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Protein Synthesis by Lake Plankton Measured Using in situ Carbon Dioxide and Sulfate Assimilation

1987; Canadian Science Publishing; Volume: 44; Issue: 12 Linguagem: Inglês

10.1139/f87-260

1205-7533

Russell L. Cuhel, D. R. S. Lean,

Isotope Analysis in Ecology

Sequential 4- to 6-h in situ measurements of carbon dioxide and sulfate uptake showed midday deepening of the depth of P max and photoinhibition of upper water column samples. Analysis of subcellular fractions accentuated total uptake measurements, with net protein synthesis providing a direct measure of growth. The percentage of carbon assimilated into protein was smallest at the depth of maximum photosynthesis and increased with light limitation. Summed incubations agreed well with all-day deployments for total carbon fixation and protein synthesis. Assimilation numbers were consistently low (<2.5 g C∙g Chl a −1 ∙h -1 with integrated (0–20 m) areal production of 616–1467 mg C∙m −2 and 7.5–32.4 mg S∙m −2 during the light day. Nonreductive sulfate assimilation (predominantly ester-SO 4 − ) accounted for up to 40% of the total sulfate uptake when diatoms predominated. Protein synthesis measured with 35 S (200–1000 mg protein∙m −2 during the light day) increased 57–89% overnight. Hourly rates were similar during light and scotophase incubations. Night metabolism substantially altered the biochemical composition (e.g. protein, lipid, and carbohydrate) of the plankton with respect to newly incorporated carbon. Combined plant-specific H 14 CO 3 − and general microbial 3S SO 4 2− techniques suggested algal dominance in the mixed layer.