Primary Productivity & Phytoplankton Growth

1. Primary Productivity&Phytoplankton 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

2. The co-occurrence of light and nutrients explainspatterns 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

3. The ocean accounts for half the photosynthesis on earth • Phytoplankton are responsible for 90-96% of marine primary production • Seaweeds contribute ~ 2-5% • Chemosynthetic organisms ~2-5%

4. Global view of primary production: https://www.youtube.com/watch?v=qgG_nAJHW6I

5. 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 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

6. 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)

7. Photosynthesis Info https://www.youtube.com/watch?v=joZ1EsA5_NY 1min 30 - 6min 17

8. sunlight water uptake carbon dioxide uptake ATP ADP + Pi LIGHT DEPENDENT REACTIONS LIGHT INDEPENDENT REACTIONS NADPH (thylakoid) (stroma) NAD+ NADP+ P glucose oxygen release new water Photosynthesis occurs in two stages: The Light-Dependent & the Light-Independent Reactions

9. Z scheme second transfer chain e– NADPH e– first transfer chain Potential to transfer energy (volts) e– e– (Photosystem I) (Photosystem II) 1/2 O2 + 2H+ H2O The “Z scheme” of non-cyclic electron flow

10. 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

11. 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, mmol m-2s-1); light history • Nutrient concentration (status); nutrient history • Temperature • Level of acclimation

12. A Cycle of Life and Death Surface Ocean Light + Nutrients Phyto Growth Zoop Consumption Nutrients  Decomposition Deep Sea Bottom

13. m (d-1) The growth rate of phytoplankton depends on light, nutrients and temperature m (d-1)

14. How much is there? (intensity) What color is it? (spectral quality) What you REALLY need to know about light in the ocean:

15. Why Light is Important Provides energy for almost all marine food webs Photosynthesis 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 Light in the Ocean

16. What happens to light in aquatic environments? Reflected Absorbed Scattered Inherent Optical Properties

17. Availability of Light in Water: Light Intensity (I) Coefficient of extinction (length) Iz = I0e-Kz Light @ depth (z) Light @ surface Low High Water surface • Importance of K: • Kdefines the depth of the euphotic zone (i.e. growth barrier) • Operationally: 1% surface irradiance • Ecologically: zone of sufficient light for phytoplankton to grow Depth (z) A higher Kd meansmore light is attenuated with depth, hence a shallowereuphotic zone. Deep

18. Relative Irradiance • 0 • . • 0 • 0 • 0 • . • 2 • 0 • 0 • . • 4 • 0 • 0 • . • 6 • 0 • 0 • . • 8 • 0 • 1 • . • 0 • 0 • 0 • . • 0 • 0 • 2 • 0 • . • 0 • 0 • ) • m • 4 • 0 • . • 0 • 0 • ( • h • t • p • e • 6 • 0 • . • 0 • 0 • D • 8 • 0 • . • 0 • 0 • 1 • 0 • 0 • . • 0 • 0 • The color spectrum of light varies with depth • Blue light penetrates deep; red light is attenuated quickly • Depth of light penetration is affected by particles and dissolved substances in the water • Euphotic Zone = from surface to the depth of 1% or 0.1% of surface irradiance

19. chlorophyll b chlorophyll a chlorophyll a chlorophyll b carotenoids phycoerythrin (a phycobilin) phycocyanin (a phycobilin)

20. Rhodomonas salina 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. Some chemotaxonomic photosynthetic pigments *All phytoplankton *Chlorophyll a Chlorophytes Chlorophyll b Cryptophytes Alloxanthin DiatomsFucoxanthin Dinoflagellates Peridinin Cyanobacteria Zeaxanthin

21. 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

22. 6 B Surface 5 75 m 4 PB (g C g Chl-1 h-1) 25m 3 2 1 100 m 0 0 500 1000 1500 2000 Irradiance (mmol m-2 s-1) 6 C 70 m P vs E curves and mixing • 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)

23. Sverdrup's Model of Critical Depth • Photosynthesis decreases exponentially with depth due to decrease in light availability • Respiration is unaffected by light and remains constant with depth • Phytoplankton are mixed by turbulence and experience different light intensities over time, sometimes above and sometimes below compensation point • Critical depth = depth at which photosynthesis of the total water column phytoplankton population equals their total respiration (no net community production)

24. Productivity and depth Why the difference in distribution???

25. 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

26. Redfield Ratio NPP is always referred to in terms of C and N…How do we really go back and forth? Nutrients <=> Production Living organism (particulate debris) in seawater have similar overall compositions Average net plankton (>64m 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

27. Fundamental Paradigm of Primary Production in the Surface 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 How do we define export in the ocean? 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

28. N2 fixation Ammonification PON and DON Ammonification New production = Export production

29. Common in subtropical gyres and oligotrophic regions Ammonium is the major N source P pico = picophytoplankton (e.g. Synecococcus, Prochlorococcus)) 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) Sarmiento and Gruber, 2006

30. Nutrient fluxes in the open ocean Surface ocean • TheBIOGEOCHEMICAL FUNCTION of plankton: mediate depletion and fluxes of nutrients from surface waters • The Redfield Ratio • 106 C : 16 N : 1 P Biology recycling uptake sinking mixing • What about trace metals? remineralization Deep ocean (Morel 2008)

31. An ‘extended Redfield ratio’

32. Metalloproteins in phytoplankton Metal Compound Function Fe Cytochromes Electron transport in photosyn./respiration Fe-S proteins Electron transport in photosyn./respiration Nitrate reductase NO3- assimilation Chelatase Porphyrin and phycobiliprotein synthesis Nitrogenase N fixation Mn O2-evolving enzyme Oxidize H2O to O2 during photosyn. Superoxide dismutase Convert O2·-to H2O2 Cu Plastocyanin Photosynthesis electron transport Cytochrome c oxidase Mitochondrial electron transport Zn Carbonic anhydrase Hydration and dehydration of CO2 Alkaline phosphatase Hydrolysis of phosphate esters DNA/RNA polymerase Nucleic acid replication/transcription Co Vitamin B12 Carbon and H transfer reactions Ni Urease Hydrolysis of urea Superoxide dismutase Convert O2·-to H2O2 Hydrogenase Oxidation of H2 Mo Nitrogenase Nitrogen fixation Nitrate reductase Nitrate reduction to ammonia Likely many more yet to be discovered

33. Light & Nutrients Synergism Nutrient-replete Nutrient-starved Richardson, Ciotti, Cullen & Lewis (1996)

35. The impacts of temperature on Primary Production 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. Thermophiles Photosynthesis Summer species Winter species Temperature

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

37. The Growth of Phytoplankton(surface layer of the ocean) DaughterCell Cell Division Photosynthesis Doubled Biomass Single Cell Daughter Cell Nutrient Uptake Result: • Moresuspended particulate organic matter (food) • Lessdissolved inorganic nutrients (N, P, Si) • Lessdissolved inorganic carbon (CO2) (from John Cullen)

38. The Growth of Phytoplankton(surface layer of the ocean) Fates: Accumulate (Bloom) Be eaten Sink Blow up (viruses) Apoptosis DaughterCell Daughter Cell

39. Unfettered growth of phytoplankton m• t = N N e • t 0 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)

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

41. Phytoplankton Counting Methods