Do tree-species richness, stand structure and ecological factors affect the photosynthetic efficiency in European forests?

No abstract available

Lipid peroxidation and chlorophyll fluorescence of photosystem ii performance during drought and heat stress is associated with the antioxidant capacities of C3 sunflower and C4 maize varieties

Agricultural production is predicted to be adversely affected by an increase in drought and heatwaves. Drought and heat damage cellular membranes, such as the thylakoid membranes where photosystem II occurs (PSII). We investigated the chlorophyll fluorescence (ChlF) of PSII, photosynthetic pigments, membrane damage, and the activity of protective antioxidants in drought-tolerant and -sensitive varieties of C3 sunflower and C4 maize grown at 20/25 and 30/35 °C. Drought-tolerant varieties retained PSII electron transport at lower levels of water availability at both temperatures. Drought and heat stress, in combination and isolation, had a more pronounced effect on the ChlF of the C3 species. For phenotyping, the maximum fluorescence was the most effective ChlF measure in characterizing varietal variation in the response of both species to drought and heat. The drought-tolerant sunflower and maize showed lower lipid peroxidation under drought and heat stress. The greater retention of PSII function in the drought-tolerant sunflower and maize at higher temperatures was associated with an increase in the activities of antioxidants (glutathione reductase, superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase), whereas antioxidant activity declined in the drought-sensitive varieties. Antioxidant activity should play a key role in the development of drought- and heat-tolerant crops for future food security

Effects of a fin edge close to a point caustic of a Gregorian antenna

The problem of edge diffraction close to a point caustic is analyzed in a typical dual-reflector Gregorian antenna in offset configuration. The diffraction phenomenon is produced by a perfectly conducting fin located between the feeder and the main reflector. This fin is sometimes used to reduce the coupling between the primary feed and the main reflector. For the sake of simplicity, the two-dimensional case is studied here, but the present technique can also be applied to practical three-dimensional configurations. © 1997 John Wiley & Sons, Inc

Des problèmes dans la classification des chênes, taxonomie en Europe et région méditerranéenne

Le genre Quercus présente de grandes difficultés taxonomiques car son polymorphisme élevé, a suscité, pour de très nombreux taxons, des descriptions qui souvent résultent de méthodes incertaines. En comparant, dans les principaux traités existants, la distribution et la classification des taxons du genre Quercus en Europe et dans la région méditerranéenne, on met en évidence une notable incertitude taxonomique : ceux qui, pour certains auteurs, sont des espèces à propement parler, ne sont pour d'autres que des sous-espèces ou variétés. Dans le présent travail, nous avons réalisés une compilation bibliographique en cherchant à regrouper les taxons, tels qu'ils sont décrits par divers auteurs, en un nombre limité d'espèces principales

Tree species diversity and forest productivity -

Scientists and policy makers have looked at Mediterranean forest biodiversity mainly from a conservation point of view. But biodiversity is increasingly considered an important aspect of ecosystem functioning. In this presentation, we review more specifically diversity-productivity relationships in forests. But it's not an easy task, because the problem is that forest condition and growth are determined by many interacting environmental and management factors. In this context, developing an international network of such experiments, including Mediterranean sites, would be very useful

Relation entre diversité des espèces d'arbres et productivité des forêts -

Les scientifiques et les décideurs se sont penchés sur la biodiversité des forêts méditerranéennes essentiellement d'un point de vue de la conservation. Mais la biodiversité est de plus en plus considérée comme un facteur important du fonctionnement même des écosystèmes. Cet article examine plus particulièrement la relation diversité-productivité en forêt. Mais la tâche n'est pas facile car l'état de la forêt et sa croissance sont déterminés par de nombreux facteurs interdépendants, environnementaux et de gestion. Dans ce cadre, un dispositif expérimental très spécifique serait utile via le développement d'un réseau international d'expériences et, tout particulièrement, sur certains sites méditerranéens

Actual and potential impact of air pollution on Italian forests: results from the long-term national forest monitoring networks under the ICP Forests

Actual and potential pressure and impacts of air pollution have been summarized by using the dataseries of the Italian forest monitoring networks (CONECOFOR), mostly on the basis of evaluations carried out within the LIFE project SMART4Action. Trends in air pollution shows only few important reductions (e.g.: sulphate and ozone). The impacts on forest health status, increments and standing volumes, plant diversity, soil and nutrient are discussed. Evidences of risk are also reported, mainly due to N deposition, on all the response factors