Taxonomic and Environmental Variability in the Elemental Composition and Stoichiometry of Individual Dinoflagellate and Diatom Cells from the NW Mediterranean Sea

Abstract

Here we present, for the first time, the elemental concentration, including C, N and O, of single phytoplankton cells collected from the sea. Plankton elemental concentration and stoichiometry are key variables in phytoplankton ecophysiology and ocean biogeochemistry, and are used to link cells and ecosystems. However, most field studies rely on bulk techniques that overestimate carbon and nitrogen because the samples include organic matter other than plankton organisms. Here we used X-ray microanalysis (XRMA), a technique that, unlike bulk analyses, gives simultaneous quotas of C, N, O, Mg, Si, P, and S, in single-cell organisms that can be collected directly from the sea. We analysed the elemental composition of dinoflagellates and diatoms (largely Chaetoceros spp.) collected from different sites of the Catalan coast (NW Mediterranean Sea). As expected, a lower C content is found in our cells compared to historical values of cultured cells. Our results indicate that, except for Si and O in diatoms, the mass of all elements is not a constant fraction of cell volume but rather decreases with increasing cell volume. Also, diatoms are significantly less dense in all the measured elements, except Si, compared to dinoflagellates. The N:P ratio of both groups is higher than the Redfield ratio, as it is the N:P nutrient ratio in deep NW Mediterranean Sea waters (N:P = 20–23). The results suggest that the P requirement is highest for bacterioplankton, followed by dinoflagellates, and lowest for diatoms, giving them a clear ecological advantage in P-limited environments like the Mediterranean Sea. Finally, the P concentration of cells of the same genera but growing under different nutrient conditions was the same, suggesting that the P quota of these cells is at a critical level. Our results indicate that XRMA is an accurate technique to determine single cell elemental quotas and derived conversion factors used to understand and model ocean biogeochemical cycles.

Zooplankton community succession and trophic links during a mesocosm experiment in the coastal upwelling off Callao Bay (Peru)

“…Comparing single-cell analysis of Dinophysis cf. punctata from this study (Table 5) with the same taxa from the Mediterranean Sea, all species analyzed here had more C, N, and O but similar P contents (Segura-Noguera et al, 2016).…”

“…The standards used for quantification were latex beads of 3 and 5 µm for C and ADP for N, O, and P. Latex beads of 3 µm were analyzed as internal standards several times during each analysis session to correct for drift and for changes in day-today beam intensity. A detailed description of the measuring approach is given in Segura-Noguera et al (2016).…”

Sequential nutrient uptake as a potential mechanism for phytoplankton to maintain high primary productivity and balanced nutrient stoichiometry

“…The fourth mechanism is related to the interference from dead plankton or organic detritus with the measurement of elemental composition of organic matter, and such interference is difficulty to assess due to lack of the measurements of non-living organic matter in oceans and coastal waters. However, the X-ray microanalysis (XRMA) technique was recently used to produce simultaneous quotas of C, N, O, Mg, Si, P and S in single-cell organisms (Segura-Noguera et al, 2016), which will not only help to understand the fourth mechanism but also understand the variability of stoichiometry of phytoplankton in the oceans.…”

Influences of micro-geomorphology on the stoichiometry of C, N and P in Chenier Island soils and plants in the Yellow River Delta, China

“…Understanding ecological stoichiometry is critical in understanding various connections between trophic interactions and nutrient cycling [ 8 – 11 ]. Ecological stoichiometric theories have influenced our knowledge of the first law of thermodynamics, natural selection and evolutionary biology, and the central dogma of molecular biology [ 12 – 13 ], resulting in successful evaluations on different scales, from molecules to organisms and from ecosystems to the biosphere [ 4 – 5 , 14 – 15 ]. Meanwhile, to date, few work on C, N, and P stoichiometric characteristics of soils and plants in coastal wetlands has been reported.…”