Primary Production: Definitions and P vs. I

OutlineReview LightBeer’s Law

PhotosynthesisPigments

Primary ProductivityP vs. I Curves

More Aquatic Habitats (Vertical)

Continental Shelf

Continental S

lope

Abyss … Trench

1% Light Depth

Neritic OceanicCoastal

Euphotic zone

Permanent Thermocline

Bathypelagic

mesopelagic

EPIpelagic25m

100m

1000m

200m

Abyssopelagic

Not shown:

Seasonal Thermocline (varies, 10 – 400 m, depending on season and location)

What happens to absorbed light?Photosynthetically active radiation (PAR) 400 – 700 nm or visible light

Absorbed PAR

• Scattered back out into the atmosphere Can be detected by sensors in air or orbit

• Absorbed by waterHeats it up

• Absorbed by plant pigmentsPhotosynthesis

• Absorbed by dissolved materialsPhotochemistry

• Attenuation = a decrease in the energy of light due to absorption and scattering in the water column

• Attenuation coefficient (K) = described the exponential decay of light with depth within the water column

• Beers Law

Beer’s Law

• Light intensity decreases with depth

• Exponential

• Observed where water well mixed

• Possible to predict light intensity

• Graph

Beer’s Law

• Iz = Io e – kz

• Iz = light intensity at any given depth

• Io = light intensity at surface (0m)

• e = natural log• K = # different in every system

(attenuation/extinction coefficient)• Z = any depth

Biogeochemical Perspective on Biological Oceanography

• Rate Processes: Chemical transformations in the environment

Primary productivityPhotosynthesisRespiration

Remineralization

• Concept: Control of rate processes• Concept: Limitation of rate processes

IMPORTANT DEFINITIONS

Primary Production (Primary Productivity)The RATE of increase of BIOMASS

(dimensions of MASS per VOLUME per TIME)Abbreviation: PP

Standing Stock # of organisms (cells)/volume of water

BiomassThe AMOUNT of LIVING MATTER

(dimensions of MASS or MOLES per VOLUME)Abbreviation: BOften expressed as amount of CARBON but living carbon cannot always be measured.

Primary Producers ORGANISMS that engage in PRIMARY PRODUCTION through AUTOTROPHY(i.e., Phytoplankton doing Photosynthesis)The BIOMASS of phytoplankton is often ESTIMATED as the concentration of Chlorophyll a

Photosynthesis

• Photosynthesis (P)

6CO2 + 6H2 O → C6H12O6 + 6 O2

• Respiration (R)

6CO2 + 6H2 O ← C6H12O6 + 6 O2

Photosynthesis

• Photosynthesis

6CO2 + 6H2 O → C6H12O6 + 6 O2

• Respiration

6CO2 + 6H2 O ← C6H12O6 + 6 O2

• Expressed as the RATE per VOLUME of the BIOMASS produced (mg C m-3 h-1) or asthe BIOMASS-SPECIFIC rate: (mg C mg Chl a-1 h-1) <- Assimilation Number

Photosynthesis can be expressed as:• Amount of carbon fixed OR • Amount of oxygen released

Photosynthetic Physiology

• Light Harvesting

• Light-dependent Photosynthesis and Photoadaptation

• Light Reactions of Photosynthesis

• Dark Reactions of Photosynthesis

Photosynthetic Physiology

• … is best assessed using short term experiments (ca. 1 hour, or less) in the light.

• Longer term experiments reflect more and more of the total organism metabolism and reflect respiration, photoadaptation, and other cell growth processes.

Phytoplankton Pigments and Photoadaptation

• Pigments

Organic compounds (or organometals)that absorb light.

• Pigment – protein (complexes)

Include chromophores (pigment molecules) bound covalently or otherwise to protein structures.

Roles of Pigments

• Absorb light energy for photosynthesis(Light Harvesting)

• Intercept or dissipate harmful light energy(Photoprotection)

• Convert light energy into chemical energy(Photochemistry)

Kinds of Pigments

• Chlorophylls

• Carotenoids

• Phycobilins

• Otherscytochromes, flavonoids, quinones, mycosporine-like amino acids…

Accessory Pigments (are all pigments except for chlorophyll a)

All of these share a common functional structure: alternating single and double bonds which result in molecular energy levels that coincide with the energy of visible photons.

Chlorophylls

• Green organometals (Mg ion coordinated)

• Several varieties• Based around porphyrin

ring (as is heme …)• Used for light harvesting

and photochemistry• Non-covalently linked to

proteins

Chlorophylls

• Chlorophyll a is present in all algae, cyanobacteria, land plants.

• Chlorophyll b is present in chlorophytes and higher plants

• Chlorophyll c is present in chromophytes and dinoflagellates

• Chlorophyll c lacks the phytol hydrocarbon tailPhytol Tail

Carotenoids• Red, orange, or yellow organic

compounds• Many varieties:

carotenes (hydrocarbons)xanthophylls (contain oxygen)

• Used for light harvesting and photoprotection (antioxidants)

• Non-covalently bound to proteins

-carotene

Phycobilins: phycobiliproteins

• Chromophore related to porphyrin (unrolled)

• Covalently linked to protein

• Found in protein structures called phycobilisomes

• Used for photosynthetic light harvesting only

Many varieties, three main:phycoerythrin (red)phycocyanin (blue)allophycocyanin (violet)

phycoerythrin

Phycobilisomes

• Clusters of phycobiliproteins with a defined structure

• Roughly hemispheric shape

• Sit on top of photosynthetic membrane

[Adapted from AN Glazer. Phycobilisome: a macromolecular complex optimized for light energy transfer. Biochemica et Biophysica Acta, 1984, p29-51]

Absorption Spectra

1. BchlA

2. Chl a

3. Chl b

4. PE

5. -Car

6. Chl c

6

6

Absorption Spectra

Fate of absorbed light energy

• Dissipated as heat

• Dissipated as fluorescence

• Used for photochemistry

Pigments and Photoadaptation“Photosynthetic Unit”

• RC is the reaction center, where photochemistry occurs. (chl a, carotenes)

• Antenna is chl a complexes that are closely associated with the RC

• LHC are light-harvesting complexes (chl a, xanthophylls, phycobiliproteins)

RC

Antenna

LHCLHC

LHC

Pigments and Photoadaptation“Photosynthetic Unit”

• Carotenes are present in RC to dissipate excess energy as heat

• Fluorescence is emitted by the antenna (also to dissipate energy)

• LHC are variable in number and size (photoadaptation)

RC

Antenna

LHCLHC

LHC

Photoadaptation – 2 kinds

• “FAST” photoadaptationChanges in short-term physiologyConnection and disconnection of components

• “SLOW” photoadaptationChanges in organism composition(Pigments, enzymes …)

Photoadaptation

• “High Light” photoadaptationLight harvesting complexes reduced (size or number)# of PSU (photosynthetic units) reducedAdditional photoprotective compounds synthesized

• “Low Light” photoadaptationLHCs increased (size or number)PSU number increased

Classes of Pigments in Marine Plants

• Chlorophylls - Porphoryn rings, magnesium in center (light harvesting and photochemistry)– Chl a– Chl b – Chl c

• Carotenoids – carotenes simple chains of carbon and hydrogen (photoprotection)– Xanthophylls 400-500 nm gives brown color to marine plants– Beta-carotene does not feed energy in but absorbs light for

plants (sunscreen) protects phototrap from receiving too many electrons

• Biliproteins water soluble accessory pigments (reds, blues, purples)– Phycoerythrin 500-570 nm, Phycocyanin 550-650 nm (red

orange)

Antenna

• Complicated array of accessory pigments

(carotenes, xanthophylls, phycobilins)

Some planktonic algae have large amounts of accessory pigments as well as Chl. What would the benefit be to that cost?

Photosynthesis : Control Points Light and Dark Reactions

• Light Availability

• Metabolic capacity (# of enzymes, etc)(Temperature)

• Resources (available carbon dioxide?)

• Downstream processes (growth)

Light Reactions

• Convert light energy and water toATP and NADPH

• ATP stores useable chemical energy • NADPH stores useable reducing power

REDUCING POWER is required to reduce CO2 to CH2O (and other oxidized nutrients to organic forms)

Light Reactions -- Photochemistry

• Light absorbed by the LHCs is passed through the antenna to the reaction centers.

• A special chlorophyll a molecule (reaction center chlorophyll) on the lumen side then oxidizes (ejects an electron).

• The electron is grabbed by an acceptor on the other side of the membrane

• Primary Charge Separation – electrical power

Light Reactions -- Photochemistry

• The reaction center chlorophyll is reduced by an enzyme complex that splits water molecules, releasing oxygen and protons inside the lumen.

• The electron that was produced by the photochemical reaction ultimately goes on to provide reducing power to NADPH.

• The protons in the lumen provide a proton motive force to join phosphates to ADP.

Dark Reactions

• The ATP and NADPH produced by the light reactions are used to “fix” carbon dioxide and reduce it to carbohydrate.

• The enzyme that actually binds CO2 is called RubisCO

• Temperature dependent• Result in high energy carbohydrates

(polysaccharides) and organic materials (lipids, aa)

IMPORTANT NOTE: Photosynthesis is not equal to Primary Production

Example: Organisms also do RESPIRATION (R)

CH2O + O2 → CO2 + H2O + Energy

PP P – R

• Gross Primary Productivity (Pg)

– Total P

• Net Primary Productivity (Pn)

– Gross PP – plant respiration

Estimating Primary Productivity

In a bottle of known volume, incubated for a whole day:

Measure the uptake of radioactive CO2 (carbon-14) in light and dark bottles: • RL: Radioactivity retained in

particles in light bottle

• RD: Radioactivity retained in particles in dark bottle

• W: Concentration of CO2 in water (overall)

• t: Time of incubation (hours)

( )L DR R WPP

R t

• Primary Productivity (PP) rate

• Respiration (R) rate

• Photosynthesis (P) rate

= mass/volume/time

mg O2/l/t

• Units PP mg C/m3*h = mass per volume per time

• If C fixed/time is coupled with chl a measurements of biomass → get a growth rate mg C/mg chl a * h = p. 49

Assimilation Index measure of PP in which plant growth is expressed in terms of amount of C fixed

per unit of chl a per unit of time

PhotosynthesisIs a function of VISIBLE LIGHT

Photosynthetically Available Radiation (PAR)is a term for the quantity of light that stimulates photosynthesis

Expressed as either the rate of ENERGY or QUANTA passing through an AREA.W m-2 (J m-2 s-1)or mol photons m-2 s-1

A MOLE OF PHOTONS (6.02x1023 photons)is one Einstein (Ein)so:1 Ein m-2 s‑1 is 6.02x1017 photons per square meter per second.

The relationship between Photosynthesis and Irradiance (PAR) is called the P-I CURVE

Photosynthesis – Irradiance Curve

• P = Pm tanh(I / Ik)• P is the photosynthesis rate (matter / volume*time)• I is the irradiance, light intensity (cal/cm2 *min) • Pmax is the maximal rate of photosynthesis• Ik is the irradiance saturation parameter (varies for different plants)• is the initial slope of the P vs. I curve

P

Irradiance (I or E)

Pmax

IkIb

Photosynthesis – Irradiance Curve

• Ib is the irradiance at which photoinhibition occurs

• is the decrease in P with increasing irradiance under photoinhibition.

P

Irradiance (I or E)

Pm

IkIb

Photosynthesis – Irradiance Curve

• Changes in reflect changes in the light harvesting capacity and efficiency of the light reactions of photosynthesis (cellular properties)

• Changes in Pm reflect changes in the enzymatic capacity (e.g. the dark reactions of photosynthesis).

P

Irradiance (I or E)

Pm

IkIb

Photosynthesis – Irradiance Curve

• Photoinhibition reflects damage (reversible or irreversible) to the photosynthetic system … can be caused by UV damage and excessive visible light flux, modulated by time of exposure.

P

Irradiance (I or E)

Pm

IkIb

Photosynthesis

• … makes carbohydrate, energy, reducing power. Respiration consumes carbohydrate and yields more energy.

• Growth requires more than just this: Nitrogen, Phosphorus, metal ions …

• Primary productivity is therefore a function of photosynthesis, respiration, and nutrient metabolism.