Comprendre et aménager la diversité fonctionnelle florale des agrosystèmes pour conserver les insectes pollinisateurs de la parcelle au territoire

La transition agroécologique des systèmes agricoles nécessite la mise en place d’écosystèmes diversifiés favorisant les régulations biologiques. Parmi elles, la pollinisation entomophile assure la reproduction de la majorité des plantes à fleurs et une stabilisation des rendements des cultures. Pour enrayer le déclin des insectes pollinisateurs, les paysages agricoles pourraient fournir des ressources florales diversifiées et continues et des habitats favorables à ces pollinisateurs comme les prairies permanentes. Mon projet de recherche a ainsi pour objectifs de comprendre et quantifier la diversité fonctionnelle florale, de favoriser une gestion sans pesticide et résiliente au changement climatique et d’évaluer la pollinisation de la parcelle au territoire agricole. Il s’inscrit dans la continuité de mes activités les plus récentes et s’appuie sur mes compétences en écophysiologie végétale, en écologie des communautés, en agroécologie et en écologie de la restauration. Mes futures recherches seront axées sur l’observation de mécanismes fonctionnels à partir d’expérimentations in et ex situ et le renforcement des liens entre mes travaux et la gestion des écosystèmes afin de favoriser l’appropriation des concepts d’écologie fonctionnelle par les gestionnaires

Projet SICFOR. Du suivi aux indicateurs de changement climatique en forêt

Afin d’identifier et de promouvoir les mesures qui permettront de diminuer la vulnérabilité de la société face aux effets du réchauffement climatique,la France a mis en place son premier Plan National d’Adaptation au Changement Climatique(PNACC) en 2011. Concernant les écosystèmes forestiers, ce plan prévoit notamment deux mesures complémentaires : la mise en ligne d’indicateurs de changement climatique en forêt (2.3) et la valorisation et l’adaptation du monitoring forestier pour le suivi de la réponse des écosystèmes au changement climatique (2.4). En France, l’Observatoire National sur les Effets du Réchauffement Climatique (ONERC) met à disposition du public un jeu d’indicateurs sur le changement climatique et ses impacts (tous milieux confondus). Le nombre d’indicateurs a progressivement augmenté depuis 2005 pour atteindre environ 25 à ce jour. Parmi eux, un seul indicateur concerne la forêt: le front d’expansion de la chenille processionnaire du pin. Le projet SICFOR a été mené durant l’année 2013 afin d’établir un jeu d’indicateurs potentiels du changement climatique en forêt. Financé par le Ministère de l'agriculture, de l'agroalimentaire et de la forêt et coordonné par le GIP Ecofor, il s’est appuyé sur une expertise associant chercheurs, agents du développement et décideurs. Le travail a été structuré en cinq groupes thématiques autour des différents types d’indicateurs : bioclimatiques, phénologiques, productivité et santé des forêts, répartition des espèces, et adaptation de la gestion forestière. Les questions auxquelles les indicateurs potentiels devaient répondre ont été formulées, puis chaque indicateur a été évalué selon une grille construite à partir de modèles existants. Les principaux résultats du projet SICFOR sont (i) une synthèse des indicateurs du changement climatique disponibles au niveau mondial, en particulier pour les écosystèmes forestiers, (ii) une proposition d’un jeu d’indicateurs potentiels et leur évaluation, (iii) le recensement des données actuellement disponibles pour la construction de ces indicateurs, notamment via les dispositifs d’observation existants, et (iv) la présentation des recherches en cours et les limites pour mener à bien les actions sus-mentionnées du PNACC

Drought response and urban-pollinator attractiveness of ornamental plant species

Faced with pollinator declines, cities could serve as refuges for biodiversity conservation by managing floral resources in public green spaces. Ornamental plants could play an important role in attracting pollinators because they form part of urban floral management. However, knowledge of how their floral traits respond to drought is lacking, and it is unknown whether they will be suitable for pollinators under future climates. The main objective of this study was to determine the covariation of floral traits of ornamental plant species and effects of drought on them. To this end, in a city greenhouse we measured floral traits of eight ornamental species commonly used in urban green spaces in France. We subjected the plants to a control treatment or a drought treatment, reducing the volume and frequency of watering. We observed interspecific variability in floral traits among these species and a change in covariation between the traits pollen quantity and nectar quantity in the drought treatment. Drought influenced morphological traits related to floral display more than other floral traits, with mean decreases of 28 % in floral height, 35 % in floral area and 58 % in the number of floral units. Ornamental plants seemed attractive to different morphotypes of pollinators depending on their floral unit number, nectar sugar concentration or nectar tube depth, with most visits made by Hymenoptera. These results are expected to encourage green-space managers to select urban plants according to their functional characteristics and adapt their choice of plants to climate change

Accumulation of metallic trace elements in Reynoutria japonica: a risk assessment for plant biomass valorization

International audienceSustainable solutions aiming at limiting Reynoutria japonica invasion consist of frequent removal of its aerial biomass. The aims of this study were to measure the accumulation of metallic trace elements (MTE) in R. japonica, and to assess the ecotoxicological risk related to the valorization of the produced biomass. R. japonica fragmented rhizomes were regenerated in pots for 41 days on a control soil (CTL) or a moderately MTE-contaminated soil (POL, 3.6 mg Cd kg −1 DM). Growth traits were recorded, as well as MTE bioconcentration (BCF) and translocation factors (TF) from soil to plant organs. Whatever the MTE and plant organs, BCF remained below one (mean Cd-BCF for stem and leaf: 0.07 and 0.29 for CTL and POL, respectively), conversely to TF (until 2.2 for Cd and Ni in POL soil). When grown on the POL soil, R. japonica stem and leaf Cd content was close to the EU maximum regulatory limit for organic amendments or animal feed. Model simulations suggested that liver and kidney Cd concentrations would exceed the regulatory limit in food when adult cattle or sheep constantly ingest R. japonica grown on the POL soil over 200 to 800 days. The results of the present study will be useful to help managers in selecting efficient and safe solutions for the control of R. japonica invasion

Permanent grassland classifications predict agronomic and environmental characteristics well, but not ecological characteristics

International audiencePermanent grasslands produce highly diverse ecosystem goods and services, which need to be easily assessed by decision makers. Naturalists and agronomists classify grasslands in different ways to predict ecological, agronomic and environmental characteristics of the grasslands. However, few studies have compared the prediction abilities of these different classifications using the same botanical relevés, and none has explored the utility of combining classifications. In this study, we attributed a grassland class from each of three classifications (phytosociological, agronomic and functional) to 250 permanent grasslands in north-eastern France to predict 16 characteristics: nine ecological, three agronomic and four environmental. We used statistical model selection to identify the classification or combination of classifications that best predicted each characteristic. Our results showed great prediction ability of agronomic classification, which created the best models for predicting agronomic (yield) and environmental (management, elevation) characteristics. We also identified a strong prediction ability of combining two or all three classifications to predict seven other grassland characteristics. However, grassland classifications did not predict most of the ecological characteristics well. We can assume that phytosociological classification, despite its mainstream use, predicts grassland characteristics less well than agronomic classification. We recommend combining grassland classifications to improve rapid prediction abilities. This study provides new knowledge useful for developing grassland classifications which meet the needs of agronomists and naturalists

Using Matching Traits to Study the Impacts of Land-Use Intensification on Plant–Pollinator Interactions in European Grasslands: A Review

International audiencePermanent grasslands are suitable habitats for many plant and animal species, among which are pollinating insects that provide a wide range of ecosystem services. A global crisis in pollination ecosystem service has been highlighted in recent decades, partly the result of land-use intensification. At the grassland scale, however, the underlying mechanisms of land-use intensification that affect plant–pollinator interactions and pollination remain understudied. In this review, we first synthesise the literature to provide new insights into the relationships between land-use intensification and pollination by using matching community and interaction traits. We then identify knowledge gaps and summarise how land-use intensification of grassland influences floral traits that may in turn be associated with modifications to pollinator matching traits. Last, we summarise how these modifications may affect pollination function on permanent grasslands. Overall, land-use intensification may lead to a shift in flower colour, a decrease in mean nectar tube depth and a decrease in reward production and pollen quality at the community level. This, in turn, may generate a decrease in pollinator mouthparts length and body size, that may favour pollinators that require a low amount of floral reward. We found no study citing the effect of land-use intensification on volatile organic compounds emitted by flowers despite the importance of these molecules in pollinator community composition. Overall, our review highlighted major knowledge gaps about the effects of land-use intensification on plant–pollinator interactions, and suggests that land-use intensification could favour plants with generalised floral traits that adversely affect pollination

Vers un outil d’aide à la décision pour l’adaptation des forêts françaises au changement climatique

The impact of climate change on forest ecosystems now encourages managers to implement adaption strategies in terms of species choice despite the uncertainty of future scenarios. To achieve this, a quantified characterization of species ecological requirements is necessary. The project Traitaut thus aimed at developing a new quantitative approach to characterize the species autoecology, especially including the functional traits. A research and development community and a web platform including a database of bibliographic sources on different species were built. The analysis of the TRY database showed that functional traits can be used to the parameterization of growth and species distribution models but it is necessary to register the values of abiotic factors for each trait measurement. Study and comparison of the European decision support tools underlined the need to establish such a tool in France and they were used to do relevant specifications for the tool building.L’impact du changement climatique sur les écosystèmes forestiers incite dès à présent les gestionnaires à mettre en place des stratégies d’adaptation en termes de choix d’essences malgré l’incertitude des scénarios futurs. Pour y parvenir, une caractérisation quantifiée des exigences des essences par rapport au milieu est nécessaire. Le projet Traitaut visait ainsi à développer une nouvelle approche quantitative de l’autécologie des essences, en intégrant notamment les traits fonctionnels. Une communauté de recherche et développement et une plateforme web contenant une base de sources bibliographiques sur différentes essences ont été mises en place. L’analyse de la base de données TRY a montré que les traits fonctionnels peuvent être utilisés afin de paramétrer des modèles de croissance et de distribution des essences mais qu’il était essentiel d’enregistrer les valeurs des facteurs abiotiques pour chaque mesure de trait. L’étude et la comparaison des outils d’aide à la décision en Europe ont souligné la nécessité d’élaborer un tel outil en France et ont permis l’élaboration d’un cahier des charges pertinent pour sa construction

Evidence of a seasonal trade-off between growth and starch storage in declining beeches: Assessment through stem radial increment, non-structural carbohydrates and intra-ring δ13C

Forest decline is reported in recent decades all over the world. However, developing a clear vision of the associated tree dysfunctioning is still a challenge for plant physiologists. In this study, our aim was to examine the seasonal carbon adjustments of beech trees in the case of a long-term drought-induced decline. We compared healthy and declining trees in terms of stem radial growth, phloem sugar content and δ13C, together with xylem carbohydrates and intra-ring δ13C patterns. The radial growth of declining trees was clearly reduced by lower growth rates and shorter growing season length (44 days compared with healthy trees). The soluble sugar content was higher in the xylem of declining trees compared with the healthy ones, but similar in the phloem except at the end of their growth. Declining trees increased their levels of xylem starch content from budburst until the date of maximal growth rate. These reserve dynamics revealed an early trade-off between radial growth and starch storage that might be the result of an active or passive process. For declining trees, the slight decrease of intra-ring cellulose δ13C pattern during the early growing season was attributed to the synthesis of 13C enriched starch. For healthy trees, δ13C patterns were characterized by a progressive 13C increase along the ring, attributed to increased water-use efficiency (WUE) in response to decreased water availability. Individual variations of the crown area were negatively correlated to the intra-ring δ13C amplitude, which was ascribed to variations in canopy WUE and resource competition for healthy trees and partly to variations in the amount of reserves accumulated during spring for declining ones. Our study highlights the carbon physiological adjustment of declining trees towards reducing spring growth while storing starch, which can be reflected in the individual intra-ring cellulose δ13C patterns

Facial area and hairiness of pollinators visiting semi-natural grassland wild plants predict their facial pollen load

International audience1. Consequences of a decline in pollination function in semi-natural ecosystems are largely unknown due to variability in pollinator effectiveness, that is, their contribution to pollen deposition alone. While pollination effectiveness has been shown to be related to body size and hairiness of pollinators for some crops, studies encompassing a wide diversity of pollinators interacting with wild plant communities are lacking. 2. Thus, the relationships between pollen load, which is a measurement of pollen transport ability and a proxy of pollinator effectiveness, and morphological traits of pollinators sampled in 16 grasslands in Moselle, France, were investigated. The area, hairiness, and pollen load of each pollinator's face were measured for 658 individuals from 127 bee and fly species interacting with 36 wild plant species. Pollinator dry mass was also measured on 543 individuals from 109 species. 3. Dry body mass and facial area of pollinators were positively linked. This study highlights that bees transported significantly more pollen grains on their face than flies. Furthermore, bees' faces were larger and hairier. We also found that pollinators' facial pollen load increased with facial area and hairiness when we considered all pollinators. However, hairiness is not significant within pollinator group (bees or flies), mirroring a potential phylogenetic signal. 4. Hence, this study shows a wide diversity of pollinator and plant species in which larger and hairier pollinators may transport more pollen grains, at least on their face. However, future studies involving other pollinator body parts are needed to generalise these relationships

Evaluation and comparison of pollination service indicators at agricultural landscape level

International audienceThe current pollinator decline is a major issue, notably because one-third of the world agricultural production depends on pollination. However, quantifying whether the loss of some pollinators translates into less efficient pollination remains challenging, particularly at the scale of farmland territories, which is a relevant scale for action. On the one hand, clear links have been established between the abundance and diversity of pollinators and pollination efficiency only over relatively small areas, because time-consuming experimental methods prohibit studies over broader areas. On the other hand, nationwide or continentwide indices exist but they either measure potential pollination only or have not been validated against other metrics characterizing pollinators or pollination.The aim of our study was to assess the relevance of two pollination indicators developed at national or broader scale, to characterize pollination over a 950-ha farmland territory of field crops (Fénay platform near Dijon, France). We specifically evaluated the realized pollination service indicator, based on cropyields and their dependence on pollinators, and the potential pollination indicator simulated by the InVEST model, based on land use and landcover as proxies for potential floral and nesting resources.We examined the spatiotemporal variation of these indicators over the Fénay area between 2005 and 2019, their environmental correlates (farming practices, landscape, and weather) and how they were related to each other.Our results suggest that the two indicators designed for large spatial extent can prove useful within farmland territories: both indicators exhibit significant variation across the study area, some of which could be related with environmental variables known to influence pollinators. For example, the spatial variation in the realized pollination service index correlates with farming practices, e.g. less efficient pollination in plots with more herbicide use. No correlation with the distance to the nearest semi-natural element was found, which contradicts results from previous studies at the field scale. The temporal variation in the pollination service index correlates negatively with the duration and intensity of summer heat waves. The potential pollination indicator will be compared with the realized pollination indicator, and in the future with field measurements of pollination efficiency for cross validation