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National audience; The States that signed the Paris Accord in 2015 at the 21st Conference of the Parties (COP21) to the United Nations Framework Convention on Climate Change (UNFCCC) set themselves the common objective of achieving a balance in anthropogenic greenhouse gas (GHG) emissions by the second half of the 21st century. According to a net emissions flow approach adopted by several European countries, France adopted a "climate plan" in July 2017, with a "zero net emissions" (ZEN) objective for GHGs by 2050. Carbon sequestration in agricultural soils is one of the means envisaged to achieve this common mitigation objective.; Les États signataires de l'Accord de Paris en 2015 dans le cadre de la 21 e conférence des parties (COP21) à la Convention-cadre des Nations unies sur les changements climatiques (CCNUCC) se sont donnés comme objectif commun de parvenir à un équilibre des émissions anthropiques de gaz à effet de serre (GES) d'ici à la seconde moitié du XXI e siècle. Selon une logique en flux d'émissions nettes adoptée par plusieurs pays européens, la France s'est dotée d'un « plan climat » en juillet 2017, avec un objectif de « zéro émission nette » (ZEN) de GES à l'horizon 2050 1. La séquestration du carbone dans les sols agricoles est l'un des moyens envisagés pour atteindre cet objectif commun d'atténuation.

International audience; The aim of this study was to evaluate the short-term effects of two grassland restoration methods on biomass yield and carbon storage in the upper soil layer. We used a grassland located on the INRAE Pin-au-Haras experimental farm (Normandy), which had been seeded 12 years ago. It was divided up into three subplots: (i) a control subplot; (ii) a subplot restored via reseeding; and (iii) a subplot restored via overseeding. Biomass yield, carbon levels in the top 10 cm of the soil, and the properties of the soil organic matter were examined 8 months and 20 months after the treatments were applied. The reseeding and overseeding methods increased annual biomass yield by 50%; the levels of organic carbon in the soil were maintained, and the amount of soil organic matter increased. Neither restoration method changed the C/N ratio or the proportion of soluble carbon in the soil. Our findings indicate that the overseeding method and the reseeding method similarly increased grassland productivity. However, the former does not require the use of glyphosate, allowing levels of carbon storage in the soil to remain stable.; L’objectif de cette étude est de déterminer l’effet à court terme de deux techniques de rénovation des prairies sur la productivité et le stock de C du sol superficiel. Une prairie semée 12 ans auparavant située sur le Domaine Expérimental INRAE du Pin-au-Haras (Normandie) a été divisée en trois sous-parcelles : (i) non rénové, (ii) rénové par resemis et (iii) rénové par sursemis. Le rendement, les stocks de C de l’horizon 0-10 cm du sol et les propriétés de la matière organique du sol ont été comparés 8 et 20 mois plus tard. Les rénovations par resemis ou sursemis ont augmenté la production annuelle de 50 %. Dans les deux sous-parcelles rénovées, le stock de C organique de l’horizon 0-10 cm a été maintenu et la quantité de matière organique a augmenté. Le ratio C/N ainsi que la proportion de C soluble dans le sol n’ont pas été modifiés. Dans cet essai, la rénovation par sursemis a abouti à un gain de productivité comparable à celui du resemis sans nécessiter d’application de glyphosate permettant de maintenir le stock de C dans le sol.

La terre a traversé plus de 4 milliards d’années en gardant à sa surface des températures compatibles avec la vie la plupart du temps. Le cycle géologique du carbone au travers l’érosion des roches et des éruptions volcaniques contribue avec d’autres processus à réguler le climat. Cependant, à travers le temps, la co-évolution entre les organismes vivants et leur environnement aboutit parfois à des ruptures de la chimie de l’atmosphère (gaz à effet de serre, GES) et du climat entrainant une extinction des espèces. Ainsi l’Homme peut être vu comme la dernière innovation technique de l’évolution en passe de provoquer un accident climatique et écologique global. La combustion d’énergie fossile et l’agriculture et ont fait passer la teneur en CO2 atmosphérique, principal GES, de 280 à 400 ppm en 150 ans avec des conséquences visibles sur les glaciers, le climat et le niveau des mers. Ces modifications anthropiques s’accompagnent d’une chute de la biodiversité. Les prévisions pour le 21ème siècle prévoient une accélération des émissions de GES et des événements climatiques extrêmes qui devraient entrainer des déplacements de populations et des conflits. Cependant, à l’inverse des autres espèces par le passé, l’Homme a la capacité de prendre conscience de ces changements et d’en corriger la trajectoire. Outre, les défis socioéconomiques que posent le changement climatique et qui ne sont pas le sujet de ce manuscrit, l’Homme a besoin de connaissances sur le fonctionnement des écosystèmes en lien avec la biodiversité afin d’anticiper les effets du réchauffement et de disposer de leviers d’actions. Ce manuscrit d’HDR résume quinze années de recherche sur les cycles biogéochimiques des écosystèmes terrestres dans un contexte de changement climatique et de développement d’une agriculture durable. Mes travaux de recherche ont contribué à 1) explorer les métabolismes et les facteurs contrôlant les flux de carbone et d’azote, en particulier dans le sol et la rhizosphère des plantes, 2) identifier les stratégies de vie des microorganismes décomposeurs et des plantes au regard de ces cycles et 3) une analyse systémique des échanges de matière entre les organismes vivants afin de comprendre les cascades d’effet et les boucles de rétroactions. La finalité première de mes recherches est de prévoir l’impact des changements globaux (réchauffement climatique, chimie de l’atmosphère et modèles agricoles) sur les services écosystémiques adossés aux processus biogéochimiques (productions, stockage de carbone...). Les résultats indiquent une capacité des sols des écosystèmes peu perturbés et diversifiés (prairies permanentes, forêts) à accumuler des matières organiques créant un puits de carbone. Le stockage de carbone dans les sols n’augmente pas nécessairement avec les entrées de carbone, il peut même diminuer. Ainsi l’augmentation de la production primaire sous CO2 élevé n’augmentera pas ou peu le puits de carbone. Cependant, les retombées d’azote atmosphérique, la fixation symbiotique et la dégradation des roches par les mycorhizes devraient intensifier le puits de carbone en levant les contraintes stœchiométriques (azote, phosphore) des plantes et des microorganismes stockeurs de carbone du sol. Le transfert du carbone organique du sol dans les horizons profonds permet un stockage de celui-ci pendant des millénaires dans certaines conditions. Cependant, un changement de profondeur d’enracinement des végétaux peut soudainement réactiver sa minéralisation en CO2 par les microorganismes de la rhizosphère. Mes investigations ont mis en lumière le paradoxe de la synchronisation entre l’offre microbienne en nutriments minéraux et la demande des végétaux dans les écosystèmes naturels. Défi majeur en l’agriculture, cette synchronisation a très peu de chances de se produire de manière spontanée puisqu’elle dépend de deux organismes indépendants dont les réponses à l’environnement diffèrent. Un mécanisme de régulation ajustant l’offre à la demande a été identifié : deux groupes fonctionnels microbiens créent un tapis roulant de nutriments minéraux sur lequel se nourrit la plante. De cette façon de grandes quantités de nutriments peuvent être transférée du sol à la plante tout en évitant les pertes par lessivage et dénitrification. Il semblerait que les cultures annuelles aient perdu ce mécanisme de synchronisation offre-demande expliquant leur piètre performance environnementale. Cependant, l’association d’un blé avec des plantes pérennes a permis de rétablir la synchronisation offre-demande et les services qui lui sont associés. Ces résultats suggèrent de nouvelles pistes de recherche. La biodiversité contribuerait à créer des systèmes auto organisés où les échanges de matière sont optimisés afin de garantir la pérennité des parties et une utilisation de l’énergie lumineuse maximisée dans le temps. Elle pourrait également contribuer à adapter les écosystèmes aux évolutions climatiques. Ainsi le rôle de la coopération entre les organismes vivants dans le processus de sélection naturelle et le fonctionnement des écosystèmes pourrait être largement sous-estimé. S’inspirant de ces nouvelles connaissances, des nouveaux systèmes de culture bio-diversifiés et à hautes performances environnementales peuvent être conçus., The earth has passed more than 4 billion years, keeping on its surface temperatures compatible with life most of the time. The geological cycle of carbon through erosion of rocks and volcanic eruptions contributes with other processes to regulate the climate. However, over time, the co-evolution between living organisms and their environment sometimes leads to breaks in the chemistry of the atmosphere (greenhouse gases, GHGs) and climate leading to species extinction. Humans can be seen as the latest technical innovation of evolution causing a global climatic and ecological accident. The combustion of fossil fuels and agriculture has increased the atmospheric CO2 concentration, the main GHG, from 280 to 400 ppm in 150 years with visible consequences on glaciers, climate and sea levels. These global changes are accompanied by a drop in biodiversity. Forecasts for the 21st century predict an acceleration of GHG emissions and extreme weather events that should lead to population displacements and conflicts. However, unlike other species in the past, humans have the capacity to become aware of these changes and to correct their trajectory. In addition to the socio-economic challenges posed by climate change, which are not the subject of this manuscript, humans need knowledge on the functioning of ecosystems in relation to biodiversity in order to anticipate the effects of global warming and to levers of action. This HDR manuscript summarizes fifteen years of research on the biogeochemical cycles of terrestrial ecosystems in the context of climate change and the development of sustainable agriculture. My research has helped to 1) explore the metabolisms and factors controlling carbon and nitrogen fluxes, especially in the soil and plant rhizosphere, 2) identify the life strategies of microorganisms and plants vis-à-vis of biochemical cycles and 3) a systemic analysis of the exchange of matter between living organisms to understand the cascade effects and the feedback loops. The applications of my research are to 1) improve the predictions on the impact of global changes (global warming, atmospheric chemistry and agricultural models) on ecosystem services backed by biogeochemical processes (production, carbon storage ...), 2) optimize the managements of grasslands and their services and 3) eco-design new grain production system inspired from the functioning of permanent grasslands. The results indicate a capacity of undisturbed biodiverse ecosystems (permanent grasslands, forests) to continuously accumulate organic matter in soil creating a global carbon sink. Carbon storage in soils does not necessarily increase with carbon inputs, it can even decrease. Thus, the increase in primary production in response to the rising atmospheric CO2 concentration will not increase the soil carbon sink. However, atmospheric nitrogen deposition, symbiotic fixation, and mycorrhizal degradation of rocks are expected to intensify the soil carbon sink by alleviating the stoichiometric constraints (nitrogen, phosphorus) of plants and soil-carbon-storing microorganisms. The transfer of organic carbon into deep soil horizons allows storage of this carbon for millennia under specific conditions. However, a change in rooting depth of plants can suddenly reactivate its mineralization in CO2 by microorganisms of the rhizosphere. My investigations have highlighted the paradox of the synchronization between the microbial supply of mineral nutrients and the demand of plants in natural ecosystems. Representing a major challenge in agriculture, this synchronization is unlikely to occur spontaneously since it depends on two separate organisms whose responses to environment factors differ. A regulating mechanism that adjusts supply to demand has been identified: two microbial functional groups create a conveyor belt of mineral nutrients on which the plant feeds. In this way large amounts of nutrients can be transferred from the soil to the plant while avoiding leaching and denitrification losses. It seems that annual crops have lost this supply-demand synchronization mechanism, which explains their poor environmental performance. However, the combination of a wheat with perennial plants has restored the synchronization supplydemand and services associated with it. These results suggest new lines of research. Biodiversity would help to create self-organized systems where exchanges of matter are optimized to ensure the durability of the parties and a maximal use of light energy. It could also contribute to adapting ecosystems to climate change. Thus the role of cooperation between living organisms in the process of natural selection and the functioning of ecosystems could be largely underestimated. Inspired by this knowledge, new bio-diversified and sustainable grain production systems can be designed.

Partie 4 : Management of Douglas-fir and technological properties of its wood; International audience

Permanent grasslands produce high-quality forage and host very diverse plant communities. They also play a key role in carbon storage. However, we still understand little about how pedoclimatic conditions and plant community management or functioning help generate ecosystem services. This study analysed 32 grasslands in Normandy, Lorraine, and Auvergne that offer different ecosystem services. Certain grasslands had high values for service indicators. However, no synergies among services were observed, which suggests that determinant factors were different. A functional traits approach showed that plant community functioning directly affected forage quality. Plant diversity was tied to agricultural management and is also likely related to grassland history and landscape structure. Carbon storage levels were related to the clay content of soils.

The stimulation of vegetation productivity in response to rising atmospheric CO 2 concentrations can potentially compensate climate change feedbacks. Vegetation and soil C storage will be however limited by nutrient availabil- ity, the allocation of C resources of vegetation into aboveground biomass versus roots and on the feedbacks with soil microorganisms. Plants can modulate the amount of carbon that is allocated to above- versus belowground in response to changing atmospheric CO 2 concentrations, with a consequent alteration of productivity and of the litter and rhizosphere inputs to the soil. Recent studies have highlighted the crucial role of mycorrhizal fungi on the response of vegetation productivity to rising CO 2 concentrations. We hypothesize that mycorrhiza can also play a key role on litter decomposition for N acquisition, therefore affecting CO 2 emissions and the amount C sequestered into the soil. In order to test this hypothesis, different levels of litter addition were implemented on trenched (root exclusion) and non-trenched plots (with roots) in a temperate deciduous forest of ectomycorrhiza-associated species (beech and oak). Soil CO 2 fluxes were continuously measured at high temporal resolution with automatic chambers, whereas the spatial and seasonal variability was determined using portable chambers. The composition of saprobiotic and symbiotic fungal communities were determined in each treatment after 2 years, as well as the changes in soil C and N stocks. Soil CO 2 effluxes showed a synergistic interaction between the increased litter inputs and the presence of roots, where the carbon mineralized in response to litter addition was much higher in the non-trenched plots. DNI sequencing of fungal communities confirmed that trenching succeeded in suppressing virtually all ectomycor- rhizas. Litter manipulation (exclusion, control, doubled addition) showed a linear relationship with ectomycorrizal (ECM) strains of divergent exploration types, where the litter exclusion treatment was dominated by ECM of short exploration types and long exploration ECM types dominate at double litter. These results together suggest that long exploration types of ECM may contribute to litter decomposition for N and/or other nutrients, thus enhancing CO 2 fluxes and N acquisition by plants. Therefore, the association of plants with ectomycorrhizal fungi not only may determine the productivity responses to rising atmospheric CO 2 concentrations, but also the rates of litter decomposition and N cycling.

Key message Short-rotation forestry using eucalyptus in degraded oak forests in the semi-arid area of NW Morocco can be a useful strategy to avoid further degradation and carbon loss from this ecosystem, but it might be constrained by nutrient and water supply in the long term.[br/] Context Land degradation and deforestation of natural forests are serious issues worldwide, potentially leading to altered land use and carbon storage capacity.[br/] Aims Our objectives were to investigate if short-rotation plantations can restore carbon pools of degraded soils, without altering soil fertility.[br/] Methods Carbon and nutrient pools in above- and below-ground biomass and soils were assessed using stand inventories, harvested biomass values, allometric relationships and selective sampling for chemical analyses.[br/] Results Carbon pools in the total ecosystem were low in the degraded land and in croplands (6–13 Mg ha−1) and high in forests (66–94 in eucalyptus plantations; 86–126 in native forests). The soil nutrient status of eucalyptus stands was intermediate between degraded land and native forests and increased over time after eucalyptus introduction. All harvest scenarios for eucalyptus are likely to impoverish the soil but, for the moment, the soil nutrient status has not been affected.[br/] Conclusion Afforestation of degraded land with eucalyptus can be a useful restoration tool relative to carbon storage and soil fertility, provided that non-intensive forestry is applied.

Tropical forests are global centres of biodiversity and carbon storage. Many tropical countries aspire to protect forest to fulfil biodiversity and climate mitigation policy targets, but the conservation strategies needed to achieve these two functions depend critically on the tropical forest tree diversity-carbon storage relationship. Assessing this relationship is challenging due to the scarcity of inventories where carbon stocks in aboveground biomass and species identifications have been simultaneously and robustly quantified. Here, we compile a unique pan-Tropical dataset of 360 plots located in structurally intact old-growth closed-canopy forest, surveyed using standardised methods, allowing a multi-scale evaluation of diversity-carbon relationships in tropical forests. Diversity-carbon relationships among all plots at 1 ha scale across the tropics are absent, and within continents are either weak (Asia) or absent (Amazonia, Africa). A weak positive relationship is detectable within 1 ha plots, indicating that diversity effects in tropical forests may be scale dependent. The absence of clear diversity-carbon relationships at scales relevant to conservation planning means that carbon-centred conservation strategies will inevitably miss many high diversity ecosystems. As tropical forests can have any combination of tree diversity and carbon stocks both require explicit consideration when optimising policies to manage tropical carbon and biodiversity., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Recent results have shown that equatorial podzols store large amounts of carbon in their deep Bh horizons. This leads to two main questions: (1) how and at what kinetics these soils were formed, (2) how climate change could induce atmospheric carbon production that could impact the global climate system.In this context, we have developed a model that allows to constrain carbon fluxes both by the observed C stocks and their 14C age. In a sufficiently simplified situation, we have established a formal relationship between the C stock evolution and its 14C age. Applied to Amazonian podzols, our model has brought new and unexpected results. It has been shown that the surface horizons of the most hydromorphic podzolized areas are the largest contributors of MOD transferred to the hydrographic network then to the sea. It is observed that the formation of Bh is only possible by considering two compartments, fast and slow. The estimate of their formation time (low estimate) allowed to differentiate between relatively young podzols (formation time 15 – 25 ky) developed on relatively recent Holocene sediments and old podzols (formation 180 – 290 ky) developed on older sediments. The carbon accumulation rate in the studied podzols ranges from 0.54 to 3.17 gC m-2 y-1, which corresponds to a carbon sequestration around 3 1011 gC an-1, which is significant at the geological scales.Column percolation experiments allowed us to show the reactivity of the Bh material and the presence, despite very high C/N ratios (63 on average), of a significant bacterial activity which modifies the nature of the MOD which percolates through it. This MOD has the capacity to transport Al and Fe in the form of complex organometallic complexes capable of migrating through very kaolinitic materials. These results contribute to the understanding of the transfers of pedologically formed MOD in the deep aquifers.Under the hypothesis of the appearance of a climate with contrasting seasons, we have been able to show that a 90-day period without rain after the disappearance of the perched water-table would not allow to reach the point of entry of air by drying of superficial horizons. Nevertheless, assuming an air entry, the extrapolation of the experimentally measured mineralization rates under oxic conditions results in a production of atmospheric C around 2.0 1014 g of CO2 per year, which may involve a positive feedback from the global climate system., Des résultats récents ont montré que les podzols équatoriaux stockent d’importantes quantités de carbone dans leurs horizons Bh profonds. Cette constatation amène deux questions principales : (1) comment et à quel rythme se sont formés ces sols (2) dans quelle mesure le changement climatique pourrait induire une production par ces sols de carbone atmosphérique susceptible d’impacter le système climatique mondial.Dans ce contexte, nous avons réalisé un modèle qui permet de contraindre les flux de carbone à la fois par les stocks observés et leur âge 14C. En situation suffisamment simplifiée, nous avons établi une relation formelle entre l’évolution des stocks et l’âge 14C de celui-ci. Appliqué aux podzols amazoniens, notre modèle a apporté des résultats nouveaux et inattendus. Il a permis de montrer que ce sont les horizons de surface des aires podzolisées les plus hydromorphes qui sont les plus gros contributeurs de MOD transférée vers le réseau hydrographique et la mer. On observe que la formation des Bh n’est possible qu’en envisageant deux compartiments, rapide et lent. Une estimation basse de leur temps de formation permet de différencier des podzols relativement jeunes (temps de formation de l’ordre de 15 103 - 25 103 ans), développés sur des sédiments Holocènes relativement récents, et des podzols âgés (temps de formation de l’ordre de 180 103 - 290 103 ans), développés sur des sédiments plus anciens. Le taux d’accumulation du carbone dans les podzols étudiés varie de 0,54 à 3,17 gC m-2 an-1, ce qui correspond à une séquestration de carbone de l’ordre de 3 1011 gC an-1, faibles à l’échelle annuelle, mais significative aux échelles géologiques.Les expérimentations de percolation en colonne nous ont permis de montrer la réactivité du Bh et la présence, malgré des rapports C/N très élevés (63 en moyenne), d’une activité bactérienne significative qui modifie la nature de la MOD qui le traverse. Cette dernière a la capacité de transporter Al et Fe sous forme de complexes organo-métalliques, complexes susceptibles de migrer à travers des matériaux très kaolinitiques. Ces résultats participent à la compréhension des transferts de MOD d’origine pédologique dans les nappes profondes.Dans l’hypothèse de l’apparition d’un climat à saisons contrastées, nous avons pu montrer qu’une durée sans pluie de 90 jours après disparition de la nappe perchée ne permettrait pas d’atteindre le point d’entrée d’air par assèchement des horizons superficiels. Néanmoins, dans l’hypothèse d’une entrée d’air, l’extrapolation des taux de minéralisation mesurés expérimentalement en conditions oxiques aboutit à une production de C atmosphérique de l’ordre de 2,0 1014 g de CO2 par an, ce qui peut impliquer une rétroaction positive du système climatique mondial.

Les engrais verts au service d’une fourniture d’azote et/ou du stockage de carbone? . Colloque chaire Agrosys

National audience; Permanent grassland provides ecosystem services such as protection of soil quality, preservation of ground and surface water quality and regulation of climate through soil carbon sequestration. Intensification of management practices through changes of mowing, fertilization and grazing intensity may threaten these services as well as climate variability through increasing drought intensity and frequency. In grassland, root activity (growth, mortality) contributes to the main inputs of C and N compounds into the soil. Understanding how root activity and soil C stock respond to management is of prime importance for the ecosystem C sequestration service. We studied during two years the dynamics of root mass production of an upland grassland subjected to different grazing intensity (abandonment, low and high stocking density with respectively 0, 6.9 and 13.8 LSU ha-1, livestock unit) and to ambient climate variability. We expected to have lower below-ground net primary production in intensive than in extensive grazing treatments due to stimulation of shoot mass at the expense of roots. The site is part of the long-term observatory network (ACBB-SOERE) located at St-Genès-Champanelle, France and included 12 plots, in which four ingrowth cores were inserted at 20 cm and collected 10 times each year during two following years. In addition root mass was measured three times during the first year to calculate root turnover. We showed strong seasonal root production in spring and autumn for all treatments either during a wet (first) or a dry (second) year. Root production started earlier in spring for both grazing treatments than in abandonment, which can be explained by higher soil temperature. However at the annual scale, root production and root stock were similar between treatments, leading to unchanged root turnover. Thus grazing intensity did not lead to change of root stock, although root dynamics, above-ground biomass and species composition were affected.

International audience; Microalgae have received much attention in the context of renewable fuel production, due to their ability to produce in high quantities carbon storage molecules such as lipids and carbohydrates. Despite significant research effort over the last decade, the production yields remain low and need to be optimized. For that, a thorough understanding of carbon storage metabolism is necessary. This paper develops a constrained metabolic model based on the dFBA framework to represent the dynamics of carbon storage in microalgae under a diurnal light cycle. The main assumption here is that microalgae adapt their metabolism in order to optimize their production of functional biomass (proteins, membrane lipids, DNA, RNA) over a diurnal cycle. A generic metabolic network comprised of 160 reactions representing the main carbon and nitrogen pathways of microalgae is used to characterize the metabolism. The optimization problem is simplified by exploiting the right kernel of the stoichiometric matrix, and transformed into a linear program by discretizing the differential equations using a classical collocation technique. Several constraints are investigated. The results suggest that the experimentally observed strategy of accumulation of carbon storage molecules during the day, followed by their depletion during the night may indeed be the optimal one. However, a constraint on the maximal synthesis rate of functional biomass must be added for consistency with the biological observations.

International audience; With the increase of global population and the threat of climate changes caused by anthropogenic gas emissions, high pressure has been put on arable lands in order to cover the needs for both food and bioenergy production. Conversion of degraded lands for such purposes represents a sustainable solution, implying the restoration of several ecosystem services which have been impaired. Construction of Technosols on degraded lands have been investigated in order to increase soil fertility and biological activity, using various organic and inorganic industrial by-products. Field trials have demonstrated the interest of this remediation technique for the production of non-food biomass and the improvement of soil biodiversity. Moreover, the construction of Technosols with materials rich in organic carbon may also represent a way to store carbon in soils for a long-time, thus alleviating the emissions of greenhouse gases associated to the traditional end-of-life of these products. However, the processes of organic matter transformation and mineralization in these newly formed soils are largely unknown. We collected data on soil organic C evolution over 12 years on two experimental sites in Lorraine, France, where different Technosol profiles were created from thermally-treated cockery soil, paper sludge and green waste compost. Data were compared to the one from natural soils in the same region, and to the available data from other constructed Technosols in the literature. RothC model (Coleman and Jenkinson, 1996), describing the evolution of soil organic carbon divided in five pools of organic matter, was adapted to the specific constraints of the constructed Technosols (e.g. with possible evolution of soil density and soil depth). The adapted model was used to predict the evolution of soil organic carbon on both experimental sites, both at short-term over the last 12 years and on the long-term over the whole 21st century. Our results suggest that the stock of organic C in the top 30 cm of constructed Technosols can reach the level usually observed in natural soils with similar climate and plant cover in less than 10 years. This evolution was well described by RothC model when taking into account the various types of organic matters introduced in the Technosols. Despite this fast degradation at the surface of the soil, the total amount of organic C stored in the whole profile of the Technosol (100 cm) remained significantly higher than the corresponding value in natural soils. Constructed Technosols could therefore be a way to optimize soil ecosystem services associated to carbon storage, e.g. global climate regulation. Further investigations and new modelling approaches are however needed to precise the dynamics of soil organic carbon in these newly formed soils, particularly regarding the influence of climate changes expected in the next decades.

Internationale; International audience; Agroforestry systems are promoted for providing a number of ecosystem services and environmental benefits, including soil protection and carbon sequestration. This study proposes a modelling approach to quantify the impact of soil redistribution on soil organic carbon (SOC) storage in a temperate hedgerow landscape. Evolution of SOC stocks at the landscape scale was examined by simulating vertical and horizontal SOC transfers in the 0–105 cm soil layer due to soil redistribution by tillage and water processes. A spatially explicit SOC dynamics model (adapted from RothC-26.3) was used, coupled with a soil-redistribution model (LandSoil). SOC dynamics were simulated over 90 years in an agricultural hedgerow landscape dedicated to dairy farming, with a mix of cropping and grasslands. Climate and land use were simulated considering business-as-usual scenarios derived from existing information on the study area. A net decrease in SOC stocks was predicted at the end of the simulation period. Soil redistribution induced a net SOC loss equivalent to 2 kg C ha−1 yr−1 because of soil exportation out of the study site and an increase in SOC mineralization. Hedgerows and woods were the only land use in which soil redistribution induced net SOC storage. Soil tillage was the main process that induced soil redistribution within cultivated fields. Soil exportation out of the study area was due to erosion by water, but remained low because of the protective role of the hedgerow network. These soil transfers redistributed SOC stocks in the landscape, mostly within cultivated fields.

In a perfect-deficit approach (Yi, 2012), the daily maximum carbon storage capacity (CPC) of a given ecosystem for each year defines the perfect annual CPC curve. Deficits are the differences in the daily observational data for a given year against a perfect curve. The area between this curve and instantaneous canopy photosynthetic rates represents the potential productivity. Using an 11-year (2004 – 2014) eddy covariance flux and meteorological data, this perfect-deficit approach was used to examine the relationship between potential productivity and droughts occurring in 2005 and 2010 in a tropical rainforest of French Guiana, South America. Surprisingly, CPC deficits were only reduced by 24% (2005) and 19% (2010) from their respective perfect CPCs, indicating a subtle effect of drought to ecosystem productivity. Highest precipitation occurred in 2010 but precipitation deficits dropped drastically during this year (71% reduction from its perfect value) which reflects a drought condition. However, its deficits showed no correlation annually and seasonally. Soil water content (SWC) appeared to be the single driver for CPC deficits during long dry periods but is weakly correlated (r = 0.30; P

Mountain soils stocks huge quantities of carbon as soil organic matter (SOM) which may be highly vulnerable to climate change and thus alter the atmospheric greenhouse gases concentration at a decadal timescale. To understand the effect of climate conditions on the dynamics of mountain soil organic carbon (SOC), a climate change experiment was set up in October 2009 in Swiss Jura subalpine grassland soils. The climate change experiment (soil transplantation) simulated two realistic climate change scenarios, with increased air temperatures ranging between 2 °C and 4 °C and decreased precipitation ranging between 20% and 40%. These changes reflect current predictions of climate change for the 21th century in temperate mountain regions.We studied the effect of climate conditions (climate manipulation and seasonal changes) after four years of climate experiment on (i) the dynamic of microbial decomposition, microbial abundance and community structure, (ii) the dynamic soil organic matter pools with contrasted turnover rate and representing the energetic resource of microbial communities, (iii) the interactions between microbial communities and soil organic matter pools and (iv) the soil organic carbon stocks.This work shows a strong seasonal dynamics of microbial decomposition with higher enzymatic activities, higher microbial abundance and shift of microbial community structure in winter than in summer. These results were linked to the seasonal organic matter labile pools dynamics. Moreover structural equation modeling shows that climate manipulation differently influences the drivers of SOC enzymatic decomposition in summer and winter.Finally, this work shows a strong decrease of soil organic carbon concentration under the climate change manipulation which cannot be explained by an increase of microbial activities. In contrast, our results suggest that the observed climate-induced decrease in bulk soil organic C content was due a SOC decrease in the most biogeochemically stable SOM fraction associated with a decrease in clay content and a decrease of soil calcareous concentration. Thus, our results hint more so towards an effect of SOM leaching (Gavazov, 2013) to explain the climate effect on SOC content than an effect of microbial and/or plant activities., Les sols de montagne constituent un réservoir majeur de carbone stocké sous forme de matière organique (carbone organique du sol, COS), potentiellement hautement vulnérable aux changements des conditions climatiques. Afin de comprendre les répercussions des changements des conditions climatiques sur la dynamique du COS des sols de montagne, cette thèse s'appuie sur une expérimentation de transplantation altitudinale de monolithes de sol de prairie subalpine calcaire, mise en place dans le Jura Suisse en 2009. Cette expérimentation permet de simuler deux scénarios réalistes de changements climatiques attendus au cours du 21éme siècle, visant à réchauffer et assécher le climat (+2°C et +4°C ; -20% et -40% de précipitations).La démarche conceptuelle de cette thèse a été d'étudier les effets des changements des conditions climatiques (variations saisonnières et manipulation climatique) au bout de quatre années d'expérimentation sur (i) la dynamique des communautés microbiennes et de leur activité enzymatique de décomposition du COS, (ii) la dynamique de différents pools de COS qui constituent la ressource énergétique des micro-organismes décomposeurs, (iii) les interactions s'établissant entre les communautés microbiennes et leurs ressources énergétiques et (iv) les stocks de COS du sol.Nos résultats montrent une très forte dynamique saisonnière du processus de décomposition microbienne se traduisant par de fortes activités enzymatiques de décomposition, une biomasse microbienne plus importante et une structure des communautés microbienne différente lors de la saison hivernale par rapport à la saison estivale. Ces résultats sont en lien avec la dynamique observée des pools les plus labiles du COS (C organique extractible à l'eau et C organique particulaire libre), et des modèles d'équations structurelles montrent que les conditions climatiques (variations saisonnières et manipulation climatique) modifient les interactions s'établissant entre les communautés microbiennes et leurs ressources pour contrôler la décomposition enzymatique du COS.Enfin, ce travail de thèse montre une forte diminution des concentrations en COS sous l'effet de la manipulation climatique, qui ne peut être expliquée par une décomposition microbienne accrue du COS. Au contraire, nos résultats suggèrent que la diminution de la concentration en COS pourrait être due à l'accélération des processus pédologiques naturels sous les scénarios de changement climatique au sein de ces sols calcaires de prairies subalpines, avec une décarbonatation accrue favorisant la lixiviation du carbone organique dissous et le lessivage du pool de COS associé aux argiles. Ces résultats inédits offrent de nouvelles perspectives de recherche sur les effets des changements climatiques sur l'évolution des stocks de COS.

The fast increase of greenhouse gases in the atmosphere, such as carbon dioxide, due to human activities is consider as the main cause of actual climate change. Terrestrial ecosystem are considered as a huge "sink" of C and may contribute to decrease greenhouse gases. Permanent grasslands cover 40% of land and their soil may contribute to sequester C (GIEC 2001). However, the processes involved and their regulations remain to be specified. The aim of the thesis was to analyze the effect of grazing management on soil C storage. This analysis was made from data acquired on two long term permanent grassland sites (SOERE ACBB) and by studying C fluxes between the different agroecosystem compartments under different grazing intensities for i) estimating our capacity to measure soil C storage after 10 years of grazing treatments by comparing two methods (soil inventories vs net carbon storage measurements), ii) to provide knowledge on the mechanisms and regulations affecting the dynamics of soil C sequestration. Comparing results of both methods, measurements indicated a net C sequestration in soil, with an average sequestration rate of 2.21 t C ha-1 yr-1 and 2.29 t C ha-1 year-1 and no significant difference between treatment but a tendency to a higher sequestration with more intensive management. Each method provides access to different information. The approach with flux towers allows a better understanding of the role and interactions between climate and practices on C fluxes in grasslands. Soil inventories showed carbon is store in deeper soil layers. While plant communities have evolved as a result of differentiated grazing treatments, measurements show no changes in total C stocks and particulate organic matter. Analysis of C fluxes after 7 years of differentiate grazing treatments, showed that treatments with low or zero grazing intensity led to a reduction of carbon fluxes between the compartments of the continuum of degradation, while carbon stocks in roots and POM were not affected by treatments. A complementary study conducted to estimate root production indicates that the response of roots (stocks and production) and stocks of particulate organic matter may be partly decoupled from the response of the aerial vegetation compartment. This study indicates that a more integrative approach on ecosystem functioning is necessary to increase our ability to predict the impact of management practices on C storage in grassland.; La rapide augmentation des gaz à effet de serre (GES) dans l’atmosphère - dont le CO2 – due aux activités humaines est considérée comme responsable des changements climatiques en cours et futurs. Les écosystèmes terrestres sont potentiellement des "puits" importants de C et pourraient contribuer à l'atténuation des GES. Les prairies permanentes (steppes, savanes, prairies de montagne, ...) couvrent 40% de la surface terrestre (hors calotte glaciaire) et leurs sols représentent potentiellement un énorme "puits" permettant de stocker du C naturellement (GIEC 2001). Cependant, les processus impliqués et leur régulation restent à préciser. L’objectif de la thèse était d’analyser l’effet des pratiques de pâturage sur le stockage de C dans le sol. Cette analyse a été réalisée à partir de données acquises sur deux dispositifs ‘long terme’ en prairie permanente (SOERE ACBB) et en s’intéressant aux flux de C entre les différents compartiments de l’agro-écosystème sous différentes intensités de pâturage afin i) d’étudier notre capacité à estimer le stockage de C dans le sol après 10 ans d’application de traitement, en comparant deux méthodes (méthode utilisant des tours à flux et mesure du stock de C du sol) ii) d’apporter des connaissances sur les mécanismes et régulations agissant sur les dynamiques de stockage du C. Les résultats de la comparaison des deux méthodes de mesures testées ont indiqué une séquestration nette de C dans le sol, avec un taux de séquestration moyen mesuré avec les deux méthodes de 2.21 t C ha-1 an-1 et de 2.29 t C ha-1 an-1, sans différence significative entre traitements, mais avec une tendance à une séquestration plus élevée avec la gestion plus intensive. Chaque méthode permet d’accéder à des informations différentes. L'approche avec les tours à flux permet d'identifier des interactions entre le climat et les pratiques de gestion sur les flux de C dans les prairies. Les inventaires de sol ont permis de montrer que le carbone se stocke également dans les couches plus profondes de sol. Alors que les communautés végétales ont évolué sous l’effet des traitements différenciés de pâturage, les mesures ne montrent pas d’évolution des stocks de C totaux ni des matières organiques particulaires. L’analyse des flux de C entre les différents compartiments de l'écosystème, après 7 ans d’application des traitements, montre que les traitements avec une intensité faible ou nulle ont conduit à une réduction des flux de carbone entre les compartiments du continuum de dégradation du C, tandis que les stocks de carbone des racines et des POM ne sont pas affectés par les traitements. Une étude complémentaire conduite pour estimer les productions racinaires indique que la réponse des racines (stocks et production) et des stocks de matières organiques particulaires pourrait être en partie découplée de la réponse du compartiment aérien de la végétation. A l’issue de cette étude, il nous apparaît qu’une approche plus intégrative du fonctionnement de l’écosystème est nécessaire pour accroître notre capacité de prédiction de l’impact des pratiques sur le stockage du C en prairie.

Agroforestry is a land use type where crops and trees are grown together in the same place and at the same time. Agroforestry systems have the advantage of providing multiple products (e.g. wood, fruits) or services (e.g. biodiversity enhancement, erosion control) whilst maintaining agricultural production. If they are known to store carbon into the biomass of the trees, they could also increase soil organic carbon (SOC) stocks. However their impact has rarely been studied under temperate conditions and has mostly concerned superficial soil layers. Our objectives were (i) to quantify and spatialize SOC stocks in an agroforestry system and in an adjacent agricultural plot, (ii) to assess what SOC fractions are responsible for possible additional carbon storage, and (iii) to quantify all organic inputs entering the soil. The trial was established in 1995 in southern France. Hybrid walnut trees are intercropped with durum wheat. SOC stocks were measured on 200 soil cores down to 2 m soil depth, and particle-size fractionation was performed on 64 soil samples. Carbon stocks of trees and of the herbaceous vegetation in the tree rows were also quantified. A trench was dug to 4 m soil depth to quantify tree fine root distribution and biomass. Minirhizotrons were installed at different depths to study tree fine root turnover. Annual additional SOC storage rates were estimated at 259 ± 59 kg C ha-1 yr-1 (0-30 cm) and at 350 ± 88 kg C ha-1 yr-1 (0-100 cm), and were mainly due to particulate organic matter fractions (> 50 μm). Only 10 to 15% was associated to clay particles. When the biomass of the trees was taken into account, total organic carbon storage rate reached 1.2 Mg C ha-1 yr-1. High tree root densities were observed at depth, but root turnover decreased with depth. Agroforestry systems provide higher amounts of carbon at depth than other agricultural practices, like no-till farming, and could therefore provide a more stable C storage in the long-term.

National audience

Les modèles intégrant les processus physiologiques et biogéochimiques sont les plus adaptés pour prédire les effets du changement climatique sur le stockage de carbone. Mais leur complexité les rend inadaptés à des applications à des échelles larges. Ce problème est exacerbé dans le cas des forêts méditerranéennes, qui se présentent souvent sous forme de mélange d'espèces, ou de couverts hétérogènes, et qui sont donc plus difficiles à modéliser que des forêts mono-spécifiques uniformes. Nous avons mis en œuvre une méthode de changement d'échelle qui consiste à créer un émulateur statistique d'un modèle, un méta-modèle, qui est beaucoup plus rapide tout en conservant le niveau de détail du modèle original. Nous avons ainsi pu méta-modéliser NOTG (Not Only Tree/Grass), un modèle de forêt spatialement explicite, auparavant limité à des simulations de quelques années. Grâce au méta-modèle, nous avons pu faire des simulations à l'échelle du siècle pour la forêt mélangée de FontBlanche (Bouches-du-Rhône). Les résultats suggèrent que le changement climatique pourrait, malgré une baisse de la pluviométrie, stimuler la production et le stockage de carbone., Models that describe physiological and biogeochemical processes are the most appropriate for predicting climate change impacts on forest carbon storage. However, their complexity prevents their application at large scales. This is particularly true in the case of Mediterranean forests, which are often composed of several tree species, or present an heterogeneous structure, both features being difficult to account for in models. This paper describes an up-scaling approach based on the creation of a statistical emulator of a model, a meta-model, which runs much faster while maintaining the same level of details than the original model. We thus produced a meta-model of NOTG (Not Only Tree/Grass), a forest model limited to simulations of a few years. With the meta-model it was possible to run century scale simulations for the Font-Blanche forest (Bouches-du-Rhône, France). Results suggested that despite a decrease in rainfall, climate change could stimulate productivity and carbon storage.

DEUG; Dans un contexte de changement global l’INRA tournent ses recherches pour une agriculture en quantité, de qualité et dans le respect des ressources naturelles et de l’environnement. De plus en plus les prairies sont reconnues pour leurs services environnementaux. Le stockage du carbone dans le sol fait partis de ces services, il est majoritairement dû à la décomposition des tissus racinaires du couvert végétal. La dynamique de production des racines pourrait alors avoir une influence sur le stockage du carbone dans les sols prairiaux. C’est dans le but de mieux comprendre le fonctionnement de l’écosystème prairial, en particulier de sa dynamique racinaire en fonction de la gestion qui est appliquée à la praire, que cette étude a été réalisée. C’est par la méthode des ingrowth-core que la production racinaire d’une prairie permanente soumise à trois intensité de pâturage différentes (abandonnée (Ab), forte (Bo+) et faible (Bo-)) de moyenne montagne du Massif central a pu être mesurée. Le stock racinaire à l’origine des entrées de carbone dans le sol a également été mesuré grâce au prélèvement de carottes de sol. Les résultats qui ont été obtenus sur la période de suivi de mars à juillet 2015, montrent comme en 2014 un pic de production précoce en début de printemps puis une diminution de cette production. Le pic pourrait être déclenché par l’absorption massive de nutriment mais également par l’augmentation des températures du sol et extérieures. La diminution de la production quant à elle serait due à l’allocation par la plante de ces ressources vers les parties aérienne, pour le développement de son appareil reproducteur. D’autre part, les résultats obtenus montrent que le pâturage à bien une influence sur le couvert végétale et sur sa production racinaire. Les traitements Ab produisent significativement moins de racines que les traitements pâturés. Pourtant les stocks racinaires qui ont été étudiés ne présentent pas de différences significative ni au cours du temps ni entre traitement. Associé à la production racinaire cela permet de dire qu’en parcelles Ab la vitesse de renouvellement des racines seraient plus lente qu’en parcelles pâturées. Il est nécessaire de continuer cette étude qui tend à montrer que même si le pâturage a un impact sur la communauté végétale des prairies tant au niveau aérien qu’au niveau racinaire, beaucoup d’autres facteurs rentrent en ligne de compte dans le stockage du C dans le sol des prairies permanentes.

La rapide augmentation des gaz à effet de serre (GES) dans l’atmosphère - dont le CO2 - due aux activités humaines est considérée comme responsable des changements climatiques en cours et futurs. Les écosystèmes terrestres sont potentiellement des "puits" importants de C et pourraient contribuer à l'atténuation des GES. Les prairies permanentes (steppes, savanes, prairies de montagne, ...) couvrent 40% de la surface terrestre (hors calotte glaciaire) et leurs sols représentent potentiellement un énorme "puits" permettant de stocker du C naturellement (GIEC 2001). Cependant, les processus impliqués et leur régulation restent à préciser. L’objectif de la thèse était d’analyser l’effet des pratiques de pâturage sur le stockage de C dans le sol. Cette analyse a été réalisée à partir de données acquises sur deux dispositifs ‘long terme’ en prairie permanente (SOERE ACBB) et en s’intéressant aux flux de C entre les différents compartiments de l’agro-écosystème sous différentes intensités de pâturage afin i) d’étudier notre capacité à estimer le stockage de C dans le sol après 10 ans d’application de traitement, en comparant deux méthodes (méthode utilisant des tours à flux et mesure du stock de C du sol) ii) d’apporter des connaissances sur les mécanismes et régulations agissant sur les dynamiques de stockage du C. Les résultats de la comparaison des deux méthodes de mesures testées ont indiqué une séquestration nette de C dans le sol, avec un taux de séquestration moyen mesuré avec les deux méthodes de 2.21 t C ha-1 an-1 et de 2.29 t C ha-1 an-1, sans différence significative entre traitements, mais avec une tendance à une séquestration plus élevée avec la gestion plus intensive. Chaque méthode permet d’accéder à des informations différentes. L'approche avec les tours à flux permet d'identifier des interactions entre le climat et les pratiques de gestion sur les flux de C dans les prairies. Les inventaires de sol ont permis de montrer que le carbone se stocke également dans les couches plus profondes de sol. Alors que les communautés végétales ont évolué sous l’effet des traitements différenciés de pâturage, les mesures ne montrent pas d’évolution des stocks de C totaux ni des matières organiques particulaires. L’analyse des flux de C entre les différents compartiments de l'écosystème, après 7 ans d’application des traitements, montre que les traitements avec une intensité faible ou nulle ont conduit à une réduction des flux de carbone entre les compartiments du continuum de dégradation du C, tandis que les stocks de carbone des racines et des POM ne sont pas affectés par les traitements. Une étude complémentaire conduite pour estimer les productions racinaires indique que la réponse des racines (stocks et production) et des stocks de matières organiques particulaires pourrait être en partie découplée de la réponse du compartiment aérien de la végétation. A l’issue de cette étude, il nous apparaît qu’une approche plus intégrative du fonctionnement de l’écosystème est nécessaire pour accroitre notre capacité de prédiction de l’impact des pratiques sur le stockage du C en prairie., The fast increase of greenhouse gases in the atmosphere, such as carbon dioxide, due to human activities is consider as the main cause of actual climate change. Terrestrial ecosystem are considered as a huge "sink" of C and may contribute to decrease greenhouse gases. Permanent grasslands cover 40% of land and their soil may contribute to sequester C (GIEC 2001). However, the processes involved and their regulations remain to be specified. The aim of the thesis was to analyze the effect of grazing management on soil C storage. This analysis was made from data acquired on two long term permanent grassland sites (SOERE ACBB) and by studying C fluxes between the different agroecosystem compartments under different grazing intensities for i) estimating our capacity to measure soil C storage after 10 years of grazing treatments by comparing two methods (soil inventories vs net carbon storage measurements), ii) to provide knowledge on the mechanisms and regulations affecting the dynamics of soil C sequestration. Comparing results of both methods, measurements indicated a net C sequestration in soil, with an average sequestration rate of 2.21 t C ha-1 yr-1 and 2.29 t C ha-1 year-1 and no significant difference between treatment but a tendency to a higher sequestration with more intensive management. Each method provides access to different information. The approach with flux towers allows a better understanding of the role and interactions between climate and practices on C fluxes in grasslands. Soil inventories showed carbon is store in deeper soil layers. While plant communities have evolved as a result of differentiated grazing treatments, measurements show no changes in total C stocks and particulate organic matter. Analysis of C fluxes after 7 years of differentiate grazing treatments, showed that treatments with low or zero grazing intensity led to a reduction of carbon fluxes between the compartments of the continuum of degradation, while carbon stocks in roots and POM were not affected by treatments. A complementary study conducted to estimate root production indicates that the response of roots (stocks and production) and stocks of particulate organic matter may be partly decoupled from the response of the aerial vegetation compartment. This study indicates that a more integrative approach on ecosystem functioning is necessary to increase our ability to predict the impact of management practices on C storage in grassland.

Key message Three options are proposed to improve the accuracy of national forest biomass estimates and decrease the uncertainty related to tree model selection depending on available data and national contexts. Introduction Different tree volume and biomass equations result in different estimates. At national scale, differences of estimates can be important while they constitute the basis to guide policies and measures, particularly in the context of climate change mitigation. Method Few countries have developed national tree volume and biomass equation databases and have explored its potential to decrease uncertainty of volume and biomasttags estimates. With the launch of the GlobAllomeTree webplatform, most countries in the world could have access to country-specific databases. The aim of this article is to recommend approaches for assessing tree and forest volume and biomass at national level with the lowest uncertainty. The article highlights the crucial need to link allometric equation development with national forest inventory planning efforts. Results Models must represent the tree population considered. Data availability; technical, financial, and human capacities; and biophysical context, among other factors, will influence the calculation process. Conclusion Three options are proposed to improve accuracy of national forest assessment depending on identified contexts. Further improvements could be obtained through improved forest stratification and additional non-destructive field campaigns.

Carbon capture and storage (CCS) is one of the most promising abatement options to curb CO2 emissions of the energy sector. Usually, in models where the atmospheric carbon stock is constrained to not exceed a given ceiling and under constant average costs, it is never optimal to deploy CCS before the time at which this ceiling is reached. In this paper, we show that, when the CCS technology is submitted to decreasing returns to scale, abatement activities must begin earlier, i.e. before the climate constraint binds. It must also cease strictly before the end of the ceiling period.

While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few ‘hyperdominant' species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only ≈1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region., The Amazon rainforest is dominated by relatively few tree species, yet the degree to which this hyperdominance influences carbon cycling remains unknown. Here, the authors analyse 530 forest plots and show that ∼1% of species are responsible for 50% of the aboveground carbon storage and productivity.

Brown algae are multicellular photosynthetic organisms belonging to the stramenopile lineage and which are mainly found in the intertidal zone. One of their metabolic characteristics is to store carbon fixed by photosynthesis through the production of mannitol, a 6-carbon non-cyclic polyol. Synthesis and recycling of mannitol in these organisms occur through the mannitol cycle, which includes two steps for synthesis and two for recycling. Among brown algae, Ectocarpus siliculosus represents the model organisms to study different aspects of their biology. During the PhD thesis, three genes coding for the enzymes involved in the first step of the mannitol cycle, the mannitol-1-phosphate dehydrogenase (M1PDH), were studied (EsM1PDH1, EsM1PDH2, and EsM1PDH3). M1PDHs catalyze a reversible reaction between fructose-6-phosphate and mannitol-1-phosphate. One modified version of the EsM1PDH1 gene, coding for a N-terminal truncated protein in order to deleted a domain of unknown function, was overexpressed in the bacteria Escherichia coli. The truncated recombinant protein was purified and biochemically characterized, notably to determine kinetic parameters in both directions of the reversible reaction catalyzed by M1PDH. These results were completed by analysis of changes in expression of genes encoding enzymes involved in the mannitol cycle during the diurnal cycle. These observations contribute to increasing the understanding of a key metabolic pathway in brown algal physiology.; Les algues brunes sont des organismes photosynthétiques multicellulaires, appartenant à la lignée des straménopiles, et dont l'habitat principal est la zone intertidale. Une de leurs caractéristiques métaboliques est d'utiliser le mannitol (polyalcool à six atomes de carbone) comme forme de stockage du carbone issu de la photosynthèse. Le métabolisme du mannitol chez ces organismes fait intervenir quatre enzymes, deux pour la synthèse et deux pour le recyclage, regroupées dans le cycle du mannitol. Parmi les algues brunes, Ectocarpus siliculosus est l'organisme modèle pour étudier différents aspects de leur biologie. Au cours de la thèse, trois gènes de cette algue codant pour les enzymes responsables de la première étape du cycle du mannitol, la mannitol-1-phosphate déshydrogénase (M1PDH), ont été étudiés (EsM1PDH1, EsM1PDH2, et EsM1PDH3). Les M1PDHs catalysent une réaction réversible entre le fructose-6-phosphate et le mannitol-1-phosphate. Une version du gène EsM1PDH, codant pour une protéine tronquée en N-terminal afin d'éliminer un domaine de fonction inconnue, a été surexprimée chez la bactérie Escherichia coli. La protéine recombinante tronquée a été purifiée et caractérisée au niveau biochimique, notamment pour déterminer ses paramètres cinétiques dans les deux sens de la réaction catalysée par les M1PDHs. Ces résultats ont été complétés par l'analyse de l'expression des gènes codant pour les enzymes du cycle du mannitol chez E. siliculosus au cours du cycle diurnal. L'ensemble de ces observations contribue à mieux comprendre une voie métabolique clé dans la physiologie des algues brunes.

How can french agriculture contribute to reducing greenhouse gas emissions ? Abatement potential and cost of technical measures. Capacity building workshop for effective policy implementation under the Effort Sharing Decision. European Commission

International audience

Soil organic carbon (SOC) has a crucial impact on global carbon storage at world scale. SOC spatial variability is controlled by the landscape patterns resulting from the continuous interactions between the physical environment and the society. Natural and anthropogenic processes occurring and interplaying at the landscape scale, such as soil redistribution in the lateral and vertical dimensions by tillage and water erosion processes or spatial differentiation of land-use and land-management practices, strongly affect SOC dynamics. Inventories of SOC stocks, reflecting their spatial distribution, are thus key elements to develop relevant management strategies to improving carbon sequestration and mitigating climate change and soil degradation. This study aims to quantify SOC stocks and their spatial distribution in a 1,000-ha agricultural bocage landscape with dairy production as dominant farming system (Zone Atelier Armorique, LTER Europe, NW France). The site is characterized by high heterogeneity on short distance due to a high diversity of soils with varying waterlogging, soil parent material, topography, land-use and hedgerow density. SOC content and stocks were measured up to 105-cm depth in 200 sampling locations selected using conditioned Latin hypercube sampling. Additive sampling was designed to specifically explore SOC distribution near to hedges: 112 points were sampled at fixed distance on 14 transects perpendicular from hedges. We illustrate the heterogeneity of spatial and vertical distribution of SOC stocks at landscape scale, and quantify SOC stocks in the various landscape components. Using multivariate statistics, we discuss the variability and co-variability of existing spatial organization of cropping systems, environmental factors, and SOM stocks, over landscape. Ultimately, our results may contribute to improving regional or national digital soil mapping approaches, by considering the distribution of SOC stocks within each modeling unit and by accounting for the impact of sensitive ecosystems.

The PROSTOCK project develops within the context of peri-urban agriculture and the aim of recycling organic waste of either agricultural or urban origin (or exogenous organic matter, EOM) in keeping with the perspective of restoring soil organic carbon stocks (SCS) in agricultural areas. Its main objective was to spatially assess the potential of EOM recycling for improving SCS over these areas. The secondary objective was to assess the resulting possible impacts of EOM use on greenhouse gas emissions (CO2, N2O in this project) and nitrate leaching. Moreover, PROSTOCK included a methodological aim oriented towards the feasibility assessment of monitoring SCS variations using spectroscopy and remote sensing in the visible near and shortwave infrared range (NIRS). The spatial level considered was that of small peri-urban agricultural regions, where waste management and its resulting effects on water and soil quality operate. The Versailles Plain and the Alluets Plateau, a peri-urban region covering 221 km² (of which 100 km² are croplands), unique in terms of available data, spatial and thematic representativeness and references on EOMs, was chosen as study region. A database of field and lab measurements (reflectance, roughness, bulk density, moisture, physico-chemical analysis…) and observations (soil surface conditions, amendment practices and cultural operations) with unprecedented size was collected and structured from more than 250 point locations spread over the cropped areas. Some fifteen remote sensing images from varied satellite and airborne sensors were acquired over the course of 3 field campaigns of field measurements synchronous with sensor acquisitions in 2011, 2012, 2013. This project enabled considerable progress in using imaging data related to field spectral measurements, for the purpose of estimating topsoil organic carbon content (SOC) from soil reflectance spectra. The accuracy that is expectable from such method not only depends on sensor type, but also on atmospherical and angular conditions of imaging, and cultural operations, which influence the performance of image atmospheric correction into reflectance units. Conversely to predictions obtained from lab or even field reflectance spectra, multispectral satellite images with medium spatial resolution do not enable to discriminate changes in SOC resulting from EOM applications over a large 15 years-duration, but they result in a rough mapping of SOC over large extents. This project also enabled to demonstrate the potential of optical/radar synergy for detecting cultural operations, which otherwise can hardly be spatially surveyed from interviews to farmers. In the same prospect of facilitating surveys, this project favoured ongoing studies about very high resolution Pleiades images showing their potential for mapping crop types and phenological stages, as well as for locating those fields having recently received EOM application. More, PROSTOCK enabled to parameterize the CERES-EGC agro-environmental model which was chosen for the purpose of simulating SCS dynamics according to various EOM applications. This parameterized model succeeds in retrospectively predicting temporal trends of SCS as observed over the course of 10 years for the QualiAgro Experiment. The inventory of actually of potentially available EOMs over the study region reveals multiple agronomical scenarios of amendment practices with EOM, depending on either their stocking or their fertilizing properties, through their proportion of easily available N: nitrogen mineralization and CO2, N2O emissions dynamics were characterized in this project for the main EOMs identified. The main N2O-emitter soils are now identified according to the EOMs applied. All required elements are therefore ready for the spatial modeling of simulations, to anticipate future evolutions. The PROSTOCK project paves the way for numerous related questions addressing the validity domain of agri-environmental models when soil types and cultural operations vary at the scale of a small agricultural region. It relied on both support and commitment from the study area farmers and appears to be rich in further developments for their common benefit, that the large size of collected data permits to anticipate. It could be continued and add value to its results with the prospect of spatially assessing soil ecosystem services according to the effects of EOM application.; Le projet PROSTOCK s’inscrit dans le contexte d’une agriculture péri-urbaine visant le recyclage des matières organiques résiduaires d’origines agricole, urbaine et de loisirs (ou produits résiduaires organiques, PRO) dans une perspective vertueuse de restauration des stocks de carbone organique (SCO) de ses sols agricoles. Son objectif principal était d’évaluer spatialement la possibilité d’accroître le SCO des sols agricoles par le recyclage des PRO. L’objectif secondaire visait à en évaluer les impacts potentiels, au même niveau d’organisation spatiale, sur les risques d’émission de GES et de lixiviation du nitrate. En outre, PROSTOCK comportait un objectif méthodologique visant à évaluer la faisabilité du suivi des variations de stocks de carbone organique des sols agricoles par imagerie de télédétection et/ou spectroradiométrie visible proche infrarouge (NIRS). Le niveau d’organisation spatiale retenu est celui de petites régions agricoles périurbaines, où se jouent la gestion des déchets et ses effets sur la qualité de l’eau et des sols. La Plaine de Versailles et du Plateau des Alluets, région périurbaine vaste de 221 km² (dont environ 100 km² de surface agricole utile), unique en termes de données disponibles, de représentativité spatiale et thématique et de références sur les PRO, a ainsi été choisie comme territoire de l’étude. Une base de données de mesures (réflectance, rugosité, masse volumique apparente, humidité, déterminations analytiques) et d’observations (états de surface du sol, pratiques d’amendement et opérations culturales) d’ampleur inédite a été recueillie et structurée et concerne plus de 250 localisations ponctuelles réparties sur la zone agricole. Une quinzaine d’images de divers capteurs satellitaires et aéroportés ont été acquises lors de 3 campagnes printanières de mesures de terrain synchrones des prises de vue de télédétection, en 2011, 2012 et 2013. Le projet a permis des avancées significatives sur l’utilisation de données imagées en lien avec les mesures spectrales au sol, pour l’estimation des teneurs en carbone organique (CO) du sol à partir de la réflectance du sol. La précision que l’on peut en espérer dépend non seulement du type de capteur, mais aussi des conditions atmosphériques et angulaires de la prise de vue, et des opérations culturales, qui affectent la performance de la correction atmosphérique des images en réflectance. Contrairement aux prédictions issues de spectres de réflectance de laboratoire ou même de terrain, les données multispectrales satellitaires de résolution moyenne haute ne permettent pas de distinguer des changements liés à des apports de PRO sur une durée de 15 ans, mais contribuent à une cartographie sommaire des teneurs en CO sur de vastes superficies. Le projet a par ailleurs permis de mettre en évidence l’intérêt de la synergie optique/radar pour la détection des opérations culturales, qui sont difficiles à répertorier spatialement par le biais d’enquêtes. Dans la même perspective d’alléger les enquêtes sur les pratiques agricoles, les travaux en cours sur les images de très haute résolution spatiale Pléiades montrent l’apport de ces images à la cartographie des types de cultures et de leurs stades phénologiques ainsi qu’au repérage des parcelles ayant récemment fait l’objet d’un épandage de PRO. Par ailleurs, le projet a permis de paramétrer le modèle agro-environnemental retenu pour simuler les stocks de C sous l’effet des apports de PRO (CERES-EGC), qui restitue fidèlement et rétrospectivement les évolutions temporelles des SCO observées sur 10 ans du dispositif expérimental QualiAgro. L’inventaire des PRO actuellement ou potentiellement disponibles réalisé sur le territoire fait ressortir une multiplicité de scenarii agronomiques d’utilisation des PRO selon leurs propriétés stockantes ou bien fertilisantes, via leur disponibilité en azote : les dynamiques de minéralisation de l’azote, d’émission de CO2 et de N2O ont été caractérisées pour les principaux PRO répertoriés dans le cadre de ce projet. On connaît désormais quels sont les sols principaux émetteurs de N2O selon les PRO qu’on leur apporte. Tous les éléments sont donc en place pour mettre en oeuvre ces simulations au niveau spatial, afin d’anticiper des évolutions futures. Le projet PROSTOCK ouvre la voie à de nombreuses questions connexes qui portent notamment sur le domaine de validité des modèles agri-environnementaux lorsque les types de sols et les opérations culturales varient à l’échelon d’une petite région agricole. Il s’est fait en lien et avec l’engagement des agriculteurs du territoire et s’avère fécond en possibles approfondissements au service de ces derniers, que permet d’envisager l’ampleur inédite des données recueillies. Il pourrait donner lieu à une suite qui valoriserait les résultats en cours dans la perspective de l’évaluation spatialisée des services écosystémiques des sols sous l’effet de l’apport des PRO.

International audience; Carbon storage is likely to enable adaptation of trypanosomes to nutritional challenges or bottlenecks during their stage development and migration in the tsetse. Lipid droplets are candidates for this function. This report shows that feeding of T. brucei with oleate results in a 4-5 fold increase in the number of lipid droplets, as quantified by confocal fluorescence microscopy and by flow cytometry of BODIPY 493/503-stained cells. The triacylglycerol (TAG) content also increased 4-5 fold, and labeled oleate is incorporated into TAG. Fatty acid carbon can thus be stored as TAG in lipid droplets under physiological growth conditions in procyclic T. brucei. beta-oxidation has been suggested as a possible catabolic pathway for lipids in T. brucei. A single candidate gene, TFE alpha 1 with coding capacity for a subunit of the trifunctional enzyme complex was identified. TFE alpha 1 is expressed in procyclic T. brucei and present in glycosomal proteomes, Unexpectedly, a TFE alpha 1 gene knock-out mutant still expressed wild-type levels of previously reported NADP-dependent 3-hydroxyacyl-CoA dehydrogenase activity, and therefore, another gene encodes this enzymatic activity. Homozygous Delta tfe alpha 1/Delta tfe alpha 1 null mutant cells show a normal growth rate and an unchanged glycosomal proteome in procyclic T. brucei. The decay kinetics of accumulated lipid droplets upon oleate withdrawal can be fully accounted for by the dilution effect of cell division in wild-type and Delta tfe alpha 1/Delta tfe alpha 1 cells. The absence of net catabolism of stored TAG in procyclic T. brucei, even under strictly glucose-free conditions, does not formally exclude a flux through TAG, in which biosynthesis equals catabolism. Also, the possibility remains that TAG catabolism is completely repressed by other carbon sources in culture media or developmentally activated in post-procyclic stages in the tsetse.

National audience

International audience; La technologie BECCS (Bioenergy and Carbon Capture & Storage) consiste à capturer le CO2 émis par des usines produisant des bioénergies afin de le stocker dans des formations géologiques. Ce procédé est de plus en plus intégré dans les modèles de simulation et d’optimisation du système énergétique mondial. Le message principal de ces travaux est que le BECCS pourrait être employé après 2050 et est - avec le CCS - quasiment incontournable pour limiter la hausse de la température à 2°C d’ici 2100, en particulier si les négociations internationales prennent du retard. Pour autant, le BECCS n’est pas encore une technologie dont l’efficacité est pleinement démontrée. La valorisation du CO2 apparaît à la fois comme une alternative au stockage du carbone et une voie d’accès au BECCS sur le long terme. Ainsi, l’écologie industrielle est une théorie pertinente pour appréhender l’intérêt économique et technologique du BECCS. Cet article montre que cette théorie ainsi que le thème de la valorisation sont quasiment absents du discours BECCS, à travers l’analyse du réseau des co-auteurs. Combler ces lacunes permettrait une meilleure compréhension du rôle du BECCS dans la transition écologique de la société.

International audience

Stocker du carbone dans les sols : pourquoi et comment ?. Journée Sols

Les stocks de Carbone dans les sols de la Plaine : résultats et questions vives. Journée Portes Ouvertes Gérer la fertilité des sols avec des matières organiques dans la Plaine de Versailles - Résultats de recherche et perspectives de mise en pratique

International audience; Soil organic carbon (SOC) is a key element of agroecosystems functioning and has a crucial impact on global carbon storage at world scale. SOC spatial variability and temporal dynamics are strongly affected by natural and anthropogenic processes occurring at the landscape scale, such as soil redistribution in the lateral and vertical dimensions by tillage and erosion processes. This study aims at modeling SOC distribution in A-horizons, at high spatial resolution, for an area of 1 000 ha in a complex agricultural landscape (NW France). The study site is characterized by high short distance heterogeneity due to an important diversity of soils (with varying redoximorphic conditions, depth), soil parent material (Aeolian loam cover, granite, hard and soft schist), topography, land use (annual crops, temporary or permanent grasslands) and hedge density. We used learning methods based on soil point data, characterized by soil description, SOC content and bulk density measurements. 200 points were selected using conditioned Latin hypercube sampling in order to cover the whole range of ancillary variables (elevation, Modified Compound Topographic Index, K emissions and land use). This sampling strategy enables to select a limited number of sampling sites coverering the study site heterogeneity. Additive sampling was designed to investigate SOC distribution near hedges (112 points sampled at fixed distances along 14 transects crossing hedges). Predictive environmental data consisted in the data used in the conditioned Latin hypercube sampling, at which were added topographic attributes derivated from the DEM and geological variables. We will discuss the ability of our model to capture and predict the SOC, considering the general SOC distribution trend at the landscape scale and the finer SOC distribution in landscape, at hedgerow proximity. The SOC 3-D map obtained will be used as soil data input in a soil evolution model, coupling SOC dynamics and soil erosion modeling.