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Conservation agriculture (CA), combining reduced or no tillage, permanent soil cover, and improved rotations, is often promoted as a climate-smart practice. However, our understanding of the impact of CA and its respective three principles on top- and subsoil organic carbon stocks in the low-input cropping systems of sub-Saharan Africa is rather limited. This study was conducted at two long-term experimental sites established in Zimbabwe in 2013. The soil types were abruptic Lixisols at Domboshava Training Centre (DTC) and xanthic Ferralsol at the University of Zimbabwe farm (UZF). The following six treatments, which were replicated four times, were investigated: conventional tillage (CT), conventional tillage with rotation (CTR), no tillage (NT), no tillage with mulch (NTM), no tillage with rotation (NTR), and no tillage with mulch and rotation (NTMR). Maize (Zea mays L.) was the main crop, and treatments with rotation included cowpea (Vigna unguiculata L. Walp.). The soil organic carbon (SOC) concentration and soil bulk density were determined for samples taken from depths of 0–5, 5–10, 10–15, 15–20, 20–30, 30–40, 40–50, 50–75 and 75–100 cm. Cumulative organic inputs to the soil were also estimated for all treatments. SOC stocks at equivalent soil mass were significantly (p<0.05) higher in the NTM, NTR and NTMR treatments compared with the NT and CT treatments in the top 5 cm and top 10 cm layers at UZF, while SOC stocks were only significantly higher in the NTM and NTMR treatments compared with the NT and CT treatments in the top 5 cm at DTC. NT alone had a slightly negative impact on the top SOC stocks. Cumulative SOC stocks were not significantly different between treatments when considering the whole 100 cm soil profile. Our results show the overarching role of crop residue mulching in CA cropping systems with respect to enhancing SOC stocks but also that this effect is limited to the topsoil. The highest cumulative organic carbon inputs to the soil were obser

Les changements climatiques sont un enjeu mondial prioritaire. L’augmentation de la concentration atmosphérique des gaz à effet de serre, notamment le CO2, en est responsable. Des causes naturelles ainsi qu’anthropiques peuvent expliquer l’augmentation de la concentration atmosphérique des gaz à effet de serre. Parmi les causes anthropiques se trouve le changement d’affectation des terres. Le changement d’affectation des terres pourrait constituer en la conversion d’une forêt en un espace urbain où des bâtiments y sont construits. Cependant, malgré la construction de bâtiments, l’expansion urbaine laisse fréquemment des terrains vagues, souvent gazonnés, présentant un potentiel pour la séquestration du carbone. Parmi les types d’aménagements pouvant être installés sur ces terrains vagues, les forêts nourricières sont celles qui font l’objet de ce mémoire. Sommairement, les forêts nourricières sont des projets d’agroforesterie urbaine aménagés en îlots comprenant des arbres, des arbustes, des herbacées, des légumes, des couvre-sols et des plantes grimpantes comestibles. Le grand nombre de forêts nourricières au Saguenay-Lac-Saint-Jean représente une opportunité d’établir leur bilan carbone. Ainsi, il a été possible d’établir le bilan du carbone séquestré par la biomasse des arbres, des arbustes et du sol. Il a été aussi possible d’établir le bilan carbone total en plus de modéliser les bilans du carbone séquestré des forêts nourricières sur 100 ans. Pour ce faire, les arbres, les arbustes et le sol de 12 forêts nourricières ont été échantillonnés et des modélisations en utilisant le logiciel MBC-SFC3 ont été réalisées pour chacune d’entre elles. Pour le carbone de la biomasse végétale et le carbone total il a été observé que les plus vieilles forêts nourricières séquestrent davantage de carbone que les terrains vagues gazonnés. Pour le carbone du sol, il a été observé que la plupart des forêts nourricières, surtout en surface, séquestrent davantage de carbone dans le

Growing awareness of the environmental impact of intensive agriculture has prompted a quest for more sustainable approaches. The most promising alternatives include the application of organic waste products (OWPs), as well as biofertilizers containing local beneficial microorganisms (BMs) on cultivated soils. This study was designed to assess the effects of BMs on carbon and nitrogen mineralization of OWPs. A 28-day laboratory incubation experiment was conducted at 28 °C with a soil, three OWPs (poultry litter (PL), cow dung (CD), and sewage sludge (SS)), and three BMs (groundnut + millet from Saint-Louis (LGM), groundnut from the southern groundnut basin (BG), and rice from the southern groundnut basin (BR) in Senegal), alone and combined. The results showed that the C mineralization from OWP + BM + soil mixtures exceeded (range 13–41%) those measured for OWP + soil. The BM input induced an increase or reduction in OWP nitrogen mineralization, depending on the type of BM and OWP. However, the net mineral nitrogen (Nmin) obtained with the PL-LGM and SS-BG combinations was 13.6- and 1.7-fold higher than with PL and SS, respectively, at 28 days. The addition of BM seemed to lead to a decrease in the C: N ratio, an improvement in the availability of nitrogen, and an increase in microbial activity in the OWP + BM + soil mixture. Our results generated new information on the variation patterns of OWP carbon and nitrogen in OWP-BM-soil systems. This novel insight will be developed to guide the most appropriate choice of OWP-BM mixtures for improved fertilization in sustainable production systems.

Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system. Remote-sensing estimates to quantify carbon losses from global forests are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced and satellite-derived approaches to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151–363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets.

Measuring the photosynthesis of entire tree crowns and pulse labelling trees with 13CO2 are valuable approaches to study carbon acquisition, transfer, and allocation; however, it is challenging for trees in the field. The objective was to develop and field test large chambers (35 - 45 m3) that enclosed the entire crown of a tree, provided a reliable estimate of tree crown photosynthesis, and ensured efficient 13CO2 labelling. The chambers, made of transparent polyethylene film pulled tightly over a frame, were equipped with an air conditioner, fans, and air blowers. Air temperature, relative humidity, and photosynthetic photon flux density were measured outside and inside each chamber. Six of 4-year-old rubber trees (Hevea brasiliensis) were pulsed-labelled with 18 L of 13CO2 in June and October 2016. The mean air temperature inside the chambers was 1.2 °C higher and the relative humidity 8 % lower than the outside air. The crown photosynthesis, calculated from the decrease in the CO2 concentration inside the chamber, was in the range 140 - 249 µmol s–1 and was significantly related to photosynthetic photon flux density, total leaf area of the tree, and average net CO2 assimilation at leaf level. The labelling efficiency, estimated as the ratio of the amount of 13C recovered in the foliage immediately after labelling divided by the amount of 13C delivered to the tree, was in the range 43 - 68 %. The designed chamber was suitable to estimate crown photosynthesis and perform 13CO2 pulse labelling of 5-m-tall trees in the field.

Energy cover crops for biogas production through anaerobic digestion (AD) are inserted between two primary crops. They replace either bare soil or nonharvested cover crops, and their management is usually intensified to produce more biomass. They allow the production of renewable energy as well as digestate, used as an organic fertilizer, without directly competing with food production. Because of the increased biomass production and export and of the return of a digested biomass to the soil, the impact of energy cover crops on soil organic carbon (SOC) is questioned. The objective of this paper was to study the difference in SOC stocks induced by the introduction of energy cover crops for AD coupled with the application of the resulting amount of digestate. We used the AD model Sys-Metha combined with the soil C model AMG to simulate SOC stocks for 13 case studies in France, with scenarios comparing different intercrop management practices, with or without cover crops, harvested or not. Our results indicated that the higher biomass production of energy cover crops (from 6.7 to 11.1 t DM ha−1) in comparison with nonharvested cover crops (2 t DM ha−1) or bare soil led to higher humified C input (belowground input and digestate), despite the high C fraction exported in AD. This resulted in an increase in SOC stocks in comparison with nonharvested cover crops or bare soil (from 0.01 to 0.12 t C ha−1 year−1 over 30 years). The uncertainties in the model parameters did not modify these results. However, in the case of equal biomass production between energy cover crops and nonharvested cover crops, SOC stocks would be lower with energy cover crops.

Despite the potential of subsoil carbon (C) to buffer or amplify climate change impacts, how fresh C and nutrients interact to control microorganismal effects on the C balance in deep soil horizons has yet to be determined. In this study, we aimed to estimate the impact of fresh C input at different soil depths on soil microbial activity. To conduct this study, Mediterranean soils from 3 layers (0–20, 20–50 and 50–100 cm of depth) were incubated over 28 days. Carbon and nutrient fluxes were measured after the addition of an amount of C equivalent to the postharvest root litter derived-C of a barley crop (4.3 atom% 13C), with and without nitrogen and phosphorus supply. We found that the microbial mineralization was C limited in the topsoil, while C and N colimited in the subsoil. These variations in stoichiometric constraints along the soil profile induced different microbial responses to C and/or nutrient addition. A stronger priming effect was observed in the topsoil than in the subsoil, and the sole C addition induced a negative C balance. Conversely, subsoil showed a positive C balance following fresh C addition, changing to critical soil C losses when nutrients were supplied with C. Our results show that fresh C input to subsoil (e.g., through deep-rooting crops) might foster soil C sequestration, but this positive effect can be reversed if such C inputs are combined with high nutrient availability (e.g., through fertilization), alleviating microbial limitation at depth.

In sub-Saharan Africa, maize is one of the most important staple crops, but long-term maize cropping with low external inputs has been associated with the loss of soil fertility. While adding high-quality organic resources combined with mineral fertilizer has been proposed to counteract this fertility loss, the long-term effectiveness and interactions with site properties still require more understanding. This study used repeated measurements over time to assess the effect of different quantities and qualities of organic resource addition combined with mineral nitrogen (N) on the change of soil organic carbon (SOC) contents over time (and SOC stocks in the year 2021) in four ongoing long-term experiments in Kenya. These experiments were established with identical treatments in moist to dry climates, on coarse to clayey soil textures, and have been conducted for at least 16 years. They received organic resources in quantities equivalent to 1.2 and 4 t C ha−1 yr−1 in the form of Tithonia diversifolia (high quality, fast turnover), Calliandra calothyrsus (high quality, intermediate turnover), Zea mays stover (low quality, fast turnover), sawdust (low quality, slow turnover) and local farmyard manure (variable quality, intermediate turnover). Furthermore, the addition of 240 kg N ha−1 yr−1 as mineral N fertilizer or no fertilizer was the split-plot treatment. At all four sites, a loss of SOC was predominantly observed, likely because the sites had been converted to cropland only a few decades before the start of the experiments. Across sites, the average decline of SOC content over 19 years in the 0 to 15 cm topsoil layer ranged from 42 % to 13 % of the initial SOC content for the control and the farmyard manure treatments at 4 t C ha−1 yr−1, respectively. Adding Calliandra or Tithonia at 4 t C ha−1 yr−1 limited the loss of SOC contents to about 24 % of initial SOC, while the addition of sawdust, maize stover (in three of the four sites) and sole mineral N addition show

Hundreds of projects to reduce emissions from deforestation and forest degradation and enhance carbon stocks (REDD+) are implemented globally, many by non-governmental organizations (NGOs) or for-profit companies. Yet, at the global level, the Paris Agreement focuses on jurisdictional (national and subnational) REDD+. We ask: (1) How much can REDD+ projects contribute to achieving national and international climate objectives? (2) What are the issues in integrating REDD+ projects into national carbon accounting? Our snapshot of 377 REDD+ projects covering 53 million ha in 56 countries is based on data from the International Database on REDD+ Projects (ID-RECCO) supplemented with new data on projects' accounting methods. The number of new REDD+ projects declined steadily from 45 new projects in 2011 to five in 2019. We examined 161 certified projects that started between 2007 and 2017; 96 of these could sell carbon credits in voluntary carbon markets by 2020 and spent on average 4.7 (± 2.4) years between project start and sales in voluntary carbon markets. Globally, REDD+ projects claim to reduce an average of 3.67 tCO2e/ha annually. This figure - combined with projects limited coverage - implies that projects need to be upscaled more than 40x to fulfil the potential contribution of tropical and subtropical forests towards limiting global warming to well below 2oC. Compared to the national carbon accounting methods, most projects in Colombia, Indonesia and Peru (63 of 86) use at least one different carbon accounting parameter. Carbon accounting inconsistencies across levels need to be addressed. Overall, the argument for REDD+ projects lies in the emissions reductions they can achieve, diversifying participation in REDD+ and providing non-carbon benefits to local communities, potentially leading to broader support for climate action.

L’aluminium est un des éléments chimiques les plus abondants dans la croute terrestre. Il se présente sous sa forme oxydée, l’alumine (Al2O3). Ce dernier est produit grâce au procédé Hall et Héroult. Cette technique consiste à réduire l’alumine en aluminium en présence d’une source de carbone (anode) et de l’énergie électrique. À ce propos, l’anode en carbone est composée des quatre principales matières premières qui sont le coke de pétrole, le brai de houille, les mégots ainsi que les déchets crus et cuits. La qualité de l’anode en carbone est affectée par celles des matières premières. Dans ces dernières années, la qualité des matières premières utilisées s’est vue dégrader. Certains chercheurs ont proposé d’améliorer la qualité du brai et du coke en ajoutant des additifs chimiques. Cette amélioration a été bénéfique d’une manière générale pour la qualité de l’anode; mais, des études supplémentaires sont nécessaires pour les appliquer au niveau industriel. D’autres chercheurs ont mélangé deux types de coke avec des teneurs en soufre différentes. Ces études ont démontré qu’avec des anodes qui contiennent plus de coke à haute teneur en soufre, la densité de l’anode est plus élevée et la réactivité à l’air et au CO2 est plus basse. Mais, on ne peut pas utiliser trop de coke à haute teneur en soufre à cause des contraintes environnementales. Ces dernières années, un autre matériau a été proposé pour être utilisé comme matière première dans le but de remplacer une partie du coke de pétrole, ce matériau est le biocharbon. Il est connu que le biocharbon est un matériau fiable au coût de production et faible teneur en soufre. L’utilisation du biocharbon dans la recette de l’anode en carbone permettra de rendre l’anode plus respectueuse pour l’environnement est cela par la réduction des gaz à effet de serre (GES). A ce propos, plusieurs chercheurs ont étudié l’impact de l’utilisation du biocharbon dans l’anode. Ils ont observé une détérioration de l’ensemble des propriétés

Pre-baked anode production for the primary aluminum industry uses only the density data of the green anode block (weight and height of the anode) for quality control of the manufactured anodes. A delay of 25 to 30 days is required after forming of green anodes to obtain the characteristics of the baked anodes, thus to have a feedback on anode quality problems. The characterization of anode paste to predict the properties of baked anodes is highly useful to avoid the baking of an anode which will be rejected once baked. Its production requires doubling of the energy used for the accepted anodes since it has to be recycled. A control method prior to of the baking process will reduce the greenhouse gas (GHG) emissions. The project highlights the links between the structure of green and baked anodes with the physical and reactivity properties of industrial anodes. An image analysis program was developed which introduces a concept of matrix localization inside and outside of coke particles. It has been found that electrical resistivity is not always related to the density or the bending strength directly, but rather to the homogenization of the pitch during baking, and it required a little more pitch than it did for the two other properties. The density is more related to the arrangement of coke particles within the matrix, the ability to fill the pores of the coke which is related to its pores’ sizes. The bending strength depends on how much the transformation of the matrix within the structure of the green anode is successful during the baking and on the distribution of coke particle sizes within the matrix. The reactivity of the anodes depends on the crystalline length of the anode, the microporosity of the cokes, and the network of macropores of the coke and that of the matrix of the anodes. The design of a kneader, a mold, and a rheology test of the anode paste helped highlight the optimization criteria for the anode paste. The raw materials and all particle sizes u

Mises en évidences dans les années 90s successivement par le Pr. Harris et le Pr. Iijima, les nanocornes de carbone (en anglais, carbon nanohorns, CNHs) sont des nanostructures de carbone graphénique de forme conique et creuse dont la pointe est fermée par une demi-sphère de type fullerène. Ces « nanocornes » mesurent environ 50 nm en longueur et ont un diamètre allant de 2 nm au niveau de la pointe à 5 nm à la base plus large. Ces nanostructures s’agencent toujours en agrégats indissociables d’une centaine de nanomètres de diamètre, dont la structure s’apparente à un oursin. Outre leurs nombreuses propriétés physiques et chimiques proches des nanotubes de carbone, la présence d’une cavité vide permet l’encapsulation de différentes molécules organiques telles que des colorants. L’internalisation de colorants dans une nanostructure vide, telle qu’une corne ou un tube, améliore nettement la réponse Raman des molécules organiques, un phénomène lié à un confinement dans la structure carbonée et à un étanchement de la fluorescence. C’est dans le cadre du développement et de l’amélioration de nanosondes Raman visant l’augmentation de la sensibilité de la détection d’allergènes dans l’industrie agroalimentaire que s’inscrit ce projet de doctorat. Les travaux présentés portent principalement sur l’étude et l’optimisation d’une nouvelle voie de synthèse de CNHs. Ce travail se divise en trois principaux chapitres décrivant l’étude des paramètres principaux de la synthèse par torche plasma radiofréquence (RF), la compréhension de l’impact du promoteur sur le plasma et la nanostructure obtenue, ainsi que la compréhension du mécanisme de nucléation et de croissance des nanocornes. La première partie met en lumière une nouvelle voie de synthèse des CNHs. Ces nanostructures sont à ce jour produites par décharge d’un arc électrique, par ablation laser CO2, ou bien par chauffage direct par effet Joule. Dans ce chapitre, nous montrons que la production de CNHs par une torche plasma R, Carbon nanohorns (CNHs) are a hollow conical carbon nanostructures that are closed on one side by fullerene hemisphere. They were identified for the first time in the 1990s by Pr. Harris and Pr. Iijima. Horns generally measure about 50 nm in length and have a diameter ranging from 2 nm at the tip to 5 nm at the wider base. An aggregate of horns forms an indissociable cluster of about 100 nm in diameter which resembles the structure of a sea urchin. In addition to similar physical and chemical properties to carbon nanotubes, the presence of an empty cavity allows the encapsulation of various organic molecules such as dyes. The internalization of dyes in an empty nanostructure, such as a horn or a tube, significantly improves the Raman response of organic molecules. This phenomenon is due to the confinement of the organic molecule inside the carbon structure which is responsible for quenching the fluorescence. At a bigger scale, this project takes part in increasing the sensitivity of allergen detection in food industry using Raman nanoprobes. The present study focuses on the development and the optimization of a new synthesis pathway of CNHs that can be used as a cap for Raman probes. This work is divided into three main chapters describing the study of the main parameters of the RF plasma torch synthesis, the understanding of the impact of the promotor on the plasma plume and the obtained nanostructure and finally the understanding of the nucleation and growth mechanism of carbon nanohorns. The first part highlights a new pathway for the synthesis of carbon nanohorns. Currently, there are three main methods to produce CNHs: (i) by CO2 laser ablation method, (ii) by arcdischarge and (iii) by Joules Heating. Contrary to carbon nanotubes (CNTs), all these syntheses of CNHs do not require any catalyst. In this chapter, we show that the production of CNHs by a RF plasma torch is a novel and interesting alternative to the current methods. Furthermore, with our m

Few studies have focused on Arenosols with regard to soil carbon dynamics despite the fact that they represent 7 % of the world's soils and are present in key areas where food security is a major issue (e.g., in Sahelian regions). As for other soil types, land use changes (from forest or grassland to cropland) lead to a loss of substantial soil organic carbon (SOC) stocks and have a lasting impact on the SOC turnover. Here we quantified long-term variations in carbon stocks and their dynamics in a 80 cm deep Mediterranean Arenosol that had undergone a forest-to-vineyard land use change over a 100 years ago. Paired sites of adjacent plots combined with carbon and nitrogen quantification and natural radiocarbon (14C) abundance analyses revealed a C stock of 53 t ha−1 in the 0–30 cm forest soil horizon, which was reduced to 3 t ha−1 after long-term grape cultivation. Total organic carbon in the vineyard was dramatically low, with around 1 g C kg−1, and there was no vertical gradient as a function of depth. 14C showed that deep plowing (50 cm) in the vineyard plot redistributed the remaining carbon both vertically and horizontally. This remaining carbon was old (compared to that of the forest), which had a C:N ratio characteristic of microbial organic matter and was probably stabilized within organomineral associations. Despite the drastic degradation of the organic matter (OM) pool in this Arenosol, this soil would have a high carbon storage potential if agricultural practices, such as grassing or organic amendment applications, were to be implemented within the framework of the 4 per 1000 initiative.