Springtime phytoplankton responses to light and iron availability along the western Antarctic Peninsula

Abstract

Light and iron availability are intertwined in controlling Southern Ocean primary production because several photosynthetic proteins require iron. Changes in light and iron availability can also affect phytoplankton species composition, which impacts nutrient cycling, carbon drawdown, and food web structure. To investigate the interactive effects of light and iron on phytoplankton growth, photosynthesis, photoacclimation strategy, micronutrient stressinduced protein expression, and species composition, we conducted five bioassay experiments during spring in waters along the western Antarctic Peninsula with four treatments: low light (LL) or high light (HL) combined with or without iron addition. This region has rarely been studied in spring. We found that light limits growth while iron does not, despite overall low iron concentrations. Our results demonstrate that phytoplankton were LL acclimated in situ but photosynthetically optimized for higher light than they were experiencing, likely due to a highly dynamic light regime. Expression patterns of micronutrient stress-induced proteins were consistent with iron stress in off-shelf regions, but remarkably this iron stress did not result in lower carbon fixation and growth rates. Notably, manganese drawdown was highest under elevated light, suggesting a possible role in managing HL, although high flavodoxin expression indicated that Phaeocystis antarctica may not have been manganese-limited. Although light and iron treatments did not impact species composition, high methionine synthase indicated that diatoms could have experienced stress induced by low vitamin B 12 , potentially contributing to P. antarctica's general dominance throughout the experiments. Our results indicate that P. antarctica may be better adapted to spring conditions than diatoms.

Photosynthetic processes in Antarctic sea ice during the spring melt

“…Fe limitation in the Southern Ocean is known to have a significant impact on phytoplankton physiology (Schallenberg et al 2020). However, Joy‐Warren et al (2022) found that Fe did not limit spring phytoplankton growth despite low concentrations in this region. In Fig.…”

Rubisco in high Arctic tidewater glacier‐marine systems: A new window into phytoplankton dynamics

“…Protein was extracted from 0.2‐ and 3.0‐ μ m polycarbonate filters and 0.22‐ μ m Sterivex™ filters and digested into tryptic peptides using S‐trap columns, following Joy‐Warren et al 2022, as described in the Supporting Information with the following modification: 750 μ L of 2% sodium dodecyl sulfate (SDS) extraction buffer (0.1 M Tris/HCl pH 7.5, 5% glycerol, 5 mM EDTA, 2% SDS) was added to each sample.…”

Effect of PAR irradiance intensity on Phaeocystis antarctica (Prymnesiophyceae) growth and DMSP, DMSO, and acrylate concentrations

“…Phaeocystis antarctica readily acclimates to a wide range of irradiances by altering its photosynthetic capacity to increase photosynthesis and decrease oxidative stress that damages the photosynthetic apparatus and forms reactive oxygen species (ROS; Falkowski & Raven, 2007; Kropuenske et al, 2009; Mills et al, 2010; Moisan & Mitchell, 1999). Under lower irradiances, cell size is reduced and pigment content (e.g., chl a per cell) and antenna size are increased (Moisan & Mitchell, 1999; van Leeuwe & Stefels, 1998), while acclimation to higher irradiances results in reduction of the pigment antenna size and an increase in photoprotective pigments including β‐carotene and xanthophyll pigments (Joy‐Warren et al, 2022; Mills et al, 2010; Moisan & Mitchell, 1999; van Leeuwe et al, 2014). Another possible advantage P. antarctica has to combat oxidative stress is high cellular concentrations of the antioxidants dimethylsulfoniopropionate (DMSP) and acrylate (Kinsey et al, 2016; Sunda et al, 2002).…”