Phytoplankton: Nutrients and Growth

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

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

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

Michaelis-Menten Kinetics V is uptake rate V m is maximum V S is substrate concentration K s is the half- saturation constant Nutrient Concentration S (e.g.,  mol l -1 ) Uptake Rate V (e.g., pmol cell -1 h -1 ) VmVm Ks

cs/mm/mm/mmApplet.htmlhttp://cti.itc.virginia.edu/~cmg/Demo/kineti cs/mm/mm/mmApplet.html

EutrophicOligotrophic High V m high K s 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 V m low K s 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.

Monod Equation μ = μ max (S/(K s + S)) μ = specific growth rate (d-1) S = concentration of limiting nutrient (M) K s = Monod coefficient Environ/GrowPresent/monod.htmhttp:// Environ/GrowPresent/monod.htm

Droop Equation μ = μ’ max (1- (Q 0 /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) Q 0 = the minimum cell quota that will sustain growth

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. carbonnitrogenphosphorusphytoplankton 106 C : 16 N : 1 P

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

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 O 2 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

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

Phytoplankton and Productivity Habitats Currents Water Motion Upwelling Productivity

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

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

Ekman Spiral

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

AC C

Coastal Upwelling N Hemisphere S Hemisphere

Coastal Upwelling * * * * ☺ *

Range of annual PP in different regions Mean annual PP (g C/m 2 /yr) Continental Upwelling Continental shelf breaks Subarctic Oceans Anticyclonic gyres Arctic Ocean<50 Antarctic

Continental Shelf Break

BasinProductivityPercentage Pacific19.7 Pg C y Atlantic Indian Southern Arctic Med Global Global Productivity- by basin

Ocean Phytoplankton Biomass

Seasonal changes Spring Summer Fall Winter

Coastal Upwelling * * * * ☺

Global Annual Production47.5 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 Global Pigment/Productivity- by season *

Species succession within a bloom Small cells High growth rates Flagellates, small diatoms Larger diatoms, high K s Spiny forms (deter grazing) Flagellates, small diatoms Slower growing forms Dinoflagellates Auxotrophs motile Complete Nutrient depletion Cyanobacteria- N- fixers