|Title||Influence of abiotic drivers (light and nutrients) on photobiology and diversity of Antarctic lake phytoplankton communities|
|Year of Publication||2016|
|Authors||Teufel, AG, Morgan-Kiss, RM|
|Academic Department||Department of Microbiology|
|Keywords||Antarctica, bacterial production, Chlamydomonas sp ICE MDV, Chlorophyll fluorescence, circadian rhythm, climate change, McMurdo Dry Valleys, nutrient amendment, photobiology, Primary production|
Arctic, Antarctic, and alpine ecosystems are recognized as sensors and sentinels of global climate change. As a consequence of their high sensitivity to minor climatic perturbations, permanently ice-covered lakes located in the McMurdo Dry Valleys (MCM), Antarctica, represent end members in the global network of inland bodies of water. Episodic climatic events in the form of increased summer glacial melt result in inputs of organic sediment and nutrients from glacial streams to these closed basins. By better understanding how Antarctic lake communities respond to mimicked climate change, we can more accurately predict how they will react to further temperature changes in the future. We began by investigating the influence of inorganic nitrogen and phosphorus availability on planktonic communities residing in the oligotrophic upper waters of two chemically distinct MCM lakes (Lakes Bonney and Fryxell) which differ in their external inputs as well as water column N:P stoichiometry. Although microbial community responses varied between the lakes and were nutrient-dependent, stimulation of phytoplankton biomass and productivity across all treatments was strongly linked with increased abundance of a single phytoplankton phylum (Chlorophyta). Despite stimulation of phytoplankton growth, primary and bacterial productivity were largely uncoupled across all enrichments. We suggest that climate-associated shifts in phytoplankton diversity influence the bacterial community structure by altering the availability and composition of autochthonous carbon for heterotrophic production. To monitor the physiological adaptations that occur over time and depth, we then transplanted two dominant phytoplankton, Chlamydomonas sp. ICE- MDV and Isochrysis sp. MDV back into the Lake Bonney water column. Our results demonstrated that both organisms are specialists for surviving specific depths of the water column and are capable of acclimating to their native environment within a short period of time, and that the chlorophyte Chlamydomonas sp. ICE-MDV most likely makes this adjustment via photoacclimation and accumulating chlorophyll-a per cell. The final study presented here investigated whether or not the dominant chlorophyte, Chlamydomonas sp. ICE-MDV has retained the ability to respond to a diel 12-hour day/night cycle. Although light levels in MCM lakes remain low during the austral summers, daily irradiation varies by as much as tenfold during the course of the day, resulting in a circadian-like light cycle for organisms residing there. With decreased ice coverage on the lakes due to climate change and increased melt, it is likely that these light variations will become amplified over time. This study tested for the presence of a circadian rhythm under various light quality, light quantity, and temperature conditions and demonstrated that although a diel rhythm was maintained in terms of growth and several photochemical parameters, a true circadian rhythm was not identified. Although it is predicted that photosynthetic communities in polar regions will be more responsive to climate warming and episodic events, the complexity of these systems provides numerous challenges to understanding how these organism will adapt in the future.