Stable‐isotope labeling and probing of recent photosynthates into respired CO <sub>2</sub> , soil microbes and soil mesofauna using a xylem and phloem stem‐injection technique on Sitka spruce ( <i>Picea sitchensis</i> )
Bibliographic record
Abstract
RATIONALE: Here we report on the successful application of a novel stem-injection stable-isotope-labeling and probing technique in mature trees to trace the spatial and temporal distribution of rhizosphere carbon belowground. METHODS: Three 22-year-old Sitka spruce trees were injected with 6.66 g of (13)C-labeled aspartic acid. Over the succeeding 30 days, soil CO(2) efflux, phospholipid fatty-acid (PLFA) microbial biomarkers and soil invertebrates (mites, collembolans and enchytraeids) were analyzed along a 50 m transect from each tree to determine the temporal and spatial patterns in the translocation of recently fixed photosynthates belowground. RESULTS: Soil δ(13)CO(2) values peaked 13-23 days after injection, up to 5 m from the base of the injected tree and was, on average, 3.5‰ enriched in (13)C relative to the baseline. Fungal PLFA biomarkers peaked 2-4 days after stem-injection, up to 20 m from the base of the injected tree and were (13)C-enriched by up to 50‰. Significant (13)C enrichment in mites and enchytraeids occurred 4-6 days after injection (by, on average, 1.5‰). CONCLUSIONS: Stem injection of large trees with (13)C-enriched compounds is a successful tool to trace C-translocation belowground. In particular, the significant (13)C enrichment of CO(2) and enchytraeids near the base of the tree and the significant (13)C enrichment of PLFAs up to 20 m away indicate that mature Sitka spruce (Picea sitchensis) have the capacity to support soil communities over large distances.
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".