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

• Published in: Frontiers in Plant Science
• Main Authors: Kennedy, Fraser, Martin, Andrew, Castrisios, Katerina, Cimoli, Emiliano, McMinn, Andrew, Ryan, Ken G.
• Other Authors: New Zealand Antarctic Research Institute
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Frontiers Media SA 2020
• Subjects: Antarctic; McMurdo Sound; Antarc*; Antarctica; ice algae; Sea ice
• Online Access: http://dx.doi.org/10.3389/fpls.2020.588005; https://www.frontiersin.org/articles/10.3389/fpls.2020.588005/full

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 (H 2 O 2 ) 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.