Vie, mort et décomposition des feuilles d'espèces de succession secondaire méditerranéenne (vers une intégration de la gestion des éléments minéraux par les végétaux)

L objectif principal de cette thèse est la recherche de liens entre la gestion des ressources dans la feuille avant, pendant et après sénescence. Nous avons mené deux types d expérimentations : l une in situ dans un gradient de succession secondaire et l autre dans un jardin expérimental où 18 espèces caractéristiques des différents stades de cette succession ont été transplantées dans deux niveaux de disponibilité en azote. Nos résultats montrent que la durée de vie des feuilles et l efficacité de résorption des nutriments sont deux stratégies primordiales et alternatives de la conservation des éléments minéraux dans les plantes. La décomposabilité des litières est prédite par les traits des feuilles vertes et en particulier par la robustesse foliaire (teneur en matière sèche, résistances à la fracture et à l étirement). Le schéma d utilisation des ressources par les plantes décrit par le compromis acquisition vs conservation des ressources a été retrouvé le long du gradient de succession chez les espèces considérées. Les espèces de stade précoce ayant un fort potentiel d acquisition des ressources sont remplacées au cours de la succession par des espèces à forte capacité de conservation des nutriments, ces dernières produisant des feuilles à décomposition lente. Enfin, afin de relier le fonctionnement des espèces à celui des écosystèmes, nous proposons d utiliser la teneur en matière sèche des feuilles comme un marqueur fonctionnel de la décomposition des litièresThe main aim of this work is to determine the links between the processes occurring before, during and after leaf senescence. Two experiments were set up: one in a gradient of an old-field succession and a second one in a common garden experiment, where 18 species characterising the three stages of this succession were transplanted in two fertilisation levels. Our results demonstrate that leaf life span and nutrient resorption efficiency are two important and alternative strategies of nutrient conservation. Litter decomposability is successfully predicted by some traits of green leaves, especially those describing leaf robustness (leaf dry matter content, leaf tensile strength and leaf resistance to fracture). The leaf economic spectrum describing nutrient use in plants was found across species differing in successional stage. Species from early succession with high resource acquisition rates are replaced during succession by species which tend to conserve resources efficiently, the latter tending to produce leaves with low decomposition rates. Finally, in order to scale up from species to the ecosystem functioning, we propose to use leaf dry matter content as a functional marker of litter decomposabilityMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Contribution of leaf life span and nutrient resorption to mean residence time: elasticity analysis

International audienceWe tested the relative contribution of leaf life span (LLS) and nutrient r?sorption efficiency (RE) to nutrient mean residence time (MRT) in plants. To do so, we introduced the use of elasticity analysis, which aims to measure the impact on MRT of a small change in one component, relative to the impact of equal changes in the other element. We also quantified the joint effect of LLS and RE on MRT, which required the calculation of the second derivatives of MRT with respect to LLS and RE. The estimation of the first derivatives showed that, although MRT increases linearly with LLS for a given value of RE, the relative effect of RE on MRT elasticity varies according to RE values; when RE > 0.5, the MRT's elasticity increases exponentially. The calculation of the second derivatives confirmed the importance of RE on MRT's variation. We used the results of the elasticity analysis to analyze how MRT responded to variation in LLS and nitrogen RE on MRT at the intra-and interspecific levels. For this, we used 18 plant species from three stages of a Mediterranean old-field succession, grown in a common garden experiment at two levels of nitrogen supply

Trajectories of weed communities explained by traits associated with species' response to management practices

Trajectories of weed communities explained by traits associated with species' response to management practice

Species dominance rather than complementarity drives community digestibility and litter decomposition in species‐rich Mediterranean rangelands

International audienc

Effet des couverts sur la flore en viticulture

International audienceThe spontaneous vegetation in vineyards is diverse and occupies an important spatial and temporal place. This vegetation is impacted by the different soil management practices and the pedoclimatic diversity of the vineyard terroirs. Its management is thought out according to the agronomic objectives of yield and quality, notably to limit competition with the vine. This management also responds to other ecological challenges: reduction in the use of herbicides, reduction in fossil fuel consumption, and the agro-ecological transition of winegrowing systems. In the "mixed" management method, which is often used, weed management in the inter-row is mainly based on mechanical weeding and/or grassing with mowing, while weeding in the row uses a chemical herbicide. In 2016, in France, inter-row weed control, whether partial or total, concerns 52% of the national vineyard area and varies greatly depending on the risk of drought and the density of plantation, which are decisive factors in the establishment and management of seeded cover.Among the many services, often linked to soil quality, potentially provided by these sown cover crops called service crops is the reduction of weeds by limiting their growth and development and inhibiting their germination. Finally, the management of spontaneous biodiversity within plots cansatisfy other services such as the production of floral resources for pollinators or the production of biomass for grazing.La flore des parcelles viticoles est diverse et occupe une place spatiale et temporelle importante dans les vignobles ; elle varie selon les pratiques d'entretien du sol et le pédoclimat. La gestion de cette flore est déterminée selon des objectifs de rendement et de qualité, et également des enjeux écologiques (herbicides, énergie fossile, et transition agroécologique). Aujourd'hui, la gestion des adventices repose majoritairement sur le désherbage mécanique et/ou l'enherbement avec tonte dans l'inter-rang, et le désherbage du rang utilise un herbicide chimique. En 2016, en France, l'enherbement sur l'inter-rang concerne la moitié du vignoble national et varie suivant le risque de sécheresse et la densité de plantation. Les cultures de services rendent de multiples services, dont la réduction des adventices. Enfin la gestion des adventices en parcelles viticoles peut fournir des services en relation avec la biodiversité (production de ressources florales pour les pollinisateurs ou de ressources fourragères)

Relative importance of environmental factors and farming practices in shaping weed communities structure and composition in French vineyards

International audienceUnderstanding the relative importance of spatial, temporal variables, environmental conditions and management practices as filters for weed assemblages is essential to promote biodiversity in agrosystems. In this study, we used a unique data set covering 46 vineyard plots in France (Champagne, Beaujolais and Languedoc winegrowing areas) with 883 flora surveys performed between 2006 and 2012. The three objectives of the present study were: (1) to characterize weed communities composition and structure (richness and abundance) in vineyards from three traditional winegrowing areas in France; (2) to evaluate the relative importance of spatial, temporal variables, environmental conditions and management practices on weed species composition and structure; (3) to determine whether or not weed composition and structure are affected by the same factors. The results of the study revealed that season (including timing of management practices) was the most important filter for weed communities in vineyards, opposing in each plot a spring community and a summer-autumn community. Furthermore, spatial variations between regions (latitude), soil types (pH) and inter-annual variations (2006 to 2012) were also seen to have a strong effect on species turnover. Farming practices explained an overall low variation in composition of weed communities but some species showed a high and consistent fit to contrasting practices. For example, herbicide applications (mostly glyphosate) promoted some species such as Malva sylvestris and Sorghum halepense whereas tillage in inter-rows selected typical annual weeds such as Cerastium glomeratum and Galium aparine. Farming practices had a much higher influence on species richness and abundance with equal effect of both herbicides and soil tillage for controlling weed species richness and abundance in inter-rows, but stronger effects of herbicides were observed on species abundance in the rows. Tillage along the rows and a combination of mowing and tillage along the inter-rows were associated to the highest level of weed richness and abundance. Our study suggests that grapevine growers have a limited ability to influence species composition (mostly determined by abiotic factors) but their choice of management can modulate the level of weed richness and abundance. Our results will contribute to guide farmers towards more integrated management practices, ensuring both an optimal management of the spontaneous vegetation in vineyards and allowing this vegetation to provide various ecosystem services

Effet des couverts sur la flore en viticulture

International audienceThe spontaneous vegetation in vineyards is diverse and occupies an important spatial and temporal place. This vegetation is impacted by the different soil management practices and the pedoclimatic diversity of the vineyard terroirs. Its management is thought out according to the agronomic objectives of yield and quality, notably to limit competition with the vine. This management also responds to other ecological challenges: reduction in the use of herbicides, reduction in fossil fuel consumption, and the agro-ecological transition of winegrowing systems. In the "mixed" management method, which is often used, weed management in the inter-row is mainly based on mechanical weeding and/or grassing with mowing, while weeding in the row uses a chemical herbicide. In 2016, in France, inter-row weed control, whether partial or total, concerns 52% of the national vineyard area and varies greatly depending on the risk of drought and the density of plantation, which are decisive factors in the establishment and management of seeded cover.Among the many services, often linked to soil quality, potentially provided by these sown cover crops called service crops is the reduction of weeds by limiting their growth and development and inhibiting their germination. Finally, the management of spontaneous biodiversity within plots cansatisfy other services such as the production of floral resources for pollinators or the production of biomass for grazing.La flore des parcelles viticoles est diverse et occupe une place spatiale et temporelle importante dans les vignobles ; elle varie selon les pratiques d'entretien du sol et le pédoclimat. La gestion de cette flore est déterminée selon des objectifs de rendement et de qualité, et également des enjeux écologiques (herbicides, énergie fossile, et transition agroécologique). Aujourd'hui, la gestion des adventices repose majoritairement sur le désherbage mécanique et/ou l'enherbement avec tonte dans l'inter-rang, et le désherbage du rang utilise un herbicide chimique. En 2016, en France, l'enherbement sur l'inter-rang concerne la moitié du vignoble national et varie suivant le risque de sécheresse et la densité de plantation. Les cultures de services rendent de multiples services, dont la réduction des adventices. Enfin la gestion des adventices en parcelles viticoles peut fournir des services en relation avec la biodiversité (production de ressources florales pour les pollinisateurs ou de ressources fourragères)

Effet des couverts sur la flore en viticulture

International audienceLa flore des parcelles viticoles est diverse et occupe une place spatiale et temporelle importante dans les vignobles ; elle varie selon les pratiques d'entretien du sol et le pédoclimat. La gestion de cette flore est déterminée selon des objectifs de rendement et de qualité, et également des enjeux écologiques (herbicides, énergie fossile, et transition agroécologique). Aujourd'hui, la gestion des adventices repose majoritairement sur le désherbage mécanique et/ou l'enherbement avec tonte dans l'inter-rang, et le désherbage du rang utilise un herbicide chimique. En 2016, en France, l'enherbement sur l'inter-rang concerne la moitié du vignoble national et varie suivant le risque de sécheresse et la densité de plantation. Les cultures de services rendent de multiples services, dont la réduction des adventices. Enfin la gestion des adventices en parcelles viticoles peut fournir des services en relation avec la biodiversité (production de ressources florales pour les pollinisateurs ou de ressources fourragères)