Biological N2 fixation in the Galician upwelling system: magnitude, relevance and main players

Víctor Moreira-Coello*, Beatriz Mouriño-Carballido, Emilio Marañón, Ana Fernández, Paloma Chouciño, Eva Sintes, Marta M. Varela & Antonio Bode

18 November 201614:45

Modified from Sohm et al., 2011

What is Biological Nitrogen Fixation?

Biological conversionN2 NH4

+

NH4+

Luo et al., 2012

Background

Tropical and subtropical regions

From TRYNITROP Project and www.whoi.edu

Trichodesmium sp.

Background

Background:evidences of N2 fixation in N-rich temperate regions

Upwelling region off NW Iberia, July 2009 (Benavides et al., 2011; Agawin et al., 2014)

Tropical and subtropical regions

1) To describe the seasonal variability of N2 fixation andquantify its biogeochemical relevance.

2) To characterize the diazotrophic community.

Our goals

Study area & Methods

MSS profiler

Hydrography

Hydrographic conditions

U: Upwelling (↑ Chl a, Bloom)

D: Downwelling (↑ Mixing)

R: Relaxation (↑ Stratification)

Mixed layer depth

Our goals

1) To describe the seasonal variability of N2 fixation andquantify its biogeochemical relevance.

2) To characterize the diazotrophic community.

N2 fixation similar to the lower-end of rates described for NASE

Downwelling Upwelling Relaxation

Depth

-Inte

gra

ted N

2fixation r

ate

s

(µm

ol m

-2d

-1)

Seasonal variability of N2 fixation

2.5

2

1.5

1

0.5

0

Depth

-Inte

gra

ted N

2fixation r

ate

s

(µm

ol m

-2d

-1)

2.5

2

1.5

1

0.5

0

Seasonal variability of N2 fixation and biogeochemical role

Downwelling Upwelling Relaxation

14

16

Contr

ibution

tonew

N

(%)

Our goals

1) To describe the seasonal variability of N2 fixation andquantify its biogeochemical relevance.

2) To characterize the diazotrophic community.

Principal Coordinate Analysis

Diazotrophic community composition

Principal Coordinate Analysis

Relaxation

Diazotrophic community composition: clusters

Bray-Curtis similarity

50%

Downwelling

Upwelling

Diazotrophic community composition

Relaxation

Downwelling

Upwelling

UCYN-A1 and UCYN-A2 abundance (nifH copies L -1)

Upwelling

Downwelling

(14%)

(14%)38

Relaxation

1) N2 fixation slightly higher during relaxation (0.1–2.5 µmol N m-2 d-1 ).

2) Minor biogeochemical role (< 14%).

3) Seasonal variability in diazotrophic community:

‒ UCYN-A2: Relaxation-Stratification.

‒ Heterotrophic bacteria: Downwelling-Mixing.

‒ Similar contribution of both groups: Upwelling-Bloom.

Conclusions

Acknowledgments:

FPU fellowship to V.M. from Spanish Ministry of Education,

Culture and Sports (FPU13/01674).

Study supported by projects NICANOR from Xunta de Galicia

(EM2013/021, Galician Government) and RADIALES (IEO).

Thank you for your attention!

Contact the author Víctor Moreira: vmoreira@uvigo.es