N. Angéli, Nadia Ignatova (1, 2), Théodora Nedeltcheva(1, 3)

D. Viville, Etienne Dambrine (1)

B. Unité and . Inra-nancy, , p.67044, 1756.

B. Touzard, ;. , and S. Lavorel, B. Clément (1), vol.1, p.3

, Present address: UMR Université de Bordeaux 1 & INRA Pierroton « BIOdiversité, Gènes et ECOsystèmes » -Equipe Ecologie des Communautés Bâtiment B8 RdC Porte 11 Avenue des Facultés 33405 Talence France Tél : 33 (0)5 56 84 87 75 Fax : 33 (0)5 56 84 26 24 mél : b.touzard@lpcv.u-bordeaux.fr Secondary succession in wet grasslands has received surprisingly little attention. We analyzed the vegetation of a eutrophic alluvial wetland of western France and the relationship between its composition and environmental variables. The objectives of our study were twofold: (1) to describe species assemblages of wet grasslands and oldfields and correlate their species composition to hydrologic stress and (2) to study the changes in species composition, species richness, and species diversity when mowed meadows are abandoned. More than 100 species were recorded, and five species assemblages ('A' to 'E') were identified. Hydrology and land use (mowing versus land abandonment) were the two main ecological factors that affected plant community development

&. B',-'c'-from-'a' and &. , No significant differences were observed. Botanical composition of these plots did not differ significantly. In the first five years of land abandonment, there was an increase of litter, which reduces the species richness, diversity, and evenness. Live, above-ground biomass of grasslands was significantly greater than that of oldfields, but total organic matter (biomass + litter) was significantly greater for oldfields than for grasslands. Total biomass showed a negative logarithmic relationship with species richness

, Key Words: wetlands, species assemblages, successional patterns, floodplain, diversity, hydrodynamic stresses, land abandonment, litter, mowing 4P7

S. Delzon, D. Loustau (1), M. Sartore (1), R. Burlett (1) R Dewar
URL : https://hal.archives-ouvertes.fr/hal-01538650

. Laboratoire-de-bioclimatologie and . Bordeaux, Under steady-state conditions, tree hydraulic conductivity per unit of leaf area, KL, can be described by the Ohm's law, and when boundary layer conductance is large relative to stomatal conductance, gs, that leads to gs = KL * (?S -?L) / D, where ?S -?L are soil and needle water potential respectively and D is air saturation deficit. Accordingly, the conservation of the minimum needle water potential implies that any reduction in KL , e.g. as trees grow in height, leads to a proportional reduction in gs, vol.69, 2001.

, Stomatal conductance per unit leaf area is systematically lower in taller trees during the daytime. As a result of needle water potential regulation, stomatal closure was directly responsive to change in the hydraulic conductance

, Key-words: hydraulic conductance ; needle water potential

, 4P13 Influence de la fermeture du couvert forestier sur l'interception de lumière, le bilan de carbone, la croissance et l'allocation de biomasse de semis de Fagus sylvatica

L. Bonosi, P. Montpied, vol.1, issue.1

. Umr-inra-uhp, Ecologie et Ecophysiologie Forestières

. Umr-inra-engref-"lerfob,

A. L. Waldbau-institut and -. Freiburg,

, Partant de l'hypothèse que la tolérance à l'ombre des semis d'arbres forestiers dépend d'un bilan de carbone individuel positif, nous avons analysé certaines composantes de ce bilan sur des semis naturels de hêtre, d'érable sycomore et de frêne en forêt sous différents climats lumineux en analysant

, ) l'assimilation de carbone à l'échelle foliaire par une démarche de modélisation et des estimations d'allocation de l'azote foliaire aux différentes fonctions photosynthétiques (carboxylation, transfert d'électrons, interception de lumière); (3.) l'allocation de la biomasse aux différents compartiments des plantes. Des différences de réponse à la lumière entre les trois espèces ont été mises en évidence tant pour les valeurs des paramètres du modèle de photosynthèse foliaire, que pour la capacité d'interception de la lumière quantifiée à l'aide du STAR [Silhouette To Total Leaf Area Ratio] et pour les valeurs de LAR

, Mots clefs: régénération forestière, climat lumineux, acclimatation, semis forestiers