Primary ProductivityPrimary Productivity&&

Phytoplankton GrowthPhytoplankton Growth

Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE

thanks to Tammi Richardson, Claudia Benitez-Nelson & Ron Benner for many of these slides

The co-occurrence of light and nutrients explainsThe co-occurrence of light and nutrients explainspatterns of primary productivity in the seapatterns of primary productivity in the sea

The co-occurrence of light and nutrients explainsThe co-occurrence of light and nutrients explainspatterns of primary productivity in the seapatterns of primary productivity in the sea

A major task is to describe the growth of phytoplankton as a function of light, temperature and nutrient concentration

• Phytoplankton are responsible for 90-96% of marine primary production

• Seaweeds contribute ~ 2-5%

• Chemosynthetic organisms ~2-5%

The ocean accounts for half The ocean accounts for half the photosynthesis on earththe photosynthesis on earth

Global view of primary production:

https://www.youtube.com/watch?v=qgG_nAJHW6I

There have been many different estimates of the total amount of primary production in the ocean. There is general consensus that the correct value is about 50 Gt C y-1

**Note: 1 Gt = 1Pg = 109 tons = 1012 kg = 1015 grams

Land Autotrophic Biomass = 500x Oceanic.

Oceanic Autotrophic biomass turns over on the scale of days while terrestrial is years to centuries.

Oceanic PP ≈ Terrestrial PP

Photosynthesis vs. Primary Production vs. Growth

Photosynthesis = The process by which carbohydrates are synthesized from carbon dioxide and water using light as an energy source. Most forms of photosynthesis release oxygen as a byproduct.

“Gross photosynthesis” = total carbon fixed

“Net photosynthesis” = Gross - carbon respired

Primary production = the synthesis of organic materials from inorganic substances by photosynthesis or chemosynthesis

If primary production exceeds respiration (losses), then “growth” may occur (an increase in size leading to cell division) ~ net primary production (more on this later)

1min 30 - 6min 17

https://www.youtube.com/watch?v=joZ1EsA5_NY

Photosynthesis Info

sunlight water uptake carbon dioxide uptake

ATP

ADP + Pi

NADPH

NAD+

glucoseP

oxygen release

LIGHT INDEPENDENT

REACTIONS

LIGHT DEPENDENT REACTIONS

new water

Photosynthesis occurs in two stages: The Light-Dependent & the Light-Independent Reactions

(thylakoid) (stroma)NADP+

Z scheme

Po

ten

tial

to

tra

nsf

er e

ner

gy

(vo

lts)

H2O 1/2 O2 + 2H+

(Photosystem II)

(Photosystem I)

e– e–

e–e–

secondtransfer

chainNADPH

firsttransfer

chain

The “Z scheme” of non-cyclic electron flow

Light Independent Reactions of Photosynthesis (Dark Reactions)

• Occur as a cyclic pathway called the Calvin-Benson Cycle• Six turns of this cycle regenerate enough RuBP to replace those used

in C fixation• ADP & NADP+ diffuse through the stroma and back to sites of light

dependent reactions

•Phosphorylated glucose is ready to be incorporated into larger molecules•Algae and plants use it as a building block for carbohydrates like cellulose and starch•Products of photosynthesis can be broken down (used as energy), or as building blocks for amino acids, lipids, etc

Measuring photosynthesis• Measured by:

– 14C fixation (usually incubation under different light levels)

– O2 evolution (usually sequential changes in irradiance)

– Active fluorescence – All approaches have problems*

• Photosynthetic rate will depend on the species and:

– Light level (E, mol m-2s-1 ); light history

– Nutrient concentration (status); nutrient history

– Temperature

– Level of acclimation

A Cycle of Life and Death

NutrientsNutrients Decomposition Decomposition NutrientsNutrients Decomposition Decomposition

Light + Nutrients Light + Nutrients Phyto Growth Phyto Growth Zoop Consumption Zoop ConsumptionLight + Nutrients Light + Nutrients Phyto Growth Phyto Growth Zoop Consumption Zoop Consumption

Bottom

Deep Sea

Surface Ocean

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 100 200 300 400 500

Light-Limited Growth

Gro

wth

rat

e (d

-1)

Irradiance (µmol m-2 s-1)

0.0

0.2

0.4

0.6

0.8

1.0

0 2 4 6 8 10

Gro

wth

Rat

e (d

-1 )

Scaled Nutrient Concentration

Nutrient-Limited Growth

The growth rate of phytoplankton depends on light, nutrients and temperature

(d

-1)

(d

-1)

14

What you REALLY need to know about What you REALLY need to know about light in the ocean:light in the ocean:

1. How much is there? (intensity)

2. What color is it? (spectral quality)

15

Light in the OceanLight in the Ocean

• Why Light is Important

• Provides energy for almost all marine food websPhotosynthesis

• Provides heat for stabilizing surface layers of the ocean

Optical measurements can be used to estimate what’s in the water

• Ocean color can be measured to estimate the abundance of phytoplankton and the rates of primary production

• Optical instruments can be used to detect phytoplankton, other particles, and dissolved matter from moorings, profilers, and drifters

What happens to light in aquatic environments?

ReflectedAbsorbedScattered

Inherent Optical Properties

Availability of Light in Water:

Light Intensity (I)

Light @ depth (z)

Light @ surface

Coefficient of extinction (length)

Iz = I0e-Kz

Water surface

Deep

HighLow

Dep

th (

z)

Importance of K:K defines the depth of the euphotic zone (i.e. growth barrier) -Operationally: 1% surface irradiance-Ecologically: zone of sufficient light for phytoplankton to grow

A higher Kd means more light is attenuated with

depth, hence a shallower euphotic zone.

18

The color spectrum of light varies with depthBlue light penetrates deep; red light is

attenuated quicklyDepth of light penetration is affected by

particles and dissolved substances in the water

0.00 0.20 0.40 0.60 0.80 1.000.00

20.00

40.00

60.00

80.00

100.00

De

pth

(m

)

Relative Irradiance

Euphotic Zone = from surface to the depth of 1% or 0.1% of surface irradiance

chlorophyll b

chlorophyll a

carotenoids

phycoerythrin (a phycobilin)

chlorophyll a

chlorophyll b

phycocyanin (a phycobilin)

Introduction to Biological Oceanography (3): John Cullen

Some chemotaxonomic photosynthetic pigments

*All phytoplankton *Chlorophyll a

Chlorophytes Chlorophyll b

Cryptophytes Alloxanthin

Diatoms Fucoxanthin

Dinoflagellates Peridinin

Cyanobacteria Zeaxanthin

Types and concentrations of pigments vary between different algal groups; measurement of phytoplankton pigments (by HPLC) is routine. Some pigments can be used as “biomarkers”; to identify algal groups in a mixed population.

Rhodomonas salina

Photoacclimation

• Short term (minutes – hours) response to changes in light quantity or quality

• Light intensity: response to light decreases or increases

• Within a species, acclimation responses may include 1) increases in the kinds or amounts of photosynthetic (or photoprotective) pigments, 2) changes in the number and/or size of PSUs

6

70 mC

0

1

2

3

4

5

6

0 500 1000 1500 2000

Surface

25m

100 m

75 m

B

PB (

g C

g C

hl-1

h-1)

Irradiance (mol m-2 s-1)• Phytoplankton can adapt to both the intensity and spectral quality of

light.

• Phytoplankton at low light should be adapted to increase the probability of capture of (scarce) photons of light. (Some species are better than others at photoacclimation; i.e. shifting in response to changes in light)

P vs E curves and mixing

Sverdrup's Model of Critical Depth

1) Photosynthesis decreases exponentially with depth due to decrease in light availability

2) Respiration is unaffected by light and remains constant with depth 3) Phytoplankton are mixed by turbulence and experience different light

intensities over time, sometimes above and sometimes below compensation point

4) Critical depth = depth at which photosynthesis of the total water column phytoplankton population equals their total respiration

(no net community production)

Productivity and depth

Why the difference in distribution???

Nutrient Limitation (Quantity vs. Quality…)

The total yield or biomass of any organism will be determined by the nutrient present in the lowest (minimum) concentration in relation to the requirements of that organism (Liebig’s law of the minimum, 1840);

Under resource competition, those species with the lowest resource requirement or with the highest ability to utilize low resources will succeed in competition

Note that the Rate of Supply is what is important, not the concentration

Living organism (particulate debris) in seawater have similar overall compositions

Average net plankton (>64m in size) compositions determined by Redfield et al., 1963

light (photosynthesis) 106 CO2+16 HNO3 + H3PO4 + 122 H2O

(CH2O)106 (NH3)16 H3PO4 + 138 O2

NPP is always referred to in terms of C and N…How do we really go back and forth? Nutrients <=> Production

Redfield Ratio

New versus Regenerated Production

Different N Sources:

New Production - NO3- as N source (from diffusion/upwelling from below the

euphotic zone and from the atmosphere via N2 fixation or nitrification)

Regenerated Production - NH4+ and urea as N source recycled in the EZ

How do we define export in the ocean?

• Nutrients that limit primary production in the surface ocean are supplied either by remineralization of organic matter within surface waters (regenerated production) •or from external sources (new production), mostly by upwelling or upward mixing of nutrients from the thermocline

• N is usually what is biomass limiting in the Oceans

Fundamental Paradigm of Primary Production in the Surface Ocean

N2 fixation

New production = Export production

PON and DON

Ammonification

Ammonification

Sarmiento and Gruber, 2006

Common in subtropical gyres and oligotrophic regions

Ammonium is the major N source

Large phytoplankton in nutrient-rich regions from upwelling or deep winter mixing

System switches between export and regeneration based on nutrients and grazing(Continued in later lectures)

P pico = picophytoplankton (e.g. Synecococcus, Prochlorococcus))

Nutrient fluxes in the open ocean

Biology uptake

sinking

recycling

remineralization

mixing

(Morel 2008)

Surface ocean

Deep ocean

• The BIOGEOCHEMICAL FUNCTION of plankton: mediate depletion and fluxes of nutrients from surface waters

• The Redfield Ratio 106 C : 16 N : 1 P

• What about trace metals?

An ‘extended Redfield ratio’

Normalized to P(mmol/mol P)

Fe Zn Mn Cu Co Ni Cd

Pacific Plankton(Bruland et al. 1991)

4.1 2.4 0.35 0.45 0.2 0.60 0.54

Cultured Plankton(Ho et al. 2003)

7.5 0.8 3.8 0.38 0.19 0.21

Metal Compound FunctionFe Cytochromes Electron transport in photosyn./respiration

Fe-S proteins Electron transport in photosyn./respirationNitrate reductase NO3

- assimilationChelatase Porphyrin and phycobiliprotein synthesisNitrogenase N fixation

Mn O2-evolving enzyme Oxidize H2O to O2 during photosyn.Superoxide dismutase Convert O2·- to H2O2

Cu Plastocyanin Photosynthesis electron transportCytochrome c oxidase Mitochondrial electron transport

Zn Carbonic anhydrase Hydration and dehydration of CO2

Alkaline phosphatase Hydrolysis of phosphate estersDNA/RNA polymerase Nucleic acid replication/transcription

Co Vitamin B12 Carbon and H transfer reactionsNi Urease Hydrolysis of urea

Superoxide dismutase Convert O2·- to H2O2

Hydrogenase Oxidation of H2

Mo Nitrogenase Nitrogen fixationNitrate reductase Nitrate reduction to ammonia

Metalloproteins in phytoplankton

Likely

many more ye

t to be disc

overed

Richardson, Ciotti, Cullen & Lewis (1996)

Nutrient-replete

Nutrient-starved

Light & Nutrients Synergism

The impacts of temperature on Primary Production

Temperature

Pho

tosy

nthe

sis

Winter species

There are winter species that grow best under cold, turbulent, high nutrient conditions. Diatoms for example.

There are summer species that grow best under warm, stratified, low nutrient conditions. Many flagellates and small cells.

Thermophiles love the extreme temperatures. Mostly species that have been isolated from tide pools and other extreme environments.

Summer species

Thermophiles

What controls PP from a Physical/Chemical perspective – e.g. quantity vs quality (composition) of nutrients???

The Growth of Phytoplankton(surface layer of the ocean)

Single Cell Doubled Biomass

DaughterCell

DaughterCellPhotosynthesis

Nutrient Uptake

Cell Division

Result: • More suspended particulate organic matter (food)

• Less dissolved inorganic nutrients (N, P, Si)• Less dissolved inorganic carbon (CO2) (from John Cullen)

The Growth of Phytoplankton(surface layer of the ocean)

DaughterCell

DaughterCell

Fates:

Accumulate (Bloom)

Be eaten

Sink

Blow up (viruses)

Apoptosis

0

200

400

600

800

1000

0 2 4 6 8 10

Re

lativ

e N

um

be

rs (

bio

ma

ss)

Time (days)

Log Scale

Nt N0 • e

• t

Net specific growth rate, µ, has units of d-1. Growth rate is frequently expressed as divisions per day or doublings per day (try to avoid that):

divisions per day = g =

(generation time = 1/g)

Growth rate can be expressed in terms of change in cell number (+/-) The specific rate of increase of cell carbon (C-specific growth rate)

The specific rate of increase of chlorophyll a (chl-specific growth rate)

Unfettered growth of phytoplankton

Seasonal cycles of phytoplankton: driven by water temperature, stability, zooplankton abundance, and NUTRIENTS

Typical seasonal pattern of phyto- and zooplankton abundance in the temperate North Atlantic. Notice the presence of a spring and fall phytopankton bloom, followed by an

abundance maximum of zooplankton

What actually controls biomass? Using light and nutrients in concert…..

Phytoplankton Counting MethodsMethod Advantages Disadvantages

Visual microscopy Brightfield

Simple, direct, only need a basic microscope

Tedious, subjective, difficult for small or rare cells

Epifluorescence Good for small, rare cells, especially good for natural bacteria, picoplankton and heterotrophs

Requires specially equipped microscope, more complicated sample/slide preparation

Image analysis Objective, automated No standard system/method, requires special equipment, software, time

Fluorometer Simple, direct, minimal sample handling, best for quick relative monitoring of cultures

Fluorescence per cell not constant, absolute cell number requires accurate cell counts for calibration

Coulter counter Rapid, precise, objective, automated, produces size spectrum, good for cultures

Requires special (expensive) equipment, high maintenance

(clogging), counts all particles

Flow cytometry Rapid, precise, objective, automated, counts cells only

Expensive instrument, must accurately measure volume analyzed