Photosynthesis and Primary ProductionGlobal Chlorophyll DistributionsMarine ver sus Terrestrial Biology/Ecology:General Considerations for Life as a Phytoplankter(versus as an oak tree, for example)1) What’s in a cell?2) Life is 3D (vs 2D)3) Go with the Flow4) Niche differentiation is gnarly(or, “Why are there so darned many of them?”)Photosynthesis and Primary ProductionWhat is the difference?Photosynthesis = the physiological process of harvesting light energy and converting it into chemical energyPrimary Production = the accumulated chemical energy = carbon fixed = DIC converted to organic C = biomass producedPhotosynthesis and Primary ProductionPhotosynthesis = the physiological process of harvesting light energy and converting it into chemical energyHow does this tak e place?Available at:http://www.life.illinois.edu/govindjee/paper/gov.html#10THE PHOTOSYNTHETIC PROCESSIn: "Concepts in Photobiology: Photosynthesis and Photomorphogenesis", Edited by GS Singhal, G Renger, SK Sopory, K‐D Irrgang and Govindjee, Narosa Publishers/New Delhi; and Kluwer Academic/Dordrecht, pp. 11‐51.John WhitmarshPhotosynthesis Research Unit, Agricultural Research Service/USDADepartment of Plant Biology and Center of Biophysics and Computational Biology,University of Illinois at Urbana‐ChampaignGovindjeeDepartment of Plant Biology and Center of Biophysics and Computational BiologyUniversity of Illinois at Urbana‐ChampaignMuch of what I hope to explain is tak en from this excellent overview on photosynthesis:In a nutshell: •light energy (photons) interact with the resonance structure of an organic compound, causing that structure to become excited.•The energy trapped in the organic compound is passed along a chain of other organic compounds, eventually the energy is used to separate charges onto two molecules, and to produce reduced compounds•In oxygenic photosynthesis the reactant is water and the products are O2,NADPH and H+•In anoxygenic photosy nthesis, the reactant is H2A and the products are A and ferredoxin•The accumulated H+creates a gradient across the chloroplast membrane. Other enzymes use the chemical potential inherent in this gradient to forge high‐energy phosphate ester bonds (= generate ATP).•ATP is then used by other enzymes (Rubisco or PEP carboxylase or …) to add CO2to an existing organic molecule, then reduce the carboxyl group that results from this.And voila –more biomass!Light energy goes in hereBiomass (chemical energy)comes out hereAnoxygenicPhotosynthesisOxygenic PhotosynthesisAntennae pigments: capture photons outside the photosynthetic reaction center and transfer them to it(they’re actually integrated into the photosynthetic membrane adjacent to the reaction centerAntenna size varies, normally ~300 antenna chlorophylls to 1 reaction center chlorophyll, but can be much less under high light conditions, nutrient (esp. N) limitation, etc: “bleaching”Changing pigment composition allows phytoplankton to adapt to differences in light qualityChanging antenna pigment quantity allow s phytoplankton to adjust to varying light intensitiesChanging the number of reaction centers allows phytoplankton to tune photosynthetic rate, esp. to factors other than lightSpecies ASpecies BLight adaptation is species‐specificRate of PhotosynthesisLight IntensityComparison of 3 SpeciesLow light adaptedHigh light adaptedWhat is the antenna composed of?Chlorophylls a, b and c, CarotenoidsBiliproteinsBacteriochlorophyll aTaxon specific (thus the basis for a widely used technique for assessing phytoplankton species composition)These are all:Conjugated aromatic structuresHydrophobicAbsorption spectra are differentCarotenoidsChlorophyllsBiliproteins(Cyanobacteria only)These contain nitrogenThese don’tWavelength, nmHow do these spectra match the light fields available to phy toplankton?Light attenuation in the atmosphere“Visible Light” = “PhotosyntheticallyActive Radiation” = “PAR”Spectral absorbance of seawaterhttp://serc.carleton.edu/images/eslabs/corals/light_penetration_by_color.jpgWavelength or ColorWavelength or ColorLight attenuation in the oceanAbsorptionScatteringTotal attenuation (thus light availability at depth) varies with locationChanging pigment composition allows phytoplankton to adapt to differences in light qualityChanging antenna pigment quantity allows phytoplankton to adjust to varying light intensitiesChanging the number of reaction centers allows phytoplankton to tune photosynthetic rate, esp. to factors other than lightWavelength, nmPlant pigments have evolved to absorb maximally at the region of highest light transmission through seawaterThus, phytoplankton are tuned to capture the most energy available to drive photosynthesisPhotosynthetic Action SpectrumPigment Absorption SpectrumThis translates into photosynthesisSubsequent intermediary metabolism converts these products to other molecules needed for biosynthesis: amino acids, nucleic acids, lipids, complex carboh ydrates, etc.So what happens if something prevents subsequent metabolism? (like nutrient limitation)If light energy is being captured faster than it can be processed by the reaction center, the energy is released (emitted) as another photon:FLUORESCENCELonger wavelength (red) because some energy has been lost in the process (heat, etc.)Fluorescence is an extremely useful property for estimating biomass distributions –both in situand remotelyChanging pigment composition allows phytoplankton to adapt to differences in light qualityChanging antenna pigment quantity allows phytoplankton to adjust to varying light intensitiesChanging the number of reaction centers allow s phytoplankton to tune photosynthetic rate, esp. to factors other than lightPhotoinhibitionSaturationCarbon Fixation RateLight IntensitySpecies SpecificGrowth RateLight IntensityExample: Deep chlorophyll maximaAn example of adaptation to light and nutrientsProducts of seasonal progressions and stable water columnsBlooms sink with time, become invisible to satellites. Why? DateDepthMay DecemberNutrient limitation eventually limits bloom. Mixed Layer ThicknessChlNutrientsWater column stratification leads to nutrient depletion in surface layer. Consumption or sinking of phytoplankton crop means gr eater light penetration. Light and nutrients are both available at the bottom of the euphotic zone.Phytoplankton biomass accumulates there as a deep chlorophyll maximumThis situation is the