Inorganic carbon acquisition in coastal Pacific phytoplankton communities
Why this work is in the frame
A frame that forgets how it found something cannot be audited. These are the routes that admitted this work.
Bibliographic record
Abstract
Despite significant advances in the understanding of carbon acquisition in eukaryotic algae and cyanobacteria, very little information is available on the mechanisms of C uptake in natural phytoplankton communities or the effects of CO 2 variations on marine primary productivity. In this article, we present the results of a 3‐yr study of C acquisition in coastal Pacific phytoplankton populations and their responses to experimental CO 2 manipulations. Diatom‐dominated phytoplankton assemblages collected without incubation showed photosynthetic characteristics indicative of a carbon concentrating mechanism. Cells possessed a high affinity for external inorganic C (apparent K m ~1 µM CO 2 ) and accumulated internal inorganic C pools that were ~3–5.5‐fold higher than those in the external medium. Evidence of in situ carbonic anhydrase expression was found in some of the phytoplankton populations we examined, and inhibitor experiments showed that this enzyme was essential for C fixation by cells. The presence of carbon concentrating mechanisms enabled the phytoplankton to maintain rapid growth rates over a wide range of CO 2 concentrations (3–32 µM). In five of six long‐term (~2–5‐d) CO 2 manipulation experiments, no difference in growth rates could be detected across treatments. However, a significant decrease in growth rate (30%) was observed in one experiment at the lowest CO 2 level tested (3 mM). Although phytoplankton growth rates were generally unaffected by the CO 2 manipulations, significant CO 2 ‐dependent changes occurred in the cellular biochemistry and physiology of two assemblages that were examined. Cells grown at low CO 2 showed higher short‐term rates of C uptake (indicative of transport system up‐regulation), as well as enhanced expression of Rubisco and carbonic anhydrase. In one of these two incubation experiments, lower C:N and carbohydrate:protein ratios were observed at low CO 2 . Phytoplankton from both incubations showed low C isotope discrimination relative to the 13 C/ 12 C of the available CO 2 . Photosynthetic fractionation factors (ϵ p ) ranged from ~3.5‰ to 7.5‰ and were independent of both cellular growth rates and aqueous CO 2 concentrations. Our data indicate that nutrient‐replete, rapidly growing coastal phytoplankton can use carbon concentrating mechanisms and respond physiologically and biochemically to changing dissolved CO 2 concentrations. Future field studies should examine the effects of CO 2 on the growth of nutrient‐limited phytoplankton and assess the potential long‐term ecological shifts that may result from CO 2 variations.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it