Flux studies in contrasting environments (obj. 2)
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Flux studies in contrasting environments (obj. 2) The role of heterotrophy (bact. microzoo). Specific objectives. Quantification of the carbon flux exported – Obj. 2.2-. What is the impact of natural iron fertilization - On the structure of the microbial food web

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Flux studies in contrasting environments (obj. 2) The role of heterotrophy (bact. microzoo)

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Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

Flux studies in contrasting environments (obj. 2)

The role of heterotrophy (bact. microzoo)


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

Specific objectives

Quantification of the carbon flux exported – Obj. 2.2-

  • What is the impact of natural iron fertilization

  • - On the structure of the microbial food web

  • On the functioning of the microbial food web

  • On the fate of primary production

  • And

  • How the magnitude of carbon fluxes (grazing, mineralization)

  • is affected by iron availability ?

  • We will focus on two axes to differentiate heterotrophic responses

  • Direct vs indirect effects on heterotrophic bacteria,

  • DOC utilization and respiration

  • - Cascade effect on the trophic web


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

? IRON ?

? ? ? ? ? ? ? ?? ? ?? ? ?? ? ?? ?

O2

CO2

nanoflagellates

copepods

ciliates

Gross Community

production GCP

and Dark Community

Respiration DCR

DOC

heterotrophic

bacteria

picophytoplankton

nanophytoplankton

CO2

O2

microphytoplankton

P, N

Silicates


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

  • Direct effect of IRON on heterotrophs

  • Are bacteria Fe limited?

O2

CO2

nanoflagellates

copepods

ciliates

Gross Community

production GCP

and Dark Community

Respiration DCR

DOC

heterotrophic

bacteria

picophytoplankton

nanophytoplankton

CO2

O2

microphytoplankton

P, N

+ iron

Silicates

Is there changes in bacterial biomass, ectoenzymatic activities,

production, respiration ?


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

Indirect effects of IRON on microbial food web

1. Is the response of the microbial food web a cascade effect from

Phytoplankton stimulation?

O2

CO2

nanoflagellates

copepods

ciliates

Gross Community

production GCP

and Dark Community

Respiration DCR

?

grazing ?

sinking ?

DOC

heterotrophic

bacteria

picophytoplankton

nanophytoplankton

?

CO2

O2

microphytoplankton

P, N

+ Fe

Silicates

What is the fate of the phytoplankton ?

Phytoplankton growth  phytoplankton grazing rates, abundance of predators, relations between predators?


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

Heterotrophy and remineralisation

Indirect effects of IRON on microbial food web:

2. Do bacteria benefit from the carbon derived from Fe stimulated primary production?

O2

CO2

nanoflagellates

copepods

ciliates

Gross Community

production GCP

and Dark Community

Respiration DCR

DOC

heterotrophic

bacteria

picophytoplankton

nanophytoplankton

CO2

O2

microphytoplankton

nutrients

Silicates

Does the Fe fertilization influence

- the production and respiration of bacterioplankton and consequently theBGE ?

- the factors limiting bacterial activity (Fe vs DOC)


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

Tools for studying biomasses

1. Structure of the food web in terms of stocks

  • Heterotrophic and phototrophic nanoflagellates

  • - epifluorescence microscopy

  • - size classes

  • - biovolumes

  • - carbon equivalents

  • Ciliates

  • - formol/lugol fixation

  • - Sedimentation and counting on inverted microscope equipped for fluorescence

  • size classes / taxonomy

  • + with flow cytometry data (pico autotrophs, heterotrophic bacteria)

  • and the microphytoplankton mesozooplancton stocks


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

Tools for studying fluxes

2. Fluxes

Bacterial production

3H-leucine incorporation into proteins, with micro-centrifuge technique

Gross community production and Dark community respiration :

24h variations of O2 in Winkler flasks, in situ-simulated conditions (running water bathes and screens)

Bacterial ectoenzymatic activity

Hydrolysis of fluorogenic substrates (aminopeptidase, glucosidase)

Grazing fluxes

Use of fluorescent labelled preys

Fluorescent labelled bacteria for bacterial grazing by flagellates

Fluorescent labelled algae for grazing of nanophytoplankton by ciliates.


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

Tools for studying fluxes

Grazing of pico and nano

autotrophs by ciliates

FLS

FLS (fluorescently labelled

Synechococcus)

Synechococcus analog

FLA

Nanochloropsis sp. (2-4 μm)

FLA (fluorescently labelled algae,

Rublee & Gallegos 1989)

Nanophytoplankton analog


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

Sampling strategy

Where do we sample ?  across gradients

Vertical profiles

(euphotic zone – 0-200m)

Kerguelen Plateau A5

Open Sea D6

The transect

Plateau – Open Sea

5 stations D1 to D5

A5

D1

M2

D2

D3

D4

D5

D6


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

  • In situ

  • Profiles : standing stocks and BP, O2/CO2 fluxes

  • Surface layer : grazing, growth of heterotrophs

  • We need :

  • to sample at the same time of the day every profile

  • to coincide with PP (14C) rosette, nutrients, DOC profile, flow cytometry, bacterial taxonomy, FISH

  • Volumes necessary :

  • BP, stocks (HNAN/PNAN, ciliates) : 750 ml

  • O2/CO2 fluxes : Grazing bact, nanophyto (surface only) : 2 litres

  • Growth (cil, flag, surface only): 10 lt


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

on-board experiments

Process studies:

Effect of Iron limitation on microbial food webs

  • OBEX 1 : microb comm. growth, on-board experiments

  • Response of the microbial food web

  • Parameters to follow

  • - BP (all time points)

  • HNAN/PNAN, ciliates stocks (T0h, T final)

  • - grazing fluxes (T0h, Tfinal)

  • OBEX 4, OBEX 3

  • < 0,8 µm mesocosms in the dark?

  • Direct iron effect on bacteria

  • BP

  • O2 consumption  BGE (bacterial growth efficiency)

  • Other Collaborations?


Flux studies in contrasting environments obj 2 the role of heterotrophy bact microzoo

  • Which material which person in charge

  • Scintillation counter : Brest ? (Stéphane, Bernard ?)

  • Microcentrifuge (Urania ?, Markus ?)

  • Spectrofluorometer : possibly that desembarked after DYNAPROC ?

  • One Millipore filtration apparatus (France, LMGEM)

  • One Millipore filtration apparatus (Urania MREN ? Markus LOV ?)

  • - Inverted flux system (membranes 142 mm) (France, LMGEM)

  • Refrigerated incubators ? Do we need on board ?


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