Download DOC

Flux studies in contrasting environments (obj. 2)
The role of heterotrophy (bact. microzoo)
Specific objectives
Quantification of the carbon flux exported – Obj. 2.2What 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
? IRON ?
? ? ? ? ? ? ? ?? ? ?? ? ?? ? ?? ?
O2
CO2
nanoflagellates
Gross Community
production GCP
and Dark Community
Respiration DCR
CO2
O2
copepods
ciliates
DOC
heterotrophic picophytoplankton
bacteria
nanophytoplankton
microphytoplankton
P, N
Silicates
Direct effect of IRON on heterotrophs
1) Are bacteria Fe limited?
O2
CO2
nanoflagellates
Gross Community
production GCP
and Dark Community
Respiration DCR
CO2
O2
copepods
ciliates
DOC
heterotrophic picophytoplankton
bacteria
nanophytoplankton
microphytoplankton
P, N
+ iron
Silicates
Is there changes in bacterial biomass, ectoenzymatic activities,
production, respiration ?
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
Gross Community
production GCP
and Dark Community
Respiration DCR
CO2
O2
copepods
ciliates
grazing ?
sinking ?
?
DOC
heterotrophic picophytoplankton
bacteria
nanophytoplankton
?
P, N
+ Fe
microphytoplankton
Silicates
What is the fate of the phytoplankton ?
Phytoplankton growth  phytoplankton grazing rates, abundance of
predators, relations between predators?
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
Gross Community
production GCP
and Dark Community
Respiration DCR
CO2
O2
copepods
ciliates
DOC
heterotrophic picophytoplankton
bacteria
nanophytoplankton
microphytoplankton
nutrients
Silicates
Does the Fe fertilization influence
- the production and respiration of bacterioplankton and consequently the BGE ?
- the factors limiting bacterial activity (Fe vs DOC)
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
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.
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
Sampling strategy
Where do we sample ?
 across gradients
Vertical profiles
(euphotic zone – 0-200m)
Kerguelen Plateau A5
Open Sea D6
A5
The transect
Plateau – Open Sea
5 stations D1 to D5
D1
M2
D2
D3
D4
D5
D6
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
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?
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 ?