Direct assessment of competitive ability and defoliation tolerance in perennial grasses
Notice bibliographique
Résumé
Stipa clarazii is a dominant, late-seral perennial grass species under exclosure or lightly grazed rangelands in semiarid Argentina, whereas S. tenuis and S. ambigua are earlier-seral perennial tussock grasses. Recent studies have demonstrated that late-seral species are more competitive and can have either similar or greater herbivory tolerance than earlier-seral species. We hyphothesized that (1) tolerance to defoliation is greater on defoliated plants of S. clarazii than on those of S. tenuis and S. ambigua, (2) competitive ability is greater in S. clarazii than in S. tenuis and S. ambigua when plants remain undefoliated or are exposed to a comparable defoliation intensity, and (3) competitive ability decreases in S. clarazii when this species is selectively defoliated within a non-defoliated, nearby neighbourhood of S. tenuis or S. ambigua. The study objectives included obtaining a direct measure of competitive ability and defoliation tolerance in the three perennial grasses when they grew either in isolation or in different neighbourhoods and were exposed to various defoliation patterns in the field. In 1998, two parallel studies were conducted within a 2-yr-old field exclosure during one growing season. In one study, responses were evaluated on either defoliated or undefoliated plants of all three species without neighbours. In a second experiment, four types of neighborhoods were selected such that a central (target) plant of one species was surrounded by five neighboring plants of a different species. Three different defoliation patterns were imposed on each neighbourhood type. Results led to acceptance of the first and second and rejection of the third hypothesis. When plants grew without nearby neighbours, greater growth rates for height, dry matter production and end-of-season daughter tiller production per parent tiller in S. clarazii relative to S. tenuis and S. ambigua contributed to greater regrowth in S. clarazii. Amounts of 15N atom excess were always greater in S. clarazii than in S. tenuis and S. ambigua independently of neighbourhood type and pattern of defoliation. However, uptake of 15N was similar in S. clarazii to that in S. tenuis or S. ambigua when S. clarazii was selectively defoliated within a non-defoliated, nearby neighbourhood of any of the other two species. Selective herbivory of S. clarazii, rather than factors associated with its competitive ability and defoliation tolerance, were found to be the major determinant driving its replacement by earlier-seral, less desirable perennial grasses in rangelands of central Argentina. Key words: 15N, Argentina rangelands, biomass, nitrogen uptake, species replacement, Stipa
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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 | 0,000 | 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 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 ».