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International audience; (1) Background: The anthropogenically induced rise in atmospheric carbon dioxide (CO2) and associated climate change are considered a potential threat to human nutrition. Indeed, an elevated CO2 concentration was associated with significant alterations in macronutrient and micronutrient content in various dietary crops. (2) Method: In order to explore the impact of elevated CO2 on the nutritional-health properties of tomato, we used the dwarf tomato variety Micro-Tom plant model. Micro-Toms were grown in culture chambers under 400 ppm (ambient) or 900 ppm (elevated) carbon dioxide. Macronutrients, carotenoids, and mineral contents were analyzed. Biological anti-oxidant and anti-inflammatory bioactivities were assessed in vitro on activated macrophages. (3) Results: Micro-Tom exposure to 900 ppm carbon dioxide was associated with an increased carbohydrate content whereas protein, minerals, and total carotenoids content were decreased. These modifications of composition were associated with an altered bioactivity profile. Indeed, antioxidant anti-inflammatory potential were altered by 900 ppm CO2 exposure. (4) Conclusions: Taken together, our results suggest that (i) the Micro-Tom is a laboratory model of interest to study elevated CO2 effects on crops and (ii) exposure to 900 ppm CO2 led to the decrease of nutritional potential and an increase of health beneficial properties of tomatoes for human health.

Tropical rainforests play a central role in the Earth system by regulating climate, maintaining biodiversity, and sequestering carbon. They are under threat by direct anthropogenic impacts like deforestation and the indirect anthropogenic impacts of climate change. A synthesis of the factors that determine the net ecosystem exchange of carbon dioxide (NEE) at the site scale across different forests in the tropical rainforest biome has not been undertaken to date. Here, we study NEE and its components, gross ecosystem productivity (GEP) and ecosystem respiration (RE), across thirteen natural and managed forests within the tropical rainforest biome with 63 total site-years of eddy covariance data. Our results reveal that the five ecosystems with the largest annual gross carbon uptake by photosynthesis (i.e. GEP > 3000 g C m(-2) y(-1)) have the lowest net carbon uptake - or even carbon losses versus other study ecosystems because RE is of a similar magnitude. Sites that provided sub canopy CO2 storage observations had higher average magnitudes of GEP and RE and lower average magnitudes of NEE, highlighting the importance of measurement methodology for understanding carbon dynamics in ecosystems with characteristically tall and dense vegetation. A path analysis revealed that vapor pressure deficit (VPD) played a greater role than soil moisture or air temperature in constraining GEP under light saturated conditions across most study sites, but to differing degrees from -0.31 to -0.87 mu mol CO2 m(-2) s(-1) hPa(-1). Climate projections from 13 general circulation models (CMIP5) under the representative concentration pathway that generates 8.5 W m(-2) of radiative forcing suggest that many current tropical rainforest sites on the lower end of the current temperature range are likely to reach a climate space similar to present-day warmer sites by the year 2050, warmer sites will reach a climate not currently experienced, and all forests are likely to experience higher VPD. Results demonstrate the need to quantify if and how mature tropical trees acclimate to heat and water stress, and to further develop flux-partitioning and gap-filling algorithms for defensible estimates of carbon exchange in tropical rainforests.

28th International Meeting on Organic Geochemistry, FLORENCE, ITALIE, 17-/09/2017 - 22/09/2017

• SPAC model to predict forest water consumption under wet and dry conditions.• Interactions and feedbacks between physical climate and ecological processes.• Control of root water uptake by water diffusion processes between roots and soil.• Key processes involved: xylem hydraulic resistances and stomatal conductance.• Buffering action of capacitive discharge on daily fluctuations of xylem tension.Modelling hydraulic functioning of a forest stand is a prerequisite to predict the future impact of climate change on forests. In this paper, we used a process-based model of the soil-plant-atmosphere continuum to investigate the links between energy budget and water balance, and to emphasize the key processes involved in the control of transpiration and water status of forest trees. The model describes stomatal conductance as a function of photosynthesis, intercellular CO2 concentration and leaf water potential. The latter in turn depends on soil and tree storage water potentials, the water flux through the soil and the trees, hydraulic resistances and stomatal conductance. We have implemented in the model a detailed tree water storage scheme, canopy interception of precipitation, and the rate of change of forest canopy energy storage. In this model, physical climate processes and ecological processes are closely coupled which involves important interactions and feedbacks. The model reproduces the observed variation in leaf water potential in dry and wet conditions. It successfully captures the decrease in soil water content under both non-limiting soil water and severe drought conditions and there is a good agreement between measured and simulated sensible and latent heat fluxes throughout the season. Simulations also show that significant amounts of intercepted water can be lost through evaporation during rain events. The results corroborate that the concept of hydraulic capacitance provides a simple and effective means of simulating the buffering action of tree water storage on tree water status. The two key parameters that control transpiration and water status of the trees are xylem hydraulic resistances and sensitivity of stomata to leaf water potential. The results confirm that stomatal conductance cannot be modelled using leaf-level processes alone, but must be incorporated into a comprehensive model of water flow from soil through the plants to the atmosphere where various self-regulation are set up to ensure a complete water status equilibrium.

European forests are an important carbon sink; however, the relative contributions to this sink of climate, atmospheric CO 2 concentration ([CO 2]), nitrogen deposition and forest management are under debate. We attributed the European carbon sink in forests using ORCHIDEE-FM, a process-based vegetation model that differs from earlier versions of ORCHIDEE by its explicit representation of stand growth and idealized forest management. The model was applied on a grid across Europe to simulate changes in the net ecosystem productivity (NEP) of forests with and without changes in climate, [CO 2] and age structure, the three drivers represented in ORCHIDEE-FM. The model simulates carbon stocks and volume increment that are comparable - root mean square error of 2 m 3 ha -1 yr -1 and 1.7 kg C m -2 respectively - with inventory-derived estimates at country level for 20 European countries. Our simulations estimate a mean European forest NEP of 175 ± 52 g C m -2 yr -1 in the 1990s. The model simulation that is most consistent with inventory records provides an upwards trend of forest NEP of 1 ± 0.5 g C m -2 yr -2 between 1950 and 2000 across the EU 25. Furthermore, the method used for reconstructing past age structure was found to dominate its contribution to temporal trends in NEP. The potentially large fertilizing effect of nitrogen deposition cannot be told apart, as the model does not explicitly simulate the nitrogen cycle. Among the three drivers that were considered in this study, the fertilizing effect of increasing [CO 2] explains about 61% of the simulated trend, against 26% to changes in climate and 13% only to changes in forest age structure. The major role of [CO 2] at the continental scale is due to its homogeneous impact on net primary productivity (NPP). At the local scale, however, changes in climate and forest age structure often dominate trends in NEP by affecting NPP and heterotrophic respiration.

International audience; Variation of dead wood decay rates among tropical trees remains one source of uncertainty in global models of the carbon cycle. Taking advantage of a broad forest plot network surveyed for tree mortality over a 23-year period, we measured the remaining fraction of boles from 367 dead trees from 26 neotropical species widely varying in wood density (0.23–1.24 g cm-3) and tree circumference at death time (31.5–272.0 cm). We modeled decay rates within a Bayesian framework assuming a first order differential equation to model the decomposition process and tested for the effects of forest management (selective logging vs. unexploited), of mode of death (standing vs. downed) and of topographical levels (bottomlands vs. hillsides vs. hilltops) on wood decay rates. The general decay model predicts the observed remaining fraction of dead wood (R2 = 60%) with only two biological predictors: tree circumference at death time and wood specific density. Neither selective logging nor local topography had a differential effect on wood decay rates. Including the mode of death into the model revealed thatstanding dead trees decomposed faster than downed dead trees, but the gain of model accuracy remains rather marginal. Overall, these results suggest that the release of carbon from tropical dead trees to the atmosphere can be simply estimated using tree circumference at death time and wood density.

Dry anaerobic digestion is a method of organic waste treatment and conversion to bioenergy, defined by a total solid content over 15%. This process is particularly suitable for lignocellulosic residues since the quantity of water to be added for the process is rather limited. However, dry anaerobic digestion processes is inhibited for a high total solid content, due to a decrease of the gas-liquid transfer within the medium, which may cause local accumulations of inhibitory byproducts, such as dissolved gases. This thesis aims to better understand the role of dissolved gas in dry anaerobic digestion at microscopic and mesoscopic scale. It was shown that hydrogen can inhibit specifically the hydrolysis step of lignocellulosic residues at microscopic level. This inhibition was reversible after addition of carbon dioxide, with remaining inhibitory effect on the acetate degradation and methanogenesis. At mesoscopic scale, the decrease of the mass transfer inhibits the hydrolysis, by dissolved hydrogen accumulation. Moreover, a local concentration gradient of hydrogen was present and seems responsible for a concentration gradient of volatile fatty acids in the medium. Moreover, adding carbon dioxide at mesoscopic scale, with a limited gas-liquid transfer, increased the volatile fatty acids concentration and decreased the pH, which showed the important role of carbon dioxide in the inhibition of anaerobic digestion under high dry matter content.; La digestion anaérobie par voie sèche est un procédé de valorisation des déchets organiques qui est défini par une teneur en matière sèche supérieure à 15%. Ce procédé est particulièrement adapté aux déchets ligno-cellulosiques puisqu’il ne nécessite qu’un ajout limité en eau. Cependant, la digestion anaérobie est inhibée pour des teneurs en matière sèche élevées, due à une diminution du transfert interfacial gaz-liquide au sein du milieu qui provoquerait des accumulations locales de produits inhibiteurs comme les gaz dissous. L’objectif de cette thèse est donc de comprendre le rôle des gaz dissous dans la digestion anaérobie par voie sèche à l’échelle microscopique et mésoscopique. Les principaux résultats montrent que l’hydrogène inhibe spécifiquement l’hydrolyse de la matière ligno-cellulosique à l’échelle microscopique. Cette inhibition est réversible en ajoutant du dioxyde de carbone, par consommation de l’hydrogène, avec cependant des effets rémanents inhibiteurs visibles sur la méthanogenèse et la dégradation de l’acétate. A l’échelle mésoscopique, la diminution du transfert de matière inhiberait l’hydrolyse, par l’accumulation locale d’hydrogène. De plus, un gradient de concentration d’hydrogène se met en place et serait responsable du gradient de concentration des acides gras volatils au sein du milieu. De plus, l’ajout de dioxyde de carbone à l’échelle mésoscopique avec un transfert interfacial gaz-liquide limitant augmente la concentration en acides gras volatils et baisse le pH du milieu, ce qui indique le rôle important du dioxyde de carbone dans la diminution des performances de la digestion anaérobie pour de fortes teneurs en matières sèches.

La digestion anaérobie par voie sèche est un procédé de valorisation des déchets organiques qui est défini par une teneur en matière sèche supérieure à 15%. Ce procédé est particulièrement adapté aux déchets ligno-cellulosiques puisqu’il ne nécessite qu’un ajout limité en eau. Cependant, la digestion anaérobie est inhibée pour des teneurs en matière sèche élevées, due à une diminution du transfert interfacial gaz-liquide au sein du milieu qui provoquerait des accumulations locales de produits inhibiteurs comme les gaz dissous. L’objectif de cette thèse est donc de comprendre le rôle des gaz dissous dans la digestion anaérobie par voie sèche à l’échelle microscopique et mésoscopique. Les principaux résultats montrent que l’hydrogène inhibe spécifiquement l’hydrolyse de la matière ligno-cellulosique à l’échelle microscopique. Cette inhibition est réversible en ajoutant du dioxyde de carbone, par consommation de l’hydrogène, avec cependant des effets rémanents inhibiteurs visibles sur la méthanogenèse et la dégradation de l’acétate. A l’échelle mésoscopique, la diminution du transfert de matière inhiberait l’hydrolyse, par l’accumulation locale d’hydrogène. De plus, un gradient de concentration d’hydrogène se met en place et serait responsable du gradient de concentration des acides gras volatils au sein du milieu. De plus, l’ajout de dioxyde de carbone à l’échelle mésoscopique avec un transfert interfacial gaz-liquide limitant augmente la concentration en acides gras volatils et baisse le pH du milieu, ce qui indique le rôle important du dioxyde de carbone dans la diminution des performances de la digestion anaérobie pour de fortes teneurs en matières sèches., Dry anaerobic digestion is a method of organic waste treatment and conversion to bioenergy, defined by a total solid content over 15%. This process is particularly suitable for lignocellulosic residues since the quantity of water to be added for the process is rather limited. However, dry anaerobic digestion processes is inhibited for a high total solid content, due to a decrease of the gas-liquid transfer within the medium, which may cause local accumulations of inhibitory byproducts, such as dissolved gases. This thesis aims to better understand the role of dissolved gas in dry anaerobic digestion at microscopic and mesoscopic scale. It was shown that hydrogen can inhibit specifically the hydrolysis step of lignocellulosic residues at microscopic level. This inhibition was reversible after addition of carbon dioxide, with remaining inhibitory effect on the acetate degradation and methanogenesis. At mesoscopic scale, the decrease of the mass transfer inhibits the hydrolysis, by dissolved hydrogen accumulation. Moreover, a local concentration gradient of hydrogen was present and seems responsible for a concentration gradient of volatile fatty acids in the medium. Moreover, adding carbon dioxide at mesoscopic scale, with a limited gas-liquid transfer, increased the volatile fatty acids concentration and decreased the pH, which showed the important role of carbon dioxide in the inhibition of anaerobic digestion under high dry matter content.

About 25 m3 of a poplar bark-poultry dung mixture were composted in a covered place with natural ventilation, air entering the lower part and going out through four shafts in the upper part. The gaseous emissions were measured and analyzed. The first heap (initial C/N of 28) was monitored for one month, then turned and more dung added. The second heap (initial C/N of 8) was monitored for seven months with two intermediate turnings. For the whole experiment, N losses were estimated at 61-74% of initial N, of which 62% was lost as NH3 (38-46% of initial N) and 1% as N2O (0.6-0.7% of initial N). N-NOx losses were 1000 times lower than N-N3 H3 losses. N2O and NOx were found only at the end of the periods before the piles were turned. As for carbon, C-CO2 emissions were estimated at 45-55% of initial C content, the ratio of CH4 to CO2 in the effluent air was 1 to 100 on average, with significant variations. The global warming potential of CH and N O was estimated at respectively 25% and 50% of total CO2 emissi...

International audience; A dynamic model for diacetyl production and reduction was developed based on experimental data from 14 laboratory-scale (15-L) lager beer fermentations carried out in various conditions of temperature (10–16°C), top pressure (50−850 mbar), initial yeast concentration (5−20 million cells per milliliter) and initial wort gravity (1,036−1,099 g/L). Uncertainties due to measurement errors, model parameters, and batch-to-batch variability were described in a probabilistic framework. The model predicts a probability distribution for the final diacetyl concentration from which a median value and an upper boundary, at a specified confidence level, are derived. It is demonstrated that in-line diacetyl measurements at early stages of fermentation greatly reduce the uncertainty about the final diacetyl level in each specific batch.; Predicción de los Límites de Confianza para la Concentración de Diacetilo en Cerveza Durante la Fermentación Se desarrolló un modelo dinámico para la producción y reducción de diacetilo durante la fermentación, basado en datos experimentales de 14 fermentaciones en el laboratorio (15 L) con cerveza lager; estas fermentaciones se realizaron en diferentes condiciones de temperatura (10-16°C), sobrepresión (50–850 mbar), concentración inicial de levadura (5–20 millones de células por mililitro) y densidad inicial del mosto (1,036–1,099 g/L). Las incertidumbres debido a los errores de medición, los parámetros del modelo y la variabilidad de lote a lote, fueron descritas en un marco probabilístico. El modelo pronostica una distribución de probabilidad para la concentración final del diacetilo, de cual se deriva un valor de la mediana y del límite superior de la concentración, a un nivel de confianza especificada. Se demuestra que las mediciones de diacetilo en línea en las fases iniciales de la fermentación reducen de manera significativa la incertidumbre de la concentración final de diacetilo de cada lote.

International audience

Esta tese foi preparada como uma tentativa de abordar uma série de questões importantes sobre os atuais meios disponíveis para medir emissões gasosas e os fluxos de ar em alojamentos animais com ventilação natural (VN). Cinco foram os principais objetivos que levaram à elaboração desta tese: (1) avaliar o desempenho operacional de um dispositivo de baixo custo para monitoramento de concentrações de dióxido de carbono (CO2) e compará-lo com dois outros métodos padrões; (2) avaliar o perfil de distribuição das razões de mistura entre o poluente amônia (NH3) e os gases marcadores hexafluoreto de enxofre (SF6) e CO2 em um galpão para vacas leiteiras com VN; (3) desenvolver um modelo CFD de um galpão de vaca leiteira com VN implementado com o modelo de produção de CO2 do CIGR; (4) desenvolver e testar um protocolo para medição das emissões de NH3 de um galpão brasileiro de frangos de corte com VN, e (5) calcular fatores de emissão de NH3 de dois galpões brasileiros com VN e ventilação mecânica (VM) para frangos de corte. Cinco artigos foram preparados para responder aos cinco objetivos desta tese, os quais incluem uma variedade de fatores e implicações relacionados a um galpão de vaca leiteiras com VN na Holanda e um galpão de frangos de corte com VN no Brasil. O primeiro trabalho versou sobre a comparação de dois métodos de monitoramento de concentrações de CO2 que são comumente usados para estudos de emissões em alojamentos animais com ventilação mecânica (VM) com um sensor de CO2 de baixo custo, e que é novo para fins de pesquisa, podendo ser mais adequado para uso galpões com VN. No segundo artigo, razões de mistura foram calculadas entre o gás NH3 e um dos dois gases marcadores distintos, o CO2 naturalmente liberado pelos animais e esterco, e o SF6 que foi artificialmente injetado no galpão. O objetivo maior deste artigo foi identificar a região dentro do galpão onde as razões de mistura possuem valores estimados aproximadamente constantes, de modo que taxas de emissão representativas para o galpão possam ser estimadas por meio do método do gás marcador. No artigo número três, um modelo em “Computational Fluid Dynamics” (CFD) de um galpão para vacas leiteiras com VN foi desenvolvido e ix 11 implementado com as equações de produção CO2 publicadas pelo CIGR, a fim de revelar os padrões de fluxo de ar e CO2 no espaço interno ventilado. O modelo foi validado com dados de concentração de CO2 medidos experimentalmente em vários pontos dentro do galpão. O quarto artigo versou sobre a determinação do algoritmo mais adequado para estimar as taxas de fluxo de ar e gases através de um galpão de frangos de corte com VN, localizado no Brasil. As estratégias de amostragem testadas consistiram de combinações de dois esquemas diferentes de monitoramento das concentrações gasosas e de duas estratégias de predição da produção de CO2 das aves. O quinto e último trabalho foi uma continuação do quarto artigo, e tratou do cálculo dos fatores de emissões de NH3 ( NH3 f ) de galpões com VN e VM para frangos de corte no Brasil. O método utilizado para calcular os fatores de emissão em ambos os galpões foi o do gás marcador, utilizando-se CO2 naturalmente produzido pelas aves. Os NH3 f calculados foram comparáveis com aqueles encontrados na literatura para as condições do Brasil e em outras partes do mundo. No geral, esta tese demonstra que, apesar das complicações relacionadas ao monitoramento dos fluxos de ar poluentes gasosos através de galpões animais com VN, os fatores de emissão obtidos podem ser comparáveis àqueles relativos a galpões animais com VM. Em síntese, o número de pontos no galpão em que as concentrações de gases serão monitoradas é mais relevante do que a utilização de métodos de medição de alta precisão e dispendiosos. Quando o método de gás marcador é utilizado, atenção deverá ser dada a determinação precisa da taxa de injeção do gás marcador ou a taxa de produção de CO2. É importante também que a razão de mistura entre os gases poluente e marcador seja determinada em vários pontos fora da zona ocupada pelos animais, porém acima dela., This thesis was prepared as an attempt to cover a number of questions and concerns regarding the current available means to measure emissions and air flows from naturally ventilated (NV) livestock buildings. Five were the main objectives that led to the preparation of this thesis: (1) to assess the operation performance of a low cost carbon dioxide (CO2) measuring device and to compare it to two other standard methods; (2) to evaluate the distribution of mixing ratios of the pollutant ammonia (NH3) and the tracer gases sulfur-hexafluoride (SF6) and CO2 in a NV dairy cow barn; (3) to develop a CFD model of a NV dairy cow barn implemented with the CIGR CO2 production model; (4) to develop and test a protocol for measuring NH3 emissions from a Brazilian NV broiler house; and (5) to calculate NH3 emission factors from a Brazilian NV and a mechanically ventilated (MV) broiler barns. Five papers were prepared to answer the five objectives of this thesis, which include a variety of factors and implications related to a NV dairy cow barn in the Netherlands and a NV broiler barn in Brazil. The first paper dealt with the comparison between two CO2 concentration measuring devices that are commonly used for emission studies in MV barns with one low cost sensor that is new to research purposes and might be more suitable for NV livestock buildings. In the second paper, we compared mixing ratios calculated with NH3 and two different tracers, the CO2 which is naturally produced in livestock houses and the artificially injected SF6 with the aim of identifying the region within the barn ventilated airspace where mixing ratios are approximately constant, from which representative estimates of emission rates through the tracer gas method can be made. In paper number three, a Computational Fluid Dynamics (CFD) model of a NV dairy cow barn was developed and implemented with the CIGR CO2 production equations in order to reveal the flow patterns of air and CO2 within the ventilated airspace. The model was validated with CO2 concentration data actually measured at multiple points within the barn. The fourth paper was about finding a more adequate algorithm for determining flow rates across a NV broiler barn in Brazil. The tested sampling strategies combined two different sampling schemes for gaseous concentrations and two different strategies to xi 13 predict CO2 production from the birds. The fifth and last paper was a follow up of paper number four, and dealt with calculation of actual NH3 emission factors ( NH3 f ) of a NV and a MV broiler barns in Brazil. The method used to estimate the emission factors in both barns was based on a tracer gas, using the CO2 naturally produced by the birds as the tracer. The calculated NH3 f were then compared to those found in the literature for Brazilian conditions and those found in other parts of the world. Overall, this thesis proves that despite the complications related to monitoring air and gaseous pollutant flows through NV buildings, emission factors can be obtained which are comparable to those of MV buildings. In general, the number of points in which gaseous concentrations are being monitored within the barn ventilated airspace with properly calibrated devices is more important than using highly accurate and expensive measurement methods. When the tracer gas method is to be used, focus should be given to accurate determination of the tracer injection rate or rate of production of CO2. It is important that the mixing ratio between pollutant and tracer gases be determined in multiple points outside the animal occupied zone, but above it.

Si l'accroissement de la température et du taux de CO2 a un effet globalement positif sur la photosynthèse, la production fourragère et la fixation symbiotique, les sécheresses et, dans une moindre mesure, une fertilisation azotée limitante des graminées, pourraient annuler cette amélioration. Les interactions entre les différents effets sont analysés, selon le type de couvert (graminée / légumineuse, espèce annuelle ou pérenne, tempérée ou méditerranéenne, plante en C3 ou en C4 (maïs, sorgho)..) ainsi que les phénomènes d'adaptation des espèces et populations aux différents types de climats. Dans le cas de températures estivales fréquemment >30° et/ou de déficit hydrique avril-aoüt >500mm, la survie des populations d'espèces prairiales d'origine tempérée est compromise. un changement de variétés cultivées est donc à anticiper, en poursuivant l'amélioration génétique des espèces., Climatic variables (average and variability) will be undergoing a significant change in the 21st century. What will be the impact on the physiology, production and perennity of forage species? Higher temperatures and increased CO2 levels will have a globally positive effect on photosynthesis, production and symbiotic fixation, but droughts (as well as limited nitrogen supplies) could cancel this. The interactions between these different effects are analyzed, per type of cover (forage grass/legumes, annual and perennial species, temperate or Mediterranean, C3 and C4 plants (maize, sorghum)...) and the way in which species adapt to different types of climate. In extreme conditions (high summer temperatures and/or hydric deficit in April-August > 500 mm), the survival of temperate grassland species is compromised. The genetic improvement of species must anticipate the change in cultivated varieties.

National audience; Climatic variables (average and variability) will be undergoing a significant change in the 21st century. What will be the impact on the physiology, production and perennity of forage species? Higher temperatures and increased CO2 levels will have a globally positive effect on photosynthesis, production and symbiotic fixation, but droughts (as well as limited nitrogen supplies) could cancel this. The interactions between these different effects are analyzed, per type of cover (forage grass/legumes, annual and perennial species, temperate or Mediterranean, C3 and C4 plants (maize, sorghum)...) and the way in which species adapt to different types of climate. In extreme conditions (high summer temperatures and/or hydric deficit in April-August > 500 mm), the survival of temperate grassland species is compromised. The genetic improvement of species must anticipate the change in cultivated varieties.; Si l'accroissement de la température et du taux de CO2 a un effet globalement positif sur la photosynthèse, la production fourragère et la fixation symbiotique, les sécheresses et, dans une moindre mesure, une fertilisation azotée limitante des graminées, pourraient annuler cette amélioration. Les interactions entre les différents effets sont analysés, selon le type de couvert (graminée / légumineuse, espèce annuelle ou pérenne, tempérée ou méditerranéenne, plante en C3 ou en C4 (maïs, sorgho)..) ainsi que les phénomènes d'adaptation des espèces et populations aux différents types de climats. Dans le cas de températures estivales fréquemment >30° et/ou de déficit hydrique avril-aoüt >500mm, la survie des populations d'espèces prairiales d'origine tempérée est compromise. un changement de variétés cultivées est donc à anticiper, en poursuivant l'amélioration génétique des espèces.

International audience; Soil respiration is one of the main CO2 sources from terrestrial ecosystems. Soil respiration is therefore a major source of greenhouse gas. Knowledge of the impact of agronomic practices such as manuring on the stability, for example resistance and resilience, of heterotrophic C-CO2 respiration to disturbance is scarce. Here, we studied the stability of soil microbial heterotrophic respiration of two tropical soils from plots annually enriched or not with manure applications during more than 20 years. Stability was quantified after heating soils artificially. We hypothesized that field manuring would change the stability of the microbial community. Additionally, the impact of both manured and unmanured soils to addition of an organic cocktail was assessed under controlled conditions in order to discriminate the metabolic capacity of the microbial community, and to link the metabolic capacity up with the microbial heterotrophic soil respiration. Our results show that total respiration was not significantly different in manured and unmanured pots. Moreover, contrary to our hypothesis, manure amendment did not affect the stability (resistance, resilience) of the microbial abundance or the basal metabolism, in our experimental conditions. By contrast, the diversity of the bacterial community in heated soils was different from that in unheated soils. After heating, surviving microorganisms showed different carbon utilization efficiency, manuring stimulating the growth of different resistant communities, that is, r-strategist or K-strategist. Microbial community of manured soils developed in the presence of the organic cocktail was less resistant to heating than microbial community of unmanured plots.

Flexas, Jaume et al.-- 14 páginas, 9 figuras, 157 referencias.-- cmartin@irnase.csic.es, Mesophyll diffusion conductance to CO 2 is a key photosynthetic trait that has been studied intensively in the past years. The intention of the present review is to update knowledge of g m, and highlight the important unknown and controversial aspects that require future work. The photosynthetic limitation imposed by mesophyll conductance is large, and under certain conditions can be the most significant photosynthetic limitation. New evidence shows that anatomical traits, such as cell wall thickness and chloroplast distribution are amongst the stronger determinants of mesophyll conductance, although rapid variations in response to environmental changes might be regulated by other factors such as aquaporin conductance.Gaps in knowledge that should be research priorities for the near future include: how different is mesophyll conductance among phylogenetically distant groups and how has it evolved? Can mesophyll conductance be uncoupled from regulation of the water path? What are the main drivers of mesophyll conductance? The need for mechanistic and phenomenological models of mesophyll conductance and its incorporation in process-based photosynthesis models is also highlighted., The study was financially supported by the Estonian Ministry of Science and Education (grant SF1090065s07), the Spanish Ministry of Science and Innovation through projects BFU2008-01072 (MEFORE), AGL2009-11310/AGR, BFU2011-23294 (MECOME) and CGL2009- 13079-C02-01 (PALEOISOTREE), and the European Commission through European Regional Fund (the Estonian Center of Excellence in Environmental Adaptation), and the Marie Curie project MCERG- 246725 (FP7). J.P.F. is supported by the Ramón y Cajal program (RYC-2008-02050). A.G. had a Swiss National Science Fellowship (PA00P3 126259). M.M.B. and C.R.W are supported by Future Fellowships from the Australian Research Council (FT0992063 and FT100100024). C.D. was supported by a grant from the French government and by the cooperation project Tranzfor (Transferring Research between EU and Australia–New Zealand on Forestry and Climate Change, PIRSES-GA-2008-230793) funded by the European Union.

absent

An unbiased partitioning of autotrophic and heterotrophic components of soil CO2 efflux is important to estimate forest carbon budgets and soil carbon sequestration. The contribution of autotrophic sources to soil CO2 efflux (FA) may be underestimated during the daytime as a result of internal transport of CO2 produced by root respiration through the transpiration stream. Here, we tested the hypothesis that carbon isotope composition of soil CO2 efflux (dFS) in a Eucalyptus plantation grown on a C4 soil is enriched during the daytime, which will indicate a decrease in FA during the periods of high transpiration. Mean dFS of soil CO2 efflux decreased to -25.7 parts per thousand during the night and increased to -24.7 parts per thousand between 11:00 and 15:00 h when the xylem sap flux density was at its maximum. Our results indicate a decrease in the contribution of root respiration to soil CO2 efflux during the day that may be interpreted as a departure of root-produced CO2 in the transpiration stream, leading to a 17 parts per thousand underestimation of autotrophic contribution to soil CO2 efflux on a daily timescale.

Measurements of carbon dioxide fluxes were performed over a temperate intertidal mudflat in southwestern France using the micrometeorological Eddy Covariance (EC) technique. EC measurements were carried out in two contrasting sites of the Arcachon flat during four periods and in three different seasons (autumn 2007, summer 2008, autumn 2008 and spring 2009). In addition, satellite images of the tidal flat at low tide were used to link the net ecosystem CO2 exchange (NEE) with the occupation of the mudflat by primary producers, particularly by Zostera noltii meadows. CO2 fluxes during the four deployments showed important spatial and temporal variations, with the flat rapidly shifting from sink to source with the tide. Absolute CO2 fluxes showed generally small negative (influx) and positive (efflux) values, with larger values up to −13 μmol m−2 s−1 for influxes and 19 μmol m−2 s−1 for effluxes. Low tide during the day was mostly associated with a net uptake of atmospheric CO2. In contrast, during immersion and during low tide at night, CO2 fluxes where positive, negative or close to zero, depending on the season and the site. During the autumn of 2007, at the innermost station with a patchy Zostera noltii bed (cover of 22 ± 14% in the wind direction of measurements), CO2 influx was −1.7 ± 1.7 μmol m−2 s−1 at low tide during the day, and the efflux was 2.7 ± 3.7 μmol m−2 s−1 at low tide during the night. A gross primary production (GPP) of 4.4 ± 4.1 μmol m−2 s−1 during emersion could be attributed to microphytobenthic communities. During the summer and autumn of 2008, at the central station with a dense eelgrass bed (92 ± 10%), CO2 uptakes at low tide during the day were −1.5 ± 1.2 and −0.9 ± 1.7 μmol m−2 s−1, respectively. Night time effluxes of CO2 were 1.0 ± 0.9 and 0.2 ± 1.1 μmol m−2 s−1 in summer and autumn, respectively, resulting in a GPP during emersion of 2.5 ± 1.5 and 1.1 ± 2.0 μmol m−2 s−1, respectively, attributed primarily to the seagrass community. At the same station in April 2009, before Zostera noltii started to grow, the CO2 uptake at low tide during the day was the highest (−2.7 ± 2.0 μmol m−2 s−1). Influxes of CO2 were also observed during immersion at the central station in spring and early autumn and were apparently related to phytoplankton blooms occurring at the mouth of the flat, followed by the advection of CO2-depleted water with the flooding tide. Although winter data as well as water carbon measurements would be necessary to determine a precise CO2 budget for the flat, our results suggest that tidal flat ecosystems are a modest contributor to the CO2 budget of the coastal ocean.

In savannah and tropical grasslands, which account for 60% of grasslands worldwide, a large share of ecosystem carbon is located below ground due to high root:shoot ratios. Temporal variations in soil CO2 efflux (R-S) were investigated in a grassland of coastal Congo over two years. The objectives were (1) to identify the main factors controlling seasonal variations in R-S and (2) to develop a semi-empirical model describing R-S and including a heterotrophic component (R-H) and an autotrophic component (R-A). Plant above-ground activity was found to exert strong control over soil respiration since 71% of seasonal R-S variability was explained by the quantity of photosynthetically active radiation absorbed (APAR) by the grass canopy. We tested an additive model including a parameter enabling R-S partitioning into R-A and R-H. Assumptions underlying this model were that R-A mainly depended on the amount of photosynthates allocated below ground and that microbial and root activity was mostly controlled by soil temperature and soil moisture. The model provided a reasonably good prediction of seasonal variations in R-S (R-2 = 0.85) which varied between 5.4 mu mol m(-2) s(-1) in the wet season and 0.9 mu mol m(-2) s(-1) at the end of the dry season. The model was subsequently used to obtain annual estimates of R-S, R-A and R-H. In accordance with results reported for other tropical grasslands, we estimated that R-H accounted for 44% of R-S, which represented a flux similar to the amount of carbon brought annually to the soil from below-ground litter production. Overall, this study opens up prospects for simulating the carbon budget of tropical grasslands on a large scale using remotely sensed data. (C) 2012 Elsevier B.V. All rights reserved.

The use of the carbon isotopic composition of CO2 (δ13C-CO2) is a promising tool to improve our knowledge about the mechanisms of CO2 production within soil. Temporal fluctuations of δ13C-CO2 soil efflux reflect the influence of climatic and edaphic conditions on (i) partitioning between the respiration sources, (ii) CO2 production intensity and (iii) CO2 transport from soil layers to surface. A better understanding of fractionation processes affecting CO2 during this transport is required to obtain quantitative information about the CO2 production. The differences in transport (diffusion, advection) properties between 13CO2 and 12CO2 cause a fractionation during CO2 transfer from sources to the surface, creating a decrease of δ13C-CO2 at surface compared to air contained in soil pores. Short-term fluctuations of this apparent fractionation is expected in case of (i) changes in diffusive properties of the soil (soil water content, temperature) and/or (ii) air pressure variations created by turbulence. As a consequence, at this time scale, the difference between δ13C-CO2 of soil atmosphere and δ13C-CO2 of soil CO2 efflux is very variable and difficult to interpret. With tunable diode laser spectrometer (TDLS) it is now possible to measure δ13C-CO2 with high frequency. TDLS offers then the possibility to quantify δ13C-CO2 of soil efflux (by coupling with soil chamber, Marron et al. 2009) and soil atmosphere if (i) soil air sampling doesn’t disturb the natural environment and (ii) soil air collected is diluted to reduce the high soil CO2 concentrations (several thousand ppmv) to values measurable by the TDLS (inferior to 1000 ppmv). To solve these limitations, we have adapted a method (Gut et al. 1998) based on the diffusion of soil pore air within a tube through a membrane having a high permeability to gases and being hydrophobic. These tubes have been placed horizontally at different depths in the soil. An air flowing in tubes allows CO2 circulation up to a diluting system composed by mass flow controllers and free CO2 injection. The output of this diluting system is coupled to the TDLS and measurements permit then to establish a vertical profile of the isotopic signature of soil CO2 concentration at hourly scale. Laboratory tests were performed to prove the absence of membrane influence on the δ13C-CO2. The membrane tube has been placed in a chamber where gases with different CO2 concentration and δ13C were introduced. Results didn’t show any fractionation for 13C during diffusion through the membrane. The δ13C difference between gas inside and gas outside the tube was always inferior to the TDLS precision ( 0.2 h ). In addition, some tests in the field have proved (i) that soil CO2 concentrations and δ13C are not significantly affected by our system functioning (observation of natural evolution) and (ii) that the values obtained are coherents with results from IRMS (R2=0.98) and with efflux measurements.[br/] This new methodology seems to be a very effective technique for measuring the δ13C-CO2 vertical profile of soil atmosphere and to understand fractionation processes that occur during this transfer. Moreover, incorporation of data collected using our methodology in mechanistic models of CO2 transport processes will permit to assess the vertical profil of sources contributions to CO2 efflux and will provide news insights into soil carbon dynamics.

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International audience; The interannual variability of CO2 exchange by forest ecosystems in Europe was analyzed at site and regional scales by identifying critical periods that contributed to interannual flux anomalies. Critical periods were defined as periods in which monthly and annual flux anomalies were correlated. The analysis was first conducted at seven European forest flux tower sites with contrasting species and climatic conditions. Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE), a generic process‐based model, represented fairly well most features of the critical period patterns and their climate drivers at the site scale. Simulations at the scale of European forests were performed with ORCHIDEE integrated at a 0.25° spatial resolution. The spatial and temporal distributions of critical periods for canopy photosynthesis, ecosystem respiration, and net ecosystem exchange (NEE) as well as their underlying climate drivers were analyzed. The interannual variability in gross primary productivity (GPP) was explained by critical periods during spring and summer months. In contrast, the interannual variability in total ecosystem respiration (TER) was explained by critical periods occurring throughout the year. A latitudinal contrast between southern and northern Europe was observed in the distributions of critical periods for GPP and TER. The critical periods were positively controlled by temperature in northern Europe and by soil water availability in southern Europe. More importantly, the latitudinal transition between temperature‐driven and water‐driven critical periods for GPP varied from early spring to late summer. Such a distinct seasonal regime of critical periods was less clearly defined for TER and NEE. Overall, the critical periods associated with NEE variations and their meteorological drivers followed those associated with GPP.

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Diplôme : Master

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International audience; In Thailand, rubber is the major tree crop covering more than 2 millions hectares. Its impact on environment, and particularly CO2 balance and water use, is a major issue. A complete flux-measuring system has been installed in a 13 years old tubber plantation (clone RRIM 600) in eastern Thailand (Chachoengsao Rubber Research Center, RRIT-DOA) in 2006. Carbon fluxes of rubber plantation ecosystem are continuously measured by eddy-covariance method (CO2 exchanges between the ecosystem and the atmosphere). Evapo-transpiration (ET) are measured by eddy-covariance and water balance together and partitioned between tree transpiration and soil evaporation. Sapflow is measured by heat dissipation method (Granier 1985, 1987) using home-made 20 mm-long radial probes, continuously heated (0.2 W). Meanwhile, amounts of C stored in the trees are evaluated by measuring biomass increment along the life cycle of the plantation, in combination with estimations of the carbon content of the different compartments. These measurements will provide the annual balance of C within plantations at different ages. Results obtained at ecosystem scale by these methods will be compared to gas exchanges measured at the level of the different compartments (canopy, trunk, root system, soil...). Particularly, Farquhar's photosynthesis model (Farquhar et al. 1980) is parameterized across the canopy. Leaf water potential, sapflow and canopy transpiration are computed to calculate canopy conductivity. Thereby, validated CO2 and H2O fluxes will be used to model gas exchanges of rubber plantation ecosystem according to climate and other environmental parameters as well as crop management.

The data quality and the selection of the correct Eddy Covariance (EC) records become an important step in the CO2 flux determination procedure. An innovative combination of existing assessment tests is used to give a relatively complete evaluation of the net ecosystem exchange measurements. For the 2005 full-leaf season at the Hesse site, the percentage of bad quality data is relatively high (59.6%) especially during night-time (68.9%). This result strengthens the importance of the data gap filling method. The filtering used does not lead to a real improvement of the accuracy of the relationship between the CO2 fluxes and the climatic factors. The soil respiration spatial heterogeneity (on a site with relatively homogenous vegetation pattern) seems to be too important to allow this improvement. However, the data rejected present some common characteristics. Their removal lead to a 10% increase in the total amount of CO2 respired (Reco) and photosynthesised (GPP) during the 2005 full-leaf season. Consequently the application of our combination of multiple quality tests is able improve the inter-annual analysis. The question of a systematic application on the large database like the CarboEurope and FLUXNET is legitimate.

Le réchauffement climatique est devenu une réalité incontournable et la réflexion pour trouver des moyens d’adaptation en agriculture devient un sujet d’actualité. Dans ce but la recherche de cultures qui sauront s’adapter aux contraintes climatiques futures devient une urgence. La Luzerne, a priori semble être une bonne alternative pour d’un côté s’adapter aux changements climatiques et de l’autre donner de bons rendements. L’objectif de cette étude est de voir grâce à la modélisation les potentialités de cette culture. Pour atteindre ce but notre démarche s’inscrit en deux étapes : la première est de simuler le comportement de cette plante à l’aide du modèle STICS. La deuxième étape est de voir comment évoluera cette culture sous des climats futurs. Ces climats sont fournis par Météo-France avec des données issues du modèle ARPEGE - climat. Il ressort de nos résultats que la production de la luzerne dans le futur suivra presque les mêmes dynamiques de production que dans le climat actuel. En prenant en compte l’effet climat et CO2. Sans l’effet CO2 la production va probablement chuter dans le futur lointain (2100) mais avec l’effet CO2 (augmentation de la photosynthèse et diminution des besoins en eau) on a enregistré une stabilisation des rendements dans le futur par rapport aux climats actuels. De plus la production augmente dans le futur avec des températures plus élevées et des précipitations suffisantes. Il ressort aussi de nos résultats que pour maintenir les niveaux de production actuels voire les améliorer il faudrait implanter la Luzerne dans des sols plus profonds avec une bonne RU. Dans ces sols le potentiel de la culture est mieux valorisé et lui permet de bons rendements car elle passe sans difficultés la période estivale et peut même donner d’autres pousses en automne, The global warming has become reality that cannot be ignored and thinking about finding means of adaptation in agriculture becomes a subject of topicality. Therefore, searching for cultures that would adapt to future climatic constraints is to be found urgently. The Lucerne, on the face of it seems to be a good alternative, as in one hand it would be adapted to the climatic changes and on the other hand it would give better yields than grasses. The objective of this study, which is done using modelling, is to see what would be the potentialities of this culture. To achieve this goal our step is registered in two stages: first is to simulate the behaviour of this plant using the crop model STICS. The second stage is to see how this culture under future climates will evolve. These climates are provided by Météo-France with data resulting from model ARPEGE - climat. It comes out from our results that the production of Lucerne in the future will follow almost the same dynamics of production along the year as in the current climate. Taking or not into account both climate and CO2 effects gives not the same results. Without the CO2 effect, productions will probably decrease in the distant future, while they seems to be higher when we apply the CO2 effect (increase of photosynthesis and decrease of transpiration, without any other effect or feedback). Moreover, crop will take advantage of high climatic potential (with high temperature) when water availability is as high as possible. It also results from our simulations that maintaining the current production levels, even improving them, would be only possible when establishing the crop in deeper grounds with a high water availability. In these grounds the potential of the culture is developed better and allows it good yields because it goes beyond the estival period and can even give others sprouts in autumn

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National audience; Dans les forêts, la respiration du sol (Rs) est le deuxième flux de CO2 en importance après la photosynthèse. Pourtant les relations permettant d'estimer Rs contiennent des paramètres dont la valeur est très dépendante du site. Il est donc actuellement difficile de simuler Rs au sein des modèles de couvert forestier sans avoir effectuer certaines campagnes de mesures de ce flux. Cela implique une imprécision lors de l'extrapolation de ces modèles hors des parcelles de mesures. Afin d'essayer de remédier à ce problème, une base de données comprenant des mesures météorologiques (température de l'air, température et contenu en eau de sol,...), des propriétés de l'écosystème (LAI, surface terrière, pH H2O du sol, contenu en carbone et en azote du sol, ...) et l'évolution saisonnière de Rs a été établie pour plusieurs parcelles forestières en France et en Belgique. L'ajustement d'une relation permettant de décrire l'influence des variables météorologiques sur Rs a été réalisé pour chaque parcelle et des valeurs de paramètres ont été obtenues également pour chaque parcelle. Ces valeurs de paramètres ont été comparées entre elles afin de tenter d'établir des dépendances vis à vis des propriétés de l'écosystème. Ce travail a nécessité la mise au point d'un protocole de mesures commun aux différentes équipes impliquées. Entre autre, les différents systèmes de mesure de Rs (PP system EGM-4, analyseur Licor 6250 + chambre Licor 6000-9 ou faite) ont été comparés et des procédures de corrections ont été établies afin d'assurer l'homogénéité des données de Rs.

Depuis 1996, un système de mesure par corrélations turbulentes permet de mesurer les flux nets de CO2, de vapeur d'eau et d'énergie à l'interface entre une hêtraie située à Hesse (France, 57) et l'atmosphère. Simultanément des mesures des principales variables météorologiques et des principales caractéristiques structurelles du couvert ont été enregistrées et permettent un suivi à long terme des conditions subies par le site-atelier de Hesse. La hêtraie de Hesse incorpore de 100 à 500 g Cm-2 an-1 selon les années, valeur en moyenne proche des estimations d'accroissement du peuplement forestier. Cette variation inter-annuelle du bilan net de carbone est très élevée par rapport à ce qui est observé sur d'autres sites qui disposent de longues séries de mesures. Une étude tentant de dissocier les effets de la variabilité des conditions météorologiques (rayonnement, température de l'air et du sol, sécheresse aérienne et édaphique) et de la modification structurelle du couvert (éclaircie...) a été entreprise. L'étude porte principalement sur la réponse des flux élémentaires que constituent l'assimilation photosynthétique (GPP) et la respiration de l'écosystème (Reco). Elle permet, entre autre, d'estimer l'impact d'une variable météorologique sur la croissance.

International audience; The aim of this study is to establish a calibration of the late wood cellulose carbon and oxygen isotopic inter-annual variability measured on four living oaks (1879-1998) in the Atlantic area (Rennes Forest, Brittany, western France) to meteorological (beginning in 1885) and hydrological (beginning in 1951) data. We find a better tree-to-tree consistency of the δ18O ratio, compared with that of the tree-to-tree variability of the ring width and the δ13C possibly affected by individual competition effects. On a century-long time scale, the δ13C ratio in the cellulose reflects the globally decreasing trend of δ13C in atmospheric CO2, which is mainly due to fossil fuel burning. In contrast with the ring width, which here shows a weak and complex dependence on meteorological parameters, the isotopic composition of the cellulose enables a reliable reconstruction (R2 > 0.45), mainly due to the δ18O signal, of selected summer climatic parameters: relative humidity, soil moisture deficit and temperature. The reconstructed parameters capture both low-frequency variations and extreme dry years (summer droughts). While both summer temperature and annual mean precipitation have a long-term increasing trend, the reconstructed water stress indicators do not show a significant trend during the 20th century. On average one summer drought occurs every seven summers, but this frequency varies in parallel to decadal changes in mean summer temperature, with fewer droughts in the 1930s and 1960s-1970s and more droughts in the 1900s, 1940s and 1990s.

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One-dimensional box model estimates of biospheric CO2 gross fluxes are presented. The simulations are based on a set of measurements performed during the EUROSIBERIAN CARBONFLUX intensive campaign between 27 July and 1 August 1999 in a natural Picea abies forest in Russia. CO2 mixing ratios and stable isotope ratios of CO2 were measured on flask samples taken in two heights within the canopy. Simultaneously, soil and leaf samples were collected and analysed to derive the O- 18/O-16 ratio of the respective water reservoirs and the C- 13/C-12 ratio of the leaf tissue. The main objective of this project was to investigate biospheric gas exchange with soil and vegetation, and thereby take advantage of the potential of the O-18/O-16 ratio in atmospheric CO2. Via exchange of oxygen isotopes with associated liquid water reservoirs, leaf CO2 assimilation fluxes generally enrich while Soil CO2 respiration fluxes generally deplete the O-18/O-16 ratio of atmospheric CO2. In the model, we parameterised intracanopy transport by exploiting soil-borne Rn-222 as a tracer for turbulent transport. Our model approach showed that, using oxygen isotopes, the net ecosystem CO2 flux can be separated into assimilation and respiration yielding fluxes comparable with those derived by other methods. However, partitioning is highly sensitive to the respective discrimination factors, and therefore also on the parameterisation of internal leaf CO2 concentrations and gradients.

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