title: THE SHORT-TERM EFFECT OF IRRADIANCE ON THE PHOTOSYNTHETIC PROPERTIES OF ANTARCTIC FAST-ICE MICROALGAL COMMUNITIES(1).
abstract: Although sea-ice represents a harsh physicochemical environment with steep gradients in temperature, light, and salinity, diverse microbial communities are present within the ice matrix. We describe here the photosynthetic responses of sea-ice microalgae to varying irradiances. Rapid light curves (RLCs) were generated using pulse amplitude fluorometry and used to derive photosynthetic yield (ΦPSII ), photosynthetic efficiency (α), and the irradiance (Ek ) at which relative electron transport rate (rETR) saturates. Surface brine algae from near the surface and bottom-ice algae were exposed to a range of irradiances from 7 to 262 μmol photons · m(-2)  · s(-1) . In surface brine algae, ΦPSII and α remained constant at all irradiances, and rETRmax peaked at 151 μmol photons · m(-2)  · s(-1) , indicating these algae are well acclimated to the irradiances to which they are normally exposed. In contrast, ΦPSII , α, and rETRmax in bottom-ice algae reduced when exposed to irradiances >26 μmol photons · m(-2)  · s(-1) , indicating a high degree of shade acclimation. In addition, the previous light history had no significant effect on the photosynthetic capacity of bottom-ice algae whether cells were gradually exposed to target irradiances over a 12 h period or were exposed immediately (light shocked). These findings indicate that bottom-ice algae are photoinhibited in a dose-dependent manner, while surface brine algae tolerate higher irradiances. Our study shows that sea-ice algae are able to adjust to changes in irradiance rapidly, and this ability to acclimate may facilitate survival and subsequent long-term acclimation to the postmelt light regime of the Southern Ocean.
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington 6012, New Zealand.
authors.forename: Ken G
authors.initials: KG
authors.lastname: Ryan
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington 6012, New Zealand.
authors.forename: Rebecca O M
authors.initials: RO
authors.lastname: Cowie
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington 6012, New Zealand.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Liggins
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington 6012, New Zealand.
authors.forename: Daniel
authors.initials: D
authors.lastname: McNaughtan
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington 6012, New Zealand.
authors.forename: Andrew
authors.initials: A
authors.lastname: Martin
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington 6012, New Zealand.
authors.forename: Simon K
authors.initials: SK
authors.lastname: Davy
keywords: Antarctic sea ice; Ek; PAM fluorometry; photoinhibition; rETRmax; rapid light curves; ΦPSII