primary productivity and optics 19 july 2007 a primary productivity primer no answers; rather the...

Primary productivity and optics 19 July 2007

A primary productivity primer

No answers; rather the “basics” – so you can ask better questions or build your own model

Note: PP = primary productivity

Global annual estimates of PP:

Schroeder (1919) speculation 22 Pg C y-1

Steemann Nielsen (1952) 14C 20 Pg C y-1

Koblentz- Mishke (1968) 14C & mapping 23 Pg C y-1

Behrenfeld (2002) SeaWiFS & 14C 41 Pg C y-1

from Søndergaard in Williams, 2002

Ryther (1956) L&O 1:61classic empirical relationship between light field and chlorophyll concentration

A preliminary method is described for estimating absolute daily photosynthesis beneath a square meter of sea surface from measurement of (1) photosynthesis of a sample at light saturation, (2) extinction coefficient of light in the water, and (3) daily surface radiation.

Productivity – something created (units) per time per something (per individual, per chl molecule, etc.)

Primary producer – entity that creates something

Secondary producer– entity that transforms or repackages something

Primary Productivity in the ocean

* background: life in ocean is –C–C– based, both for energy and structure (lipids, protein, etc.)

* who are 1º producers? phytoplankton in broadest sense (oxygenic, oxygen-evolving, single-celled organisms) in ocean and green plants on land; also deep biosphere

* what is PP? PP is synthesis of new organic C (from CO2), either by photosynthesis or by chemolithotrophy (oxidation of a reduced chemical, like Fe+2, by some bacteria and archeae)

* what is photosynthesis?

CO2 + H2O ----> –(CH2O–) + O2

* what is photosynthesis? really a whole series of steps:

Initial step: capture of light by PS pigments; electron goes to excited state; transfer of the exciton (energy but not electron) from one molecule to another, ultimately to “reaction center” for charge separation and transfer of energized electron to a primary electron acceptor, Q. Lost chlorophyll electron is replenished by splitting water apart (forming H+ and O2).



Intermediate steps: series of redox reactions (Z scheme) leading to generation of ATP and NADPH+ –> that can be used by a number of reactions, including CO2 reduction.



Intermediate steps: series of redox reactions (Z scheme) leading to generation of ATP and NADPH+ –> that can be used by a number of reactions, including CO2 reduction.

Alternative final steps: C reduction via Calvin cycle (primer reaction that reduces CO2 and makes a C–C bond ), or NO3

- reduction, synthesis of other compounds like energy rich lipids, etc.

1. photon absorption by chlorophyll & accessory pigment

2. excitation transfer to reaction center

3. transmembrane charge separation to electron acceptor (plastoquinone or pre-ferrodoxin)

4a. electron transport leading to NADPH & P700+

4b. H+ gradient leading to ATP production

5. H2O splitting at PS II to regenerate electrons; O2 is by-product

6. ATP, NADPH used to reduce CO2, NO3-, etc.

Summary of Photosynthesis

http://www.bio.ic.ac.uk/research/barber/index.html

Summary: carbon fixation into new –C– is typically referred to as PP

Method question: should O2 production = –C– fixation (CO2 reduction)?which variable was basis for the PP model? for testing model?photosynthetic quotient = O2 evolved (range ~ 1.0 – 1.6)

C reduced

Optics question: what is relationship between rate of light absorption andrate of CO2 reduction?

PS = moles carbon fixed . moles photons absorbed

8 to 10 photons required to fix one –C–; if all photons went to PS, PS = 0.12 or 0.10 (theoretical PS–MAX); actually lower becauseof alternatives for absorbed photons ––> fluorescence & heat

But, several variants to the PP concept:

* Gross – total amount of new C (your theoretical paycheck)

* Net – amount of new C remaining after autotrophic energy requirements are met (after taxes & living expenses); this C is what is available to 2º producers and C-flux

* Community net – amount of new C remaining after heterotrophs consume some of it (your savings??)

Which PP is the basis of the model parameters?

Which PP is the desired model output?

What is integration period? hour? day? season? year?

What’s the nature of the food web? microloop? diatom bloom?

gross net community net










What is integration period? hour? day? season? year?

What’s the nature of the food web? microloop? diatom bloom?

Is there a difference in exportable or sequester-able C?



1. O2 – Winkler (1888) methodchanges in light and dark bottles

2. CO2 – pH sensitive dye, Hassuk (1888);not adapted for seawater until 1910’sreintroduced by Clayton and Byrne (1993)

3. 14C method – 1952 Steeman Nielsen

4. Probe fluorometry (pump and probe, PAM, FRRF)terms for PS electron flow model

# 1–3 require incubation; in situ, simulated in situ, P vs. E

To make results transportable (i.e., applicable to other data sets; usage in models), need to normalize rates to biomass (typically, chlorophyll a concentration or absorption – aps)

How do we measure rates of PS (photosynthesis)?

1. Changes in O2 in light/dark bottles (1916, Gran)

O2 in light = PS – respiration O2 in dark = respiration PS = light – dark

(note: “dark” is added back) (note: assumes dark respiration = light

respiration) For low biomass, need long incubations.Williams new method more sensitive.

Which term is gross PP? net PP? community net PP?

2. Changes in CO2 system; here as change in pH

(remove CO2 , pH increases – carbonate buffer)

Damariscotta River Estuary;Chlorophyll concentration ~ 3 g L-1

Does the change in pH reflect gross, net, community net PP?

3. Radio-labeled 14C incorporation (tracer method) – introduced by E. Steeman Nielsen in 1950

CO2 + H2O ---> -(CH2O)- + O2

12HCO3- 12C in new biomass

14HCO3-

14C in new biomass~

Known concentration of 14CKnown total dissolved inorganic C - from salinity / alkalinityMeasure 14C in particulate (and dissolved) after incubation

Calculate rate of production of new carbon

Patterns of 14C results:

surface photo inhibition

variability in rates (normalized to Chl)

compensation depth net PP = 0

Problems * dark bottle: subtract or not? (blank? carboxylation may occur)

* what does 14C measure?gross PP, net PP, or in between?

is “old” carbon respired for metabolic energy? short incubation - 14C measures closer to gross PS long incubation - 14C measures closer to net PS

Other issues with 14C* incubation – bottle conditions =/= ocean conditions (light level,

grazing, nutrient flux, temperature, surfaces, etc.; damage to

fragile organisms, including protozoan grazers)* duration (hours, dawn-to-dusk, 24 hours) * toxicity of 14C stock, collection and incubation bottles* CaCO3 of coccoliths (acidify) * dissolved organic carbon (lost through filter)

4. Probe fluorometry (pump and probe, PAM, FRRF) terms for PS electron flow model

Advantages: little or no incubation (light or dark adapted) can be in situ

Is it gross, net, or community net? What is the basis of the “calibration” data set?

Alternative ways to measure rates of PP (other than PS)?

production of new cellular biomass

– change in cell number (FCM), need Lagrangian framework

– change in biomass (in situ changes in beam c);

dP = Po [ - g -s +/- a] dt Gordon Riley

– cell cycling (% of cells in S, G2 phase); FDC

empirical (maximal) growth rates as function of environment

– upper limit to growth vs. temperature; vs. light

empirical growth rates as function of physiological index

– growth rate vs. internal nutrient cell quota

– pigment/cell as function of growth irradiance, invert

P E model (P vs. E, P vs. I)Pmax

Ek = Pmax/

Chlorophyll model --primary productivity normalized to biomass, B, where B is typically chlorophyll

PB = PBmax [1 - e ]

–(E * EK)

E = irradiance units of mole photon m-2 t-1

PBmax=maximal, light-saturated photosynthetic rate

normalized to chlorophyll concentration units of g C (g chl)-1 t-1

= slope of the P vs E cure units of g C (g chl)-1 t-1 (mole photon m-2 t-1)-1

EK = Pbmax / units of mole photon m-2 t-1

Ek vs depth: photadaptation

absorption cross section,from probe fluorescence

Bio-optical quantum yield model

PS = aPS * E * PS

where PS = moles product (C or O2) from slope of PE curve) moles photons absorbed by PS pigments = aps * E

NOTE: aps * E should be () and PS_MAX < 0.10

E

PS

0.1

What do you need to model PS bio-optically?

Z

PS = aPS * E * PS

PB = PBmax [1 – exp–(E * EK

-1)]

where “B” denotes Chl normalization

Behrenfeld, M., and P. Falkowski (1997).A consumer’s guide to phytoplankton primary productivity models. Limnology and Oceanography 42 (7), 1479–1491.

Carr et al. 2006 A comparison of global estimates of marine primary production from ocean color DSR II 53: 741

Third PP algorithm round robin (PPARR3) compares output from 24 models that estimate depth integrated primary production from satellite measurements of ocean color.

Compare global PP fields corresponding to eight months of 1998 and 1999 using common input fields of PAR, SST, MLD and Chl.

Global average PP varies by a factor of two among models. Models diverged most for the Southern Ocean, SST under 10 C, and chlorophyll concentration exceeding 1mg Chlm 3.

Further progress in primary production modeling requires improved understanding of the effect of temperature on photosynthesis and better parameterization of the maximum photosynthetic rate.

primary productivity and optics 19 july 2007 a primary productivity primer no answers; rather the...

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