Responses of Picea mariana to elevated CO2 concentration during growth, cold hardening and dehardening: phenology, cold tolerance, photosynthesis and growth
Bibliographic record
Abstract
Seedlings from a northern and a southern provenance of black spruce (Picea mariana Mill. BSP) from eastern Canada were exposed to 37 or 71 Pa of carbon dioxide (CO2) during growth, cold hardening and dehardening in a greenhouse. Bud phenology, cold tolerance and photosynthetic efficiency were assessed during the growing and over-wintering periods. Bud set occurred earlier in elevated [CO2] than in ambient [CO2], but it was later in the southern provenance than in the northern provenance. An increase in seedling cold tolerance in early fall was related to early bud set in elevated [CO2]. Maximal photosystem II (PSII) photochemical efficiency (F(v)/F(m)), effective quantum yield (phi(PSII)), photochemical quenching (q(P)), light-saturated photosynthesis (Amax), apparent quantum efficiency (alpha'), light-saturated rate of carboxylation (Vcmax) and electron transport (Jmax) decreased during hardening and recovered during dehardening. Although Amax and alpha' were higher in elevated [CO2] when measured at the growth [CO2], down-regulation of photosynthesis occurred in elevated [CO2] as shown by lower F(v)/F(m), phi(PSII), Vcmax and Jmax. Elevated [CO2] reduced gene expression of the small subunit of Rubisco and also decreased chlorophyll a/chlorophyll b ratio and nitrogen concentration in needles, confirming our observation of down-regulation of photosynthesis. Elevated [CO2] increased the CO2 diffusion gradient and decreased photorespiration, which may have contributed to enhance Amax despite down-regulation of photosynthesis. Total seedling dry mass was higher in elevated [CO2] than in ambient [CO2] at the end of the growing season. However, because of earlier bud formation and cold hardening, and down-regulation of photosynthesis during fall and winter in elevated [CO2], the treatment difference in dry mass increment was less by the end of the winter than during the growing season. Differences in photosynthetic rate observed during fall, winter and spring account for the inter-annual variations in carbon assimilation of black spruce seedlings: our results demonstrate that these variations need to be considered in carbon budget 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) | 0.000 | 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) | 0.001 | 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".