Phytoplankton Growth, Nutrients, and Temperature

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Phytoplankton Growth, Nutrients, and Temperature
Introduction to Biological Oceanography2004John
Cullen (Storm-Stayed)
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Required Reading McCarthy, J. J. (1981). The
kinetics of nutrient utilization. In Platt, T.
(ed) Physiological Bases of Phytoplankton
Ecology. p. 83-102.
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What we should have learned so far
marine.rutgers.edu/opp/
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Phytoplankton provide food energy for marine food
webs and strongly influence chemical cycles in
the sea
Coscinodiscus waelesii Phytopia CD-ROM Bigelow
Laboratory
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The measurement of light tells us much about the
ocean, including distributions of phytoplankton
and influences on their growth
marine.rutgers.edu/opp/
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The major causes of variations in primary
productivity are related to light and nutrients
marine.rutgers.edu/opp/
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Because phytoplankton need light for
photosynthesis and nutrients to support growth
carbohydrates
Photosynthesis
http//staff.jccc.net/pdecell/biochemistry/carbohy
d.html
Lipids
Protein
nucleid acids
http//www.agen.ufl.edu/chyn/age2062/lect/lect_02
/
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The Growth and Chemical Composition
of Phytoplankton is a Major Driver of Ocean
Chemistry
Light Nutrients ? Growth ? Consumption
Nutrients ? Decomposition
Bottom
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Chemical Composition of Phytoplankton(protein is
a major constituent)
Like the form of nutrient for growth, the
chemical composition of phytoplankton can vary
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Stoichiometry depends on N source and chemical
composition of phytoplankton
Generalized reactions for growth on nitrate and
ammonium
Understand and remember the definition and
significance of the photosynthetic quotient, PQ
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Growth on CO2 and the Macronutrients N and P
It is convenient (and often necessary) to
consider the growth and decomposition of an
average phytoplankter. Redfield (Redfield,
Ketchum and Richards 1963) showed strong and
profound relationships between dissolved elements
that were consistent with the growth and
decomposition of phytoplankton
CNP 106161 - Termed the Redfield Ratios
Nitrate and phosphate to proteins, phospholipids,
nucleotides, etc.the implicit PQ is 1.30
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Micronutrients (Trace Elements)
e.g., Cu, Zn, Ni, Co, Fe, Mo, Mn, B, Na, Cl
Generally, these are required to act as cofactors
in enzymes (Ferredoxin Fe, Flavodoxin Mn,
Carbonic Anhydrase Zn) Iron is well recognized
as being in short supply over large parts of the
ocean. It is particularly important in Nitrogen
Fixation. Copper, Zinc and Nickel have also been
implicated in influencing the growth of
open-ocean phytoplankton. Trace element
interactions are complex, and incompletely
understood.
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One of our jobs is to describe how light,
nutrients, and temperature influence the
photosynthesis, growth, and chemical composition
of phytoplankton. Quite a job!
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Temperature
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Temperature Effects in the Ocean
Eppley 1972
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Nutrients and Growth

• Growth of phytoplankton depletes nutrients
  consistent with their chemical composition
• Growth cannot continue when nutrients run out
• When one nutrient is depleted first, unbalanced
  growth can proceed
• We need to know how growth conditions and
  nutrient limitation affect chemical composition
  and growth rates of phytoplankton

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Effects of Nutrient ConcentrationMichaelis-Mente
n Kinetics
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Nutrient-uptake kinetics and ecological/evolutio
nary selection It was subsequently
demonstrated that phytoplankton isolated from
oligotrophic environments had lower Ks values
than phytoplankton from eutrophic environments
(consistent with prediction based on ecological
theory)
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However Nutrient uptake experiments are
generally performed under unnatural conditions.
Procedure for measuring nitrate uptake
kinetics a culture is grown on nitrite (easy to
measure) until the point of depletion, then
subsamples are supplemented with different
concentrations of nitrate the initial rate of
uptake is then determined and described as a
function of initial concentration. The
complication arises because the phytoplankton are
in unbalanced growth, adjusting physiologically
to changing conditions as the experiment is
performed. (In the field, nitrate and ammonium
assimilation is measured with 15N tracers)
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Nutrient kinetics for growth (rather than for
uptake) are more difficult to determine
experiments involve growth in chemostat culture
Ks lt 0.1 µg-at L-1
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The chemostat work produced another type of
nutritional pattern that was easier to measure
Cell Quota
from Droop, in McCarthy, 1981 Algal growth could
be described as a function of internal stores of
a limiting nutrient.
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Consequently, chemical composition responds to
growth conditions
N-Limited ltgt N-sufficient
The chemical composition of phytoplankton is very
responsive to growth conditions. Here, nitrogen
content is lower when growth rate is limited by
the supply of N (carbohydrates are accumulated).
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A consequence of variable cell quota (e.g., N
cell-1) is that even if nutrient uptake per cell
(nmol N cell-1 h-1) is constant as a function of
nutrient limitation, the maximum specific rate of
nutrient uptake (Vm µg-at N (µg-at cell N)-1
h-1) will increase with nitrogen limitation.
from McCarthy, 1981
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Two reasons for luxury uptake
see Morel, F. M. M. 1987. Kinetics of nutrient
uptake and growth in phytoplankton. J. Phycol.
22 1037-1050.
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Kinetics of uptake vs for growth are not the same
Ks for growth lt 0.1 µg-at L-1
Uptake Growth
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Photoacclimation affects chemical composition
High Light
Low Light
L
P
E
L
P
S
S
E
P Photosynthate
Sizes of arrows are proportional to flux
E Enzymes
Sizes of boxes ? pool size ? growth rate
S Storage
L Light Harvesting
after Geider et al. 1996
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Photoacclimation and P vs E
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Chemical composition responds to growth conditions
N-Limited ltgt N-sufficient
The chemical composition of phytoplankton is very
responsive to growth conditions. Here, nitrogen
content is lower when growth rate is limited by
the supply of N (carbohydrates are accumulated).
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Chemical composition responds to growth conditions
N-Limited ltgt N-sufficient
Carbon content is also higher when irradiance is
higher. How does chemical composition change?
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Unbalanced growth

High gt Low
Low gt High
L
E
P
L
P
S
S
E

see Geider et al. 1996
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Unbalanced Growth
When nitrogen ran out (day 6), photosynthesis
continued, but C was stored as starch. Growth was
unbalanced, and much different than Redfield.
When N was supplied, starch was used, protein was
synthesized, and Redfield was restored. When we
measure growth in the field, we do not generally
know if balanced growth is occurring.
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Chemical composition responds to growth conditions
A central tendency is toward Redfield
CN 6.6 by atoms CChl of about
50 Higher light, N or P limitation CChl
goes up Further reading Geider, R.J. (1987).
Light and temperature dependence of the carbon to
chlorophyll a ratio in microalgae and
cyanobacteria implications for physiology and
growth of phytoplankton. New Phytol. 1061-34.
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Chemical composition responds to growth conditions
Lower temperature is like higher light N
limitation CN goes up P limitation CP
goes up Further reading Goldman, J.C. (1980).
Physiological processes, nutrient availability,
and concept of relative growth rate in marine
phytoplankton ecology. In Falkowski P.G., (ed.)
Primary Productivity in the Sea. Plenum, New
York, pp. 179-194.
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Summary
Phytoplankton are microscopic organisms that
provide food for life in the sea. They do this
by growing (cell division). This
requires Light CO2 major nutrients (N, P, and
Si for some), and micronutrients (including
Fe) The growth process is fueled
by Photosynthesis and Nutrient Assimilation
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Summary
Phytoplankton cells are composed of Protein
(cellular structure and enzymes contains
N) Carbohydrate (energy storage) Lipids (energy
storage, membranes) and other stuff The
relative proportions of these constituents change
between taxa and with physiological state or
nutrient limitation. That alters the
stoichiometry of nutrient assimilation and
growth. This stoichiometry strongly influences
biogeochemical cycles in the sea.