A comparative biogeochemical study of extant, and fossil gymnosperm wood from Axel Heiberg Island, Canada
Notice bibliographique
Résumé
An analysis of the main lignin, polysaccharide and hemicellulose components of modern and fossil Metasequoia and Larix woods was conducted through the application of Py-GC/MS, tetramethylammonium .hydroxide (TMAH) thermochemolysis, 13C NMR, Py-MS and TG-DSC in order to discern the main similarities and differences between modern and fossil woods, an~ to discover the main reasons for their preservation, the main processes involved in the initial stages of fossilisation, and the palaeoenvironment associated with their depositional sites in Axel Heiberg Island, Canada. Four modern Larix species woods were compared to each other, and then to the only extant Metasequoia species wood to discover the exact similarities and .any differences between them. This was done because the exact species of fossil Larix and Metasequoia are unknown. No differences were found and it is assumed that as no differences exist between modern species, no differences exist between fossil species. The Py-GC/MS total ion chromatogram of the modern woods showed carbohydrate and guaiacyl lignin-derived compounds indicative of gymnosperm wood. A decrease in carbohydrates relative to the modern woods was discovered in the fossil woods and a relative increase in methoxyphenols and tannins. Similarities to the effects of degradation through fungal invasion were noted in the analysis of the fossil woods with a relatively decreased polysaccharide compared to their modern counterpart, with the possibility of fungal degradation during early diagenesis. The TMAH thermochemolysis total ion chromatograms showed an increase of threo/erythro 1-(3,4-dimethoxyphenyl)-1,2,3-trimethoxypropane (G14/G15 - long chain) over 3,4-dimethoxybenzaldehyde/3,4-dimethoxybenzoic acid methyl ester (G4/G6 - short chain) guaiacyl structures from modern to fossil. Similarities to the effects of degradation through fungal invasion were again noted in the analysis of the fossil woods where long chain guaiacyl structures dominate over the short chain guaiacyl structures, reinforcing the possibility of fungal input during early diagenesis. 13C NMR analysis highlighted an increase in side chain degradation from the guaiacyl units thus forming condensed guaiacyl structures, and a decrease in carbohydrate content from the fossil woods relative to the modern woods. Possible tannin input was detected contributing to wood preservation. TG-DSC and Py-MS analysis showed carbohydrate content decreased from modern relative to fossil sample and condensed lignin structures increased. Polysaccharides were shown to be more in abundance within the Metasequoia than Larix sample indicating less degradation had occurred. The fossil woods although degraded, had maintained their basic carbohydrate/lignin structure and were comparable to modern woods degraded through fungal invasion. In addition the nature of the degradation was found to resemble that caused by white rot fungi. The general state of degradation was less severe in the Metasequoia than the Larix. The Metasequoia wood had probably been deposited after that of the Larix and in different environmental conditions, being slightly anoxic, with less fungal input. The presence of tannins together with the subsequent extreme cold of Axel Heiberg Island probably contributed to the woods preservation over time.
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 machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| 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 | 0,003 | 0,003 |
| Études des sciences et des technologies | 0,002 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 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 source (Gemma direct ou Codex distillé), 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 ».