productivity and the coral symbiosis iv: reef photosynthesis
TRANSCRIPT
Productivity and the Coral Symbiosis IV:
Reef Photosynthesis
Productivity
• the production of organic compounds from inorganic atmospheric or aquatic carbon sources – mostly CO2
• principally through photosynthesis– chemosynthesis much less important.
• All life on earth is directly or indirectly dependant on primary production.
gC/m2/d
TropicalCoral Reef 4.1 - 14.6
Tropical open ocean 0.06 - 0.27
Mangrove 2.46
Tropical Rain Forest 5.5
Oak Forest 3.6
Productivity
• no single major contributor to primary production on the reef
• a mixture of photosynthetic organisms– can be different at different locations
• net productivity values (varies with location):
gC/m2/d
Calcareous reds 1 - 6
Halimeda 2 -3
Seagrass 1 - 7
N.S. kelp 5
• Overall productivity of the reef:
4.1 - 14.6 gC/m2/d
• from– epilithic algae, on rock, sand etc., – few phytoplankton– seagrasses– Zooxanthellae (in coral etc.)– Fleshy and calcareous macroalgae
• One obvious differences between different algae is their colour
• Different colours due to the presence of different photosynthetic pigments
• The visible light spectrum includes– the colors of light we can see– the wavelengths that drive photosynthesis
• Photosynthetic pigments absorb light
Light
ReflectedLight
Chloroplast
Absorbedlight
Granum
Transmittedlight
Light and Photosynthesis
• Air & water both absorb light– a plant at sea level receives 20% less light than
a plant on a mountain at 4,000m
– this reduction occurs faster in seawater – depends a lot on location
• get 20% light reduction in 2m of tropical seawater
• get 20% light reduction in 20cm of Maritime seawater
Photosynthesis uses a very specific part of the EM spectrum
• PAR
• Photosynthetically Active Radiation
• 350-700 nm
Gammarays X-rays UV Infrared
Micro-waves
Radiowaves
10–5 nm 10–3 nm 1 nm 103 nm 106 nm1 m
106 nm 103 m
380 450 500 550 600 650 700 750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energy
Gammarays X-rays UV Infrared
Micro-waves
Radiowaves
10–5 nm 10–3 nm 1 nm 103 nm 106 nm1 m
106 nm 103 m
380 450 500 550 600 650 700 750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energy
• Measure it as IRRADIANCE– moles of photons per unit area per unit time– mol.m-2.s-1
– E = Einstein = 1 mole of photons
E.m-2.s-1
• As light passes through seawater it gets ABSORBED & SCATTERED – = ATTENUATION (a reduction in irradiance)
• pure water– attenuation lowest at 465nm
– increases towards UV and IR ends of spectrum
• TRANSMITTANCE is highest at 465nm
• not dealing with pure water– seawater has all kinds of dissolved salts, minerals,
suspended material etc.:
• Attenuation is different in different locations - different light transmittance spectra:
To fully exploit a particular location, marine plants have a wide variety of PS pigments they can use.
Chloroplast
Mesophyll
5 µm
Outermembrane
Intermembranespace
Innermembrane
Thylakoidspace
Thylakoid
GranumStroma
1 µm
CO2
CALVINCYCLE
O2
[CH2O](sugar)
NADP
ADP+ P i
An overview of photosynthesis
H2O
Light
LIGHT REACTIONS
Chloroplast
ATP
NADPH
Light Reactions
• In the thylakoid membrane,
– chlorophyll molecules, other small molecules & proteins, are organized into photosystems
– photosystems composed of a reaction center surrounded by a number of light-harvesting complexes (LHC)
• LHC = pigment molecules bound to proteins
• LHC = pigment molecules bound to proteins
• funnel energy of photons to the reaction center
• reaction-center chlorophyll absorbs energy– One of its electrons gets bumped up to a primary
electron acceptor– electron transport– ATP & NADPH production
Photosystems
Primary electionacceptor
Photon
Thylakoid
Light-harvestingcomplexes
Reactioncenter
Photosystem
STROMAT
hyla
koid
mem
bran
e
Transferof energy
Specialchlorophyll amolecules
Pigmentmolecules
THYLAKOID SPACE(INTERIOR OF THYLAKOID)
e–
• different pigments have different absorption spectra
• combine in different amounts in different species to give each a unique absorption spectrum
• tells us which wavelengths of light are being absorbed (and thus it’s colour)
Ab
sorp
tion
of
ligh
t b
ych
loro
pla
st p
igm
en
ts
Chlorophyll a
Wavelength of light (nm)
Chlorophyll b
Carotenoids
Absorption spectra of pigments
• doesn’t tell us what the alga is doing with the light
• For this you need to look at the ACTION SPECTRUM– measures photosynthesis at different
wavelengths
• The action spectrum of a pigment
– show relative effectiveness of different wavelengths of radiation in driving photosynthesis
• Plots rate of photosynthesis versus wavelength
Marine PS pigments
• 3 major groups of PS pigments in marine organisms
– Chlorophylls– Phycobiliproteins– Carotenoids
• Chlorophyll a is essential
– find it in all plants and algae
• the other pigments are accessory pigments
– in the antennae complexes – funnel electrons to chlorophyll a in the reaction
centres
• 5 types of chlorophyll commonly found in marine organisms
• all are tetrapyrrole rings with Mg++ in the middle
• chlorophyll a, b, c1, c2 & d
• a all green plants and algae• b Chlorophyceae• c1 & c2 Phaeophyceae• d Rhodophyceae
• Chlorophyll a– Is the main photosynthetic pigment
• Chlorophyll b, c, d– Are accessory pigments
C
CH
CH2
CC
CC
C
CNNC
H3C
C
CC
C C
C
C
C
N
CC
C
C N
MgH
H3C
H
C CH2CH3
H
CH3C
HHCH2
CH2
CH2
H CH3
C O
O
O
O
O
CH3
CH3
CHO
in chlorophyll a
in chlorophyll b
Porphyrin ring:Light-absorbing“head” of moleculenote magnesiumatom at center
Hydrocarbon tail:interacts with hydrophobicregions of proteins insidethylakoid membranes ofchloroplasts: H atoms notshown
Accessory pigments absorb different wavelengths of light and pass the energy to chlorophyll a
• Also a wide range of carotenoids– C40 TETRATERPENES– very hydrophobic– sit in membranes
• 2 types of carotenoids
– CAROTENES (hydrocarbons)– XANTHOPHYLLS (have 1 or 2 oxygens)
-CAROTENE is the most common carotenoid in marine organisms
• often see a mixture of -CAROTENE & FUCOXANTHIN in the Phaeophyceae– gives the brown colour
• PHYCOBILINS are linear tetrapyrroles attached to proteins– red pigments
– no ring, no chelation of a metal
• Only found in Rhodophyceae & Cyanophyceae– and a few species of Cryptophyceae
• Algae from different locations will often have different absorption and action spectra
– CHROMATIC ADAPTATION
• difference in pigment composition due to a difference in light quality
• most pronounced when comparing algae grown at different depths
• Allows for optimal PS with the different wavelengths of light seen at different depths
• occurs within and between species
• In general, less light means more pigment
• e.g. Sea Lettuce (Ulva spp)
• move from high to low light– 10x less: 300 to 30 E.m-2.s-1
• chl a,b & c go up 700%
• One pigment doesn’t respond in this way
• FUCOXANTHIN– yellowish pigment found in brown algae
– probably because it performs 2 functions
• light harvesting
• protection from high light levels