Stockage de carbone dans les sols par les variétés de blé anciennes et modernes

Les émissions anthropiques de gaz à effet de serre sont le principal moteur du changement climatique. Le plan Climat, issu de la COP 21 tenue à Paris en 2015, vise à atteindre la neutralité carbone à l'horizon 2050. Pour atteindre cette neutralité carbone, les gaz à effet de serre doivent d'abord être stabilisés, puis fortement réduits au cours du siècle prochain. Dans cette dynamique, l'initiative « 4 pour 1000 » fixe comme objectif d'atteindre un taux de croissance annuel du stock de carbone dans les sols de 0,4% par an. Ce stockage additionnel devrait compenser les émissions de CO2 dans l'atmosphère liée aux activités humaines. Les sols agricoles sont identifiés comme un compartiment de la biosphère continentale sur lequel l'adoption de bonnes pratiques permettrait d'atteindre l'objectif 4. Dans le même temps, le gouvernement français souhaite faire de l'agriculture « une alliée de la biodiversité » en promulguant le Plan biodiversité (Plan Biodiversité, 2018) qui vient renforcer et actualiser les plans antérieurs favorisant l'agroécologie. Ce dernier intègre la prise en compte de la diversité génétique, indispensable pour préserver l'adaptabilité du vivant aux conditions de vie future, dont la diversité des espèces cultivées en agriculture de rente ou vivrière. À la croisée de ces dispositifs gouvernementaux, le sujet de thèse a pour vocation d'aider au développement de systèmes de culture agroécologique pluri performants en capacité à maximiser de nombreux services écosystémiques, dont le stockage de carbone, via la mobilisation d'un patrimoine génétique délaissé que constituent les variétés anciennes de blé. L'un des critères de performance critique, au-delà du rendement, résidera en la capacité de production de biomasse racinaire et de stockage de la matière organique non simplement dans les horizons organo-minéraux de surface, mais aussi dans les horizons minéraux profonds souvent non considérés, mais pourtant puits de carbone et source d'alimentation minérale et hydrique. Cette thèse s'articulera autour de deux chantiers. Dans le premier, une expérimentation agronomique aura pour objectif de comparer quatre variétés modernes et quatre variétés anciennes en présence et absence d'intrants de synthèse. Les différents compartiments pouvant être affectés par le génotype des plantes, à savoir la biomasse aérienne (notamment les grains), la biomasse racinaire (et sa distribution), les exsudats racinaires et la biomasse microbienne, seront comparés pour les variétés modernes et anciennes. Le second chantier, analytique, aura pour objectif de déterminer la cinétique de minéralisation, par des incubations en conditions contrôlées, des échantillons prélevés dans le premier chantier. Ces échantillons, seront incubés dans des flacons placés dans des étuves. La minéralisation de la matière organique sera suivie par des mesures régulières de CO2. La détermination des paramètres des cinétiques de minéralisation par modélisation statistique permettra une projection de cette minéralisation afin de prévoir la part de carbone des différents compartiments qui sera stabilisée à long terme. Le couplage des résultats sur la taille des compartiments dans la première approche et sur la cinétique de minéralisation dans la seconde devrait permettre de définir si les variétés de blé anciennes permettent de stocker plus de carbone dans les sols agricoles que les modernes. Et, le cas échéant la surface à convertir en variétés anciennes pour parvenir à l'objectif 4 . Le rendement des variétés sera également suivi afin d'évaluer le compromis potentiel à trouver entre production de grain et stockage de carbone, en fonction de l'usage d'intrants.Titre traduit : Carbon storage in soils by ancient and modern wheat varietiesAnthropogenic emissions of greenhouse gases are the main driver of climate change. The Climate Plan, resulting from the COP 21 held in Paris in 2015, aims to achieve carbon neutrality by 2050. To achieve this carbon neutrality, it must first be stabilized during the next century. In this dynamic, the "4 per 1000" initiative aims to achieve an annual growth rate of carbon stock in soils of 0.4% per year. This additional storage should offset CO2 emissions in the atmosphere related to human activities. Agricultural soils are identified as a compartment of the continental biosphere on which the adoption of good practices could achieves goal 4. At the same time, the French government wants to make agriculture "an ally of biodiversity" by promulgating the Biodiversity Plan which has strengthened and updated previous plans promoting agroecology. It integrates the consideration of genetic diversity, essential to preserve the adaptability of life to future living conditions, including the diversity of species grown in cash crops or food. At the crossroads of these governmental devices, the subject of the PhD thesis aims to help the development of multi-performing agroecological culture systems with the capacity to maximize many ecosystem services, including carbon storage, through the mobilization of a neglected genetic heritage that are the ancient varieties of wheat. One of the critical performance criteria, beyond yield, will lie in the capacity to produce root biomass and to store organic matter not just in the surface organo-mineral horizons, but also in the deep mineral horizons often not considered, but carbon sink and mineral and water supply source. This thesis will be structured around two projects. In the first, an agronomic experiment will aim to compare four modern and four old varieties in the presence and absence of synthetic inputs. The different compartments that can be affected by the genotype of plants, namely above ground biomass (including grain), root biomass (and its distribution), root exudates and microbial biomass, will be compared for modern and old varieties. The second project, analytical, will aim to determine the kinetics of mineralization, by incubations under controlled conditions, samples taken from the first site. These samples, undisturbed, will be incubated in flasks placed in ovens. The mineralization of organic matter will be followed by regular measurements of CO2. The determination of kinetic parameters of mineralization by statistical modeling will allow a projection of this mineralization to predict the carbon content of the different compartments, which will be stabilized in the long term. The coupling of the results on the size of the compartments in the first approach and on the kinetics of mineralization in the second should make it possible to define whether old wheat varieties can store more carbon in agricultural soils than modern ones. And, the appropriate surface to convert into old varieties to achieve the 4 goal. Varietal yield will also be monitored to assess the potential trade-off between grain production and carbon storage, based on input use

Capacité de stockage de carbone dans le sol de variétés anciennes et modernes de blés

National audienceGérer convenablement les puits de carbone pourrait permettre de compenser les émissions deCO2. Étant donné la superficie des terres arables, les pratiques sur les sols agricoles peuventservir de levier d'action. Dans ce projet de thèse, nous faisons l’hypothèse que la séquestrationdu carbone est modifiée par le développement et la profondeur du système racinaire descultures. À ce titre, les variétés de blé anciennes sont réputées pour leur système racinaire plusprofond que celui des modernes. De plus, l’apport d’intrants chimiques de synthèse, dont lesengrais azotés, pourrait modifier la dynamique du carbone du sol. Dans une étude de terrain,des variétés modernes et anciennes ont été cultivées avec ou sans intrants. La morphologieracinaire, les activités cataboliques potentielles et les émissions de CO2 de sol et racines incubésont été mesurés pour estimer le stockage de carbone. Le génotype et les intrants considérésindépendamment n’ont pas impacté la biomasse, la surface et le diamètre moyen des racines.Toutefois, il existe un effet de l’interaction génotype*intrants : en absence d’intrants, lesvariétés anciennes présentaient une longueur racinaire plus importante que les modernes à laprofondeur 0-15cm. En présence d’intrants, la longueur racinaire et le diamètre moyen desvariétés modernes augmentaient. Les analyses MicroResp ont montré que la présence d’intrantsentrainait une modification de la respiration pour le sol prélevé à 15-30cm. Les incubationsavec suivi de CO2 sont en cours. Une expérience similaire a été mise en place sur trois autressites pour tester la généricité des résultats

Response of Wheat Root System and its Mineralization to Chemical Inputs, Plant Genotype and Phenotypic Plasticity

Agricultural lands represent vast terrestrial surfaces, in which agricultural practices are likely to offer leverages to store carbon in soil. We hypothesize that ancient wheat varieties could store more carbon than modern ones, due to a likely bigger and deeper root system. Since modern varieties are often cultivated using synthetic chemical inputs known to modify soil carbon dynamics, it is important to decouple the effect of breeding types (ancient versus modern varieties) and inputs to assess breeding type’s storing potential. We conducted a field experiment with four modern and four ancient varieties, with and without chemical inputs (nitrogen, herbicide and fungicide). Root morphology was assessed by image analysis, potential catabolic activities of specific substrates (fructose, alanine, citric acid) by MicroResp™ and overall CO 2 emissions by incubating soil and roots from each modality of the experiment for 60 days. Results show that the breeding type did not affect root traits, substrates respiration nor overall CO 2 emissions in our environmental conditions. Application of inputs did not affect root traits but influenced the respiration of specific substrates and CO 2 emissions. The most noticeable response was due to the “breeding type x inputs” interaction : inputs increased CO 2 emissions from soil and root tissues of ancient varieties by 19%, whereas no effect was observed for modern varieties. Taken together, our results did not support the hypothesis that ancient varieties produce more root biomass and more recalcitrant root tissues. It is thus unlikely that they could be more performant than modern ones in storing carbon

Effects of chemical inputs, plant genotype and phenotypic plasticity on soil carbon storage by wheat root systems

International audiencePurposeThe main goal of this study was to determine if ancient wheat varieties could store more carbon than modern ones in the presence or absence of inputs, due to a likely bigger and deeper root system and a slower mineralization rate.MethodsWe conducted a field experiment with four modern and four ancient varieties (released before 1960 and often grown without inputs), with and without chemical inputs (nitrogen, herbicide and fungicide taken as a single factor). Root morphology was assessed by image analysis, potential catabolic activities of fructose, alanine, citric acid by MicroResp™ and overall CO2 emissions by incubating soil and roots from each modality for 60 days.ResultsThe breeding type did not affect root traits, substrates respiration nor CO2 emissions in our environmental conditions. The application of inputs did not affect root traits but influenced the respiration of specific substrates and CO2 emissions. The most noticeable response was due to the “breeding type x inputs” interaction: inputs increased CO2 emissions from soil and root tissues of ancient varieties by 19%, whereas no effect was observed for modern varieties.ConclusionTaken together, our results did not support the hypothesis that ancient varieties could be more performant than modern ones in storing carbon in our experimental conditions. Increased CO2 emissions by ancient varieties in the presence of inputs showed that ancient and modern varieties differed in their phenotypic plasticity

Soil organic carbon storage capacity of old and modern wheat varieties

National audienceDespite the possible mitigation of carbon emissions by favoring carbon transfer to terrestrial carbon sinks, little is knownabout the capacity of different crop genotypes to enhance soil carbon sequestration. We hypothesize that carbon sequestrationpotential linked to old wheat varieties (released before 1960) is higher than the one linked to modern ones while old varietiesare known to develop bigger and deeper root systems. Moreover, modern varieties are often cultivated using syntheticchemical inputs known to modify soil carbon dynamics. We conducted a field experiment by cultivating four modern andfour old wheat varieties, with and without chemical inputs (nitrogen, herbicide and fungicide), in Calcaric Cambisolconditions. After root and soil sampling, root morphology was assessed by image analysis, whereas potential catabolicactivities by soil microbial communities was assessed by MicroResp ™ measurements. Additionally, CO2 emissionsmeasurements were done by incubating soil and roots from each agronomic modality. Results suggest that the genotype (oldversus modern varieties) did not affect root traits nor substrates respiration, but the soil from old variety modalities released6% more CO2 than the one from modern ones. Application of inputs did not affect root traits, but increased soil microbialrespiration by 11%. Inputs also increased the respiration of citric acid by 19.1%, while it decreased respiration of fructose andalanine by 8.84% and 16.79%, respectively. Taken together, our results invalidate the hypothesis that old varieties could bemore performant than modern ones in storing carbon in this specific soil

Ancient and modern wheat varieties: A trade‐off between soil CO2 emissions and grain yield?

Abstract Introduction Humanity is facing two great challenges: producing enough food for a growing population and mitigating greenhouse gas emissions. In this study, we investigated the choice of specific wheat varieties to improve carbon storage in soil while producing enough grain to assure food security. We hypothesize that ancient wheat varieties could store more carbon than modern ones, due to a likely bigger and deeper root system or to more recalcitrant root organic matter. Materials and Methods We conducted a field experiment with four modern and four ancient wheat varieties, on four different sites with contrasted soil properties. Root morphology was assessed by image analysis and potential CO2 emissions by incubation for 60 days. Since in situ carbon storage differences between ancient and modern varieties were expected to be weak and not cumulated due to rotation, we estimated expected CO2 emissions from root biomass and potential CO2 emissions. The grain yield was also measured. Results The breeding type (ancient vs. modern varieties) affected root length in two of our four sites, with longer roots for ancient varieties, but it did not affect other root traits such as biomass. The breeding type also affected CO2 emissions, with higher measured CO2 emissions for modern than ancient varieties in Arenic Cambisol conditions (Morvan), and higher estimated (considering root biomass variations) CO2 emissions for modern varieties in Rendzic Leptosol conditions (Saint Romain). Root traits and estimated CO2 emissions were also dependent on the soil properties of the different sites. We did not find any significant differences in grain yield between ancient and modern varieties. Conclusion A possible trade‐off between carbon storage and grain production was expected, but our results suggest that some types of soil can support both high grain yield and C storage, especially those with an important depth, a neutral pH and a fine texture

Ancient and Modern Wheat Varieties: A Trade-Off between Soil Co2 Emissions and Crop Yield?

International audienceHumanity is facing two great challenges: produce enough food for a growing population and mitigate greenhouse gas emissions. In this study, we investigated the choice of specific wheat varieties to improve carbon storage in soil while producing enough grain to assure food security. We hypothesize that ancient wheat varieties could store more carbon than modern ones, due to a likely bigger and deeper root system or to more recalcitrant root organic matter. We conducted a field experiment with four modern and four ancient wheat varieties, on four different sites chosen for their different soil properties. Root morphology was assessed by image analysis and potential CO 2 emissions by incubating soil and roots from each agronomic modality for 60 days. Since in situ carbon storage is not possible to detect in one year and since wheat is included in crop rotations that prevent repeating the same experiment for several years in the same place, we estimated expected CO 2 emissions by calculating the quantity of CO 2 that would have been emitted for one square meter, given the measured amount of root organic matter. The yield was also measured for ancient and modern varieties. The breeding type (ancient versus modern varieties) affected root length in two of our four sites, with longer roots for ancient varieties, but it did not affect other root traits such as biomass. The breeding type also affected CO 2 emissions, with higher measured CO 2 emissions for modern than ancient varieties in Arenic Cambisol conditions (Morvan), and higher estimated (considering root biomass variations) CO 2 emissions for modern varieties in Rendzic Leptosol conditions (Saint Romain). Root traits and CO 2 emissions were also dependent on the soil properties of the different sites. We did not find any significant differences in grain yield between ancient and modern varieties. A possible trade-off between carbon storage and grain production was expected, but our results suggest that some types of soil can support both high yield and C storage, especially those with an important depth, a neutral pH and a fine texture

Earthworms do not increase greenhouse gas emissions (CO2 and N2O) in an ecotron experiment simulating a realistic three-crop rotation system

Abstractmeasurements. To address this, we conducted a two-year study using large lysimeters in an ecotron facility, continuously measuring ecosystem-level CO 2 , N 2 O, and H 2 O fluxes. We investigated the impact of endogeic and anecic earthworms on GHG emissions and ecosystem water use efficiency (WUE) in an agricultural setting. Although we observed transient stimulations of carbon fluxes in the presence of earthworms, cumulative fluxes over the study indicated no significant increase in CO 2 emissions. Endogeic earthworms marginally reduced N 2 O emissions during the wheat culture (-44.6%), but this effect was not sustained throughout the experiment. No consistent effects on ecosystem evapotranspiration or WUE were found. Our study suggests that earthworms do not significantly contribute to GHG emissions over a two-year period in experimental conditions that mimic an agricultural setting. These findings highlight the need for realistic experiments enabling continuous GHG measurements

Earthworms do not increase greenhouse gas emissions (CO2 and N2O) in an ecotron experiment simulating a three-crop rotation system

International audienceEarthworms are known to stimulate soil greenhouse gas (GHG) emissions, but the majority of previous studies have used simplified model systems or lacked continuous high-frequency measurements. To address this, we conducted a 2-year study using large lysimeters (5 m 2 area and 1.5 m soil depth) in an ecotron facility, continuously measuring ecosystem-level CO 2 , N 2 O, and H 2 O fluxes. We investigated the impact of endogeic and anecic earthworms on GHG emissions and ecosystem water use efficiency (WUE) in a simulated agricultural setting. Although we observed transient stimulations of carbon fluxes in the presence of earthworms, cumulative fluxes over the study indicated no significant increase in CO 2 emissions. Endogeic earthworms reduced N 2 O emissions during the wheat culture (-44.6%), but this effect was not sustained throughout the experiment. No consistent effects on ecosystem evapotranspiration or WUE were found. Our study suggests that earthworms do not significantly contribute to GHG emissions over a two-year period in experimental conditions that mimic an agricultural setting. These findings highlight the need for realistic experiments and continuous GHG measurements