Lecture 5

Lecture 5 - Phytoplankton Bio-optics: Absorption, Pigments,...

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Unformatted text preview: Phytoplankton Bio-optics: Absorption, Pigments, Biomass Phytoplankton Homework: Chapter 2 in your reader: C. Miller “The phycology of phytoplankton” Roles of Phytoplankton 1. 2. Light absorption & related heat Light budgets budgets Inorganic to organic conversion of Inorganic C, N, P, S, etc for consumption by food web food Formation of DOC (=DOM, of Formation which cDOM is a component) which Sinking and loss of POC to the Sinking deep sea/ fossil fuel ALL Biogeochemical Cycles Harmful Algal Blooms Cloud formation/Climate Cloud modification modification Optical Signaling Optical (satellites/moorings/submarines) (satellites/moorings/submarines) ~ 40 % global photosynthesis and 40 related primary productivity related 3. 4. 5. 5. 6. 7. 8. 9. Last Lecture and reading emphasized that A quantum of sunlight getting into surface water column is either absorbed, scattered and/or absorbed scattered transmitted to deeper depths, due to water properties, phytoplankton, cDOM, particles, detritus transmitted etc. etc This and the next Lectures and readings emphasize that • A quantum of light reaching the surface a phytoplankton cell is also either scattered (mostly at scattered cell surfaces), absorbed (PAR, mostly by pigments and cell metabolites: UVR by DNA and cell absorbed protein), or transmitted through the cell to penetrate deeper in the water column. protein), transmitted through • In addition some absorbed light by pigments can be reemitted as light (= fluorescence) fluorescence • The measurable proportionalities of incoming irradiance in the photon budget of a phyto change The photon with different taxonomic groupings, physiology, photosynthetic activity &cell growth. with Therefore, much can be learned about phytoplankton by looking at their Therefore, effects on the underwater light field; hence, the study of the bio-optics of phytoplankton is central to aquatic ecology phytoplankton Fundamental review, see readings for additional detail. Fundamental Several kinds of Dinoflagellates 1. Phytoplankton shapes/sizes and surface composition/roughness largely control light scatter light 2. Phytoplankton cellular components and their 2. internal distribution in the cell largely determine how much of light getting into the cell is absorbed or transmitted. transmitted 3. Phytoplankton cell absorption of light occurs largely in photosynthetic lamellae (thylakoids) 3. absorption where ALL photosynthetic pigments are located. Thylakoids are in chloroplasts organelles within eukaryotic phytoplankton and located in cytoplasm (no organelles) of prokaryotic bacteria Even at the organizational level of a chloroplast, incoming light can be scattered, Even absorbed or transmitted. absorbed Major differences in thylakoid arrangements exist in Major different phytoplankton groups and affect with how light energy is absorbed and utilized. light Diatoms, Dinoflagellates And other chromophytes thylakoid stroma Green algae CHLOROPLAST REVIEW • All photosynthetic pigments are in thylakoids All • Thylakoids give cell color Thylakoids • Photosynthesis light reactions in thylakoids Photosynthesis • Photosynthesis dark reactions in stroma; Photosynthesis Optional excellent review of basic photosynthesis given as a self test (based upon green plants) http:// ghs.gresham.k12.or.us/science/ps/sci/soph/energy/photorev/basics/rev.htm Chlorophyll a is only pigment required for photosynthesis required Because Chl a (C) is the only pigment that comprises the photochemical reaction Because centers of Photosystem I and Photosystem II centers Photosystem Photosystem P700 = special Chl a dimer of Ps I P680 = special Chl a dimer of Ps II Chemical Chemical electron acceptor acceptor PS I Ejects electron Chl a Chl a is in all photosynthetic Chl phytoplankton and its abundance in a water sample is used to indicate the relative BIOMASS of phytoplankton BIOMASS Common Method for Determining Chl Biomass: • Filter phytos (can size fraction) Filter • Extract Chl with organic solvents Extract • Measure magnitude of Chl red peak absorption Measure • Convert to [concentration units] of ng/L =mg/m3 [concentration Note how depth is not in meters (Z) but scaled to light field as % surface QPAR …this approach allows distribution of Chl in Chl a euphotic zones of different depths to be intercompared. Caveat: [Chl a] is imperfect measure of phytoplankton biomass & interpretations of findings must recognize the possible sources of error. How would your view of phytoplankton distribution in the above graphs change if I told you that each phyto cells at 1%Qpar have 10x Chl of that of cells at the surface? So, if Chl a is all that is needed for photosynthesis, what are all those other pigments doing and where are they located? pigments They are absorbing light energy and passing the They excitation energy on to Chl a-doinated PS I and PS II reaction centers to do photochemistry reaction As such they are called Antenna or As Light-Harvesting Complexes (LHCs) In vivo whole cell absorption or LHCs This is an example for a chlorophyte This (green algae) LHCs, giving rise to a whole cell absorption spectrum that is a summation of the absorption properties of each of these pigments bound to proteins in the thylakoid membrane membrane Pure pigment in organic solvent LH Pigments evolved to efficiently capture aquatic QPAR(λ ) that Chl a does not absorb well LH Case I: Open Ocean 400 nm 400 700 nm Case II: Coastal waters/most lakes Case Found in large quantities in red colored cyanobacteria and in some red algae Cyanobacteria and some red algae Phytoplankton pigments: types, function and taxonomic distribution Phytoplankton If phycoerythrin abundant then red colored If phycocyanin abundant, then blue colored Micro flagellates You need to know this information very well to study phytoplankton community You ecology as well as regional differences in aquatic primary production ecology Transect of Santa Barbara Channel West Front East Depth (meters) Chlorophytes, Prochloron? Phytoplankton Biomass Diatoms Phytoflagellates Examples of phytoplankton absorption spectra for different phytoplankton groups a c fuco c a Chl a + Chl c (1+2) + fucoxanthin Chl a + Chl c (2) + peridinin Chl a (which absorption peaks?) + phycobilin containing phytoplankton Phycocyanin, PC Phycoerythrin, PE In ocean, these are picophytoplankton that tend to dominate phytoplankton communities of oligotrophic waters. How pigment data is used in oceanography 1. To map distribution of Chl a as proxy measure of phytoplankton biomass Dense spring bloom in North Atlantic Ocean Low phyto biomass in Gyres of N. and S. Atlantic Ocean High phyto biomass In coastal currents But not all Chl is the same phytoplankton community.. How do we know which Groups of phytoplankton are in which locations? ...
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This note was uploaded on 01/07/2010 for the course EEMB 142B taught by Professor Prezelin/macintyre during the Winter '08 term at UCSB.

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