Uptake of urea by “drunken” trees on permafrost
Bibliographic record
Abstract
Boreal forest productivity on permafrost is limited by availability of soil nitrogen (N) in the active layer. Low soil temperature and summer flooding limit microbial N mineralization on shallow permafrost table. Uptake of amino acids by plant root-mycorrhizal association is known to mitigate N limitation in boreal forest soils. However, amino acid hypothesis can not fully explain advantage of black spruce trees in drunken forests due to competition of amino acids between plants, bryophytes, and microbes. Based on the observation of urea accumulation in deeper soil, we test another hypothesis that black spruce trees take up intact urea in deeper soil. Mixture solutions (glutamic acid, urea, ammonium, nitrate), with only one N form labeled by 13C and/or 15N, was injected into the organic/mineral soil layers. We compared two black spruce forest sites with/without shallow permafrost table in northern Canada. We found that black spruce trees take up intact urea as well as amino acids in the shallow permafrost sites. Urea accumulation is explained by low microbial activities to mineralize 14C-labeled urea. The other plants or bryophyte compete with black spruce for amino acids, but not for urea. Since the other black spruce trees in the deeper soil sites rely on amino acids and inorganic N, urea uptake strategy is specific to black spruce trees on shallow permafrost table. The root expansion on hummocky microrelief provides opportunity for leaning trees to access urea. The uptake of intact urea could be one of strategy of black spruce trees to mitigate N limitation in permafrost-affected hummocky soils.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".