Temporal variations in the understory photosynthetic photon flux density of deciduous stand: the effects of canopy development, solar elevation, and sky conditions
Notice bibliographique
Résumé
The effects of canopy development, solar elevation, and sky conditions on temporal variation in photosynthetic photon flux density (PPFD) were examined within a 9-year-old bigleaf maple stand on Vancouver Island (Canada). PPFD was measured every second and stored as 10-min averages from 18 May to 14 October 1996, at 52 microsites characterised according to their growing season %PPFD (GSP). PPFD and %PPFD variability was examined at three different temporal levels. Specific days in May, July, and September with clear and overcast sky conditions were selected to separate the effects of canopy development and solar elevation on diurnal and seasonal light variability. \nDiurnal light variability expressed as the mean of the difference between two consecutive 10-min averages of PPFD and %PPFD decreased with increasing GSP on clear days in May. For clear days in July and September, variability was characterised by arc-shaped relationships with high variability for microsites receiving between 20 and 80% GSP and lower variability for microsites below 20 and above 80% GSP. On overcast days, diurnal variability in PPFD increased with increasing GSP while diurnal variability in %PPFD showed an arc-shape relationship. The coefficient of variation of PPFD and %PPFD decreased with increasing GSP on clear days and sunflecks decreased with decreasing GSP and from May to September. \nDay-to-day light variability expressed as the mean difference between consecutive daily PPFD increased with increasing GSP while the mean difference between consecutive daily %PPFD was higher for microsites receiving between 20 and 80% GSP. The coefficient of variation for the daily PPFD and %PPFD was higher for microsites receiving <20% GSP compared to other microsites. Seasonal light variability showed that microsites with <50% GSP received up to eight times more light in May than in July on both clear and overcast sky conditions because of canopy development. From July to September in clear sky conditions, decrease in light was variable for microsites receiving <40% GSP; probably because of the position of microsites in relation to the solar track. On overcast days, mean daily PPFD above canopy and in the understorey was 2 to 3 times higher in July than in September while mean daily %PPFD remained stable. The possible effects of the types of diurnal and day-to-day light variability on physiological and morphological responses of understorey plants are discussed.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».