Contrasting effects of warming and drought on autumn phenology of photosynthesis and growth in white spruce
Bibliographic record
Abstract
Evergreen conifers rely on photoperiod and temperature cues to regulate autumn phenology. Climate change delays autumn cooling, whereas photoperiod remains unaffected, and this mismatch might have consequences for the timing of autumn phenology. Climatic stresses, such as drought and heat during summer, might also impact the timing of phenological events, including photosynthetic downregulation and growth cessation. We investigated the single and combined impacts of summer drought and autumn warming on photosynthetic downregulation and growth cessation in a northern and southern family of white spruce (Picea glauca). In a temperature free-air controlled experiment combined with rainout structures, we exposed white spruce seedlings to ambient temperature and rainfall, summer drought, autumn warming, or a combination of summer drought followed by autumn warming. Warming delayed the downregulation of photosynthesis in both families compared to the control seedlings, with the southern family showing increased photosynthetic activity compared to the northern family. Despite extended photosynthetic activity, secondary growth cessation was not delayed by warming and did not vary between families. Warming affected latewood xylem development, an important component of secondary growth, by increasing and decreasing lumen area in the northern family and southern family, respectively, indicating the northern family may have been more cold-limited under past selective pressures. Summer drought had minimal impacts on photosynthetic downregulation and growth cessation in either family. We conclude that warming-induced extension of photosynthetic activity in autumn may not translate into increased growth and carbon sequestration due to strong photoperiodic and genetic constraints on growth cessation in white spruce.
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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".