Structuring factors and processes of microbial food webs in french alpine lakes Domaizon Isabelle Personnic S. Lepère C.* Dorigo U. Comte J. Duhamel S. Mbade Sene A. Sime Ngando T.* Debroas D.* Leberre B. Millery A. Perney P. Fontvieille D. Jacquet Stephan UMR 42 CARRTEL INRA Thonon les Bains - Université de Savoie Le Bourget du Lac * UMR CNRS 6023 Laboratoire Biologie des Protistes - Université Blaise Pascal Clermont II
GLOBAL OBJECTIVES
Assess diversity, diversity, dynamics, dynamics, and interactions to better understand functioning and structuring processes within microbial trophic food webs
and in fine understand global pelagic food web functioning
DYNAMICS DYNAMICS
Investigating the Dynamics and Trophic links of microbial communities Using ecosystemic approaches
DYNAMICS DYNAMICS Lake Geneva Picocyanobacteria
Depth (m)
10 20 0 2e+4 4e+4 6e+4 8e+4 1e+5
30 40
PE rich synechococcus spp. (cells.ml-1)
50
Heterotrophic Bacteria
Depth (m)
10 1e+6
20
2e+6
3e+6 4e+6
30 40
5e+6 6e+6 7e+6 8e+6 9e+6
Het. Bacteria (cells.ml-1)
50
Viruses
Depth (m)
10 20
Lake Geneva (Mesotrophic)
30 40
5e+7 1e+8 2e+8 2e+8
Viruses (part.ml-1)
50 Nov
May
Nov
2003
May
Nov
2004
May
Nov
2005
Bimonthly flow cytometric analysis at 8 depths between 0-50 meters
Altitude Length Max. Depth Area
372 m 72 km 309 m 585 km2
DYNAMICS DYNAMICS Lake Bourget Picocyanobacteria
Depth (m)
10 20 0 2e+4 4e+4 6e+4 8e+4 1e+5
30 40
PE rich synechococcus spp. (cells.ml-1)
50
Heterotrophic Bacteria
Depth (m)
10 1e+6
20
2e+6
3e+6 4e+6
30 40
5e+6 6e+6 7e+6 8e+6 9e+6
Het. Bacteria (cells.ml-1)
50
Viruses
Depth (m)
10 20 30 40
5e+7 1e+8 2e+8 2e+8
Viruses (part.ml-1)
50 Nov
May
Nov
2003
May
Nov
2004
May
Nov
2005
Bimonthly flow cytometric analysis at 7 depths between 0-50 meters
Lake Bourget (Mesotrophic) Altitude Length Max. Depth Area
232 m 18 km 147 m 45 km2
DYNAMICS DYNAMICS Lake Annecy Picocyanobacteria
Depth (m)
10 20 0 2e+4 4e+4 6e+4 8e+4 1e+5
30 40
PE rich synechococcus spp. (cells.ml-1)
50
Heterotrophic Bacteria
Depth (m)
10 20 1e+6 2e+6 3e+6 4e+6 5e+6
30 40
Het. Bacteria (cells.ml-1)
50
Viruses
Depth (m)
10 20 30 40
5e+7 1e+8 2e+8 2e+8
-1
Viruses (part.ml )
50 Nov
May
Nov
2003
May
Nov
2004
May
Lake Annecy (Oligotrophic) Nov
2005
Bimonthly flow cytometric analysis at 7 depths between 0-50 meters
Altitude Length Max. Depth Area
447 m 15 km 65 m 28 km2
DYNAMICS DYNAMICS
Low Inter annual variability in dynamics of microbial communities (cyanobacteria, heterotrophic bacteria, Virus Like Particles) with seasonal succession repeated from one year to another
Specificities linked to the trophic status of the systems : picocyanobacteria dynamics, microbes abundances , proportion of mixotrophic taxa … Maximal abundance of viruses in October suggesting a viral termination of bacterial blooms in autumn
heterotrophic bacterial Bactéries hétérotrophes/ml Flagellés pigmentés/m mai Mai
sept. Sept
janv. Janv
Prof (m)
10 20 30 20 40 60 80
40 50 Janv
ciliates Ciliés/ml Mai
Sept
Janv
Mai
Sept
Janv
JFMAMJJASONDJFMAMJJASONDJ 2004
2005
TROPHIC TROPHIC LINKS LINKS
=> Distinct periods were defined in the organisation of microbial communities
[H bact]
Comte et al, 2006
TROPHIC TROPHIC LINKS LINKS
Investigating Trophic Links and Structuring Factors Using experimental approaches 1. Predation impacts size – dependent trophic interactions were examined using a size fractionnation approach at various periods Principle : Truncate the food web at various predator sizes and measure the response of microbes
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