Rapid Manipulation in Irradiance Induces Oxidative Free-Radical Release in a Fast-Ice Algal Community (McMurdo Sound, Antarctica)

Fraser Kennedy; Andrew Martin; Katerina Castrisios; Emiliano Cimoli; Andrew McMinn; Ken G Ryan

doi:10.3389/fpls.2020.588005

Rapid Manipulation in Irradiance Induces Oxidative Free-Radical Release in a Fast-Ice Algal Community (McMurdo Sound, Antarctica)

Front Plant Sci. 2020 Nov 25:11:588005. doi: 10.3389/fpls.2020.588005. eCollection 2020.

Authors

Fraser Kennedy¹, Andrew Martin¹, Katerina Castrisios¹, Emiliano Cimoli^{1

2}, Andrew McMinn¹, Ken G Ryan³

Affiliations

¹ Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia.
² Geography and Spatial Sciences, School of Technology, Hobart, TAS, Australia.
³ School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.

Abstract

Sea ice supports a unique assemblage of microorganisms that underpin Antarctic coastal food-webs, but reduced ice thickness coupled with increased snow cover will modify energy flow and could lead to photodamage in ice-associated microalgae. In this study, microsensors were used to examine the influence of rapid shifts in irradiance on extracellular oxidative free radicals produced by sea-ice algae. Bottom-ice algal communities were exposed to one of three levels of incident light for 10 days: low (0.5 μmol photons m^-2 s^-1, 30 cm snow cover), mid-range (5 μmol photons m^-2 s^-1, 10 cm snow), or high light (13 μmol photons m^-2 s^-1, no snow). After 10 days, the snow cover was reversed (either removed or added), resulting in a rapid change in irradiance at the ice-water interface. In treatments acclimated to low light, the subsequent exposure to high irradiance resulted in a ~400× increase in the production of hydrogen peroxide (H₂O₂) and a 10× increase in nitric oxide (NO) concentration after 24 h. The observed increase in oxidative free radicals also resulted in significant changes in photosynthetic electron flow, RNA-oxidative damage, and community structural dynamics. In contrast, there was no significant response in sea-ice algae acclimated to high light and then exposed to a significantly lower irradiance at either 24 or 72 h. Our results demonstrate that microsensors can be used to track real-time in-situ stress in sea-ice microbial communities. Extrapolating to ecologically relevant spatiotemporal scales remains a significant challenge, but this approach offers a fundamentally enhanced level of resolution for quantifying the microbial response to global change.

Keywords: Antarctica; hydrogen peroxide (H2O2); microelectrodes; nitric oxide (NO); oxidative stress; photophysiology; sea-ice algae; snow.