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

• Published in: Marine Ecology Progress Series
• Main Authors: Mock, Thomas, Gradinger, Rolf
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2000
• Subjects: Arctic; ice algae; Sea ice
• Online Access: https://ueaeprints.uea.ac.uk/id/eprint/33146/; https://doi.org/10.3354/meps202001

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 ...