Effets de l'intensification de l'agriculture et de la déprise agricole sur la dynamique paysagère en Bretagne intérieure

Middle Brittany landscape have been studied at St Julien. Many alterations occur since 30 years, especially, following the break caused by the recession of agriculture. At the level of the study area, landscape diversity and complexity increased strongly after agriculture abandonment. This trend seems to be linked with the introduction of new landscape units and the abandonment of parcels. However, at the village's scale the large abandoned areas promote more shaded effects because of the uniformisation of the space. The importance of vegetation dynamics in former and abandoned agricultural lands is then emphasized. Concurrently, hedgerows' network has sustain deep damages that caused a loss of landscape's diversity in term of corridors.Le paysage en Bretagne intérieure, étudié au travers de la commune de St Julien (Côtes d’Armor) a subi d’importantes mutations depuis trente ans. En particulier, une cassure provoquée par la régression de l’agriculture s’est révélée avec force. Les abandons de parcelles sont une des principales causes de changement. La diversité et la complexité du paysage se sont alors accrues à l’échelle du groupe de villages. L’introduction de nouvelles unités écologiques et la dynamique propre des unités abandonnées sont apparues être le moteur de cette évolution. Par contre à l’échelle du village la forte vague de déprise agricole apparaît avoir des effets plus nuancés, provoquant l’homogénéisation de l’espace. La dynamique de la végétation des zones abandonnées est désormais le moteur de la dynamique paysagère. Parallèlement, le réseau bocager a connu en trente ans de profondes dégradations, sources d’une diminution de la diversité paysagère en terme de corridors.Diquélou Sylvain, Rozé Françoise. Effets de l'intensification de l'agriculture et de la déprise agricole sur la dynamique paysagère en Bretagne intérieure. In: Ecologia mediterranea, tome 23 n°1-2, 1997. pp. 91-106

Diversité floristique des prairies permanentes de Basse-Normandie (synthèse des travaux antérieurs)

National audienceThere has been a large number of studies of the floristic diversity in the permanent pastures of Lower Normandy during the latter half of the past century. Presently, when the consumers show a strong renewed interesting the products linked to local peculiarities and when the quality of dairy products has been shown by recent research work to be influenced by the grassland flora, it seemed useful to sum up all past studies and set up an inventory of the species and grassland communities present regionally; Lower Normandy has five dairy labels of origin ('AOC') for dairy products; the present study makes objective data available on the specific features of the pastures of Lower Normandy. By collecting phytosociological and agronomical surveys with a specific conversion method, it was possible to set up a data base with 2436 floristic surveys. The floristic diversity of the permanent pastures in Lower Normandy is large, with a total of 612 pasture species, viz. 61 grasses, 45 legumes, and 506 'forbs', the latter comprising both monocotyledons and dicotyledons. There is indeed a common 'botanical background' in the various dairy production basins of this region (11 species have a frequency between 50 and 80 %); nevertheless, there is a considerable floristic diversity in certain zones (with a number of species approaching 300 there). A total of 45 different plant communities were identified. Some of them, with a wide ecological range, are to be found on the whole of Lower Normandy. It is mainly the very rich accompaniment of forbs which gives Lower Normandy its singular character.Les études floristiques des prairies permanentes de Basse-Normandie ont été très nombreuses depuis 50 ans. Alors que les travaux de la recherche montrent l'impact de la flore prairiale sur la qualité des produits laitiers, il a semblé important de dresser l'inventaire des espèces et des communautés végétales prairiales rencontrées dans cette région qui produit 5 AOC laitières. En rassemblant relevés phytosociologiques et agronomiques par une méthode propre de conversion, une base de données de 2 436 relevés floristiques a été constituée. Les prairies permanentes bas-normandes présentent une forte diversité floristique : 612 espèces prairiales dont 61 espèces de graminées, 45 de légumineuses et 506 de "diverses". Il existe un "fonds prairial" commun aux différents bassins de production laitière de cette région (11 espèces présentent une fréquence comprise entre 50 et 80%), mais la diversité floristique peut être considérable dans certaines zones (le nombre d'espèces y étant voisin de 300). 45 communautés végétales ont été identifiées. Certaines communautés d'amplitude écologique large sont répandues sur tout le territoire bas-normand. C'est surtout par le cortège très riche de plantes diverses que la Basse-Normandie peut se singulariser

Réponses d'une lande atlantique au piétinement expérimental

National audienceLes réponses au piétinement d’une lande atlantique dominée par des ajoncs sont déterminées expérimentalement. Elles concernent deux niveaux d’organisation des systèmes biologiques : la communauté végétale (échelle communautaire) et les espèces végétales (échelle intracommunautaire). Deux expérimentations de piétinement sont menées : l’une en été, l’autre en hiver. Le piétinement est exercé pendant quatre mois, à différentes intensités : 10, 30 et 90 personnes par jour. Que le piétinement soit exercé en été ou en hiver, les réponses immédiates de la lande (échelle communautaire) sont semblables : la résistance de cette communauté végétale ne varie pas avec la saison de piétinement. Ces réponses montrent aussi qu’il n’y a pas de relation linéaire entre la dégradation de la végétation et l’intensité de piétinement. Les réponses différées de la végétation sont semblables, mais au sein de la lande (échelle intracommunautaire), les réponses d’un groupe taxinomique peuvent dépendre de la saison de piétinement. Par exemple, la résilience des ajoncs piétinés en hiver est plus grande que celle des ajoncs piétinés en été. Tous ces résultats sont à prendre en compte pour établir des orientations de gestion des landes piétinées

A study of 15^{15}N transfer between legumes and grasses

The overuse of classical N fertilisers contributes substantially to environmental degradation by pollution of groundwater by nitrates. This leaching of N in waters is also an economic flaw for farmers because only a part of the fertiliser is used by the plants. Here, systems involving mixtures of legumes and grasses represent a sustainable alternative because legumes can fix atmospheric N$_{2}$ using symbiotic microbes. N transfer in those mixtures has been thoroughly investigated but little is known concerning the effect of N fertiliser on N transfer between N-fixing legumes and companion grasses. In white clover (Trifolium repens L.) – perennial ryegrass (Lolium perenne L.) associations, N is transferred mostly through rhizodeposition into the soil by clover followed by re-uptake by ryegrass. Rhizodeposition of N occurs through senescence and decomposition of legume tissue or through exudation of N compounds by living cells. Ammonium and amino acids are the main compounds exuded and their exudation is thought to occur by passive diffusion attributed to a concentration gradient from root to soil. In this study, we test the hypothesis that greater N transfer from clover to grass, as seen in N-rich soils or nutrient solutions, is due to greater N rhizodeposition brought about by higher ammonium and amino acid content of roots. The relations between N input, root N content, N net exudation and N transfer between legumes and grasses were investigated using $^{15}$N by growing white clover and perennial ryegrass with increasing N application in axenic microlysimeters or in pots. Ammonium and amino acid concentrations were measured in root tissues, in root bathing solutions and in soils. We found that mineral N application strongly reduced atmospheric N fixation by clover, from 3.0 to 0.9 mg per plant, and root amino acid content, from 164 to 49 nmoles per g dry weight, but had no effect on ammonium and amino acid concentrations in sterile exudates, showing for the first time that amino acid net exudation is independent of root content. In contrast, ammonium and amino acid concentrations in clover soils increased with N fixation, showing the link between N fixation and N rhizodeposition in soils. Nitrate application increased ryegrass root growth by 7–8 times, and transfer of N between clover and ryegrass (by 3 times). It is concluded that N fertiliser does not modify N exudation but decreases N fixation and ammonium rhizodeposition in soil by clover. N fertiliser increases N transfer between clover and ryegrass by increasing soil exploration by ryegrass and giving a better access to different available N sources, including the N compounds exuded from clover

Transcriptomic, Metabolomic and Ionomic Analyses Reveal Early Modulation of Leaf Mineral Content in Brassica napus under Mild or Severe Drought

While it is generally acknowledged that drought is one of the main abiotic factors affecting plant growth, how mineral nutrition is specifically and negatively affected by water deficit has received very little attention, other than being analyzed as a consequence of reduced growth. Therefore, Brassica napus plants were subjected to a gradual onset of water deficits (mild, severe, or severe extended), and leaves were analyzed at the ionomic, transcriptomic and metabolic levels. The number of Differentially Expressed Genes (DEGs) and of the most differentially accumulated metabolites increased from mild (525 DEGs, 57 metabolites) to severe (5454 DEGs, 78 metabolites) and severe extended (9346 DEGs, 95 metabolites) water deficit. Gene ontology enrichment analysis of the 11,747 DEGs identified revealed that ion transport was one of the most significant processes affected, even under mild water deficit, and this was also confirmed by the shift in ionomic composition (mostly micronutrients with a strong decrease in Mo, Fe, Zn, and Mn in leaves) that occurred well before growth reduction. The metabolomic data and most of the transcriptomic data suggested that well-known early leaf responses to drought such as phytohormone metabolism (ABA and JA), proline accumulation, and oxidative stress defense were induced later than repression of genes related to nutrient transport

Comparative Omics Analysis of Brassica napus Roots Subjected to Six Individual Macronutrient Deprivations Reveals Deficiency-Specific Genes and Metabolomic Profiles

International audienceThe early and specific diagnosis of a macronutrient deficiency is challenging when seeking to better manage fertilizer inputs in the context of sustainable agriculture. Consequently, this study explored the potential for transcriptomic and metabolomic analysis of Brassica napus roots to characterize the effects of six individual macronutrient deprivations (N, Mg, P, S, K, and Ca). Our results showed that before any visual phenotypic response, all macronutrient deprivations led to a large modulation of the transcriptome and metabolome involved in various metabolic pathways, and some were common to all macronutrient deprivations. Significantly, comparative transcriptomic analysis allowed the definition of a subset of 3282, 2011, 6325, 1384, 439, and 5157 differentially expressed genes (DEGs) specific to N, Mg, P, S, K, and Ca deprivations, respectively. Surprisingly, gene ontology term enrichment analysis performed on this subset of specific DEGs highlighted biological processes that are common to a number of these macronutrient deprivations, illustrating the complexity of nutrient interactions. In addition, a set of 38 biochemical compounds that discriminated the macronutrient deprivations was identified using a metabolic approach. The opportunity to use these specific DEGs and/or biochemical compounds as potential molecular indicators to diagnose macronutrient deficiency is discussed

Drought specifically downregulates mineral nutrition: Plant ionomic content and associated gene expression

International audienc

Identifying generic proxies for assessing ecosystem properties and conservation status of semi-natural grasslands

International audienc

Leaf mineral nutrient remobilization during leaf senescence and modulation by nutrient deficiency

Higher plants have to cope with fluctuating mineral resource availability. However, strategies such as stimulation of root growth, increased transporter activities, and nutrient storage and remobilization have been mostly studied for only a few macronutrients. Leaves of cultivated crops (Zea mays, Brassica napus, Pisum sativum, Triticum aestivum, Hordeum vulgare) and tree species (Quercus robur, Populus nigra, Alnus glutinosa) grown under field conditions were harvested regularly during their life span and analyzed to evaluate the net mobilization of 13 nutrients during leaf senescence. While N was remobilized in all plant species with different efficiencies ranging from 40% (maize) to 90% (wheat), other macronutrients (K-P-S-Mg) were mobilized in most species. Ca and Mn, usually considered as having low phloem mobility were remobilized from leaves in wheat and barley. Leaf content of Cu-Mo-Ni-B-Fe-Zn decreased in some species, as a result of remobilization. Overall, wheat, barley and oak appeared to be the most efficient at remobilization while poplar and maize were the least efficient. Further experiments were performed with rapeseed plants subjected to individual nutrient deficiencies. Compared to field conditions, remobilization from leaves was similar (N-S-Cu) or increased by nutrient deficiency (K-P-Mg) while nutrient deficiency had no effect on Mo-Zn-B-Ca-Mn, which seemed to be non-mobile during leaf senescence under field conditions