Weekly carbon and oxygen isotope dynamics in black spruce: A case study in the northeastern boreal forest of Quebec, Canada
Bibliographic record
Abstract
• Stomatal conductance controls δ 13 C and δ 18 O fractionation in the cambial region. • Post-carboxylation processes have minimal impact on δ 13 C in cambium and xylem. • P ex effect alters δ 18 O signals in forming xylem cellulose of black spruce. • Cambium and xylem use different water sources during the growing season. The stable isotopic composition of carbon (δ 13 C) and oxygen (δ 18 O) in tree rings is widely used to explore tree eco-physiological dynamics across various time scales. However, interpreting these isotopic signals is challenging due to multiple interacting factors, including gas exchange at the leaf level, stored carbohydrate reserves, and xylem water, whose timing and interactions during the growing season remain poorly understood. In this study, weekly δ 13 C and δ 18 O signals were tracked within the cambial region and forming xylem of black spruce ( Picea mariana (Mill.) BSP.) in boreal forests of Quebec, Canada. The study covered three consecutive growing seasons (2019–2021) at two forest sites with differing temperature and soil water content. Weekly isotopic profiles were developed for the cambial region (δ 13 C cam and δ 18 O cam ) and developing xylem cellulose (δ 13 C xc and δ 18 O xc ). Strong positive correlations were observed between δ 13 C cam and δ 18 O cam , with an increasing trend along the growing season. Conversely, negative relationships were observed between δ 13 C xc and δ 18 O xc , characterized by an increasing trend in δ 13 C xc and a decreasing trend in δ 18 O xc . The results illustrated that stomatal conductance is the dominant physiological factor controlling seasonal fractionation of δ 13 C cam and δ 18 O cam . Increasing proportional exchanges between xylem water and sugars at the sites of cellulose synthesis (i.e., P ex effect) are thought to be strong enough to completely blur the observed trends in δ 18 O cam during the growing season. This suggests that δ 18 O xc signals differ from those originating in the earlier cambium sink. These findings highlight the need to carefully consider the processes influencing isotopic signals to avoid misinterpretations in dendroclimatological studies.
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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 | 0.001 | 0.003 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 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".