Changes in photosynthetic carbon allocation in algal assemblages of Arctic sea ice with decreasing nutrient concentrations and irradiance

Mock, Thomas and Gradinger, Rolf (2000) Changes in photosynthetic carbon allocation in algal assemblages of Arctic sea ice with decreasing nutrient concentrations and irradiance. Marine Ecology Progress Series, 202. pp. 1-11. ISSN 0171-8630

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Photosynthetic carbon assimilation into protein, low-molecular-weight metabolites (LMWM), polysaccharides, total lipids and into 3 lipid classes (neutral lipids, glycolipids and phospholipids) was determined in batch-culture experiments with natural assemblages of Arctic-ice algae under simulated in situ irradiance. Photosynthate allocation in 3 parallel batch incubations revealed a high contribution of lipid assimilation to total particulate carbon production (54.6 ± 0.4%) followed by LMWM (35.0 ± 1.0%), carbohydrates (7.3 ± 0.1%) and proteins (3.0 ± 0.8%). Total lipids were mainly composed of glycolipids (67.4 ± 3.5%) with a relatively lower allocation into phospholipids (28.1 ± 6.7%) and neutral lipids (4.5 ± 3.2%). Nutrient addition (final concentrations: Si(OH)4 = 65.5 ± 0.4 µmol l-1, NO3 = 42.9 ± 0.6 µmol l-1, PO4 = 2.6 ± 0.0 µmol l-1) caused algal community growth of 0.22 ± 0.0 d-1 until nutrients became limiting 10 d later. Si(OH)4:NO3 ratios and NO3:PO4 ratios in the cultures decreased from initially 1.5 ± 0.0 to 0.2 ± 0.1 and 16.8 ± 0.2 to 1.2 ± 0.5, respectively. During the first few days of incubation, relative proportions of carbon production for proteins increased 3-fold (max. 11.1 ± 1.0%), those for LMWM 1.5-fold (max. 45.7 ± 6.4%), whereas lipids decreased (min. 32.0 ± 0.4%). Increasing relative proportions of carbon production for carbohydrates were only observed at the end of exponential growth (max. 12.9 ± 1.3%). A dramatic increase of lipids was measured under nutrient depletion (max. 70.9 ± 3.6%) after Day 10, which was the result of glycolipid production, while protein and carbohydrate production decreased to values below 5% of total particulate carbon production. LMWM also attained lower incorporation rates under nutrient depletion (min. 23.5 ± 1.1%). Production of glycolipids during exponential algal growth is attributed to an acclimation to decreasing irradiance as a consequence of an increase in algal biomass. Decreasing particulate carbon:chlorophyll a ratios during the experiment indicate a physiological response to a reduction in irradiance with simultanous glycolipid production. Glycolipids are the main lipid class in chloroplasts, and especially in thylakoidmembranes, which are strongly developed during low-light acclimation. Excess light energy during stationary algal growth after Day 10 is dissipated in the form of glycolipids and/or neutral lipids. But the latter are probably more significant under high-light conditions.

Item Type: Article
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Rosie Cullington
Date Deposited: 01 Jul 2011 08:57
Last Modified: 28 Apr 2022 22:45
DOI: 10.3354/meps202001

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