Potential of temperature- and salinity-driven shifts in diatom compatible solute concentrations to impact biogeochemical cycling within sea ice

Hannah M Dawson,Katherine R Heal,Laura T Carlson,Jodi N Young,Anitra E Ingalls,Angela K Boysen,Detlev Helmig,Kevin Arrigo

doi:10.1525/elementa.421

Hannah M Dawson, Katherine R Heal + Show 6 more

Open Access

https://doi.org/10.1525/elementa.421

Copy DOI

Abstract

Sea-ice algae are an important source of primary production in polar regions, yet we have limited understanding of their responses to the seasonal cycling of temperature and salinity. Using a targeted liquid chromatography-mass spectrometry-based metabolomics approach, we found that axenic cultures of the Antarctic sea-ice diatom, Nitzschia lecointei, displayed large differences in their metabolomes when grown in a matrix of conditions that included temperatures of –1 and 4°C, and salinities of 32 and 41, despite relatively small changes in growth rate. Temperature exerted a greater effect than salinity on cellular metabolite pool sizes, though the N- or S-containing compatible solutes, 2, 3-dihydroxypropane-1-sulfonate (DHPS), glycine betaine (GBT), dimethylsulfoniopropionate (DMSP), and proline responded strongly to both temperature and salinity, suggesting complexity in their control. We saw the largest (&gt; 4-fold) response to salinity for proline. DHPS, a rarely studied but potential compatible solute, had the highest intracellular concentrations among all compatible solutes of ~85 mM. When comparing the culture findings to natural Arctic sea-ice diatom communities, we found extensive overlap in metabolite profiles, highlighting the relevance of culture-based studies to probe environmental questions. Large changes in sea-ice diatom metabolomes and compatible solutes over a seasonal cycle could be significant components of biogeochemical cycling within sea ice.

Highlights

Sea ice is one of the most extensive habitats on Earth, accounting for 15–22 million km2, or 4.1–6.1%, of global ocean area throughout the year (Arrigo et al, 2014)
Carbon content per cell was, on average, 30% higher at warmer temperatures compared to colder temperatures, and 20% higher at lower salinity compared to high salinity (p < 0.001 and p < 0.01, respectively; Figure 1c, Table S2)
Our matrix of temperatures (–1°C vs 4°C) and salinities (32 vs 41) reflect conditions seaice diatoms may experience in bottom sea ice flushed with seawater and in the water column upon melt, and intentionally included a treatment not matched to the sea-ice environment (4°C and 41) to allow us to disentangle the individual influences of temperature and salinity on metabolite abundances in N. lecointei

Summary

Introduction

Sea ice is one of the most extensive habitats on Earth, accounting for 15–22 million km, or 4.1–6.1%, of global ocean area throughout the year (Arrigo et al, 2014). This unique biome is host to diverse microbial assemblages, including unicellular microalgae that are able to exploit microhabitats produced during sea-ice formation and aging (Arrigo, 2016). Sea-ice algae contribute to carbon fixation via photosynthesis in polar ecosystems, fixing an estimated 10–36 Tg C year–1 in the Arctic and 24–36 Tg C year–1 in the Antarctic, 2–10% and 1–3% of total annual production (ice + water column) in those regions, respectively (Arrigo, 2016). Diatoms dominate sea ice (Horner, 1985; Arrigo, 2014), with pennate diatoms (e.g., Nitzschia, Fragilariopsis, Navicula) being the most common (Günther and Dieckmann, 2001; Fiala et al, 2006)

Methods

Results

Discussion

Conclusion