Linking phytoplankton community composition to seasonal changes in f-ratio

Abstract

Seasonal changes in nitrogen assimilation have been studied in the western English Channel by sampling at approximately weekly intervals for 12 months. Nitrate concentrations showed strong seasonal variations. Available nitrogen in the winter was dominated by nitrate but this was close to limit of detection from May to September, after the spring phytoplankton bloom. The 15 N uptake experiments showed that nitrate was the nitrogen source for the spring phytoplankton bloom but regenerated nitrogen supported phytoplankton productivity throughout the summer. The average annual f-ratio was 0.35, which demonstrated the importance of ammonia regeneration in this dynamic temperate region. Nitrogen uptake rate measurements were related to the phytoplankton responsible by assessing the relative abundance of nitrate reductase (NR) genes and the expression of NR among eukaryotic phytoplankton. Strong signals were detected from NR sequences that are not associated with known phylotypes or cultures. NR sequences from the diatom Phaeodactylum tricornutum were highly represented in gene abundance and expression, and were significantly correlated with f-ratio. The results demonstrate that analysis of functional genes provides additional information, and may be able to give better indications of which phytoplankton species are responsible for the observed seasonal changes in f-ratio than microscopic phytoplankton identification.

Why are biotic iron pools uniform across high‐ and low‐iron pelagic ecosystems?

“…Unlike in the oceanic nitrogen cycle, where small cells tend to exclusively utilize regenerated nitrogen and larger cells like diatoms take up mainly new nitrogen [ Ward et al , ], the iron cycle appears to be driven by different rules regarding bioavailability. Both large and small cells, from a range of phytoplankton groups, can take up new iron [ Boyd et al , ], but it is less clear to what extent large cells can take up regenerated iron, which may have its bioavailability (such as the degree of complexation to strong iron‐binding L1 class ligands) altered during recycling [see Boyd et al , , Figure 3].…”

“…The relative contribution of new versus regenerated iron to biological iron uptake is described by the f e ratio [biological uptake of new iron / (uptake of new + regenerated iron)] [ Boyd et al , ]. This ratio is analogous to the classical f‐ratio for nitrogen [see Ward et al , ]. The f e ratio is computed by comparing measured heterotrophic and autotrophic iron uptake (using the 55 Fe radio‐isotope) versus measured iron recycling [by viral lysis (burst size and microscopy), bacterivory (prey‐labelling with 55 Fe), and micro‐ and mesozooplankton herbivory (prey‐labelling with 55 Fe and SXRF measurements)] as detailed in Boyd et al [] and Boyd et al [].…”

Analysis of diversity of chromophytic phytoplankton in a mangrove ecosystem using rbcL gene sequencing

“…Therefore, greater resolution can be obtained at the level of gene sequences (e.g., Ward et al. ). Since the regulation and activity of key genes in individual phytoplankton lead to regulation of enzyme activity, therefore gene sequences provide high‐resolution for the investigation into the community structure and temporal dynamics of individual phytoplankton taxa (Paul et al.…”

“…Enzyme activity can be linked to key metabolic processes in phytoplankton but it is not possible to determine enzyme activity associated with individual components of a natural phytoplankton assemblage. Therefore, greater resolution can be obtained at the level of gene sequences (e.g., Ward et al 2011). Since the regulation and activity of key genes in individual phytoplankton lead to regulation of enzyme activity, therefore gene sequences provide high-resolution for the investigation into the community structure and temporal dynamics of individual phytoplankton taxa (Paul et al 1999, 2000, Wawrik and Paul 2004.…”

South Africa in the Antarctic Circumnavigation Expedition: A multi-institutional and interdisciplinary scientific project

“…Microbial community composition will be assessed through a combination of methods selected to maximise spatial coverage and resolution. These methods include: phytoplankton and zooplankton taxonomy; phytoplankton DNA/RNA microarrays that evaluate phytoplankton diversity and gene expression related to N-and carbon cycle processes [22][23][24] ; phenotypic arrays that characterise the metabolic activity of bacterial communities 25,26 ; Next Generation Sequencing for microbial diversity 27 , and rRNA and cDNA for the identification of metabolically active microbial taxa. Finally, the physical, chemical, and biological data will be incorporated into ongoing high-resolution numerical modelling efforts to produce an integrated view of the Subantarctic systems.…”