Phytoplankton: Nutrients and Growth

1. Phytoplankton: Nutrients and Growth

2. Outline • Growth • Nutrients • Limitation • Physiology • Kinetics • Redfield Ratio (Need to finish today) • Critical Depth (Sally will cover)

3. Nutrient Physiology • Enzyme – controlled • Assimilation : involves - Uptake (transport across membrane) - Reduction before incorporated into organic molecules • Rates dependent upon concentration of nutrients • Nutrient uptake subject to saturation

4. Light and Nutrient Limitation • If light is available, nutrients are consumed by phytoplankton until a limit is reached. • Example: spring bloom in temperate waters North Atlantic: Pronounced spring bloom, often a fall bloom

5. Uptake Rate V (e.g., pmol cell-1 h-1) Nutrient Concentration S (e.g., mmol l-1) Michaelis-Menten Kinetics Vm • V is uptake rate • Vm is maximum V • S is substrate concentration • Ks is the half-saturation constant Ks

6. http://cti.itc.virginia.edu/~cmg/Demo/kinetics/mm/mm/mmApplet.htmlhttp://cti.itc.virginia.edu/~cmg/Demo/kinetics/mm/mm/mmApplet.html

7. High Vm high Ks dominated by one or 2 fast-growing, r-selected phytoplankton species Opportunistic species, live in variable, unpredictable environments Respond quickly to favorable conditions - Bloom and bust cycles Diatoms - form resting spores when environmental conditions are bad, cell becomes hard and sinks to the bottom Low Vm low Ks many competing k-selected species Constant, predictable nutrient supply, slow-growing, long lived Utilize resources efficiently, each species dependent of a different limiting nutrient – the community tends to be in equilibrium with the total nutrient supply Phyto can take up nitrate or ammonium at ambient concentrations. Photosynthetic dinos - migrate to deeper layers where nutrients are more abundant - toward the nutricline, the zone where nutrient concentrations increase rapidly with depth. Take nutrients into their cell & return to sunlite waters to carry out PS. Eutrophic Oligotrophic

8. Monod Equation • μ = μmax (S/(Ks + S)) μ = specific growth rate (d-1) S = concentration of limiting nutrient (M) Ks = Monod coefficient • http://www.rpi.edu/dept/chem-eng/Biotech-Environ/GrowPresent/monod.htm

9. Droop Equation • μ = μ’max (1- (Q0/Q)) • μ = specific growth rate (d-1) • μ’max = the growth rate at Q ==infinity • Q = cell quota of the limiting nutrient (total within cell) • Q0 = the minimum cell quota that will sustain growth

10. Stoichiometry of Growth • Elemental composition of the planktonic community – A.C. Redfield (1934) • This reflects • how elements are taken from the water column during primary production • phytoplankton have elemental ratios/molar ratio • Redfield ratio or Redfield stoichiometry is the molecular ratio of carbon, nitrogen and phosphorus in phytoplankton. 106 C : 16 N : 1 P

11. Redfield Ratio Utility: If you know 1 elemental uptake rate, others can be estimated because the constant relationship. Important Assumption (usually not met): Balanced Growth (all elements taken up at same rate at same time - not realistic). • Factors affecting Redfield: • Timing • Cell condition • Growth rate • Nutrient availability

12. Applications of the Redfield Ratio • Health of the organismal community: if growth is less than optimal, C:X goes up. • AOU: Apparent Oxygen Utilization:Deficit in O2 compared to saturation … indicates how much biomass increased over a long period of time. • Modeling: In computer models of the carbon cycle, you trace one element (i.e. nitrogen) and assume how carbon goes based on the ratio

13. Given that the photosynthetic machinery is so conserved among plants and algae in the sea, then why is diversity so high? Moreover, given the special adaptations for light and nutrient acquisition in the sea, why do you still see high diversity at any single point in time and space? Expect competitive exclusion: G. Evelyn Hutchinson’s Paradox of the Plankton

14. Phytoplankton and Productivity Habitats Currents Water Motion Upwelling Productivity

15. What affects values of PP? • Light • Nutrients • Seasonal and Global variations in PP

16. Aquatic Habitats (Horizontal) Polar High Latitude High Latitude Coastal Subtropical Gyre Subtropical Gyre Coastal Equatorial Equatorial Coastal Coastal Subtropical Gyre Subtropical Gyre Subtropical Gyre High Latitude Temperate Polar

18. Ekman Spiral

19. Eastern – Canary, California Western – Gulf Stream, Kuroshio, W E

20. C AC AC

22. Coastal Upwelling N Hemisphere S Hemisphere

23. Coastal Upwelling * * * * * ☺

24. Range of annual PP in different regions Mean annual PP (g C/m2/yr) • Continental Upwelling 500-600 • Continental shelf breaks 300-500 • Subarctic Oceans 150-300 • Anticyclonic gyres 50-150 • Arctic Ocean <50 • Antarctic 50-200

25. Continental Shelf Break

27. Global Productivity- by basin Basin Productivity Percentage Pacific 19.7 Pg C y-1 42.8 Atlantic 14.5 31.5 Indian 8.0 17.3 Southern 2.9 6.3 Arctic 0.4 0.9 Med. 0.6 1.2 Global 46.1 100

28. Ocean Phytoplankton Biomass

29. Seasonal changes Fall Winter Spring Summer

30. Coastal Upwelling * * * * ☺

31. Global Pigment/Productivity- by season Global Annual Production 47.5 Pg C y-1 Seasonal Prod.: March-May 10.9 Seasonal Prod.: June-Aug. 13.0 Seasonal Prod.: Sept.-Nov. 12.3 Seasonal Prod.: Dec.-Feb. 11.3 *

32. Species succession within a bloom 1 2 3 4 Small cells High growth rates Flagellates, small diatoms Slower growing forms Dinoflagellates Auxotrophs motile Larger diatoms, high Ks Spiny forms (deter grazing) Flagellates, small diatoms Complete Nutrient depletion Cyanobacteria- N- fixers