Carbon and nitrogen fluxes in the marine coccolithophore Emiliania huxleyi grown under different nitrate concentrations

Abstract

Information on interaction of C and N at the cellular level is lacking for ecologically relevant phytoplankton species. We examined the effects of NO 3 -availability on C and N fluxes in the widely distributed marine coccolithophore Emiliania huxleyi. Cells were cultured at replete (∼280 μM) and ambient (∼10 μM) NO 3 -, the latter representing a typical surface water nitrate concentration of the North Atlantic Ocean during spring. While growth rates and C to N ratios were not altered by the NO 3 -availability, organic C and N as well as inorganic C quotas were reduced under ambient NO 3 -. Growth at ambient NO 3 -caused a higher proportion of fixed C to be allocated to lipids relative to carbohydrates and especially to proteins. Ambient NO 3 --grown cells showed lower ). The CO 2 uptake and the maximum light use efficiency of photosynthesis (α) were unaffected by the concentration of NO 3 -. The affinities of NR for NO 3 -, of NiR for NO 2 -, of GS for Glu, and of the inorganic carbon uptake system for HCO 3 -were higher under ambient NO 3 -(ambient/replete: K m NR = 0.074/0.099 mM; K m NiR = 1.69/3.14 mM; K m GS = 1.62/ 3.81 mM; K m HCO3 -= 195/524 μM). Our data suggest that a concerted regulation of the intracellular CO 2 and NO 3 -concentrations is required to maintain balanced C and N metabolic fluxes resulting in a constant C to N ratio.

Calcification of Calcidiscus leptoporus under nitrogen and phosphorus limitation

“…In another chemostat experiment, morphology of N-limited cells did not appear to differ from morphology of non-limited cells (Fritz, 1999). Recently, an increased percentage of incomplete coccoliths, but not malformed ones, was observed in an N-limited semi-continuous culture (Kaffes et al, 2010). In the present study we grew C. leptoporus under both N and P limitations in batch culture.…”

“…Hence the effect of N-limitation on the "stop-signal" for coccolith growth appears to be species-specific. Moreover, comparison of the data in Kaffes et al (2010) with observations made by Paasche (1998) and Fritz (1999) suggests that it is even strainspecific. Fritz (1999) stated that E. huxleyi cells grown under Nlimitation in a chemostat did not exhibit altered coccolith morphology compared to the control.…”

“…Unfortunately this inference has to be based on very few and more often than not semi-quantitative or qualitative data. Quantitative data stem from a batch culture experiment with Coccolithus braarudii (Benner, 2008) and a semi-continuous culture experiment with E. huxleyi (Kaffes et al, 2010). In the latter study the cells were subjected to N-limitation and it was observed that, compared to the control, the percentage of incomplete coccoliths greatly increased whereas the percentage of malformed coccoliths did not change.…”

“…Fritz (1999) stated that E. huxleyi cells grown under Nlimitation in a chemostat did not exhibit altered coccolith morphology compared to the control. Unfortunately this statement was not based on quantification of coccolith morphology, but it should nevertheless suffice to exclude obvious changes in morphology as observed by Kaffes et al (2010). Paasche (1998) reported that E. huxleyi grown in batch as well as chemostat under N-limitation showed 10-15% malformed coccoliths.…”

Influence of changing carbonate chemistry on morphology and weight of coccoliths formed by <i>Emiliania huxleyi</i>

“…Riebesell et al, 2000;Langer et al, 2006;Müller et al, 2010). In cases where these these malformations were quantified, it was done by visual comparisons of individual coccoliths and subsequent classifications to fixed categories like for example "normal", "slightly malformed", "strongly malformed", and "incomplete" (Langer et al, 2006Kaffes et al, 2010;Bach et al, 2011). Here, we propose an alternative method to approximate malformations of E. huxleyi, which aims to quantify malformations by direct measurements of fine-scale morphological structures (see Sect.…”