Carbon and nitrogen in the silt-size fraction and its HCl-hydrolysis residues from coarse-textured Canadian boreal forest soils
Bibliographic record
Abstract
Preston, C. M., Norris, C. E., Bernard, G. M., Beilman, D. W., Quideau, S. A. and Wasylishen, R. E. 2014. Carbon and nitrogen in the silt-size fraction and its HCl-hydrolysis residues from coarse-textured Canadian boreal forest soils. Can. J. Soil Sci. 94: 157-168. Improving the capacity to predict changes in soil carbon (C) stocks in the Canadian boreal forest requires better information on the characteristics and age of soil carbon, especially more slowly cycling C in mineral soil. We characterized C in the silt-size fraction, as representative of C stabilized by mineral association, previously isolated in a study of soil profiles of four sandy boreal jack pine sites. Silt-size fraction accounted for 13-31% of the total soil C and 12-51% of the total soil N content. Solid-state 13C nuclear magnetic resonance spectroscopy showed that silt C was mostly dominated by alkyl and O,N-alkyl C, with low proportions of aryl C in most samples. Thus, despite the importance of fire in this region, there was little evidence of storage of pyrogenic C. We used HCl hydrolysis to isolate the oldest C within the silt-size fraction. Consistent with previous studies, this procedure removed 21-74% of C and 74-93% of N, leaving residues composed mainly of alkyl and aryl C. However, it failed to isolate consistently old C; 11 out of 16 samples had recent 14C ages (fraction of modern 14C > 1), although C-horizon samples were older, with Δ14C from -17 to -476‰. Our results indicate relatively young ages for C associated with the silt-size fractions in these sites, for which mineral soil C storage may be primarily limited by good drainage and coarse soil texture, exacerbated by losses due to periodic wildfire.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".