Phosphorus limitation and heat stress decrease calcification in &amp;lt;i&amp;gt;Emiliania huxleyi&amp;lt;/i&amp;gt;

Andrea C Gerecht,Luka Šupraha,Jorijntje Henderiks,Gerald Langer

doi:10.5194/bg-15-833-2018

Abstract

Abstract. Calcifying haptophytes (coccolithophores) sequester carbon in the form of organic and inorganic cellular components (coccoliths). We examined the effect of phosphorus (P) limitation and heat stress on particulate organic and inorganic carbon (calcite) production in the coccolithophore Emiliania huxleyi. Both environmental stressors are related to rising CO2 levels and affect carbon production in marine microalgae, which in turn impacts biogeochemical cycling. Using semi-continuous cultures, we show that P limitation and heat stress decrease the calcification rate in E. huxleyi. However, using batch cultures, we show that different culturing approaches (batch versus semi-continuous) induce different physiologies. This affects the ratio of particulate inorganic (PIC) to organic carbon (POC) and complicates general predictions on the effect of P limitation on the PIC ∕ POC ratio. We found heat stress to increase P requirements in E. huxleyi, possibly leading to lower standing stocks in a warmer ocean, especially if this is linked to lower nutrient input. In summary, the predicted rise in global temperature and resulting decrease in nutrient availability may decrease CO2 sequestration by E. huxleyi through lower overall carbon production. Additionally, the export of carbon may be diminished by a decrease in calcification and a weaker coccolith ballasting effect.

Highlights

Emiliania huxleyi is an abundant and ubiquitous phytoplankton species, belonging to the coccolithophores (Haptophyta), a group of calcifying microalgae
Particulate inorganic carbon production, on the other hand, was significantly lower in P-limited cultures (Table 4; F value = 13.25, p = 0.0066) and P-limited cells were covered by one to two fewer coccoliths (Table 2; Fig. 4a, b), which led to a decrease in the particulate inorganic (PIC) / particulate organic (POC) ratio (Table 4; F value = 19.01, p = 0.0024)
By employing semi-continuous cultures, we show that both P limitation and heat stress decrease calcification rate in a temperate strain of E. huxleyi

Summary

Introduction

Emiliania huxleyi is an abundant and ubiquitous phytoplankton species, belonging to the coccolithophores (Haptophyta), a group of calcifying microalgae. Many studies have addressed the production of organic and inorganic carbon (calcite) in E. huxleyi, as well as its modification by environmental factors such as carbonate chemistry (Riebesell et al, 2000; Meyer and Riebesell, 2015), nutrient availability (Paasche and Brubak, 1994; Langer and Benner, 2009), temperature (Watabe and Wilbur, 1966; Langer et al, 2010), salinity (Paasche et al, 1996; Green et al, 1998) and light (Paasche, 1968, 1999). This study investigates the physiological and morphological response of E. huxleyi to two environmental stressors, phosphorus (P) limitation and increased temperature. These are predicted to occur simultaneously as a rise in global temperature will increase the likelihood of nutrient limitation in the photic zone due to a stronger stratification of the water column (Sarmiento et al, 2004).

Methods

Results

Discussion

Conclusion