3.
a. m = growth rate (or nutrient uptake
rate)
b. S = substrate concentration
c. Ks = substrate concentration where growth rate is half of
maximum
F. Factors affecting uptake rate
1. Cell size – amount of
surface area relative to volume; surface area/volume gets lower as cell
gets bigger
(4Pr2 = area of a sphere; 4/3Pr3
= volume; so A/V = 3/r)
2. Nutritional state of
cell
a. Luxury uptake – cells take up more than they need
b. Inhibition by internal stores
3. Transport limitation
a. sinking
speed or swimming speed
b. turbulence
4. Inducible enzyme systems
affect Ks
5. Toxicity effects (if
nutrient abundance too high)
G. Determining the limiting nutrient – How do we
determine the limiting nutrient?
1. Liebig’s law of the
minimum – only 1 thing limits growth at any one time (something
else
may be close)
nutrient in shortest supply relative to needs
2. Stoichiometries –
again, deviations
from the expected Redfield ratio.
3. Bioassay techniques
4. Co-limitation
H. Other nutrient factors
1. Organic nutrients and
mixotrophy
a. Happens most often under several conditions:
1) DOM at high concentrations
2) Under the ice when light is low
3) If the algae can produce specific enzymes to assist taking up
organic
nutrients – e.g., alkaline phosphatase & DOP
b. Problems: bacteria have a lower Ks than do algae
2. Vitamins – B12 is
essential
for cyanobacteria, diatoms, greens and dinoflagellates
3. Organic compounds – antibiosis
– chemical warfare between algae or between some macrophytes and algae;
-species B has a lower maximum growth rate, but higher growth rate at a low nutrient conc.
B. Incorporation of loss/death rates
But you also have death
rates (natural loss, sinking, grazing, viruses) – if algae are growing
below the death rate level,
then the populations will not persist
N*B
and N*A are the concentrations of nutrients
needed
to get growth rates equal to the death rates for the two species –
break-even nutrient points.
If nutrient value is greater than the N*, then that algal species will
increase.
If not, then growth rate, m, will be less
than
the death rate
C. What happens if you have two nutrients?
1. Example with two diatom
species
Now add a second nutrient:
At low Si, Cyclotella will win.
At low Si, Cyclotella will win.
The outcome of competition between these diatoms depends on the relative abundance (ratio) of the two nutrients
Easy way to view – isoclines of the two nutrients:
P/Si
increases, then Cyclotella
will win
P/Si decreases, then Asterionella will win
Predictions from growth curves match the competition results in lab and in the field
2. Diatoms versus blue-greens
blue-greens have little N requirement (or Si requirement), but a high P requirement – low N:P ratios favor blue-greens
VI. Interaction of Factors Affecting Growth Control (temperate lake
examples)
A. Temperature cycle
C. Nutrient supply
D. Integration of growth factors
How can we integrate these three major growth
factors?
Best times for growth when these factors match
Right after ST ends and before FT begins – temp ok, light high,
nutrients
ok
Second best time – mid summer
Worst at winter time – low light and temperature
Sometimes there is a bloom right after the fall turnover due to
increased
nutrients
VII. Attrition control
A. Sinking rate
- Under the ice there is
often dominance of phytoflagellates that can control their position in
the water column
D. Parasitism
a. Fungi – chytrids (can
infect many cells – range <1-70% of cells)
b. Viruses – can have large
periodic effects; are often species specific
VIII. General seasonal succession
Can now make generalizations
about which algae will dominate when
(These events also happen in tropical lakes, but are prompted by
wet/dry
seasons or turnover events – different periodicity)
SPRING
SUMMER
LATE SUMMER
Diatoms
Greens
Blue-greens
High nutrients Good
competitors
at low
nutrients
Lowest nutrients (N fix.)
Low grazing
Moderate
grazing
High grazing – resist by being unpalatable (sheath/toxin)
Low sinking High
sinking rates (many
flagellated)
Moderate sinking
WINTER – small phytoflagellates; sometimes motile dinoflagellates
-Each major group’s
abundance
curve is made up of individual species curves
-Hundreds of species of
algae live in any one lake over the course of a year
-To predict each you need
to know nutrient requirements, responses to temperature, light,
grazing,
sinking rates
PRIMARY PRODUCTION
I. Fate of Energy
NPP = GPP – E – R
The whole process is 0.03-2%
energy efficient
Standing crop/biomass vs. production
II. Measurement
A. General equation and units
1. units of carbon produced
or oxygen emitted (sometimes calories; 1 mg C~10 cal energy,
depending on storage material – fat, starch…)
2. per volume or surface
area of lake
3. per time
B. oxygen change method
1. light-dark bottles
Measure
initial and incubate the others for a period of time
R=I-D
NPP=L-I (assumes the same respiration in the light and dark)
GPP=L-D
Problems
with this method:
(1) Enclosure/bottle effects
(2) Sensitivity
2. whole environment
measure oxygen change in a lake or stream over a day
avoid enclosure effects
must compensate for invasion and evasion of oxygen to the lake
C. C change -- 14C method
Add radioisotope of carbon
(14C) as bicarbonate, H14CO3-,
and it is converted to labeled carbon by the algae
Incubate in light and dark
bottles
Measure of roughly NPP (how
much 14C is incorporated into the algae)
Is more sensitive than
oxygen
method
Problems with this method
(1) 14C and 12C don’t have the same reactivity
(2) Doesn’t measure 14C that entered the cell and then left
by excretion or respiration before the end of the experiment
D. yield method
Look at the change in algal
biomass over time
No bottle effects
Only used with lots of
growth
so that there is no sensitivity problem
What is the problem with
this measure? Doesn't account for attrition – gives an
underestimate
of production
Also a problem with moving
water masses – spatial heterogeneity – may be sampling different water
masses
III. Patterns of productivity
A. Productivity versus latitude