Effects of increasing UV radiation on Arctic phyto-and bacterioplankton biogeochemical activity

Clara Ruiz-González, Martí Galí, Josep M.Gasol & Rafel Simó

Institut de Ciències del Mar (Barcelona, Spain)

Ozone depletion

Reduction of Arctic andAntarctic ice cover

Higher doses of UVR in polar regions

Marine bacteria are among the groups of plankton more susceptible to sunlight damage!

• Photochemical transformations of DOM

• Cellular damage

UVR (280-400nm) affects microbial activity through:

Direct damage Indirect damage

Direct absortionby biologicalmolecules

Formation ofreactive oxigenspecies or free radicals

ATOS project

July, 2007

5

712

19

AIM: Determine the role of natural sunlight on Arctic phyto- andbacterioplankton biogeochemical activity

DARK PAR PAR+UV DARK PAR PAR+UV

3H-leucine 35S-DMSP

Bacterial production

Bacterial abundance

Size fractionatedassimilation

MAR-FISH

CandN source S source

AIM: Determine the role of natural sunlight on Arctic phyto- andbacterioplankton biogeochemical activity

0

50

100

150

200

250

300

0

5

10

15

20

25

30

st5 st7 st12 st19

Tota

l UV

R(k

J/m

2)

Total radiation (MJ/m

2/day)

UVRTotal rad.

5

7

1219

0

1 106

2 106

3 106

4 106

0

10

20

30

40

50

60

70

80

St.5 St.7 St.12 St.19

Bact. ab. Bact. prod.

Cel

ls/m

l

pmol Leu/L h

0

10

20

30

40

0

10

20

30

40

st5 st7 st12 st19

Sal

inity

(psu

)

Salinity

Temp (ºC)

Fluorescence Temp(ºC

) & Fluorescence

Bloom of Phaeocystis!!

0

1 106

2 106

3 106

4 106

5 106

6 106

St.5 St.7 St.12 St.19

Bac

teria

l abu

ndan

ce(c

ells

/ml)

Bact. abundance

0

20

40

60

80

100

120

140

St.5 St.7 St.12 St.19

Bac

teria

l pro

duct

ion

(pm

ol L

eu/L

h)

Before and after 10 h exposure… DARKDARK

PARPAR

FULLFULL

Higher inhibition afterexposure to full light

Bact. production

Higher cell concentrationafter DARK incubation

Time 0Time 0

5 µm

0.2 µm

Size fractionated leucineassimilation

0

2

4

6

8

10

12

14

st5 st7 st12 st19

% a

ssim

ilate

d Le

u

DARKDARK

PARPAR

FULLFULL

0

2

4

6

8

10

12

14

st5 st7 st12 st19

% a

ssim

ilate

d Le

u

Phaeocystis sp.

0

1

2

3

4

5

6

st5 st7 st12 st19

% a

ssim

ilate

d D

MSP

DARKDARK

PARPAR

FULLFULL

5 µm

0.2 µm

Size fractionated DMSPassimilation

0

1

2

3

4

5

6

st5 st7 st12 st19

% a

ssim

ilate

d D

MSP

MICROAUTORADIOGRAPHY: detection of single cells active in the uptake ofone radiactive substrate by precipitation of silver grains from a photographic

emulsion around them

Algae Bacteria

+ FISH

… What is going on at the single cell level?

Specific hybridization ofbacteria with RNA-

targeted oligonucleotideprobes which label cells

fluorescently

MAR-FISH(Alonso & Pernthaler, 2005)

Silver grains = active cell

Bacterial community composition (Fluorescent in situ hybridization- FISH)

Gammaproteobacteria

Bacteroidetes

SAR11

Roseobacter

Other bacteriaB

5 7 12 19

A SAR11 dominated bacterial community!

Single cell activity (FISH + microautoradiography = MAR-FISH)

0

20

40

60

80

100

St.5 St.7 St.12 St.19

Leucine-Eub

% h

ybrid

ized

cel

ls a

ctiv

e in

leu

upta

ke

0

20

40

60

80

100

St.5 St.7 St.12 St.19

DMSP-Eub

% h

ybrid

ized

cel

ls a

ctiv

e in

DM

SP u

ptak

e

DARKDARK

PARPAR

FULLFULL

DARKDARK

PARPAR

FULLFULL

0

500

1000

1500

2000

2500

3000

DARKDARK

PARPAR

FULLFULL

Pseudonitzschia spp.

Phaeocystis sp.

Dinoflagellates

Navicula spp.

Other algae

DMSP assimilation in terms of silver grain area: different light responses!

µm2 sg

/ µm

2 ce

ll

Diatoms

Main conclusions

• UVR inhibited leucine uptake by bacteria either during exposure ofafter exposure to full sunlight

• No changes in bacterial community composition were found, butprobably after continued exposure phototolerant species would be selected

• Results on light effects on single cell bacterial activity were notconclusive probably due to early labeling of most of the cells:silvergrain area quantification needed!

• Most of the algae were very active in the uptake of the organiccompound DMSP!! (osmoheterotrophy)

• Light affected DMSP uptake by algae (PAR activation in diatomsand UV inhibition in the rest of the groups)

In a global warming scenario, ozone depletion, ice coverreduction and stronger stratification might all lead to increases in the UVR doses of the surface oceans

Since most of the energy and nutrients are channelled throughbacteria and algae, any potential effect of UV on them will leadultimately to changes in the productivity and elemental fluxes ofthe overall system

Implications…

In a global warming scenario, ozone depletion, ice coverreduction and stronger stratification might all lead to increases in the UVR doses of the surface oceans

Since most of the energy and nutrients are channelled throughbacteria and algae, any potential effect of UV on them will leadultimately to changes in the productivity and elemental fluxes ofthe overall system

Understanding and even predicting these changes requiresgaining knowledge of the sentitivity of microorganisms and theirassociated biogeochemistry to increased UVR doses

Implications…

THANK YOU!

ACKNOWLEDGMENTS

• Carlos Duarte (chief scientist of ATOS)

• Crew of R/V Hespérides

• Gerhard Herndl & Eva Sintes

• Renate Scharek & Dolors Vaqué