q
( pg
organic
15
organic
N
20
-I
)
-i
rv
P
A
0
60
PARTICULATE
0”
I
0
600
N . mg
30
1
Q-’
I
50
(pg
I
100
Chl
[’
0 121
15 6
I
1
90
120
.pmole
P-’
)
I
200
I
150
800
C
-1
)
Fig. 8. Photosynthesis
vs. organic nitrogen content of’Phormidium
molle: A-linear
transformation
of hyperbolic
model; B-hyperbolic
model. Value
in brackets is 95% confidence limit for PoptS.
of the photosynthesis:Chl:light
relationship have produced conflicting
results,
The data presented here clearly indicate
that the photosynthetic
efficiency
of a
chlorophyll
unit is not constant, as assumed by Tett et al. (1975) in their analysis of Chl:C ratios in marine phytoplankton,
but rather varies with the
nutritional
state of the algal population.
Equation 2 represents an explicit formulation of the dependence of light-saturated rates of gross photosynthesis
on internal nutrient
stores.
Mathematical
representations
of photosynthesis-light
relationships
in phytoplankton
do not incorporate
this functional
dependency
and so a new photosynthesis-light
expression is needed (Senft in prep.).
These results are not unique to the two
algae studied nor to phosphorus as a limiting nutrient.
Keenan and Auer (1974)
reported changes in the rate of photosynthesis of Anabaena jlos-aquae
cells as
levels of extractable
phosphorus
decreased. When I replotted
Daley and
PARTICULATE
Q
( nmoles
P.pg
Chl-’
)
Fig. 9. Optimal photosynthesis
vs. particulate
phosphorus
for Halsted Bay, Lake Minnetonka,
1974: A-linear
transformation
of hyperbolic
model; B-hyperbolic
model. Value in brackets is 95%
confidence limit of Popts. Optimal rates of photosynthesis (P,,J were calculated
from photosynthesisdepth curves of half-day incubations in situ.
Brown’s (1973) data on oxygen evolution
by Phormidium
molle, I found a hyperbolic relationship
similar to those discussed here (Fig. 8). Changes in the specific rates of gross photosynthesis
of algae
during development
of a large phytoplankton
bloom in Halsted Bay (Lake
Minnetonka)
corresponded to changes in
the cellular phosphorus levels of the algae (Megard in prep.). This population,
comprised predominantly
of Aphanixomenon flos-aquae
(K. Baker unpublished), has a photosynthesis-nutrient
curve resembling
that of Anabaena (cf.
Fig. 4 and 9B). It has a high nutrient-saturated photosynthetic
rate and a high
minimal cell quota (Fig. 9A). In this one
case, photosynthesis-nutrient
relationships found in the laboratory
for one
blue-green
alga are in good agreement
with those of a mixed blue-green population in nature. Further interpretations
of natural phytoplankton
processes should
Intracellular
be possible as photosynthesis-nutrient
relationships
for different algal species
become known.
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Submitted: 2 February
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1977
1977