Efecto de la dinámica de producción de mazorcas de cacao y las fuentes de inóculo en el desarollo de la moniliasis (Moniliophthora roreri) en Costa Rica

La moniliose des cacaoyers est une maladie qui à énormément d'impacts, causant plus de 80% de pertes de récolte pour certains génotypes. L'influence du climat sur le processus épidémique n'a été, pour le moment, que peu étudiée dans les zones de production. L'objectif de ce travail est d'étudier l'influence de facteurs microclimatiques (pluviosité, température, mouillure, humidité relative), l'effet de la dynamique de production et la quantité d'inoculum local sur l'infection, le développement et l'impact de la moniliose du cacao. Cette étude a été conduite au Costa Rica sur le terrain expérimental " La Lola " appartenant au CATIE (Centre Agronomique Tropical de recherche et d'enseignement) : 92 arbres ont étés observés répartis sur 12 parcelles. Nous avons étudié les clones CATIE R4, Pound 7 et CC137. Il y a quatre parcelles par clones. Ces variétés ont des niveaux de résistances différents à la moniliose : CATIE R4 est résistant, Pound 7 est moyennement résistant et CC137 ne l'est pas du tout. Chaque semaine les cabosses récemment nées sont marquées. Les données concernant la maladie, ont étés collectés toutes les semaines après la date de marquage et les variables climatiques ont étés collectés toutes les 15 minutes. Dans deux des quatre parcelles de chaque clone, nous emballons les cabosses dès l'apparition d'une maladie afin d'éliminer ou de réduire, en cas de moniliose, l'inoculum primaire et la dispersion des spores. Des arbres de régressions, des analyses de composantes principales et des analyses graphiques ont étés réalisés pour mieux comprendre les relations entre l'incidence de la maladie et les facteurs climatiques ainsi que le comportement de celle-ci. Cette étude montre clairement une forte interaction entre les trois facteurs : sac, génération et clone. La mouillure et l'humidité relative apparaissent comme les facteurs ayant une plus grande influence sur le taux de croissance de la maladie. Il y a un étalement dans le temps de l'apparition des symptômes de la moniliose et celle-ci est une maladie monocyclique. Ce travail jette les bases d'un modèle d'avertissement agricole afin de mieux conseiller les agriculteurs dans la gestion des risques épidémiques. Il s'agit d'une importante étape pour mieux comprendre les relations quantitatives entre l'intensité de la maladie et les variables climatiques. (Résumé d'auteur

Bayesian calibration of the nitrous oxide emission module of an agro-ecosystem model

Nitrous oxide (N2O) is the main biogenic greenhouse gas contributing to the global warming potential (GWP) of agro-ecosystems. Evaluating the impact of agriculture on climate therefore requires a capacity to predict N2O emissions in relation to environmental conditions and crop management. Biophysical models simulating the dynamics of carbon and nitrogen in agro-ecosystems have a unique potential to explore these relationships, but are fraught with high uncertainties in their parameters due to their variations over time and space. Here, we used a Bayesian approach to calibrate the parameters of the N2O submodel of the agro-ecosystem model CERES-EGC. The submodel simulates N2O emissions from the nitrification and denitrification processes, which are modelled as the product of a potential rate with three dimensionless factors related to soil water content, nitrogen content and temperature. These equations involve a total set of 15 parameters, four of which are site-specific and should be measured on site, while the other 11 are considered global, i.e. invariant over time and space. We first gathered prior information on the model parameters based on the literature review, and assigned them uniform probability distributions. A Bayesian method based on the Metropolis–Hastings algorithm was subsequently developed to update the parameter distributions against a database of seven different field-sites in France. Three parallel Markov chains were run to ensure a convergence of the algorithm. This site-specific calibration significantly reduced the spread in parameter distribution, and the uncertainty in the N2O simulations. The model’s root mean square error (RMSE) was also abated by 73% across the field sites compared to the prior parameterization. The Bayesian calibration was subsequently applied simultaneously to all data sets, to obtain better global estimates for the parameters initially deemed universal. This made it possible to reduce the RMSE by 33% on average, compared to the uncalibrated model. These global parameter values may be used to obtain more realistic estimates of N2O emissions from arable soils at regional or continental scales

La dénitrification dans les sols : régulation de son fonctionnement et applications à la dépollution

International audienceLors des premiers travaux sur la dénitrification dans les sols (Dehérain et Maquenne, 1882), cette transformation était perçue comme une perte d'azote utilisable par la plante. On ne s'est intéressé à son rôle épurateur et protecteur de la qualité des eaux que plus tard, avec l'accroissement des pollutions azotées (Mariotti, 1994). En effet, les entrées d'azote dans la biosphère ont fortement crû depuis un siècle avec la production de fertilisants de synthèse, l'intensification de la culture des légumineuses et le retour au sol des pollutions azotées atmosphériques dues à la combustion des carburants fossiles ; elles ont été accompagnées d'un accroissement généralisé des teneurs en azote minéral des eaux de surface ou profondes, conduisant à des situations préoccupantes comme dans le Nord de l'Europe ou l'Ouest de la France. La dénitrification conduit aussi à la production de protoxyde d'azote (N2O), gaz fortement impliqué dans l'accroissement de l'effet de serre (Germon et al., 1999). La dénitrification dans le sol et le sous-sol apparaît donc comme un mécanisme protecteur de la qualité des eaux. On peut essayer de tirer profit de son fonctionnement naturel ou induit pour réduire les pollutions nitriques d'origines diffuses ou pour mettre en place des systèmes de traitement de pollutions azotées localisées. Il importe de s'assurer en même temps qu'elle n'accentue pas les émissions de N2O

Systematic investigation of changes in oxidized cerebral cytochrome c oxidase concentration during frontal lobe activation in healthy adults

Using transcranial near-infrared spectroscopy (NIRS) to measure changes in the redox state of cerebral cytochrome c oxidase (Δ[oxCCO]) during functional activation in healthy adults is hampered by instrumentation and algorithm issues. This study reports the Δ[oxCCO] response measured in such a setting and investigates possible confounders of this measurement. Continuous frontal lobe NIRS measurements were collected from 11 healthy volunteers during a 6-minute anagram-solving task, using a hybrid optical spectrometer (pHOS) that combines multi-distance frequency and broadband components. Only data sets showing a hemodynamic response consistent with functional activation were interrogated for a Δ[oxCCO] response. Simultaneous systemic monitoring data were also available. Possible influences on the Δ[oxCCO] response were systematically investigated and there was no effect of: 1) wavelength range chosen for fitting the measured attenuation spectra; 2) constant or measured, with the pHOS in real-time, differential pathlength factor; 3) systemic hemodynamic changes during functional activation; 4) changes in optical scattering during functional activation. The Δ[oxCCO] response measured in the presence of functional activation was heterogeneous, with the majority of subjects showing significant increase in oxidation, but others having a decrease. We conclude that the heterogeneity in the Δ[oxCCO] response is physiological and not induced by confounding factors in the measurements. © 2012 Optical Society of America

Agroforestry for a climate-smart agriculture – a case study in France. [P95]

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. (Résumé d'auteur

The contribution of agroforestry systems to climate change mitigation – Assessment of C storage in soils in a Mediterranean context. [P-2218-01]

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 or Mediterranean 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). Additional storage was mainly due to particulate organic matter fractions (> 50 μm) and 10 to 15% was associated to clay particles. When the aboveground biomass of the trees was taken into account, total organic carbon storage rate reached 1.11 ± 0.16 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, such as no-till farming, and could therefore provide a more stable C storage in the long-term. (Résumé d'auteur

Consequence of clear-cutting and drought on deep soil CO2 and N2O profile concentrations and surface fluxes in Brazilian eucalypt plantations

The major factors driving greenhouse gas effluxes from forest soils (substrate supply, temperature, water content) vary with soil depth. Our study aimed to assess the consequences of drought on the temporal variability of CO2 and N2O fluxes throughout very deep soil profiles in Eucalyptus grandis plantations at the end of the rotation and the first 16 months after clear-cut, in coppice. Two treatments were compared: one with 37% of throughfall excluded by plastic sheets (TE), and one without rain exclusion (WE). Every two weeks for 19 months, soil CO2 and N2O surface fluxes were measured using the closed-chamber method and the profile concentrations were measured at 7 depths in the soil down to 15.5m from in each treatment. CO2 and N2O concentrations measured in treatment TE were on average 17.3 and 5.8% lower than in treatment WE, respectively, throughout the soil profile. Across the two treatments, CO2 concentrations increased from 4102 ±2310 ppm at 10cm deep to 14480±2854 ppm at 15.5m and N2O concentrations remained roughly constant down to 15.5m. Improving our understanding of the spatiotemporal dynamics of gas concentrations in deep soil layers is an important issue for the management of tropical planted forests in the context of climate change. (Résumé d'auteur

Consequences of clear-cutting on the production of fine roots, CO2, CH4 and N2O down to the water table in Eucalyptus grandis stands conducted in coppice in a throughfall-exclusion experiment

Tree growth is highly dependent on the absorptive function of fine roots for water and nutrients. Fine roots also play a major role in the global carbon (C) cycle, mainly through production, respiration, exudation and decomposition processes. Improving our understanding of the spatio-temporal dynamics of fine roots down to the root front is an important issue to identify more sustainable silvicultural practices for planted forests installed in areas with low soil fertility and prolonged drought periods. The Eucalyptus gender is the most planted in Brazil covering about 5.1 million hectares in 2012. Coppice management can be an advantage against water stress in eucalyptus plantations because the trees are likely to benefit of a root system exploring deep soil layers where the availability of water can be higher than in the topsoil. The objective of this study is to assess the production of fine roots, CO2, CH4 and N2O down to the water table after cutting the trees in Eucalyptus grandis plantation conducted in coppice, under two contrasting water supply regimes,. Two pits were excavated down to a depth of 17 m in a throughfall exclusion experiment: one in a plot with 37% of throughfall excluded by plastic sheets, and one without rain exclusion. Another pit in an adjacent stand of the same age not harvested will make it possible to assess the effect of cutting the trees. Fine roots dynamics will be studied using the Minirhizotron technique: twenty four transparent polyvinyl chloride tubes were installed in the pits in 2014 (12 per pit) down to 17 m deep and 7 tubes down to 4 m deep in the stand not harvested. Images will be obtained by a circular scanner every 14 days over 1 year before cutting the trees and over 1.5 years in coppice after harvesting. The winrhizotron software will be used to estimate root growth in length and area. Gas sampling will be performed every two weeks for 24 months (6 months before and 1.5 years after cutting the trees) throughout the soil profiles down to the groundwater. Gas samples will be analysed by gas chromatography and a modelling approach will be used to estimate CO2, CH4 and N2O production rates. Dynamics of gas concentrations can provide additional insights into the heterogeneous gas exchange processes through soil depth and how the control of the fluxes at the soil surface are correlated to root dynamics in the whole soil profile. Improving our understanding of the factors controlling the fluxes of greenhouse gases throughout very deep soil profiles is needed to develop reliable process-based models likely to predict wood production at a large scale in forest companies

Connaissance des émissions gazeuses dans les différentes filières de gestion des effluents porcins

Cet article résume les apports du programme "Porcherie verte" dans la connaissance et la maîtrise des émissions gazeuses intervenant lors des différentes phases de l'élevage porcin. Ces émissions comprennent des gaz à effet de serre, particulièrement le méthane (CH4) et le protoxyde d'azote (N2O), ainsi que l'ammoniac (NH3), nocif pour les animaux et pour l'Homme et qui a un impact sur l'environnement en termes d'acidification et d'eutrophisation. Les émissions de NH3 ont été modélisées pour le cas des bâtiments d'élevage sur caillebottis. Ces émissions peuvent être réduites en diminuant la teneur en protéines de l'aliment distribué aux animaux ou en renouvelant fréquemment le lisier dans les bâtiments. Le traitement biologique du lisier permet aussi de réduire ces émissions, surtout en l'absence de séparation de phases. Le brassage du lisier dans les fosses de stockage les favorise au contraire. Les émissions de NH3 varient fortement en fonction du substrat utilisé pour la litière et de son mode de conduite. Pendant le compostage, elles dépendent aussi fortement des caractéristiques initiales du substrat composté, mais aussi de la technique utilisée. Les émissions de N2O sont en général plus élevées avec de la litière que sur caillebotis, mais il y a de très fortes variations en fonction de son mode de conduite. Le compostage peut aussi conduire à des émissions de N2O, tout particulièrement s'il est pratiqué en couche mince. Lors du traitement biologique des lisiers, ces émissions sont assez faibles mais dépendent de la technique d'aération utilisée. Dans le sol, les émissions de N2O ne sont pas plus importantes après apports d'effluents animaux qu'après apports de fertilisants minéraux et restent difficiles à quantifier. Les émissions de CH4 sont plus faibles sur litière que sur caillebotis. Elles sont faibles également lors du compostage, sauf s'il est réalisé en couche mince. Le traitement biologique du lisier conduit à une forte réduction des émissions par rapport à un simple stockage. Les litières et le compostage ont une excellente image de marque auprès du grand public et sont souvent réputées avoir beaucoup moins d'impact sur l'environnement que le lisier. Nous avons pu montrer cependant qu'elles génèrent en général davantage de gaz à effet de serre, que ce soit de façon directe (émissions de N2O) ou indirecte (gaspillage de fertilisants azotés dont la synthèse est très "énergivore"), et ce d'autant plus que l'on cherche à rogner sur les coûts en augmentant la densité animale ou en diminuant la quantité de paille utilisée comme substrat de compostage. De même, le traitement biologique du lisier, qui semble à première vue avoir un impact favorable puisqu'il conduit à réduire les émissions de NH3 sans trop relarguer de N2O, a en fait un bilan environnemental très défavorable du fait qu'il est très "énergivore" aussi bien directement qu'indirectement (gaspillage de fertilisants). On a là un double transfert de pollution, du sol et de l'eau vers l'atmosphère d'une part, et de l'exploitation vers l'extérieur de l'exploitation d'autre part. (Résumé d'auteur