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The recent expansion of Aedes albopictus across continents in both tropical and temperate regions and the exponential growth of dengue cases over the past 50 years represent a significant risk to human health. Although climate change is not the only factor responsible for the increase and spread of dengue cases worldwide, it might increase the risk of disease transmission at global and regional scale. Here we show that regional and local variations in climate can induce differential impacts on the abundance of Ae. albopictus. We use the instructive example of Réunion Island with its varied climatic and environmental conditions and benefiting from the availability of meteorological, climatic, entomological and epidemiological data. Temperature and precipitation data based on regional climate model simulations (3 km × 3 km) are used as inputs to a mosquito population model for three different climate emission scenarios. Our objective is to study the impact of climate change on the life cycle dynamics of Ae. albopictus in the 2070–2100 time horizon. Our results show the joint influence of temperature and precipitation on Ae. albopictus abundance as a function of elevation and geographical subregion. At low-elevations areas, decreasing precipitation is expected to have a negative impact on environmental carrying capacity and, consequently, on Ae. albopictus abundance. At mid- and high-elevations, decreasing precipitation is expected to be counterbalanced by a significant warming, leading to faster development rates at all life stages, and consequently increasing the abundance of this important dengue vector in 2070–2100.

Aim: Elevational gradients are a useful approach to evaluate how environmental factors affect animal diversity. Decades of studies on the elevation-diversity gradient have revealed that this gradient varies greatly with taxa and geographic regions. One potential explanation for this may be the dependence of the relationship on landscape features. We explore the impact of fragmentation, habitat diversity and habitat amount on insect diversity (alpha and beta) and abundance along elevational gradients. We hypothesize that insect diversity and abundance will relate negatively with elevation, but positively with these landscape features. We also hypothesize that landscape features will interact in a way that the positive effect of a given variable on insect diversity may be offset by the others. Location: Reunion Island (Indian Ocean). Taxon: The insect order thrips (Thysanoptera). Methods: Insects were sampled along replicated elevational gradients, and at each sampling plot landscape features and abiotic variables were estimated within buffers surrounding the site. Insect alpha diversity was estimated using abundance-based rarefaction methods, whereas beta diversity was estimated calculating the "Local contributions to beta diversity" metric. The effect of elevation, rainfall, landscape features and their interactions was assessed on insect alpha and beta diversity and abundance during two consecutive seasons using linear mixed effects models. Results: We found that thrips alpha and beta diversity was negatively related with elevation, but the relationship varied between seasons and rainfall regimes. Among the different landscape features considered, we found that habitat amount had the strongest effect on diversity. The effect of habitat amount on diversity, however, was offset in areas of low habitat (or land cover) diversity. Main conclusions: Generalizing the factors that underlie the elevation diversity gradient has become a cornerstone in ecological theory because it can help to understand the impact of human activities on diversity. Here we show that taking landscape information into account may help to fulfil this objective because landscape effects co-vary with elevation with often intricate consequences for diversity.

Malaria is a permanent threat to health in western Burkina Faso. Research has shown that geographical variables contribute to the spatial distribution in its transmission. The objective of this study is to assess the relationship between malaria prevalence and potential explanatory geographical variables in the Houet province in Burkina Faso. Statistics on malaria prevalence registered by health centres in the Houet province in 2017 and potential geographical variables identified through a literature review were collected. An Ordinary Least Squares (OLS) regression was used to identify key geographical variables and to measure their association with malaria while the Getis Ord Gi* index was used to locate malaria hotspots. The results showed that average annual temperature, vegetation density, percentage of clay in the soil, total annual rainfall and distance to the nearest waterbody are the main variables associated with malaria prevalence. These variables account for two-thirds of the spatial variability of malaria prevalence observed in Houet province. The intensity and direction of the relationship between malaria prevalence and geographical factors vary according to the variable. Hence, only vegetation density is positively correlated with malaria prevalence. Average temperature, for soil clay content, annual rainfall and for distance to the nearest water body are negatively correlated with the disease prevalence. These results show that even in an endemic area, malaria prevalence has significant spatial variation. The results could contribute to the choice of intervention sites, as this choice is crucial for reducing the malaria burden.

Faidherbia albida et Balanites aegyptiaca sont deux espèces caractéristiques et emblématiques de la zone semi-aride tchadienne. Elles revêtent une grande importance socio-économique dans toutes leurs zones naturelles de répartition du fait de leurs multiples usages. La présente étude de nature exploratoire a consisté à comprendre le déterminisme des variations des caractéristiques du bois des deux espèces en relation avec leurs variations de conditions de croissance. Sa finalité est de mieux connaitre l'hétérogénéité de comportement technologique des bois de ces deux espèces afin de mieux les valoriser dans les processus de reboisement et d'élargir leur domaine d'utilisation locale. L'étude a été réalisée selon deux approches. La première a consisté à déterminer par des méthodes conventionnelles et normalisées une sélection de caractéristiques physiques, mécaniques et chimiques des bois prélevés dans deux zones climatiques tchadiennes (zone sahélienne et zone soudanienne) et une zone climatique sénégalaise (zone sahélienne), et à étudier leurs variations en fonction des conditions de croissance liées essentiellement aux différences climatiques. La seconde a consisté à étudier les variations radiales de caractéristiques physiques, mécaniques, et de la composition isotopique de carbone 13 (δ13C), ceci en fonction de la croissance des arbres, par des mesures réalisées sur des micro-échantillons prélevés au niveau des cernes. Les résultats du premier volet de l'étude ont mis en évidence pour les deux espèces des tendances variables pour toutes les caractéristiques étudiées. Pour Faidherbia albida, l'infradensité, la masse volumique, les retraits de séchage et les trois caractéristiques mécaniques étudiées sont significativement plus élevés dans la zone sahélienne sénégalaise que dans les deux provenances tchadiennes. Cette même tendance est observée pour les taux d'extractibles et de lignine, mais les taux de cellulose et d'hémicellulose sont significativement plus élevés dans la zone sahélienne tchadienne. Pour Balanites aegyptiaca, les tendances sont variables suivant les propriétés, avec un effet inverse des provenances pour le retrait tangentiel et le retrait radial, et aucune tendance marquée pour le retrait volumique. Le point de saturation des fibres est faible pour les trois provenances (inférieur à 25 %). En zone soudanienne tchadienne, la masse volumique est significativement plus élevée que dans les deux autres zones, alors que la contrainte de rupture en compression et le module d'élasticité longitudinal sont moins élevés. Les taux de lignine et d'hémicellulose sont plus élevés en zone sahélienne tchadienne. Une analyse des extractibles par GC-MS a mis en évidence des différences marquées entre les deux espèces d'une part et les trois provenances d'autre part. Ces différences pourraient être mises en relation avec celles observées entre provenances et espèces pour certaines propriétés physiques et mécaniques du bois telles que les retraits de séchage, le PSF, la masse volumique et le module d'élasticité. L'effet de chaque extractible sur ces propriétés resterait cependant à établir, en tenant compte des probables impacts conjugués de ces différents composés. Le second volet de l'étude a montré que l'accroissement moyen était légèrement supérieur en zone soudanienne qu'en zone sahélienne ce qui reflète les différences de conditions climatiques qui impactent la croissance des arbres. Pour Faidherbia albida, l'absence de différence significative de δ13C entre les deux provenances peut s'expliquer par le fait que cette espèce est une phréatophyte. Pour Balanites aegyptiaca, le δ13C moyen dans la zone sahélienne est significativement inférieur à celui de la zone soudanienne, tendance inverse à celle à laquelle on pouvait s'attendre. Ce résultat tend à montrer que cette espèce présente une bonne efficacité et une bonne stratégie opportuniste d'utilisation de l'eau. L'étude des relations entre les variables prises deux à deux a donné des résultats contrastés. L'absence de relation entre la largeur de cerne et la pluviométrie peut être liée à plusieurs causes : pluviométrie sur les sites de prélèvement des bois différente de celle de la station météorologique éloignée de ces sites, comportement phréatophile avéré de Faidherbia albida et possible pour Balanites aegyptiaca, et délimitation incertaine des cernes liée à leur structure. Les perspectives de recherche à venir sur les deux espèces sont multiples, et concernent aussi bien le protocole d'échantillonnage (utilisation de branches au lieu de troncs), l'étude des rythmes de croissance afin de comprendre le phénomène de disparition/fusion partielle des cernes, que l'élargissement de l'étude à d'autres provenances.

International audience; In this study, we present an operational methodology for mapping irrigated areas at plot scale, which overcomes the limitation of terrain data availability, using Sentinel-1 (S1) C-band SAR (synthetic-aperture radar) and Sentinel-2 (S2) optical time series. The method was performed over a study site located near Orléans city of north-central France for four years (2017 until 2020). First, training data of irrigated and non-irrigated plots were selected using predefined selection criteria to obtain sufficient samples of irrigated and non-irrigated plots each year. The training data selection criteria is based on two irrigation metrics; the first one is a SAR-based metric derived from the S1 time series and the second is an optical-based metric derived from the NDVI (normalized difference vegetation index) time series of the S2 data. Using the newly developed irrigation event detection model (IEDM) applied for all S1 time series in VV (Vertical-Vertical) and VH (Vertical-Horizontal) polarizations, an irrigation weight metric was calculated for each plot. Using the NDVI time series, the maximum NDVI value achieved in the crop cycle was considered as a second selection metric. By fixing threshold values for both metrics, a dataset of irrigated and non-irrigated samples was constructed each year. Later, a random forest classifier (RF) was built for each year in order to map the summer agricultural plots into irrigated/non-irrigated. The irrigation classification model uses the S1 and NDVI time series calculated over the selected training plots. Finally, the proposed irrigation classifier was validated using real in situ data collected each year. The results show that, using the proposed classification procedure, the overall accuracy for the irrigation classification reaches 84.3%, 93.0%, 81.8%, and 72.8% for the years 2020, 2019, 2018, and 2017, respectively. The comparison between our proposed classification approach and the RF classifier built directly from in situ data showed that our approach reaches an accuracy nearly similar to that obtained using in situ RF classifiers with a difference in overall accuracy not exceeding 6.2%. The analysis of the obtained classification accuracies of the proposed method with precipitation data revealed that years with higher rainfall amounts during the summer crop-growing season (irrigation period) had lower overall accuracy (72.8% for 2017) whereas years encountering a drier summer had very good accuracy (93.0% for 2019).

Bacterial panicle blight (BPB) caused by Burkholderia glumae is one of the main concerns for rice production in the Americas since bacterial infection can interfere with the grain-filling process and under severe conditions can result in high sterility. B. glumae has been detected in several rice-growing areas of Colombia and other countries of Central and Andean regions in Latin America, although evidence of its involvement in decreasing yield under these conditions is lacking. Analysis of different parameters in trials established in three rice-growing areas showed that, despite BPB presence, severity did not explain the sterility observed in fields. PCR tests for B. glumae confirmed low infection in all sites and genotypes, only 21.4% of the analyzed samples were positive for B. glumae. Climate parameters showed that Montería and Saldaña registered maximum temperature above 34°C, minimum temperature above 23°C, and Relative Humidity above 80%, conditions that favor the invasion model described for this pathogen in Asia. Our study found that in Colombia, minimum temperature above 23°C during 10 days after flowering is the condition that correlates with disease incidence. Therefore, this correlation, and the fact that Montería and Saldaña had a higher level of infected samples according to PCR tests, high minimum temperature, but not maximum temperature, seems to be determinant for B. glumae colonization under studied field conditions. This knowledge is a solid base line to design strategies for disease control, and is also a key element for breeders to develop strategies aimed to decrease the effect of B. glumae and high night-temperature on rice yield under tropical conditions.

This work is dedicated to Serge Quilici who has been leading prolific research on the tephritids of Reunion his whole career. This article has been reviewed and recommended by Peer Community in Ecology, https://doi.org/10.24072/pci.ecology.100080. The peer review history for this article is available at https://publo ns.com /publo n/10.1111/ele.13825.; International audience; The relative importance of ecological factors and species interactions for shaping species distributions is still debated. The realised niches of eight sympatric tephritid fruit flies were inferred from field abundance data using joint species distribution modelling and network inference, on the whole community and separately on three host plant groups. These estimates were then confronted the fundamental niches of seven fly species estimated through laboratory-measured fitnesses on host plants. Species abundances depended on host plants, followed by climatic factors, with a dose of competition between species sharing host plants. The relative importance of these factors mildly changed among the three host plant groups. Despite overlapping fundamental niches, specialists and generalists had almost distinct realised niches, with possible competitive exclusion of generalists by specialists on Cucurbitaceae. They had different assembly rules: Specialists were mainly influenced by their adaptation to host plants, while generalist abundances varied regardless of their fundamental host use.

Meeting food demand for the growing population will require an increase to crop production despite climate changes and, more particularly, severe drought episodes. Sorghum is one of the cereals most adapted to drought that feed millions of people around the world. Valorizing its genetic diversity for crop improvement can benefit from extensive phenotyping. The current methods to evaluate plant biomass, leaves area and plants height involve destructive sampling and are not practical in breeding. Phenotyping relying on drone based imagery is a powerful approach in this context. The objective of this study was to develop and validate a high throughput field phenotyping method of sorghum growth traits under contrasted water conditions relying on drone based imagery. Experiments were conducted in Bambey (Senegal) in 2018 and 2019, to test the ability of multi-spectral sensing technologies on-board a UAV platform to calculate various vegetation indices to estimate plants characteristics. In total, ten (10) contrasted varieties of West African sorghum collection were selected and arranged in a randomized complete block design with three (3) replicates and two (2) water treatments (well-watered and drought stress). This study focused on plant biomass, leaf area index (LAI) and the plant height that were measured weekly from emergence to maturity. Drone flights were performed just before each destructive sampling and images were taken by multi-spectral and visible cameras. UAV-derived vegetation indices exhibited their capacity of estimating LAI and biomass in the 2018 calibration data set, in particular: normalized difference vegetative index (NDVI), corrected transformed vegetation index (CTVI), seconded modified soil-adjusted vegetation index (MSAVI2), green normalize difference vegetation index (GNDVI), and simple ratio (SR) (r2 of 0.8 and 0.6 for LAI and biomass, respectively). Developed models were validated with 2019 data, showing a good performance (r2 of 0.92 and 0.91 for LAI and biomass accordingly). Results were also promising regarding plant height estimation (RMSE = 9.88 cm). Regression plots between the image-based estimation and the measured plant height showed a r2 of 0.83. The validation results were similar between water treatments. This study is the first successful application of drone based imagery for phenotyping sorghum growth and development in a West African context characterized by severe drought occurrence. The developed approach could be used as a decision support tool for breeding programs and as a tool to increase the throughput of sorghum genetic diversity characterization for adaptive traits.

Dacryodes edulis (G. Don) H.J. Lam is an underexploited oil-bearing fruit tree highly appreciated in the Central Africa rainforest. To improve horticultural management and provide relevant data to scientists for physiological studies, the reproductive phenology of D. edulis as well as their fruit (safou) development and ripening indexes has been defined and correlated to climatic conditions. Changes in safou were assessed in four production localities in Cameroon. Fruit-set-to-ripening time was evaluated over 2 consecutive production years. Four fruits developmental and ripening stages and their durations were determined as follows: The putative cell division (1–2 weeks); putative elongation (10–14 weeks); pre-ripening (2–7 weeks); and ripening phases (3–5 weeks). Rainfall, average, and cumulative temperatures were found to be correlated with the chronology of reproductive phenophases. The average temperature during the period ranging from the floral bud emergence to the fruit set can be used to predict the thermal time. Similarly, the average ambient temperature during the period from floral bud emergence to anthesis can help to determine the temperature to be cumulated during the ripening phase. These findings are considerable contributions that could help producers to enhance the industrial management of safou sector, reduce fruit perishability, and better control their harvesting time.

International audience; Rubber powdery mildew disease (Oidium heveae) is a serious threat to natural rubber production (Hevea brasiliensis) in some rubber developing regions of the world. Both phenological- and meteorological-related factors have been reported influencing the powdery mildew disease. However, few studies have investigated the effects of both phenological- and meteorological-related factors on the disease. The objective of this study is to quantify the contributions of phenological- and meteorological-related factors to affect the disease. We used the partial least squares (PLS) regression method to comprehensively quantify the effects of thirty-five phenological related factors and six meteorological factors on the infection level of powdery mildew of rubber trees over 9-year records (2003–2011). The relative contributions of significant factors were further investigated by the variation partition analysis. We found that the most influential variables were the mean temperature during winter and the duration of leaf development to maturation which explained 32 and 26% of the variations in the infection level. We found the controlling role of winter mean temperature, for the first time, on the infection level of powdery mildew. The controlling role of winter temperature may have directly increase the infection level when winter temperature is high and indirectly increase the infection level through prolonging the duration of leaf development to maturation, although the duration itself had smaller influences. We detected a warming trend of the winter temperatures from 2003 to 2011, which indicates that the infection level of powdery mildew will be increased if the winter warming continues.

Climate change is already affecting agro-ecosystems and threatening food security by reducing crop productivity and increasing harvest uncertainty. Mobilizing crop diversity could be an efficient way to mitigate its impact. We test this hypothesis in pearl millet, a nutritious staple cereal cultivated in arid and low-fertility soils in sub-Saharan Africa. We analyze the genomic diversity of 173 landraces collected in West Africa together with an extensive climate dataset composed of metrics of agronomic importance. Mapping the pearl millet genomic vulnerability at the 2050 horizon based on the current genomic-climate relationships, we identify the northern edge of the current areas of cultivation of both early and late flowering varieties as being the most vulnerable to climate change. We predict that the most vulnerable areas will benefit from using landraces that already grow in equivalent climate conditions today. However, such seed-exchange scenarios will require long distance and trans-frontier assisted migrations. Leveraging genetic diversity as a climate mitigation strategy in West Africa will thus require regional collaboration., Replacement of local crops with alternative varieties adapted to future conditions may improve food security under climate change. Here the authors apply landscape genomics and ensemble climate modelling to pearl millet in West Africa, supporting the potential of transfrontier assisted seed exchange.

Mango is one of the most economically important fruit crop in the north of Côte d’Ivoire. However, its production and productivity are limited by various biotic and abiotic factors. Amongst fungal disease, mango anthracnose is recorded to be the most important disease in the northern districts. This study assessed the incidence and severity of pre- and post-harvest anthracnose to compare the level of orchard infestation in the seven mango producing districts in the north of Côte d’Ivoire. Anthracnose disease incidence and severity varied from locality to locality both in dry and rainy season. Disease intensity was higher in rainy season than dry season. In dry and rainy seasons, the highest disease incidence (19.08% and 32.25%) was recorded in Bèrèdougou and the least in Zèguèrè. Pre and post-harvest anthracnose correlated significantly indicating that infection initiated in field and remained latent until fruits repining. The disease was also more severe on fruits than leaves. On fruits disease incidence and severity were higher in Dianra village (90% and 100%) and Bèrèdougou (36% and 40%). The lowest disease incidence (7.5%) and severity (1.5%) on fruits were observed in Zèguèrè. This study showed that anthracnose disease is one the most important threat to production and marketing of fresh mango fruits in the north of Côte d’Ivoire.Keywords: Anthracnose, incidence, severity, mango, symptoms.

Understanding evapotranspiration and its long-term trends is essential for water cycle studies, modeling and for water uses. Spatial and temporal analysis of evapotranspiration is therefore important for the management of water resources, particularly in the context of climate change. The objective of this study is to analyze the trend of reference evapotranspiration (ET0) as well as its sensitivity to climatic variables in the Senegal River basin. Mann-Kendall&rsquo, s test and Sen&rsquo, s slope were used to detect trends and amplitude changes in ET0 and climatic variables that most influence ET0. Results show a significant increase in annual ET0 for 32% of the watershed area over the 1984&ndash, 2017 period. A significant decrease in annual ET0 is observed for less than 1% of the basin area, mainly in the Sahelian zone. On a seasonal scale, ET0 increases significantly for 32% of the basin area during the dry season and decreases significantly for 4% of the basin during the rainy season. Annual maximum, minimum temperatures and relative humidity increase significantly for 68%, 81% and 37% of the basin, respectively. However, a significant decrease in wind speed is noted in the Sahelian part of the basin. The wind speed decrease and relative humidity increase lead to the decrease in ET0 and highlight a &ldquo, paradox of evaporation&rdquo, in the Sahelian part of the Senegal River basin. Sensitivity analysis reveals that, in the Senegal River basin, ET0 is more sensitive to relative humidity, maximum temperature and solar radiation.

This study set out to determine which environmental factors of growth and silvicultural practices can affect the properties of Eucalyptus robusta coppice wood and also to study variability in those properties depending on the factors. Hundred and thirty-five coppice logs aged 2 to 10 years were collected from five zones in the Highlands of Madagascar. Wood density at 12% moisture content was measured by X-ray microdensitometry. Chemical properties, such as the total extractives, Klason lignin and holocellulose contents were predicted using near infrared spectrometry prediction models. The results significantly showed (p-value

Environmentally-induced changes in fitness are mediated by direct effects on physiology and behaviour, which are tightly linked. We investigated how predicted ocean warming (OW) and acidification (OA) affect key ecological behaviours (locomotion speed and foraging success) and metabolic rate of a keystone marine mollusc, the sea hare Stylocheilus striatus, a specialist grazer of the toxic cyanobacterium Lyngbya majuscula. We acclimated sea hares to OW and/or OA across three developmental stages (metamorphic, juvenile, and adult) or as adults only, and compare these to sea hares maintained under current-day conditions. Generally, locomotion speed and time to locate food were reduced ~1.5- to 2-fold when the stressors (OW or OA) were experienced in isolation, but reduced ~3-fold when combined. Decision-making was also severely altered, with correct foraging choice nearly 40% lower under combined stressors. Metabolic rate appeared to acclimate to the stressors in isolation, but was significantly elevated under combined stressors. Overall, sea hares that developed under OW and/or OA exhibited a less severe impact, indicating beneficial phenotypic plasticity. Reduced foraging success coupled with increased metabolic demands may impact fitness in this species and highlight potentially large ecological consequences under unabated OW and OA, namely in regulating toxic cyanobacteria blooms on coral reefs.

International audience; Fruit abscission facilitates the optimal conditions and timing of seed dispersal. Environmental regulation of tropical fruit abscission has received little attention, even though climate change may have its strongest impacts in tropical regions. In this study, oil palm fruit abscission was monitored during multiple years in the Benin Republic to take advantage of the climatic seasonality and the continuous fruit production by this species. An innovative multivariable statistical method was used to identify the best predictors of fruit abscission among a set of climate and ecophysiological variables, and the stage of inflorescence and fruit bunch development when the variables are perceived. The effects of climate scenarios on fruit abscission were then predicted based on the calibrated model. We found complex regulation takes place at specific stages of inflorescence and bunch development, even long before the fruit abscission zone is competent to execute abscission. Among the predictors selected, temperature variations during inflorescence and fruit bunch development are major determinants of the fruit abscission process. Furthermore, the timing of ripe fruit drop is determined by temperature in combination with the trophic status. Finally, climate simulations revealed that the abscission process is robust and is more affected by seasonal variations than by extreme scenarios. Our investigations highlighted the central function of the abscission zone as the sensor of environmental signals during reproductive development. Coupling ecophysiological and statistical modeling was an efficient approach to disentangle this complex environmental regulation. K E Y W O R D S climate change, Elaeis guineensis, environmental regulation, fruit abscission, multivariable models

Made available in DSpace on 2020-12-12T02:29:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Colorado State University North Carolina State University Universidade Federal de Lavras Universidade Federal do Rio Grande do Norte Università degli Studi di Sassari U.S. Forest Service Universidade de São Paulo ArcelorMittal International Paper Brazilian roundwood industry is one of the most important and productive in the world, with Eucalyptus plantations alone representing 73% of the total planted forests. Deep rooting in these plantations represents a more common phenomena than generally expected. However, there is still a lack of information on environmental factors that drive root growth in deep soil layers, with particular emphasis on edaphoclimatic conditions, and related consequence in terms of soil water behavior. As a part of a larger project, this research aimed to investigate soil water and fine root system distribution in deep tropical soils under a commercial Eucalyptus plantation chronosequence. Along a 2800-km gradient (from south- to north-east Brazil), 14 experimental areas were planted with a “plastic” clone (E. urophylla) and investigated in terms of climatic conditions, soil and water features, and plant/stand development for an entire 6-years rotation period. Fine roots distribution were investigated in one site (in Brazil) till to 20 m deep at 3, 9, 24, 48, and 65 months after planting. Results showed a fast displacement of the root front down to 75, 325, 825, 1250, and 1575 cm at month 3, 9, 24, 48, and 65 after planting, respectively. Fine root densities (g cm−3) and proportional water capture exponentially decreased with soil depth. Deep fine roots showed a relativelly higher efficiency in acquiring water than the shallower, denser roots. The relationship between stand height vs root front depth followed an exponential trend, suggesting that these stands developed relatively faster in height rather than in depth during the first 48 months, with the opposite characterizing plantation afterwards. Regardless of stand age, E. urophylla trees rapidly explored a considerable volume of soil at a relatively limited carbon cost. Multivariate statistics showed that edaphoclimatic conditions play a major role in Eucalyptus plant/stand development. This study outlined the major role played by soil development. From poorly developed sandy Entisols, to medium developed Inceptisols, and to most developed fine textured Oxisols, both plant growth and stand productivity greatly improved accordingly. This study suggests that soil type, together with other environmental factors, are likely to influence both the development and behavior of Eucalyptus plantations for an extent greater than commonly anticipated. Vimef-Soluções Florestais Ltda, Rua Juca Prates, 1014 UNESP São Paulo State University School of Agricultural Sciences Department of Plant Protection Rural Engineering and Soils School of Engineering São Paulo State University Universidade de São Paulo Center of Nuclear Energy in Agriculture, Av. Centenário, 303 Institute of Food and Agricultural Sciences Indian River Research and Education Center University of Florida Eco&Sols Univ Montpellier CIRAD INRA IRD Montpellier SupAgro CIRAD UMR Eco&Sols Dipartimento di Scienze e Tecnologie Ambientali Biologiche e Farmaceutiche Università della Campania “Luigi Vanvitelli”, Via Vivaldi n◦ 43 Dipartimento di Architettura Design e Urbanistica Università degli Studi di Sassari Polo Bionaturalistico, Via Piandanna n° 4 School of Agricultural Forest and Food Sciences Bern University of Applied Science, Laenggasse 85 Desertification Research Centre Università degli Studi di Sassari, Viale Italia n◦ 39 UNESP São Paulo State University School of Agricultural Sciences Department of Plant Protection Rural Engineering and Soils School of Engineering São Paulo State University

L'agriculture de décrue est un mode de production ancestral qui a permis aux populations des plaines inondables africaines de survivre, et même de développer des sociétés avancées comme l'Égypte pharaonique, le Tekrour, le Ghana, les empires malien ou songhaï. Elle a l'avantage de fournir une production appréciable en saison sèche, et nécessite très peu d'intrants et un travail limité. Si les rendements à l'hectare sont faibles, la productivité du travail est appréciable et explique l'engouement des riverains à son endroit, malgré la fréquente possibilité de la remplacer par une agriculture irriguée moderne. L'importance de cette pratique dans la sous-région ouest-africaine reste peu connue, car les services statistiques nationaux ont tendance à la négliger. Dans ce chapitre, nous passons en revue la littérature existante pour l'Afrique de l'Ouest et centrale, c'est-à-dire du Sénégal jusqu'au Tchad. L'objectif est de mieux appréhender les perspectives de cette agriculture, qui avait presque disparu pendant les grandes sécheresses des années 1980 et qui était censée disparaître définitivement avec la construction de plusieurs dizaines de barrages régulateurs sur les grands fleuves de la sous-région. Depuis, les plans de barrages ont été suspendus à cause de l'endettement des États et du rapport alarmant rendu par la Commission mondiale des barrages (WCD, 2000). Par ailleurs, les pluies sont en partie revenues, permettant aux riverains de certaines plaines inondables de relancer cette production, notamment dans plusieurs plaines du bassin du lac Tchad. Depuis quelque temps, les plans de barrages sont réapparus sur l'agenda des États et des agences de bassin. Si les bailleurs traditionnels sont toujours réticents, la Chine se montre déterminée à financer et réaliser ces projets de barrages qui avaient été enterrés dans les années 1990. Dans ce chapitre, les auteurs font un bilan zone par zone, en comparant les surfaces potentiellement inondables, les surfaces cultivées, les cultures pratiquées et les techniques de production spécifiques à ces zones.

International audience; Much effort has been spent on formulating guidelines for inorganic fertilizer use in millet crops in Sub-sahelian farms. However, these guidelines do not take into account the diversity of manuring practices. In this study we analyzed over two years (2016–2017) the use efficiency of an inorganic NPK fertilizer as affected by the two most contrasted categories of organic manure strategies (OMS) found in millet fields of central Senegal. 19 farmers’ fields were selected in a village typical of that region, 11 and 8 of which respectively corresponding to categories OMS1 and OMS2 as follows: OMS1, locally referred to as Homefields, were fields continuously cropped with millet over the last 15 years, having received organic manure regularly in the past, and manured again at the onset of the 2016 rainy season. OMS2 fields locally referred to as Outfields, were not manured in 2016 and were rarely manured in the past. Four of them were continuously cropped with millet and the others had followed a triennial millet-peanut-fallow rotation. In 2017, no manure was applied in any of the OMS1 or OMS2 fields. A pairwise treatments with and without the same inorganic fertilizer dose was applied in each field in both 2016 and 2017 cropping seasons. In 2016, the higher the manure application, the higher the use efficiency of the inorganic fertilizer applied. The use efficiency of the inorganic N was most closely related to soil bulk density and P availability. In 2017, with no new manure amendment, millet yield in OMS1 was about three times higher than in 2016. It was close to the water-limited yield, suggesting that the residual effect of the manure applied in 2016 was high. The use efficiency of the inorganic N was generally low under these conditions. In OMS2, millet yield and use efficiency of inorganic fertilizer remained low in both years. The crop rotation with peanuts did not enrich the soil compared to the millet returning every year, but it reduced Striga hermontica infestation and increased the millet 1000-grain weight. The methodological approach developed here may help in formulating guidelines to deal with the diversity of farming practices in Sub-sahelian villages.

Resilience of cocoa agroforestry vs. full sun under extreme climatic conditions. In the specific case of our study, the two shade tree species associated with cocoa resulted in strong competition for water and became a disadvantage to the cocoa plants contrary to expected positive effects.

Increasing soil organic matter (SOM) is of primary importance for maintaining soil fertility and mitigating climate change. Leaving crop residues on top of soil is not always an efficient means of increasing SOM because (i) of the high mineralization of the crop residues, (ii) crop residues may increase the mineralization of existing SOM (priming effect) and (iii) wetting-drying cycles may increase mineralization of SOM and crop residues. Little research has been carried out into these mechanisms under Sudano-Sahelian conditions where the rainfall is mostly irregular with wetting-drying cycles during the transition between the wet and the dry season. To evaluate the effect of wetting-drying cycles on the mineralization of SOM and crop residues and the priming effect, an agricultural soil from the North Region of Cameroon with or without (controls) 13 C-labeled rice straw amendment as crop residues was either subjected to five wetting-drying cycles or maintained at constant water potential after a single rewetting event. Soil samples were incubated for 70 days at 28 °C and the CO 2 and 13 CO 2 emissions and mineral N were monitored. Adding straw (+ 833 μg C g − 1 soil) increased the cumulative CO 2 emissions from the soil (+ 921 μg C-CO 2 g − 1 soil). A positive priming effect was observed (+ 92 μg C-CO 2 g − 1 soil). Only the first wetting cycle created a mineralization flush of the SOM and the straw. This flush did not recur probably because of a lack of labile SOM. However an extra addition of straw after 28 days increased CO 2 emissions but did not result in further mineralization flushes after re-wetting while SOM mineralization was not limited by N availability. We conclude that SOM depletion under Sudano-Sahelian conditions was not explained by SOM mineralization enhancement due to multiple rewetting events or to priming effect following crop residues addition. Indeed, SOM depletion could rather be explained by a high level of mineralization of both, SOM and crop residues, when the soil reached its water retention capacity.

Aim: Leaf traits strongly impact biogeochemical cycles in terrestrial ecosystems. Understanding leaf trait variation along environmental gradients is thus essential to improve the representation of vegetation in Earth system models. Our aims were to quantify relationships between leaf traits and climate in permanent grasslands at a biogeographical scale and to test whether these relationships were sensitive to (a) the level of nitrogen inputs and (b) the inclusion of information pertaining to plant community organization. Location: Permanent grasslands throughout France. Methods: We combined existing datasets on climate, soil, nitrogen inputs (fertilization and deposition), species composition and four traits, namely specific leaf area, leaf dry matter content and leaf nitrogen and phosphorus concentrations, for 15,865 French permanent grasslands. Trait–climate relationships were tested using the following four climatic variables available across 1,833 pixels (5 km × 5 km): mean annual temperature (MAT) and precipitation (MAP), and two indices accounting for the length of the growing season. We compared these relationships at the pixel level using either using community-level or species’ trait means. Results: Our findings were as follows: (a) leaf traits related to plant nutrient economy shift consistently along a gradient of growing season length accounting for temperature and soil water limitations of plant growth (GSLtw); (b) weighting leaf traits by species abundance in local communities is pivotal to capture leaf trait–environment relationships correctly at a biogeographical scale; and (c) the relationships between traits and GSLtw weaken for grasslands with a high nitrogen input. Main conclusions: The effects of climate on plant communities are better described using composite descriptors than coarse variables such as MAT or MAP, but appear weaker for high-nitrogen grasslands. Using information at the community level tends to strengthen trait–climate relationships. The interplay of land management, community assembly and bioclimate appears crucial to the prediction of leaf trait variations and their effects on biogeochemical cycles.