Low cobalt limits cyanobacteria heterocyst frequency in culture but potential for cobalt limitation of frequency in nitrogen-limited surface waters is unclear
Bibliographic record
Abstract
Impacts of three cobalt (Co) concentrations were examined on heterocyst frequency and growth rate in four diazotrophic cyanobacteria species in nitrogen (N)-depleted culture and growth rate in one non-diazotrophic species in N-replete culture.After 11 days in batch culture, heterocyst frequency (HF, % of all cells that are heterocysts) increased from 4.1-5.7% to 5.4-7.4% to 5.9-9.3% at 0.17, 17 and 170 nmol L -1 Co, implicating Co in heterocyst differentiation.Growth rate was not significantly affected by Co in any of the species suggesting that the impact of low Co on other metabolic pathways was minimized.2. Stoichiometric extrapolation of culture results to N-limited natural systems with lower nutrient concentrations infers that HF could be limited by sub-nanomolar Co concentrations.3. In experimentally fertilized N-limited Lake 227, mean summer HF in 2000-2020 was 3.4% (epilimnion) and 4.0% (metalimnion).However, in 2017 (the only year for which Co data are available) dissolved Co increased from 0.7 to 2.0 nmol L -1 during the bloom simultaneously with increasing HF and cyanobacteria biomass, hence, Co probably did not limit HF and biomass.HF was significantly higher after 2015 following a shift in dominant bloom species from Aphanizomenon schindlerii to smaller A. skujae.The smaller cell size may have required a higher HF in order to maintain a relatively constant supply rate of fixed N per unit biomass.4. Surveys of ambient Co in over 280 aquatic systems across Canada and elsewhere indicate that Co is sometimes low enough to theoretically limit HF in N-limited waters.However, numerous variables influence HF so a clear understanding of relationships between Co and HF in natural systems remains elusive.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| 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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".