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International audience; The CarboEurope Regional Experiment Strategy took place in the South West of France in 2005 and 2007 gathering several intensive observation periods to estimate the regional carbon balance. Eddy covariance fluxes, atmospheric CO2 concentrations, and the solar induced fluorescence were measured from both towers and aircraft. Additional meteorological observations were used to evaluate the performance of mesoscale models to simulate the observed concentrations. Top-down and bottom-up methods were applied and evaluated against direct ecosystem measurements, demonstrating the potential and the reliability of the carbon flux estimates over the region. Mesoscale modeling showed promising results by simulating most of the observed atmospheric variability. Inverse methodology was used to optimize the carbon balance over the area. The aircraft fluxes aggregated over large footprints (few km) showed an overall agreement with the final estimates from the inversion and the eddy flux towers. The photosynthesis activity was also correlated to the sun-induced fluorescence from ground based and aircraft measurements. Potential improvement of the continental carbon balance and recommendations for designing future regional observation networks are discussed.

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International audience; Over the last decades many studies have been performed to determine mass and energy budgets of forests, croplands and grasslands. However, most measurements have been made in different geographical regions and at different periods of time. As the results depend on the meteorological conditions and vary in time it is difficult to intercompare them directly and evaluate the relative contribution of each ecosystem to global water and carbon exchanges. Therefore, there is a need to measure fluxes over different types of ecosystem during a given period of time, in a given region with similar meteorological conditions. In the present study we report flux data, as performed above four different canopies submitted to the same climate forcing. As a contribution to the Regional Experiment component of the CarboEurope-IP project, the carbon and energy budgets of four typical ecosystems of Les Landes region in South West of France, a forest clear-cut, a mature forest, a vineyard and an irrigated maize crop, were measured during an entire growing season, from 17 May to 12 October 2005. The energy balance closure is fairly good at all sites. CO 2 flux measurements show that the maize crop before irrigation and the clear-cut behave as sources of CO 2, whereas the vineyard and the mature forest act as sinks. However the maize crop becomes a substantial sink of CO 2 after the start of irrigation and canopy growth, with fluxes three times as large as for the 35- year old forest. Evapotranspiration is largest over the irrigated maize and lowest over the clear-cut, while the vineyard and the mature forest exhibit similar water fluxes. The data collected provides a good basis for a comparative study of the main ecosystems of the region, and for upscaling fluxes at the regional level, in conjunction with all other measurements performed during the 2005 CERES experiment.

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Maize is one of the most cultivated plants in the world. For over five centuries people have been adapting it to better fit their needs. Selective breeding, cross-breeding and more recently, genetic engineering have led to numerous varieties of maize. Cross pollination has become a subject of scientific inquiry. In relation to co-existence of genetically modified crops with conventional and organic crops, it is now a major concern. This work aims atbetter understanding the release and dispersion processes of maize pollen through a mechanistic approach rather than the statistical approach typically used to evaluate outcrossing. The approach in this study is twofold. Firstly, because existing data do notinclude enough parameters, field experiments were set up and carried out. Secondly, a mechanistic model initially developed for atmospheric ammonia dispersion was adapted to maize pollen dispersion., Le maïs est l'une des plantes les plus utilisées dans le monde. Le maïs cultivé aujourd'hui résulte de cinq siècles d'amélioration par l'homme. Les techniques d'hybridation ainsi que l'utilisation des biotechnologies ont abouti à une grande diversité de variétés demaïs, face auxquelles les croisements intervariétaux nécessitent d'être maîtrisés. En particulier, la coexistence entre maïs transgénique et non transgénique est actuellement aucœur du débat scientifique. Pour répondre à cette question, l'approche actuelle est de mesurer directement la fécondation croisée. Cependant, elle ne permet pas de fournir un outil prédictif car elle ne fait pas le lien avec les conditions de l'environnement physique, et plus particulièrement les conditions météorologiques. L'objet de ce travail est de mieux comprendre les processus de dispersion atmosphérique du pollen de maïs à l''aide d''une approche mécaniste à l'échelle de la parcelle. Dans un premier temps, un modèle mécaniste initialement développé pour étudier la dispersion atmosphérique de l'ammoniac a été adapté à la dispersion du pollen de maïs. Ensuite, pour valider le modèle, des mesures dispersion de pollen ont été effectuées.

Le transport atmosphérique du pollen est un mécanisme important de la dispersion de gènes dans l'environnement, en particulier pour des plantes comme le maïs. Les mécanismes physiques sous-jacents à la libération, la dispersion par le vent et le dépôt du pollen de maïs ont été peu étudiés par le passé. Dans cette étude, nous présentons les résultats d'une expérimentation menée par l'INRA (UMR-EGC) et l'AGPM en juillet 2000 à proximité de Montargis, au sud de Paris. Les concentrations dans l'air, les flux horizontaux ainsi que les dépôts de pollen ont été mesurés à plusieurs distances (x) en aval d'une parcelle expérimentale de maïs de 20 m ´ 20 m, située au milieu d'une parcelle de sol nu de 120 m de coté. En parallèle, les conditions micrométéorologiques (vent, température, humidité, rayonnement, ), ainsi que la production de pollen par les plantes ont été mesurées, afin d'interpréter les flux et concentrations et d'avoir les données nécessaires pour valider le modèle SMOP-2D. La concentration en pollen dans l'air mesurée avec des « rotorods » variait entre 1 et 210 grains/m³. En utilisant une méthode de bilan de masse, qui combine la concentration en pollen et la vitesse du vent, nous avons estimé le flux horizontal de pollen entre 0 et 5 m de hauteur. Ce flux variait entre 10 et 480 grains/m²/s à x = 3 m et 3 et 210 grains/m²/s à x = 10 m. Le flux total de pollen émis par la parcelle a été estimé à partir du flux à 3 m comme étant compris entre 20 000 000 et 800 000 000 grains/jours, ce qui est à peu près d'un ordre de grandeur plus petit que la production de pollen par les plantes. Le dépôt de pollen estimé comme la différence entre les flux horizontaux entre x = 3 m et x = 10 m (défaut de bilan) variait de 10 à 270 grains/m/s. Le dépôt estimé à partir de pièges placés sur le sol est très comparable aux estimations par défaut de bilan. Nos estimations indiquent que la quantité de pollen déposée entre x = 1 m et x = 32 m varie entre 28 % et 90 % de la quantité émise. Le jeu de données recueilli servira, avec d'autres jeux de données similaires obtenues en 2001, à la validation du modèle SMOP-2D)., The atmospheric transport of pollen is an important mechanism of gene dispersal in the environment, especially for plants such as maize. The physical mechanisms underlying the release, the wind-dispersal and the deposition of maize pollen were little studied in the past. In this study, we present the results of an experimentation carried out by the Inra and the AGPM in July 2000 near Montargis, in the south of Paris, France. The airborne concentrations, the horizontal fluxes as well as the deposition rates of pollen were measured at several distances (x) downstream from a 20 m × 20 m experimental maize plot, located in the middle of a bare soil field of 120 m. The micrometeorological conditions (wind, temperature, moisture, radiation...), as well as the production of pollen by the plants were measured, in order to interpret the fluxes and concentrations and to have the necessary data to validate the SMOP-2D model. The aiborne pollen concentration measured with "rotorods" (rotating impactors) varied between 1 and 210 grains m³. By using a mass-balance method, which combines the concentration in pollen and the wind-speed, we have evaluated the horizontal flux of pollen between 0 and 5 m high. This flux varied between 10 and 480 grains/m²/s at x = 3 m and 3 and 210 grains/m²/s at x = 10 m. The total flux of pollen emitted by the maize field was evaluated at x = 3 m as lying between 20,000,000 and 800,000,000 grains/day, which is smaller than the production of pollen by the plants. The deposition of pollen evaluated as the difference between the horizontal fluxes at x = 3 m and x = 10 m varied from 10 to 270 grains/m²/s. The deposition evaluated from cups placed on the ground is very comparable to these estimations by mass balance. Our evaluations indicate that the quantity of pollen deposited between x = 1 m and x = 32 m varies between 28% and 90% of the emitted quantity. The data file collected has been used, along with other similar data files obtained in 2001, for the validation of the SMOP-2D model.

International audience; With the introduction of genetically modified (GM) crops, predictive tools modelling wind velocity and pollen concentration fields as well as pollen deposition rate over heterogeneous canopies are required to assess the cross-pollination rates between GM and conventional crops. Over the last decade several numerical flow models have been developed to simulate dynamic mean and turbulent fields within and above the vegetation layer. In this paper, an Eulerian advection–diffusion conservation equation for pollen particles has been incorporated into one of these flow models, Aquilon. The relative velocity between air parcels and particles is simply represented through the addition of a particle settling velocity, i.e. the particle fall velocity in still fluid. The dynamic part of this model has been previously validated in two-dimensional heterogeneous cases (roughness change, forest edge flow) and tested in a more complex three-dimensional heterogeneous case (urban forested park). In order to test the ability of this Eulerian approach to simulate accurately airborne pollen concentration and pollen deposition rate within and above heterogeneous vegetation canopies, the model is validated against two field experiments where the airborne concentration and the deposition rate of maize pollen (Zea mays) were measured downwind from source plots.We also compare the outputs of Aquilon with those of a Lagrangian model previously tested against the same dataset. Generally speaking the model performs well, with a similar accuracy to the Lagrangian model. However, both models underestimate the measured maximum in ground pollen deposition just downwind from the maize plot. It is shown that this discrepancy may be due to an underestimation of the pollen settling velocity in this region. As the Stokes number, defined as the ratio between the maize pollen response time and the characteristic time of the turbulent structures at dissipation-range scale, is about 1 in the wake region behind the source plot, it is likely that turbulence leads to an increase in the apparent settling velocity there.