Constraints to Nitrogen Fixation by Cryptogamic Crusts in a Polar Desert Ecosystem, Devon Island, N.W.T., Canada
Bibliographic record
Abstract
Polar desert ecosystems, which dominate the landscape throughout much of the High Arctic, are environmentally stressed and limited in their development. Scattered intermittently over these landscapes are areas of cryptogamic crust development that are associated with increased vascular plant abundance. Since nutrient limitation, especially nitrogen, is significant in these ecosystems, I wished to examine the role of these cryptogamic crusts in the supply of fixed nitrogen and the constraints to that fixation. Nitrogen fixation rates (as measured by acetylene reduction) were highest in sites with a well-developed cryptogamic crust, lowest in sites with only bare mineral soil, and intermediate in sites with a partially developed crust. Highest rates of acetylene reduction (i.e., nitrogen fixation) were seen within a few days of snowmelt (late June to early July) and declined as the season progressed, until near the end of the growing season (1–5 August) when rates were approximately 50% of early season rates. Late season precipitation events restored acetylene reduction rates to near original levels. In manipulative experiments, acetylene reduction rates dropped dramatically as crust moisture content declined and rates increased as soil surface temperature increased to 24°C. A significant finding was that acetylene reduction at 3°C was 40% of that found at 12 to 13°C. Thus, there is a potential for nitrogen accumulation even during the colder periods of the growing season. As calculations show, the quantity of nitrogen fixed by these cryptogamic crusts was adequate to support the nitrogen needs of the mosses and vascular plants of these developing ecosystems.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".