Notice bibliographique
Résumé
The specific physiological mechanisms governing the process of diatom sedimentation were not well understood. This study investigated the possibility of a short term energy requirement for buoyancy maintenance in marine diatoms which varied predictably with physiological state. The maximum sinking rate (MSR) of Ditylum brightwellii was measured under progressive energy limitation which allowed the determination of the energydependent potential for a cell to reduce its MSR. There was systematic experimental evidence that this diatom's ability to gain energy from storage products via respiration is the principal determinant of its sinking rate. This study provides the first quantification of the negative exponential relationship between respiration rate and sinking rates. Preliminary studies with two other species indicate that a spectrum of energy-dependence may exist. Diatom blooms are the annual periods of highest "new" production and carbon sedimentation. Results from a 5-year study in Auke Bay, Alaska showed that termination of the spring bloom consistently occurred at limiting nitrate concentrations. The sinking response of diatoms to ambient nutrients influenced both species succession during the spring bloom and the subsequent sedimentation of new production. Threshold nitrate concentrations approximating Ks values of the species present, were found to signal initiation of increased sedimentation. Results suggested genus-specific differences in sinking-rate sensitivity to nitrate exhaustion. Overall, sinking rates of the three principal genera ranked (high to low) Thalassiosira spp.--> S. costatum --> Chaetoceros spp., while the nitrate sensitivities of the sinking rates of the genera ranked (high to low) Thalassiosira spp. --> Chaetoceros spp. --> S. costatum. For Thalassiosira aestivalis, sinking rates over all five years did not vary significantly with physical water properties such as ambient temperature, salinity or sigma-t. However daily irradiance showed a significant negative correlation with sinking rates, as did ambient nutrient concentrations. At low daily irradiances (< 3 x 10^21 quanta m^-2 d^-1), ambient nutrient concentration was a better predictor of sinking rate than at high irradiances. The fastest-sinking, most nutrient-sensitive diatoms, the Thalassiosira species, constituted the major source of vertical carbon flux in this embayment during the spring bloom and, considering their cosmopolitan distribution, probably do so in many other such coastal ecosystems. In general, the tendency to sink to the benthos during and/or after a bloom was highly dependent on species-specific cell physiology. Sexuality was observed in Ditylum brightwellii, both in the laboratory and during a fall bloom of this species off Jericho Beach, Vancouver B.C. The field observations indicated that a fraction (ca. 3 %) of the natural population blooming in the upper 3 m became sexual, about a week after the species was first observed to dominate the community. In the laboratory, when sexuality was induced through NO3 limitation and an increase in irradiance, sinking rates increased over 100 times. Maximum sinking rates occurred for zygotes and early post-auxospore cells. Post auxospore cells quickly reduced their sinking rates, and a large fraction of post-auxospore cells began to float at substantial rates (up to 0.4 m d^-1) within one week of formation. Sexuality may have a special role in the life cycle of diatoms such as D. brightwellii, including a mechanism for rapid escape from the photic zone, vertical partitioning of a physiologically stressed population into sexual and non-sexual fractions, and subsequent recolonization of the surface waters by positively buoyant postauxospore cells. The timing and magnitude of diatoms' sinking response to physiological stress may be important in all life history stages of diatoms, and may ultimately affect the balance of selective forces in their evolution.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
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 | 0,000 | 0,000 |
| 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) | 0,001 | 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 ».