17 research outputs found
Nitrogen fixation in the upwelling region off NW Iberia
Comunicación oralPicoplankton are the most abundant organisms in the ocean, often dominate planktonic biomass and primary production, and they could represent a substantial contribution to the global export of carbon. Nowadays, we have a limited understanding about the factors that control the picoplankton community structure. A recent analysis indicates that light and temperature are the main factors explaining Prochlorococcus and Synechococcus distributions, whereas nutrient concentrations play a minor role (Flombaum et al., PNAS 2013). Methodological difficulties to quantify mixing in the marine enviroments have motivated the use of indirect approaches to determine the input of nutrients into the euphotic zone, however, nutrient concentrations are not necessarily a proxy of nutrient supply. We present a large data set, including open-ocean and coastal regions, of simultaneous measurements of picoplankton abundance, temperature and irradiance, together with estimates of nutrient supply. The transport of nutrients across the nutricline was computed combining nutrient concentrations and small-scale turbulence observations collected with a microstructure profiler. Our preliminary results indicate that nutrient supply also plays a role in the distribution of functional groups of picoplankton in the ocean
Short term variability of bacterial communities in the shelf waters off Galicia (NW Iberian Peninsula): Patterns and drivers shaping the diversity
PósterEcological and biogeochemical processesEcological and biogeochemical processes in the ocean are dependent on a diverse assemblage of microbes, including members of Bacteria (Glöckner et al, 2012). These bacterial assemblages occurs in vast numbers and represent a huge genetic diversity, fulfilling a wide of ecological roles in the marine system such as carbon geochemical cycle and energy transfer into higher trophic levels.We combined flow cytometry, CARD-FISH and 16S rRNA gene tag pyrosequencing to investigate the short-term variability of the bacterial communities in samples collected along a transect in the shelf off NW Iberian Peninsula over one week
Control of tHe structure of marine phytoplAnkton cOmmunities by turbulence and nutrient supply dynamicS (CHAOS)
extended abstract del posterIn order to investigate the role of turbulence mixing on structuring marine phytoplankton communities, the CHAOS project included a multidisciplinary approach involving specifically designed field observations supported by remote sensing, database analyses, and modeling and laboratory chemostat experiments. Field observations carried out in the outer part of Ría de Vigo in summer 2013 showed that, as a result of increased mixing levels, nitrate diffusive input into the euphotic layer was approximately 4-fold higher during spring tides. This nitrate supply could contribute to explain the continuous dominance of large-sized phytoplankton during the upwelling favorable season. Simultaneous estimates of nitrate diffusive fluxes, derived from microturbulence observations, and picoplankton abundance collected in more than 100 stations, spanning widely different hydrographic regimes, showed that the contribution of eukaryotes to picoautotrophic biomass increases with nutrient supply, whereas that of picocyanobacteria shows the opposite trend. These findings were supported by laboratory and modeling chemostat experiments that reproduced the competitive dynamics between picoeukaryote and picocyanobacteria as a function of changing nutrient supply. The results derived from this project confirm that turbulence and mixing control the availability of light and nutrients, which in turn determine the structure of marine phytoplankton communities.RADIALES-20 (IEO), CHAOS (CTM 2012-30680), Malaspina-2010(CSD2008-00077
Nutrient supply does play a role on the structure of marine picophytoplankton communities
Conference communicationThe Margalef´s mandala (1978) is a simplified bottom-up control model that explains how mixing and nutrient concentration determine the composition of marine phytoplankton communities. Due to the difficulties of measuring turbulence in the field, previous attempts to verify this model have applied different proxies for nutrient supply, and very often used interchangeably the terms mixing and stratification. Moreover, because the mandala was conceived before the discovery of smaller phytoplankton groups (picoplankton <2 µm), it describes only the succession of vegetative phases of microplankton. In order to test the applicability of the classical mandala to picoplankton groups, we used a multidisciplinary approach including specifically designed field observations supported by remote sensing, database analyses, and modeling and laboratory chemostat experiments. Simultaneous estimates of nitrate diffusive fluxes, derived from microturbulence observations, and picoplankton abundance collected in more than 200 stations, spanning widely different hydrographic regimes, showed that the contribution of eukaryotes to picoautotrophic biomass increases with nutrient supply, whereas that of picocyanobacteria shows the opposite trend. These findings were supported by laboratory and modeling chemostat experiments that reproduced the competitive dynamics between picoeukaryote sand picocyanobacteria as a function of changing nutrient supply. Our results indicate that nutrient supply controls the distribution of picoplankton functional groups in the ocean, further supporting the model proposed by Margalef.Spanish Governmen
Biological N2 fixation in the upwelling region off NW Iberia: magnitude, relevance and abundance of diazotrophs.
The classical paradigm about marine N2 fixation establishes that this process is mainly constrained to nitrogen-poor tropical and subtropical regions, and sustained by the colonial cyanobacterium Trichodesmium spp. and diatom-diazotroph symbiosis. However, the application of molecular techniques allowed determining a wide distribution and high phylogenic diversity of marine diazotrophs, which extends the range of marine environments where biological N2 fixation may be relevant. Between February 2014 and December 2015, we carried out 10 one-day samplings in the upwelling system off NW Iberia in order to: 1) investigate the seasonal variability in the magnitude of N2 fixation, 2) determine its biogeochemical role as a mechanism of new nitrogen supply, and 3) quantify the main diazotrophs in the region under contrasting hydrographic regimes. Our results indicate that the magnitude of N2 fixation in this region was relatively low (0.001±0.002 – 0.095±0.024 µmol N m-3 d-1), comparable to the lower-end of rates described for the subtropical NE Atlantic. Maximum rates were observed at surface during both upwelling and relaxation conditions. The comparison with nitrate diffusive fluxes revealed the minor role of N2 fixation (<2%) as a mechanism of new nitrogen supply into the euphotic layer. Small diazotrophs (<10 µm) were responsible for all N2 fixation activity detected in the region. Quantitative PCR targeting the nifH gene revealed the highest abundances of two sublineages of UCYN-A (UCYN-A1 and UCYN-A2) mainly at surface waters during upwelling and relaxation conditions, and of Gammaproteobacteria γ-24774A11 at deep waters during downwelling. Maximum abundance for the three groups were up to 6.7 × 102, 1.5 × 103 and 2.4 × 104 nifH copies L-1, respectively. Our findings demonstrate measurable N2 fixation activity and presence of diazotrophs throughout the year in a nitrogen-rich temperate region.This work was funded by the NICANOR project (Galician Government, EM2013/021) granted to Beatriz Mouriño-Carballido and by the RADIALES project of the Instituto Español de Oceanografía (www.seriestemporales-ieo.com). Víctor Moreira-Coello was supported by a FPU predoctoral fellowship from the Spanish Ministry of Education, Culture and Sports (FPU13/01674).En prens
Nitrogen fixation and diffusive fluxes in the upwelling region off NW Iberia.
extended abstractThe classical paradigm about m rine N2-fixation establishes that this
process is
mainly constrained to
oligotrophic tropical
and subtropical regions and attributed
mostly to the cyanobacterium Trichodesmium.
However, the development of molecular techniques led to the discovery of a larger variety
of marine
diazotrophs, which extends the range of environments where N2-fixation may be relevant. Between February 2014 and December 2015 we carried out 16 cruises in the upwelling ecosystem off NW Iberia with the following goals: 1) to quantify the magnitude of N2-fixation, 2) to investigate its biogeochemical role as mechanism of new
nitrogen
supply, and
3) to identify and quantify the main diazotrophs in the region under contrasting
hydrographic regimes. Our results indicate that the magnitude of N2-fixation in this region is comparable to the lower-end of rates described for subtropical regions. All the N2-fixation activity was detected in the smaller- sized (<10µm) fraction. The comparison with nitrate diffusive fluxes reveals the minor role of this process (<1%) as a mechanism of new nitrogen supply into the productive euphotic layer. Results obtained through phylogenetic analyses by Illumina® (NGS) show that the composition of the diazotrophic community presents a seasonal variability depending on hydrographic conditions. Additional expe iments carried out in the field and in the lab demonstrate that 15N-labeled contaminants included in some commercial 15N2 stocks are assimilable by non-diazotrophs organisms. This could result in an up to 15-fold overestimation of N2-fixation rates. Overall, our findings support the emerging view that mesotrophic regions should be considered in global budgets of marine N2-fixation.RADIALES-20 (IEO), NICANOR (Xunta de Galicia, EM2013/021
Quantifying the overestimation of planktonic N2 fixation due to contamination of 15N2 gas stocks
The 15N2-tracer assay [Montoya et al. (1996) A simple, high-precision, high-sensitivity tracer assay for N2 fixation.
Appl. Environ. Microbiol., 62, 986–993.] is the most used method for measuring biological N2 fixation in terrestrial and
aquatic environments. The reliability of this technique depends on the purity of the commercial 15N2 gas stocks used.
However, Dabundo et al. [(2014) The contamination of commercial 15N2 gas stocks with 15N-labeled nitrate and 142
ammonium and consequences for nitrogen fixation measurements. PLoS One, 9, e110335.] reported the contamination
of some of these stocks with labile 15N-labeled compounds (ammonium, nitrate and/or nitrite). Considering that the
tracer assay relies on the conversion of isotopically labeled 15N2 into organic nitrogen, this contamination may have led
to overestimated N2 fixation rates. We conducted laboratory and field experiments in order to (i) test the susceptibility
of 15N contaminants to assimilation by non-diazotroph organisms and (ii) determine the potential overestimation of
the N2 fixation rates estimated in the field. Our findings indicate that the contaminant 15N-compounds are assimilated
by non-diazotrophs organisms, leading to an overestimation of N2 fixation rates in the field up to 16-fold under
hydrographic conditions of winter mixing
Biological N2 fixation in the upwelling region off NW Iberia: magnitude, relevance and main players
Conference communicationThe classical paradigm about marine N2 fixation establishes that this process is mainly constrained to oligotrophic tropical and subtropical regions, and attributed mostly to the filamentous cyanobacterium Trichodesmium. However, the development of molecular techniques led to the discovery of a larger variety of marine diazotrophs, which extends the range of environments where N2 fixation may be relevant. Between February 2014 and December 2015 we carried out 10 cruises in the upwelling ecosystem off NW Iberia in order to: 1) quantify the magnitude of N2 fixation, 2) investigate its biogeochemical role as a mechanism of new nitrogen supply, and 3) identify and quantify the main diazotrophs in the region under contrasting hydrographic regimes. Our results indicate that the magnitude of N2 fixation in this region is comparable to the lower-end of rates described for subtropical regions. The comparison with nitrate diffusive fluxes reveals the minor role of N2 fixation (<5%), as a mechanism of new nitrogen supply into the productive euphotic layer. All the N2 fixation activity was detected in the smaller-sized (<10μm) fraction. Results obtained through phylogenetic analyses by Illumina® (NGS technology) show that the diazotrophic community was dominated by UCYN-A (the most abundant sublineage UCYN-A2), bacteria from Class γ-Proteobacteria and from Phylum Firmicutes. However, the diazotrophic community composition exhibited an important seasonal variability, being the highest diversity associated with autumn and winter mixing and downwelling conditions. Overall, our findings support the emerging view that mesotrophic regions should be considered in global budgets of marine N2 fixation.Xunta de Galicia (EM2013/021
Factors controlling the community structure of picoplankton in contrasting marine environments
22 pages, 4 tables, 5 figuresThe effect of inorganic nutrients on planktonic assemblages
has traditionally relied on concentrations rather
than estimates of nutrient supply. We combined a novel
dataset of hydrographic properties, turbulent mixing, nutrient
concentration, and picoplankton community composition
with the aims of (i) quantifying the role of temperature, light,
and nitrate fluxes as factors controlling the distribution of autotrophic
and heterotrophic picoplankton subgroups, as determined
by flow cytometry, and (ii) describing the ecological
niches of the various components of the picoplankton
community. Data were collected at 97 stations in the Atlantic
Ocean, including tropical and subtropical open-ocean waters,
the northwestern Mediterranean Sea, and the Galician coastal
upwelling system of the northwest Iberian Peninsula. A generalized
additive model (GAM) approach was used to predict
depth-integrated biomass of each picoplankton subgroup
based on three niche predictors: sea surface temperature, averaged
daily surface irradiance, and the transport of nitrate
into the euphotic zone, through both diffusion and advection.
In addition, niche overlap among different picoplankton
subgroups was computed using nonparametric kernel density
functions. Temperature and nitrate supply were more
relevant than light in predicting the biomass of most picoplankton
subgroups, except for Prochlorococcus and lownucleic-
acid (LNA) prokaryotes, for which irradiance also
played a significant role. Nitrate supply was the only factor
that allowed the distinction among the ecological niches
of all autotrophic and heterotrophic picoplankton subgroups.
Prochlorococcus and LNA prokaryotes were more abundant
in warmer waters ( > 20 C) where the nitrate fluxes were
low, whereas Synechococcus and high-nucleic-acid (HNA)
prokaryotes prevailed mainly in cooler environments characterized
by intermediate or high levels of nitrate supply. Finally,
the niche of picoeukaryotes was defined by low temperatures
and high nitrate supply. These results support the
key role of nitrate supply, as it not only promotes the growth
of large phytoplankton, but it also controls the structure of
marine picoplankton communitiesThis research was supported by the Spanish Ministry of
Economy and Competitiveness (MINECO) through projects
CTM2012-30680 to Beatriz Mouriño, CTM2008-0626I-C03-01
to Mikel Latasa, REN2003-09532-C03-01 to Ramiro Varela Benvenuto,
CTM2004-05174-C02 to Emilio Marañón, and CTM2011-
25035 to Pedro Cermeño; by the Galician government through
grants 09MMA027604PR to Manuel Ruiz Villareal and
EM2013/021 to Beatriz Mouriño; by the Instituto Español de
Oceanografia (IEO) through the time series project RADIALES coordinated
by Antonio Bode and by the 7th Framework Programme
of the European Commission through grant FP7 SPACE.2010.1.1-
01 261860 to Manuel Ruiz Villareal. Jose Luis Otero Ferrer
acknowledges the receipt of a FPI contract from MINECO
(CTM2012-30680) and Bieito Fernádez Castro a Juan de La Cierva
Formación fellowship (FJCI-641 2015-25712, Ministerio de
Economía y Competitividad, Spanish government)Peer reviewe
Factors controlling the community structure of picoplankton in contrasting marine environments.
The effect of inorganic nutrients on planktonic assemblages has traditionally relied on concentrations rather
than estimates of nutrient supply. We combined a novel
dataset of hydrographic properties, turbulent mixing, nutrient concentration, and picoplankton community composition
with the aims of (i) quantifying the role of temperature, light,
and nitrate fluxes as factors controlling the distribution of autotrophic and heterotrophic picoplankton subgroups, as determined by flow cytometry, and (ii) describing the ecological niches of the various components of the picoplankton
community. Data were collected at 97 stations in the Atlantic
Ocean, including tropical and subtropical open-ocean waters,
the northwestern Mediterranean Sea, and the Galician coastal
upwelling system of the northwest Iberian Peninsula. A generalized additive model (GAM) approach was used to predict depth-integrated biomass of each picoplankton subgroup
based on three niche predictors: sea surface temperature, averaged daily surface irradiance, and the transport of nitrate
into the euphotic zone, through both diffusion and advection. In addition, niche overlap among different picoplankton
subgroups was computed using nonparametric kernel density functions. Temperature and nitrate supply were more
relevant than light in predicting the biomass of most picoplankton subgroups, except for Prochlorococcus and lownucleic-acid (LNA) prokaryotes, for which irradiance also
played a significant role. Nitrate supply was the only factor that allowed the distinction among the ecological niches
of all autotrophic and heterotrophic picoplankton subgroups.
Prochlorococcus and LNA prokaryotes were more abundant
in warmer waters ( > 20 ◦C) where the nitrate fluxes were
low, whereas Synechococcus and high-nucleic-acid (HNA)
prokaryotes prevailed mainly in cooler environments characterized by intermediate or high levels of nitrate supply. Finally, the niche of picoeukaryotes was defined by low temperatures and high nitrate supply. These results support the
key role of nitrate supply, as it not only promotes the growth
of large phytoplankton, but it also controls the structure of
marine picoplankton communitie