Photoacclimation by Arctic cryoconite phototrophs.
Cryoconite is a matrix of sediment, biogenic polymer and a microbial community that resides on glacier surfaces. The phototrophic component of this community is well adapted to this extreme environment, including high light stress. Photoacclimation of the cryoconite phototrophic community on Longyearbreen, Svalbard, was investigated using in situ variable chlorophyll fluorescence. Rapid light curves (RLCs) and induction-recovery curves were used to analyse photosystem II quantum efficiency, relative electron transport rate and forms of downregulation including non-photochemical quenching (NPQ) and state transitions in cyanobacteria. Phototrophs used a combination of behavioural and physiological photochemical downregulation. Behavioural downregulation is hypothesised to incorporate chloroplast movement and cell or filament positioning within the sediment matrix in order to shade from high light, which resulted in a lack of saturation of RLCs and hence overestimation of productivity. Physiological downregulation likely consisted of biphasic NPQ, comprising a steadily induced light-dependent form and a light-independent NPQ that was not reversed with decreasing light intensity. State transitions by cyanobacteria were the most likely physiological downregulation employed by cyanobacteria within the mixed phototroph community. These findings demonstrate that cryoconite phototrophs combine multiple forms of physiological and behavioural downregulation to optimise light exposure and maximise photosynthetic productivity. This plasticity of photoacclimation enables them to survive productively in the high-light stress environment on the ice surface.
Cold Climate Research, School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff CF10 3AT, UK.
Rupert G
RG
Perkins
Cold Climate Research, School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff CF10 3AT, UK.
Elizabeth
E
Bagshaw
Department of Geography and Environmental Management, UWE Bristol, Coldharbour Lane, Bristol BS16 1QY, UK.
Lisa
L
Mol
School of Biological Sciences, Life Sciences Building, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
Christopher J
CJ
Williamson
School of Biological Sciences, Life Sciences Building, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
Dan
D
Fagan
School of Biological Sciences, Life Sciences Building, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
Maggie
M
Gamble
School of Biological Sciences, Life Sciences Building, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
Marian L
ML
Yallop
D000064:Acclimatization / Q000502:physiology*; D001110:Arctic Regions; D002734:Chlorophyll / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism*; D004579:Electron Transport / Q000502:physiology*; D019015:Geologic Sediments / Q000382:microbiology; D046448:Ice Cover / Q000382:microbiology; D008027:Light; D064307:Microbiota / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D013538:Svalbard
D045332:Photosystem II Protein Complex; D002734:Chlorophyll
cryoconite; downregulation; fluorescence; non-photochemical quenching; photoacclimation; productivity