Flux studies in contrasting environments (obj. 2)

The role of heterotrophy (bact. microzoo)

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

Specific objectives

Quantification of the carbon flux exported – Obj. 2.2-

ciliatescopepods

heterotrophic bacteria

picophytoplanktonnanophytoplankton

microphytoplankton

DOC

P, N

nanoflagellates

Silicates

CO2O2

O2CO2

Gross Communityproduction GCPand Dark CommunityRespiration DCR

? IRON ?

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

ciliatescopepods

heterotrophic bacteria

picophytoplanktonnanophytoplankton

microphytoplankton

DOC

P, N+ iron

nanoflagellates

Silicates

CO2O2

O2CO2

Gross Communityproduction GCPand Dark CommunityRespiration DCR

Direct effect of IRON on heterotrophs 1) Are bacteria Fe limited?

Is there changes in bacterial biomass, ectoenzymatic activities, production, respiration ?

ciliatescopepods

heterotrophic bacteria

picophytoplanktonnanophytoplankton

microphytoplankton

DOC

P, N + Fe

nanoflagellates

Silicates

CO2O2

O2CO2

Gross Communityproduction GCPand Dark CommunityRespiration DCR

Indirect effects of IRON on microbial food web 1. Is the response of the microbial food web a cascade effect from Phytoplankton stimulation?

What is the fate of the phytoplankton ?Phytoplankton growth phytoplankton grazing rates, abundance of predators, relations between predators?

?

? grazing ?sinking ?

ciliatescopepods

heterotrophic bacteria

picophytoplanktonnanophytoplankton

microphytoplankton

DOC

nutrients

nanoflagellates

Silicates

CO2O2

O2CO2

Gross Communityproduction GCPand Dark CommunityRespiration DCR

Heterotrophy and remineralisation Indirect effects of IRON on microbial food web: 2. Do bacteria benefit from the carbon derived from Fe stimulated primary production?

Does the Fe fertilization influence- the production and respiration of bacterioplankton and consequently the BGE ?- the factors limiting bacterial activity (Fe vs DOC)

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

Tools for studying biomasses

1. Structure of the food web in terms of stocks

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 fluxesUse of fluorescent labelled preysFluorescent labelled bacteria for bacterial grazing by flagellatesFluorescent labelled algae for grazing of nanophytoplankton by ciliates.

Tools for studying fluxes

2. Fluxes

FLS (fluorescently labelled Synechococcus)Synechococcus analog

FLS

FLA (fluorescently labelled algae, Rublee & Gallegos 1989)Nanophytoplankton analog

FLA Nanochloropsis sp. (2-4 μm)

Grazing of pico and nanoautotrophs by ciliates

Tools for studying fluxes

M2

D6

D5D4D3D2

D1

A5

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

Sampling strategy

In situ

Profiles : standing stocks and BP, O2/CO2 fluxesSurface 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 mlO2/CO2 fluxes : Grazing bact, nanophyto (surface only) : 2 litres Growth (cil, flag, surface only): 10 lt

on-board experiments

Process studies:Effect of Iron limitation on microbial food webs

OBEX 1 : microb comm. growth, on-board experimentsResponse 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?

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 ?