Cascading influence of inorganic nitrogen sources on DOM production, composition, lability and microbial community structure in the open ocean

Recent work suggests that temperature effects on marine heterotrophic bacteria are strongly seasonal, but few attempts have been made to concurrently assess them across trophic levels. Here, we estimated the temperature sensitivities (using activation energies, E) of autotrophic and heterotrophic microbial plankton net growth rates over an annual cycle in NE Atlantic coastal waters. Phytoplankton grew in winter and late autumn (0.41 ± 0.16 SE d ) and decayed in the remaining months (-0.42 ± 0.10 d ). Heterotrophic microbes shared a similar seasonality, with positive net growth for bacteria (0.14-1.48 d ), while nanoflagellates had higher values (> 0.4 d ) in winter and spring relative to the rest of the year (-0.46 to 0.29 d ). Net growth rates activation energies showed similar dynamics in the three groups (-1.07 to 1.51 eV), characterized by maxima in winter, minima in summer and resumed increases in autumn. Microbial plankton E values were significantly correlated with nitrate concentrations as a proxy for nutrient availability. Nutrient-sufficiency (i.e., > 1 μmol l nitrate) resulted in significantly higher activation energies of phytoplankton and heterotrophic nanoflagellates relative to nutrient-limited conditions. We suggest that only within spatio-temporal windows of both moderate bottom-up and top-down controls will temperature have a major enhancing effect on microbial growth.

Section: Discussionmentioning

confidence: 97%

Temperature sensitivities of microbial plankton net growth rates are seasonally coherent and linked to nutrient availability

Morán

Calvo‐Díaz

Arandia-Gorostidi

et al. 2018

“…Two mock communities containing 22 taxonomically distinct clones (Supporting Information Table S2) were constructed from cloned full‐length bacterial and archaeal 16S rRNA gene amplicons from 4 surface samples, covering multiple seasons and diverse physicochemical conditions, and 1 subeuphotic zone (150 m) sample, all from the time‐series study (see Supporting Information Experimental Procedures). Taxonomies were assigned both with mothur (v1.39; Schloss et al ., ) using a non‐redundant subset of the SILVA SSU Ref16S alignment database (v115; Quast et al ., ) custom curated as in Goldberg and colleagues () and with the SILVA Incremental Aligner V1.2.11 (Pruesse et al ., ) using SILVA v132. Because bacterial and archaeal taxonomies remain in flux, we have used the SILVA v115 taxonomy throughout for consistency, but clone identities based on both v115 and v132 are specified in Supporting Information Table S3.…”

Section: Methodsmentioning

confidence: 99%

Primer selection impacts specific population abundances but not community dynamics in a monthly time‐series 16S rRNA gene amplicon analysis of coastal marine bacterioplankton

Wear

Wilbanks

Nelson

et al. 2018

Self Cite

107

SummaryPrimers targeting the 16S small subunit ribosomal RNA marker gene, used to characterize bacterial and archaeal communities, have recently been re‐evaluated for marine planktonic habitats. To investigate whether primer selection affects the ecological interpretation of bacterioplankton populations and community dynamics, amplicon sequencing with four primer sets targeting several hypervariable regions of the 16S rRNA gene was conducted on both mock communities constructed from cloned 16S rRNA genes and a time‐series of DNA samples from the temperate coastal Santa Barbara Channel. Ecological interpretations of community structure (delineation of depth and seasonality, correlations with environmental factors) were similar across primer sets, while population dynamics varied. We observed substantial differences in relative abundances of taxa known to be poorly resolved by some primer sets, such as Thaumarchaeota and SAR11, and unexpected taxa including Roseobacter clades. Though the magnitude of relative abundances of common OTUs differed between primer sets, the relative abundances of the OTUs were nonetheless strongly correlated. We do not endorse one primer set but rather enumerate strengths and weaknesses to facilitate selection appropriate to a system or experimental goal. While 16S rRNA gene primer bias suggests caution in assessing quantitative population dynamics, community dynamics appear robust across studies using different primers.

“…Although nitrification does not directly influence the system inventory of N, it alters the presence of N from its most reduced form, ammonia (NH 3 ), to its most oxidized form, nitrate (NO − 3 ) (Ward, 2005). This may affect not only the productivity of the system but also the composition of the phytoplankton and the microbial community since different groups are known to have preferences for nitrate or ammonium respectively Glibert et al, 2016;Goldberg et al, 2017). Further, nitrate is important as substrate for denitrification, and nitrification may therefore indirectly facilitate N loss .…”

Section: Introductionmentioning

confidence: 99%

Extensive nitrification and active ammonia oxidizers in two contrasting coastal systems of the Baltic Sea

Happel

Bartl

Voß

et al. 2018

Nitrification is important in nitrogen (N) cycling of aquatic environments, but knowledge about its regulation and importance is sparse. Here we examined nitrification and ammonia oxidizers in the Baltic Sea. We investigated two sites with different catchment characteristics (agricultural and forest), the Bay of Gdánsk (south) and the Öre Estuary (north), and measured pelagic nitrification rates and abundance, composition and expression of ammonia monooxygenase (amoA) genes. Highest nitrification rates were found in the nutrient rich Bay of Gdańsk. Interestingly, abundances of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were orders of magnitude lower than reported from other sites. Although AOA were most abundant at both sites, the highest expression levels were from AOB. Interestingly, few AOA and AOB taxa dominated amoA gene expression, with a Nitrosomarinus related phylotype showing widespread expression. AOA and AOB communities differed between sites and depths, respectively, with the composition in rivers being distinct. A storm event, causing an even depth distribution of nitrification and particles in the Bay of Gdańsk, indicated that the presence of particles stimulate nitrification. The study highlights coastal regions as dynamic sites of extensive pelagic nitrification, which may affect local food web dynamics and loss of N mediated by denitrification.