Trembling aspen (Populus tremuloides) leaf litter decomposition under simulated nitrogen and sulfur deposition in a mixedwood boreal forest
Notice bibliographique
Résumé
As one of the largest oil sands deposits in the world, the Athabasca oil sands region (AOSR) has generated and released large amounts of nitrogen oxides (NOx) and sulfur dioxide (SO2) to the atmosphere and the surrounding area. Long-term N and S deposition at elevated rates can cause soil acidification, decrease forest productivity, and change plant community composition. Litter decomposition is an important component of nutrient and carbon (C) cycling in terrestrial ecosystems which relate to forest productivity and greenhouse gas emissions. Litter decomposition rates are affected by many factors such as climate, litter chemistry, N and S addition, soil properties, and litter enzyme activities. To better understand how N and S deposition impacts litter decomposition in a boreal forest, I conducted laboratory (100-day) and field (18-month) experiments in this study. Litter and forest floor (F and H layers, after removing current litter layer) samples were collected from a mixedwood boreal forest located about 100 km southeast of Fort McMurray, northern Alberta. Litter C, N and S concentrations were determined using an elemental analyzer. Litter lignin concentration was analyzed by measuring absorbance at 280 nm following acetyl bromide digestion. Other elemental concentrations including calcium (Ca), magnesium (Mg), aluminum (Al), and manganese (Mn) were determined using an ICP-MS method. The MBC and MBN concentrations from the forest floor were determined using a fumigation-extraction method. Extracellular enzyme activities involved in C, N and S cycling were analyzed using fluorimetric and colorimetric methods: β-1, 4-glucosidase (GLU, enzyme classification (EC) EC 3.2.1.21) for C, β-1, 4-N-acetylglucosaminidase (NAG, EC 3.2.1.14) for N, and arylsulfatase (ARS, EC 3.1.6.1) for S. In the laboratory study, 10 years of N and S deposition changed trembling aspen (Populus tremuloides) litter chemistry and forest floor microbial properties. Cumulative CO2 emission (Ccum) from the litter was negatively correlated with C/N and lignin/N ratios in litter (P < 0.05), but not with forest floor microbial properties (P > 0.05). This laboratory study provided evidence that N and S addition can enhance litter decomposition through changed litter chemistry, suggesting that C cycling in the boreal forest ecosystem in the oil sands region can be significantly affected by long-term N and S deposition. However, these results need to be testified in the field. In the field study, N and S addition did not directly affect litter decomposition rates (P > 0.05) (Experiment I), and nutrient-induced changes in litter chemistry did not regulate litter decomposition rates under N and S addition (P > 0.05) (Experiment II). Litter N exhibited an immobilization phase followed by an initial release phase, while an initial leaching phase occurred followed by an immobilization phase until the end of study for S in both experiments. And extracellular enzyme activities in litter did not correlate with litter decay constants. To fully understand the effect of N and S deposition on litter decomposition, a long-term decomposition study is recommended.
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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 | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| 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) | 0,000 | 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 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 ».