How does sulphur availability modify N acquisition of white clover (Trifolium repens L.)?

The role of S in legume growth, N uptake, and N2 fixation was investigated using white clover (Trifolium repens L.) as a model species. We examined whether the effect of sulphate addition on N fixation resulted from a stimulation of host plant growth, a specific effect of S on nodulation, or a specific effect of S on nodule metabolism. Clones of white clover, inoculated with Rhizobium leguminosarum, were grown for 140 d in a hydroponic system with three levels of sulphate concentration (0 mM, 0.095 mM, and 0.380 mM). Nodule morphological and biochemical traits, such as root length, nodule biomass and volume, nodule protein contents (nitrogenase and leghaemoglobin obtained by an immunological approach), and root amino acid concentrations, were used to analyse the effect of sulphate availability on N2 fixation. The application of sulphate increased whole plant dry mass, root length, and nodule biomass, expressed on a root-length basis. N uptake proved less sensitive than N2 fixation to the effects of S-deficiency, and decreased as a consequence of the lower root length observed in S-deficient plants. N2 fixation was drastically reduced in S-deficient plants as a consequence of a low nodule development, but also due to low nitrogenase and leghaemoglobin production. This effect is likely to be due to down-regulation by a N-feedback mechanism, as, under severe S-deficiency, the high concentration of whole plant N and the accumulation of N-rich amino acids (such as asparagine) indicated that the assimilation of N exceeded the amount required for plant growth

Quand l’élevage est garant de la conservation de milieux patrimoniaux

National audienceSemi-natural grasslands present opportunities for delivering multiple services but their conservation is tightly dependent on livestock farming. Wetlands and steppes represent two contrasting examples of semi-natural lands for which water in excess or deficit drives both natural habitats and livestock farming. Wetlands deliver environmental services such as support of biodiversity, particularly birds and flood protection. They constitute complex territories as many stakeholders interact to manage water levels. Among them, livestock farmers play a key role by managing those flooded grasslands. Wet grasslands are still endangered by both conversion to improved grasslands or crops and abandonment due to the difficulties associated with exploiting constrained lands. In south east France, transhumant sheep breeding allows to maintain open vegetation that decreases the risk of both fires in the Alpilles hills and avalanche in the Alp mountains. In La Crau, maintaining Sheep grazing appears to be the only way to ensure the durability of the “Coussoul” habitat, the last steppe area in Europe. The crisis of sheep farming, return of wolves to the area and industrial development in La Crau all constitute a significant threat to this breeding system. The maintenance of breeding activities constitutes a challenge for the conservation of areas which have a high heritage value. Farming sectors face natural constraints which make management of the system more difficult and affect the economic viability, resulting in a need for an agroenvironmental policy. An increased market value of quality products, which are linked to production region, appears to be a lever to preserve livestock farming while conserving natural habitats.La conservation de nombreux écosystèmes patrimoniaux est conditionnée par le maintien d’une activité d’élevage extensive. Les prairies humides et les systèmes transhumants de Méditerranée constituent deux exemples contrastés de territoires à forts enjeux naturels où excès d’eau dans le premier cas et sècheresses annuelles dans l’autre conditionnent à la fois la végétation et les conditions d’élevage. Les marais portent des services environnementaux majeurs comme l’accueil de la biodiversité, notamment de l’avifaune ou la régulation des crues. Ce sont des territoires complexes où de nombreux acteurs interagissent autour de la gestion des niveaux d’eau. Parmi eux, les éleveurs jouent un rôle clé en gérant des prairies contraignantes à exploiter. Les prairies de marais sont fragilisées par un double mouvement d’intensification et de déprise agricole. L’élevage craven, exemple de système ovin transhumant de la plaine de Crau en zone méditerranéenne, permet de lutter contre la fermeture des milieux et joue un rôle de protection contre certains risques naturels comme les incendies dans les collines en Provence ou contre les risques d’avalanche dans les Alpes. Dans la plaine de la Crau, les éleveurs sont au coeur des enjeux de biodiversité dans la conservation du « Coussoul », dernière steppe européenne. Crise de la filière ovine, retour du loup et pression foncière grandissante sur les espaces de Crau menacent ce système d’élevage. Le maintien de l’élevage représente un véritable enjeu pour la conservation des espaces à forte valeur patrimoniale. Il dépend de la viabilité économique de formes d'élevage soumises à de fortes contraintes naturelles et nécessite donc une politique agroenvironnementale adaptée. La dynamique des territoires, à travers une valorisation de produits de qualité, apparaît également comme un levier pour préserver les activités d’élevage et conserver les habitats naturels

Analyse de photosynthèse sur plante entière avec le LI-COR LI6400. Construction et couplage d'une chambre

National audienc

LES DUNES GRISES DES COTES ATLANTIQUES (FONCTIONNEMENT, DYNAMIQUE POTENTIELLE, PRINCIPES DE GESTION CONSERVATOIRE ET PROCESSUS DE RESTAURATION)

LES DUNES GRISES DES COTES ATLANTIQUES FRANCAISES CONSTITUENT UNE VEGETATION DE PELOUSES RASES TRES DIVERSIFIEES. LES FACTEURS EDAPHIQUES, MECANIQUES, LES CONTRAINTES LITTORALES, LES PERTURBATIONS, AINSI QUE LES CARACTERISTIQUES INTRINSEQUES DES ESPECES, SONT AUTANT DE PARAMETRES RESPONSABLES DE LA STRUCTURE SPATIALE DES PELOUSES DUNAIRES EN MOSAIQUE. CETTE ETUDE FAIT APPARAITRE LE ROLE PREPONDERANT DES PERTURBATIONS DANS LES PROCESSUS DYNAMIQUES DE LA VEGETATION. LE SAUPOUDRAGE EST LE FACTEUR LE PLUS LIMITANT DANS LA DUNE DE TRANSITION. A INTENSITE LIMITEE, LE PATURAGE SEMI-NATUREL PAR LES LAPINS PERMET UN ACCROISSEMENT DE LA DIVERSITE DES DUNES GRISES. ENFIN, LES EFFETS DU PIETINEMENT SONT COMPLEXES. LA DUNE GRISE EST L'UNITE DU PAYSAGE QUI RESISTE LE MIEUX AU PIETINEMENT, ELLE RESTE NEANMOINS LA PLUS VULNERABLE CAR SA RESILIENCE EST TRES FAIBLE. LES PROCESSUS DE RESTAURATION DES DUNES GRISES DEPENDENT DE L'INTENSITE DE LA DEGRADATION. UNE SIMPLE OUVERTURE DU TAPIS VEGETAL PEUT CICATRISER RAPIDEMENT DES LORS QU'ELLE EST PROTEGEE. EN REVANCHE, UNE TROUEE NE SE RESTAURE QUE LENTEMENT ET FAIT INTERVENIR DES PROCESSUS LIES A UNE SUCCESSION PRIMAIRE ET D'AUTRES LIES A UNE SUCCESSION SECONDAIRE. AFIN DE FACILITER LA RESTAURATION, LA PLANTATION D'AMMOPHILA ARENARIA OU DE CAREX ARENARIA PEUT PERMETTRE UN BON RECOUVREMENT DU SOL. L'UTILISATION DE BRANCHAGES EST PLUS PROBANTE ET CONDUIT ASSEZ RAPIDEMENT A UN BON RECOUVREMENT ET A UNE DIVERSIFICATION FLORISTIQUE. DANS UN BUT CONSERVATOIRE, IL SERAIT INTERESSANT D'ENVISAGER UNE RESTAURATION DES DUNES GRISES A PARTIR DES PINEDES. LA NATURE FONDAMENTALE DU SOL DES PINEDES NE SEMBLE PAS IRREVERSIBLEMENT TRANSFORMEE, ET LES SOLS DES CLAIRIERES TENDENT A SE RAPPROCHER DE CEUX DES DUNES. LA RESTAURATION DE LA DUNE GRISE APRES UN ABATTAGE DES PINS NE POURRAIT SE BASER SUR UNE BANQUE DE SEMENCES PERSISTANTE MAIS POURRAIT BENEFICIER DE FLUX DE SEMENCES IMPORTANTS. LA COMPOSITION VEGETALE DES CLAIRIERES DE PINEDES SUR DUNE VARIE EN FONCTION DE LEUR POSITION GEOGRAPHIQUE, MAIS DEUX SCENARIOS DYNAMIQUES SEMBLENT GENERALISABLES : LA FERMETURE DE LA VEGETATION AVEC LE DEVELOPPEMENT DE FOURRES ET DE LANDES HAUTES, OU LE DEVELOPPEMENT D'UNE VEGETATION OUVERTE DE LANDES BASSES OU DE PELOUSES. DANS LA DERNIERE SITUATION, LA RESTAURATION DES DUNES GRISES SEMBLE POSSIBLE.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Ecologie de la restauration des dunes de Quiberon à Plouharnel.

34 p.Rapport de Contrat

A study of the dynamics of seed banks in a complex dune system, with the aim of restoration.

International audienceTo assess the possibility of restoring the original plant community of grey dune from a pine plantation, a synchronic study of the seed banks of three habitats, the grey dune, the pine plantation, and a clearing, was conducted at Quiberon (France). Five stations were selected: a Grey dune, Pine plantation 1, Pine plantation 2, Clearing 1, and Clearing 2. In contrast to the pine plantations, clearing 1, subject to heavy human disturbance, had a great similarity between its seed banks and its established vegetation. The larger clearing (C2) tend to resemble the grey dune, whereas the other was dominated by ruderal species. The analysis of the seed banks demonstrated differences between the clearings and the pine plantations from which they were derived. The potential vegetation of the clearings was closer to that of the grey dune and had a larger number of species with a short life cycle than the pine plantations. The seed banks of the pine plantations were not similar to that of the grey dune, but also differed from that of closed vegetation. This study suggested that it may not be possible to obtain a short term restoration of a grey dune after just clear felling only with the help of seed banks. On the other hand, seed dissemination could facilitate a restoration in a larger time scale as for clearings

Ecologie de la restauration des dunes de Quiberon à Plouharnel.

34 p.Rapport de Contrat

Grassland species are more efficient in acquisition of S from the atmosphere when pedospheric S availability decreases

International audienceAims Plants can absorb Sulfur (S) either through roots as sulfate or via leaves in a gas form such as SO2 or H2S. This study aims to examine whether the most efficient competitors for root uptake of sulfate among grassland species are also those with the greatest ability for foliar uptake and to test whether all species can increase their ability to use atmospheric S when available sulfate decreases. Methods Six grassland species were grown together in a non-S-enriched-atmosphere for 60 days with two levels of sulfate concentrations. Sulfate was 34S-enriched to distinguish root uptake of sulfate and foliar uptake of gaseous S. Results Grasses were more competitive for sulfate uptake and more efficient at producing biomass for the same amount of S in comparison to the non-fixing forb and the legumes. All species studied were able to increase their ability to use atmospheric sources of S when sulfate availability decreased. The percentage of S derived from the atmosphere was strongly related to sulfate concentration in leaves. Conclusion Grasses were more efficient for root sulfate uptake but forbs seemed more efficient for foliar uptake. Sulfate in plant tissues could play a key role in regulation between the foliar and root S uptake