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International audience; The intensification of biological processes coping with salt stress became a major issue to mitigate land degradation. The Sine-Saloum Delta in Senegal is characterized by salt-affected soils with vegetation dominated by salt-tolerant grass Sporobolus robustus and shrubs like Prosopis juliflora. Plant experiments in controlled conditions suggested that arbuscular mycorrhizal (AM) fungi might be the key actors of facilitation process observed between S. robustus and P. juliflora, but the AM fungal community determinants are largely unknown. The current field-based study aimed at (1) characterizing the environmental drivers (rhizosphere physico-chemical properties, plant type and season) of the AM fungal community along an environmental gradient and (2) identifying the AM fungal taxa that might explain the S. robustus-mediated benefits to P. juliflora. Glomeraceae predominated in the two plants, but a higher richness was observed for S. robustus. The pH and salinity were the main drivers of AM fungal community associated with the two plants, negatively impacting richness and diversity. However, while a negative impact was also observed on mycorrhizal colonization for S. robustus, P. juliflora showed opposite colonization patterns. Furthermore, no change was observed in terms of AM fungal community dissimilarity between the two plants along the environmental gradient as would be expected according to the stress-gradient and complementary hypotheses when a facilitation process occurs. However, changes in intraspecific diversity of shared AM fungal community between the two plants were observed, highlighting 23 AM fungal OTUs associated with both plants and the highest salinity levels. Consequently, the increase of their abundance and frequency along the environmental gradient might suggest their potential role in the facilitation process that can take place between the two plants. Their use in ecological engineering could also represent promising avenues for improving vegetation restoration in saline Senegalese's lands.

Background and AimsImproved modelling of carbon assimilation and plant growth to low soil moisture requires evaluation of underlying mechanisms in the soil, roots, and shoots. The feedback between plants and their local environment throughout the whole spectrum soil-root-shoot-environment is crucial to accurately describe and evaluate the impact of environmental changes on plant development. This study presents a 3D functional structural plant model, in which shoot and root growth are driven by radiative transfer, photosynthesis, and soil hydrodynamics through different parameterisation schemes relating soil water deficit and carbon assimilation. The new coupled model is used to evaluate the impact of soil moisture availability on plant productivity for two different groups of flowering plants under different spatial configurations.MethodsIn order to address different aspects of plant development due to limited soil water availability, a 3D FSP model including root, shoot, and soil was constructed by linking three different well-stablished models of airborne plant, root architecture, and reactive transport in the soil. Different parameterisation schemes were used in order to integrate photosynthetic rate with root water uptake within the coupled model. The behaviour of the model was assessed on how the growth of two different types of plants, i.e. monocot and dicot, is impacted by soil water deficit under different competitive conditions: isolated (no competition), intra, and interspecific competition.Key ResultsThe model proved to be capable of simulating carbon assimilation and plant development under different growing settings including isolated monocots and dicots, intra, and interspecific competition. The model predicted that (1) soil water availability has a larger impact on photosynthesis than on carbon allocation; (2) soil water deficit has an impact on root and shoot biomass production by up to 90 % for monocots and 50 % for dicots; and (3) the improved dicot biomass production in interspecific competition was highly related to root depth and plant transpiration.ConclusionsAn integrated model of 3D shoot architecture and biomass development with a 3D root system representation, including light limitation and water uptake considering soil hydraulics, was presented. Plant-plant competition and regulation on stomatal conductance to drought were able to be predicted by the model. In the cases evaluated here, water limitation impacted plant growth almost 10 times more than the light environment.

In the tropics, the reduction in fallow periods in shifting rice cultivation and deforestation have led to soil degradation. How crop diversity is managed by farmers to adapt to this change remains poorly studied. Our study in Madagascar focuses on the management of 38 species in agroforestry, a practice that was gradually adopted by Betsimisaraka farmers to replace shifting rice cultivation. We describe how farmers perceived changes in the soil and how they adapted their farming practices to these changes, and analyze their knowledge of the interactions between the different plant species and the soil (soil-agrobiodiversity interactions) that underlie these adaptations. The farmers' perceptions of changes in the soil, their causes and consequences, were recorded in 19 individual interviews and three focus groups. Farmers' knowledge of soil-agrobiodiversity interactions was recorded in 84 individual surveys and one focus group. Farmers grouped soils in two main classes according to the topography and used four criteria to characterize them. The main change in the soil they observed was the decline in soil fertility due to deforestation. In response to these changes, farmers changed their crop species and management practices (e.g., spatial organization of crops, fertilization, species associations). These adaptations are based on shared knowledge of the soil requirements of crop species and their effect on fertility, despite the recent adoption of agroforestry. Our study highlights the dynamic and holistic dimension of farmers' knowledge of the soil and its interactions with different plant species.

Made available in DSpace on 2021-06-25T10:21:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-03-01 Aims: Belowground interactions are still poorly understood in mixed-species forests. We investigated the effects of soil fertility on belowground processes in mixed planted forests. Methods: The dynamics and traits of Eucalyptus and Acacia mangium fine roots (diameter < 2 mm) in plantations with 50% of each species were studied in a randomized block design established in a nutrient depleted soil. Stands with NPK fertilization applied at planting (F+) were compared to unfertilized stands (F-). Results: In the 0–15 cm soil layer, Eucalyptus root mass density (RMD) was higher than Acacia RMD by 50% in F+ and 10% in F-, considering both ages. At 34 months of age, Eucalyptus RMD was 94% higher near Acacia trees than near Eucalyptus trees in F-. In this layer, Eucalyptus specific root length (SRL) was 21% higher than Acacia SRL at 16 months of age and was 10% higher in F- than in F+ at 34 months of age. The cumulative Eucalyptus fine root length production between 16 and 34 months was 66% higher in F- than in F+ in the 0–1 m soil layer. Conclusions: Fertilization increased the competition between species and led to a partial exclusion of Acacia fine roots from the nutrient-rich topsoil. Soil exploration by Eucalyptus roots in the vicinity of Acacia trees was higher in F- than in F+, which suggests that unfertilized trees benefited from facilitation through higher soil N availability and direct N transfer from Acacia trees. ESALQ Forest Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo Université de Lorraine AgroParisTech INRAE UMR Silva School of Agriculture São Paulo State University (UNESP) Eco&Sols CIRAD INRA IRD Montpellier SupAgro Univ Montpellier CIRAD UMR Eco&Sols ESALQ Soil Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo UFES Centro de Ciências Agrárias e Engenharias Alto Universitário, S/N Guararema School of Agriculture São Paulo State University (UNESP)

Sixty year ago, Charles Elton posed that species-rich communities should be more resistant to biological invasion. However, still little is known about which processes could drive the diversity-invasibility relationship. Here we examined whether soil-microbes-mediated apparent competition on alien invaders is more negative when the soil originates from multiple native species. We trained soils with five individually grown native species, and used amplicon sequencing to analyze the resulting bacterial and fungal soil communities. We mixed the soils to create trained soils from one, two or four native species. We then grew four alien species separately on these differently trained soils. In the soil-conditioning phase, the five native species built species-specific bacterial and fungal communities in their rhizospheres. In the test phase, it did not matter for biomass of alien plants whether the soil had been trained by one or two native species. However, the alien species achieved 11.7% (95% CI: 3.7% ~ 20.1%) less aboveground biomass when grown on soils trained by four native species than on soils trained by two native species. Our results revealed soil-microbes-mediated apparent competition as a mechanism underlying the negative relationship between diversity and invasibility. published

International audience; The sensitivity of C and N mineralization in soil to water potential is mostly described in simulation models as a linear function independent of the pedoclimatic conditions. We hypothesized that water sensitivity could be sitespecific and dependent of climate or soil properties. In this study, we characterized the responses of C and N mineralization to water stress in ten soils representing a range of French arable cropping systems and evaluated whether the responses differ between soils and pedoclimatic contexts. C and N mineralization kinetics were quantified in laboratory incubations at four soil water potentials (pF) ranging from pF = 2.0 (~field capacity) to 4.2 (~permanent wilting point). The C and N mineralization rates, calculated by curve fitting, were linearly correlated with pF or relative water content (RWC). The slope of the linear regression, representing the sensitivity to water potential, differed significantly between sites, ranging from 0.12 to 0.35 pF-1 for C mineralization and 0.20 to 0.44 pF-1 for N mineralization. The sensitivity of C or N mineralization rate to pF or RWC could be well predicted by a couple of two soil properties: either microbial quotient (ratio of microbial biomass-C to total organic C) and soil pH or soil organic C:N ratio and soil pH. The sensitivity of soil to water stress was more accurately predicted by these site-specific variables than a model common to all pedoclimatic conditions. These results open the possibility of improving soil and soil-crop models for a more accurate prediction of water stress on C and N mineralization particularly in the context of climate change.

Family farms in the tropics mainly rely on rainfed agriculture. Water availability is limited to rainfall and is one of the main constraints to crop productivity. Conservation agriculture (CA) is promoted as an alternative that, among other functions, enhances water infiltration and limits evaporation from the soil thanks to a mulch of crop residues left on the soil surface. These functions are assumed to reduce the water availability constraint by limiting water stress during crop growth. But the variability of rainfall distribution combined with the wide range of agroecological conditions and the variety of crop husbandries in the tropics makes it difficult to evaluate the efficiency of mulching. The aim of this study was to capture the variability through a simple modeling approach using the crop growth model PYE-CA, which requires a limited set of parameters and a virtual experiment (VE). We applied our approach to a case study of upland rice in the Lake Alaotra region in Madagascar, where rainfall distribution is highly variable. The VE used a 17-year series of weather data with a range of soil water conditions, sowing dates, and growth and yield limitations that cover the variability of agroecological conditions and management systems in the study area. The VE revealed that variable successions of wet and dry episodes during the rainy season resulted in both water stress and an increase in deep drainage. In the majority of conditions simulated, enhancing water infiltration through CA mainly increased water loss through drainage. However, better water infiltration may also reduce the production risks involved in early sowing or crop intensification, thereby offering new opportunities to farmers. As an alternative to time consuming and labor intensive experimentation, we propose a suitable modeling approach to identify the main drivers of rainfall × crop interactions that could be extrapolated to other regions in the tropics.

La subéraie est écosystème forestier occupant une place socio-économique et écologique majeure au Maroc. Cet écosystème est cependant fortement impacté par l'augmentation des pressions anthropiques et l'aggravation des conditions climatiques, entrainant une forte régression de sa superficie et une accélération des processus de désertification. L'étude avait pour objectif de caractériser l'impact du mode de gestion de la subéraie sur une composante majeure de son fonctionnement, la communauté de champignons ectomycorhiziens (EcMs) associées au chêne-liège, et de déterminer des bio-indicateurs EcMs relatifs aux perturbations. La communauté de champignons EcMs a été suivie au cours de la période estivale et hivernale au sein de deux sites de la subéraie de la Maâmora (Maroc), caractérisés soit par une exploitation ou non de la subéraie. Un impact significatif du mode de gestion de la subéraie sur la communauté de champignons EcMs a été mis en évidence, avec les différences les plus notables à la période estivale. Ces travaux ont permis de confirmer l'importance écologique probable de plusieurs groupes de champignons (e.g. Cenococcum) dans le maintien des fonctionnalités de la subéraie, mais aussi de l'association préférentielle de certains champignons EcMs (Pachyphloeus, Russula, Tomentella) à une perturbation ou une saison, et par conséquent à l'état de la subéraie ou à des conditions climatiques, respectivement. La généralisation de ce type d'étude à l'ensemble de la subéraie méditerranéenne pourrait permettre l'établissement de modèles plus robustes pour prédire l'impact des changements globaux sur cet écosystème emblématique des régions méditerranéennes.

There is increasing concern that due to land pressure and the need to maximize income, smallholder coffee farmers are increasingly being forced to cultivate in areas which are considered to be sub-optimal for coffee. Little is known about optimal coffee and tree combinations in these conditions and the degree to which crops and trees compete or are synergistic. In environmental conditions which were sub optimal for coffee cultivation in Nicaragua (1470 mm annual rainfall, 27 °C mean annual temperature and 455 m altitude compared to optima of 2000 mm, 23–24 °C and altitude between 1000 and 1400 m at that latitude, respectively), coffee and shade tree transpiration and soil evaporation were directly and separately measured in agroforestry (AFS) and full sun systems (FS). AFS was found to be a more efficient water user than FS because a greater proportion of rainfall was used by plant transpiration rather than being lost by soil evaporation. Plant transpiration accounted for 83% and 69% of evapotranspiration while soil evaporation represented 17% and 31%, in AFS and FS respectively. In AFS most of the water transpiration was due to coffee (72.5%) and much less by deciduous Tabebuia rosea (19%) and evergreen Simarouba glauca shade trees (8.5%). Furthermore, the study demonstrated the vastly different behaviour in water use by the shade trees. When in leaf, Tabebuia rosea transpired at four to six times the rate of evergreen Simarouba glauca, although crown sizes were similar. Contrasting precipitation between two consecutive years of study demonstrated that competition for water between coffee and shade tree occurred only in a severe dry season when coffee leaf water potential (LWP) reached its lowest values of −2.33 MPa in AFS. It was concluded that in most circumstances there was sufficient water for both coffee and trees, that coffee in AFS was a more efficient user of water than FS coffee, and that evergreen Simarouba glauca was more suitable as coffee shade tree compared to deciduous Tabebuia rosea in the sub optimal environmental condition studied. (Resume d'auteur)

International audience; The impacts of Conservation Agriculture (CA) practices on soil characteristics have been largely studied. However, changes in soil electrical properties induced by CA cropping systems have been rarely studied for soil electrical conductivity (EC), and have never been reported for soil redox potential (Eh). Electrical conductivity is a key parameter and is largely used in precision agriculture to characterize various soil properties. Conversely, soil redox potential (Eh) has been overlooked by agronomists despite its being able to provide essential information to characterize soil conditions. This study set out to characterize the changes in soil electrical properties (Eh, pH and EC) induced by CA practices. For four contrasting soil types, varying in texture, pH and organic matter content, we showed that CA alters soil electrical activity (characterized by Eh corrected to pH7 or pe + pH) and soil electrical conductivity. Fields under CA or conventional practices displayed reversed soil profiles for electrical activity: surface soil (0–5 cm) was found to be more oxidized under conventional systems than under CA practices, while the lower horizon (15–25 cm) was more oxidized in CA systems than in conventional systems. CA systems also decreased electrical conductivity when it was initially high, and increased it when it was low, especially in the surface horizon (0–5 cm). We discuss the possible mechanisms explaining such changes, the possible implications in the global functioning of soil/plant/microorganism system, and the interests and opportunities to use soil Eh-pH-EC as an indicator of soil health.

International audience; The ISO-standardized RHIZOtest is used here for the first time to decipher how plant species, soil properties, and physical chemical properties of the nanoparticles and their transformation regulate the phytoavailability of nanoparticles. Two plants, tomato and fescue, were exposed to two soils with contrasted properties: a sandy soil poor in organic matter and a clay soil rich in organic matter, both contaminated with 1, 15, and 50 mg-kg(-1) of dissolved Ce-2(SO4)(3), bare and citrate coated CeO2 nanoparticles. All the results demonstrate that two antagonistic soil properties controlled Ce uptake. The clay fraction enhanced the retention of the CeO2 nanoparticles and hence reduced Ce uptake, whereas the organic matter content enhanced Ce uptake. Moreover, in the soil poor in organic matter, the organic citrate coating significantly enhanced the phytoavailability of the cerium by forming smaller aggregates thereby facilitating the transport of nanoparticles to the roots. By getting rid, of the dissimilarities between the root systems of the different plants and the normalizing the surfaces exposed to nanoparticles, the RHIZOtest demonstrated that the species of plant did not drive the phytoavailability, and provided evidence for soil plant transfers at concentrations lower than those usually cited in the literature and closer to predicted environmental concentrations.

Made available in DSpace on 2018-11-26T17:18:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-02-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Fine roots of orange trees reached a depth of approx. 6 m in a sandy tropical soil. Root area index was more responsive to irrigation than leaf area index. Although the crucial role of deep rooting on the hydraulic functioning of tropical trees has been pointed out, studies dealing with root development below 2 m are still scarce. Our study aimed to gain insight into the fine root traits of rainfed and irrigated orange trees down to the root front in deep tropical soils. Irrigation was applied during dry periods, only 3-15% more than the annual amounts of water supplied by rain. Fine roots were sampled down to a depth of 8 m on four dates in a randomized block design. The effects of soil depth and irrigation on major fine root traits, total fine root length and the relationship between leaf area index (LAI) and root area index (RAI) were studied. The total fine root mass was 728 g m(-2) in rainfed plots and 536 g m(-2) in irrigated plots during the driest period (Sept/Oct 2012). Across the four sampling dates, the mean depth of the root front was 6.1 m in rainfed plots and 5.5 m in irrigated plots close to the trees, and approximately 4.5 m in the inter-row covered by Brachiaria decumbens plants. LAI was little influenced by irrigation (about 4.5 m(2) m(-2)), but mean RAI was 19.1 m(2) m(-2) in rainfed plots and 13.7 m(2) m(-2) in irrigated plots. Small irrigation rates reduced root development in very deep soil layers, and increased fruit production by 9% during the dry year. Deep rooting provides access to water stored in deep soil layers during the rainy season, and thus might have an important functional role during dry periods in tropical orange orchards. Univ Estadual Paulista, Vegetal Prod Dept, BR-18610300 Botucatu, SP, Brazil CIRAD, UMR Eco&Sols, 2 Pl Viala, F-34060 Montpellier, France Univ Estadual Paulista, Dept Solos & Recursos Ambientais, BR-18610300 Botucatu, SP, Brazil Univ Estadual Paulista, Dept Bot, BR-18618970 Botucatu, SP, Brazil Univ Estadual Paulista, Vegetal Prod Dept, BR-18610300 Botucatu, SP, Brazil Univ Estadual Paulista, Dept Solos & Recursos Ambientais, BR-18610300 Botucatu, SP, Brazil Univ Estadual Paulista, Dept Bot, BR-18618970 Botucatu, SP, Brazil FAPESP: 2012/03342-7

International audience; There are strong uncertainties regarding LAI dynamics in forest ecosystems in response to climate change. While empirical growth & yield models (G&YMs) provide good estimations of tree growth at the stand level on a yearly to decennial scale, process-based models (PBMs) use LAI dynamics as a key variable for enabling the accurate prediction of tree growth over short time scales. Bridging the gap between PBMs and G&YMs could improve the prediction of forest growth and, therefore, carbon, water and nutrient fluxes by combining modeling approaches at the stand level. Our study aimed to estimate monthly changes of leaf area in response to climate variations from sparse measurements of foliage area and biomass. A leaf population probabilistic model (SLCD) was designed to simulate foliage renewal. The leaf population was distributed in monthly cohorts, and the total population size was limited depending on forest age and productivity. Foliage dynamics were driven by a foliation function and the probabilities ruling leaf aging or fall. Their formulation depends on the forest environment. The model was applied to three tree species growing under contrasting climates and soil types. In tropical Brazilian evergreen broadleaf eucalypt plantations, the phenology was described using 8 parameters. A multi-objective evolutionary algorithm method (MOEA) was used to fit the model parameters on litterfall and LAI data over an entire stand rotation. Field measurements from a second eucalypt stand were used to validate the model. Seasonal LAI changes were accurately rendered for both sites (R-2 = 0.898 adjustment, R-2 = 0.698 validation). Litterfall production was correctly simulated (R-2 = 0.562, R-2 = 0.4018 validation) and may be improved by using additional validation data in future work. In two French temperate deciduous forests (beech and oak), we adapted phenological sub-modules of the CASTANEA model to simulate canopy dynamics, and SLCD was validated using LAI measurements. The phenological patterns were simulated with good accuracy in the two cases studied. However, IA/max was not accurately simulated in the beech forest, and further improvement is required. Our probabilistic approach is expected to contribute to improving predictions of LAI dynamics. The model formalism is general and suitable to broadleaf forests for a large range of ecological conditions. (C) 2014 Elsevier B.V. All rights reserved.

Past applications of chlordecone, a persistent organochlorine pesticide, have resulted in diffuse pollution of agricultural soils, and these have become sources of contamination of cultivated crops as well as terrestrial and marine ecosystems. Chlordecone is a very stable and recalcitrant molecule, mainly present in the solid phase, and has a strong affinity for organic matter. To prevent consumer and ecosystem exposure, factors that influence chlordecone migration in the environment need to be evaluated. In this study, we measured the impact of incorporating compost on chlordecone sequestration in andosols as a possible way to reduce plant contamination. We first characterized the transfer of chlordecone from soil to plants (radish, cucumber, and lettuce). Two months after incorporation of the compost, soil-plant transfers were reduced by a factor of 1.9-15 depending on the crop. Our results showed that adding compost modified the fractal microstructure of allophane clays thus favoring chlordecone retention in andosols. The complex structure of allophane and the associated low accessibility are important characteristics governing the fate of chlordecone. These results support our proposal for an alternative strategy that is quite the opposite of total soil decontamination: chlordecone sequestration.

Methods are presented testing the suitability of PROSAIL radiative transfer model for analysing HyMap imaging spectroscopy data over grassland. The presented methods include forward modelling and cross-checks of 2D correlation plots. In the forward modelling, it is taken into account that the in situ data are not error free. To increase the predictive power of PROSAIL, a simple and fully automatic feature selection (FS) algorithm is presented identifying and discarding poorly modelled wavebands, yielding more reliable parameter retrievals.

Il est maintenant admis que le climat de la planète change et que les activités humaines en sont majoritairement responsables via l'émission de gaz à effet de serre (GES). Les rapports internationaux et des études de synthèse pointent du doigt la contribution des activités d'élevage aux émissions de gaz à effet de serre (CO₂, CH₄, N₂O) et au changement climatique évaluant la contribution mondiale de l'élevage aux émissions de GES directes et indirectes à environ 14,5%. Les écosystèmes pastoraux d'Afrique sub-saharienne sont responsables de hauts niveaux d'émissions de GES par unité de produits animaux, à cause de la faible productivité du bétail et de rations fortement méthanogènes. Les systèmes pastoraux extensifs valorisent cependant de vastes espaces caractérisés par une hétérogénéité édaphique et une forte variabilité du climat. Cette thèse vise à évaluer l'impact des troupeaux de ruminants sur le bilan GES vis-à-vis de l'atmosphère d'un écosystème sylvopastoral sous climat tropical semi-aride. L'aire de desserte du forage de Widou (cercle de 30 km de diamètre autour du forage, soit une superficie de 706 km²) dans la région sylvopastorale du Ferlo au Nord du Sénégal a été retenue comme unité spatiale d'analyse. Pour réaliser ce bilan, l'ensemble des émissions liées au fonctionnement de l'écosystème (fermentation entérique des animaux d'élevage et des termites, émissions de GES du sol et des eaux, le feu de végétation et le fonctionnement de la motopompe du forage) et des accumulations de carbone dans les principaux réservoirs (matière organique des sols, bois et racines des ligneux et masse animale) ont été évaluées à l'échelle de temps mensuelle et sur le cycle annuel en tenant compte de l'hétérogénéité spatiale de la zone étudiée (6 unités paysagères distinguées)...

Le recyclage des produits résiduaires organiques (PRO) en agriculture urbaine et périurbaine permet de réduire l'utilisation des engrais chimiques et d'améliorer la fertilité des sols, mais induit des effets négatifs sur les agrosystèmes en raison de la présence de contaminants tels que les éléments traces métalliques (ETM). Ces contaminants peuvent s'accumuler dans les sols, impacter la qualité des cultures via le prélèvement par les racines, ou polluer les eaux souterraines par lixiviation. Les objectifs de ce travail ont été (i) de caractériser les risques de pollution par quatre ETM (Zn, Cu, Pb et Cd) suite à des apports répétés de PRO dans deux agrosystèmes périurbains de Dakar localisés respectivement sur un Arénosol (sol sableux) et un Fluvisol (sol sablo-argilo-limoneux et modérément calcaire), et (ii) de mieux appréhender les mécanismes qui gouvernent la disponibilité, la biodisponibilité et la mobilité de ces ETM dans le système sols-eau-plante. L'approche multi-échelle utilisée est constituée d'une enquête diagnostique sur le terrain et des expérimentations en conditions de laboratoire et de serre. L'enquête a permis de diagnostiquer les risques de contamination des sols par les ETM liés aux pratiques culturales dans les bassins maraîchers de Pikine (sur Arénosol) et de Rufisque (sur Fluvisol). La spéciation des ETM dans les sols et PRO a été étudiée par la méthode d'extraction chimique séquentielle. La disponibilité et la biodisponibilité des ETM dans les mélanges sols-PRO incubés en conditions contrôlées ont été mesurées respectivement par la technique DGT (Diffusive Gradient in Thin film) et un test biologique (RHIZOtest). La mobilité des ETM a été étudiée en colonnes de sols. Pour ces expérimentations, deux doses (20 et 60 T.ha -1 ) d'apport de boues de STEP et de fientes ont été apportées sur les deux sols. L'étude diagnostique a révélé une contamination en ETM des horizons de surface des sols pour les parcelles cultivées comparativement aux zones non cultivées. Les horizons agricoles de l'Arénosol sont plus contaminés en ETM que ceux du Fluvisol en raison des pratiques culturales contrastées observées entre les deux bassins maraîchers. Dans le bassin de Pikine, les productions des cultures à cycle court sont intensifiées sur de petites superficies (< 0,5 ha) avec un recours à l'utilisation dominante de boues de STEP et des eaux usées épurées. Par contre, dans le bassin de Rufisque, les productions des cultures à cycle long sur de grandes superficies (variant de 0,5 à 5 ha), dominent avec une utilisation prépondérante des fientes de volailles et de fumiers divers. L'extraction chimique séquentielle des ETM dans les sols non fertilisés a montré une abondance des fractions facilement disponibles pour Zn et Cd, tandis que Cu et Pb sont présents sous la forme de fractions plus stables, liées à la matière organique (MO), aux oxyhydroxydes, et fraction résiduelle. Le fractionnement chimique des ETM dans les PRO a révélé une abondance des fractions facilement disponibles pour Zn et Cd dans les boues (72 et 60 % respectivement), et pour Zn et Pb dans les fientes (69 et 42 % respectivement). L'application des boues et fientes de volailles a augmenté la disponibilité et la biodisponibilité des ETM dans l'Arénosol et le Fluvisol. Les plus fortes disponibilités et biodisponibilités en ETM ont été induites par les boues appliquées à 60 T.ha -1 dans les deux sols. La disponibilité des ETM est plus importante dans l'Arénosol que dans le Fluvisol. Zn est l'ETM le plus disponible et biodisponible dans les deux sols. Ces résultats indiquent que la disponibilité des ETM dépend fortement des propriétés physico-chimiques des sols (pH, teneurs en MO, argiles, carbonates et phosphates), du type et de la dose des PRO appliqués, et de la spéciation des ETM dans ces sols et ces PRO. La biodisponibilité des ETM dépend non seulement des propriétés physico-chimiques des sols, mais aussi des processus rhizosphériques qui régulent le prélèvement des ETM par la plante. Les apports répétés de boues de STEP et de fientes de volailles ont engendré de fortes accumulations d'ETM dans les couches superficielles des colonnes des deux sols étudiés. Les quantités d'ETM lixiviés vers les profondeurs sont faibles dans les deux sols. Toutefois, les flux d'ETM lixiviés vers les profondeurs sont plus élevés dans l'Arénosol comparativement au Fluvisol. La Fiente appliquée à 60 T.ha -1 a induit la plus forte mobilité des ETM dans les deux sols. Ainsi, la mobilité des ETM dans les sols étudiés dépend fortement de la quantité du carbone organique dissous apporté par les PRO et des caractéristiques physico-chimiques des sols. Un traitement préalable comme le co-compostage des boues de STEP et des fientes de volailles avec des additifs inorganiques (la chaux par exemple) et une réglementation portant sur leur utilisation permettraient de réduire la contamination par les ETM de ces agrosystèmes périurbains de Dakar.

International audience; Carboxylic groups located in plant cell walls (CW) are generally considered to be the main copper binding sites in plant roots, despite the presence of other functional groups. The aim of this study was to investigate sites responsible for copper binding in root apoplasts, i.e. CW and outer surface of the plasma membrane (PM) continuum. Binding sites in root apoplasts were investigated by comparing isolated CW of a monocotyledon (Triticum aestivum L.) and dicotyledon (Solanum lycopersicum L.) crop with their respective whole roots. Copper speciation was examined by X-ray absorption (XAS) and C-13-nuclear magnetic resonance spectroscopies while the affinity of ligands involved in copper binding was investigated by modeling copper sorption isotherms. Homogeneous speciation and binding of copper was found in wheat and tomato root apoplasts. Only Cu-N and Cu-O bonds were detected in wheat and tomato root apoplasts. Nitrogen/oxygen ligands were identified in slightly higher proportions (40-70%) than single oxygen ligands. Furthermore, low-and high-affinity binding sites contributed in an almost equivalent proportion to copper binding in root apoplasts. The high-affinity N functional groups embedded in root apoplasts participated in copper binding in the same magnitude than the low-affinity carboxylic groups.

Rubber tree is a very important crop in Thailand, representing an essential source of income for farmers. In the past two decades, rubber tree plantations have been greatly expanding in unfavorable areas, where climate conditions are difficult and soil fertility is very poor. To optimize latex yields, mineral fertilizers have been widely used. A better understanding of the roles of the biological compartment in soil fertility is essential to determine alternative management practices to sustain soil fertility and optimize latex yields. Arbuscular mycorrhizal fungi (AMF) are widely recognized as beneficial for plants, mainly through their role in improving plant nutrient uptake. The objective of this study was to assess the AMF populations in rubber tree plantations and the impact of both soil characteristics and plantation age on these communities. Our results showed that all rubber trees were highly colonized, regardless of the soil structure and nutrient contents. AMF colonization was not affected by the age of the trees, suggesting that maintaining the symbiosis is likely to be beneficial at all stages. A better understanding and management of the microbial communities would contribute to maintaining or restoring soil fertility, leading to a better tree growth and optimized latex yield.

International audience; The finite element (FE) method has been used in recent years to simulate overturning processes in trees and to better comprehend plant anchorage mechanics. We aimed at understanding the fundamental mechanisms of root-soil reinforcement by simulating direct shear of rooted and non-rooted soil. Two- (2D) and three-dimensional (3D) FE simulations of direct shear box tests were carried out using readily available software for routine strength assessment of the root-soil composite. Both rooted and non-rooted blocks of soil were modelled using a simplified model of root distribution and root material properties representative of real roots. Linear elastic behaviour was assumed for roots and the soil was modelled as an ideally plastic medium. FE analysis showed that direct shear tests were dependent on the material properties specified for both the soil and roots. 2D and 3D simulations of direct shear of non-rooted soil produced similar results and any differences between 2D and 3D simulations could be explained with regard to the spatial complexity of roots used in the root distribution model. The application of FE methods was verified through direct shear tests on soil with analogue roots and the results compared to in situ tests on rooted soil in field conditions

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; Nonpathogenic Fusarium oxysporum endophytes from healthy banana roots were evaluated for their ability to reduce Fusarium wilt of banana (Panama disease). Isolates were identified morphologically and by using species-specific primers. Pathogenicity was confirmed by inoculating banana plantlets in the greenhouse. Nonpathogenic F. oxysporum isolates were grouped into 14 haplotype groups by polymerase chain reaction restriction fragment length polymorphism analysis of the intergenic spacer region, and representative isolates evaluated for biocontrol of F. oxysporum f. sp. cubense. In the greenhouse, 10 nonpathogenic F. oxysporum isolates were able to significantly reduce Fusarium wilt of banana. The isolate that protected banana plantlets best in the greenhouse, a nonpathogenic F. oxysporum from the root rhizosphere, and Pseudomonas fluorescens WCS 417 were then field tested. When the putative biological control organisms were tested in the field, neither the nonpathogenic F. oxysporum, P. fluorescens, nor combinations thereof reduced Fusarium wilt development significantly. A number of factors could contribute to the lack of field protection, including soil microbial and chemical composition and reduced survival of biocontrol organisms in banana roots. A lack of knowledge regarding the etiology of Fusarium wilt of ‘Cavendish’ banana in the subtropics and the effect of F. oxysporum f. sp. cubense race and banana cultivar in protection of banana by biocontrol organisms should be further investigated.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Potato crop is the fourth main food crop in the world and it will certainly feed a big part of the global population in the next years. The economical outlets for this crop are great; however, numerous diseases either soil- or air-borne can cause huge losses in the production. Worldwide, about 40 soil-borne diseases affect potato and cause severe damages especially on tubers, the economically most important part of the plant. The occurrence and development of soil-borne diseases depend on very diverse factors affecting either the pathogen or the plant. Favorable conditions for potato diseases development are frequently the same as the conditions needed for potato growth: temperature between 10°C and 25°C, high humidity, medium pH, etc. Adapted cultural practices such as a rotation longer than 4 years, appropriate fertilization and water management, an adapted delay between haulm killing and harvest, and dry and cool conditions for tuber storage are good ways to control potato diseases. In most cases, potato pathogens develop specific survival forms, dissemination ways and host penetration methods. The genetic variability of the pathogens implies the use of adapted diagnostic and control methods. Decision support systems developed to predict yield losses allow choosing good control methods such as the use of healthy seeds, adapted pesticides, cultural practices, and biological control agents for each potato disease. The complexity of the interactions between a pathogen and its host, influenced by biotic and abiotic factors of the environment, make the control of the diseases often very difficult. However, deep knowledge of pathosystems allows setting up integrated pest management systems allowing the production of healthy and good quality potatoes.

In a changing context, farmers adapt their cropping systems and, in this respect, the response time of the soil-crop system (changes in the soil resources and in the grapevine vegetative or reproductive development) has to be considered to maintain its agronomic performances. This is particularly true for perennial crops such as grapevine. This paper aims to analyse the short- and long-term effects of changes in soil surface management on grapevine performances. Avineyard in which bare soil inter-rows had been compared with a tall fescue intercrop since 2002 had each of these treatments split into two in 2007, with half of the intercrop being ploughed in and half of the bare soil being sown with fescue, resulting in four treatments whose effects were studied in 2008-2009. Grapevine growth, yield formation and grape quality were assessed. After intercrop destruction, grapevine vegetative growth was enhanced by the mineralization of organic matter from the first year, whereas after intercrop introduction, the competition for soil resources affected growth only in the second year. The grape yield depended on the number of bunches, elaborated the year before. One year after the change in soil surface management, the ranking of yield was as follows: permanent intercrop < intercrop destroyed < intercrop introduced < bare soil. The second year, this ranking altered (still in relation to the number of bunches) to: intercrop introduced < permanent intercrop < bare soil=intercrop destroyed. This study shows that the response times of the processes of grapevine vegetative growth and yield formation to a change in the cropping system vary from one to two years, and therefore, have to be considered carefully to manage the cropping system well.

A mapping population of 114 lines from Bala × Azucena was grown under drought stress at two field sites with contrasting soil physical properties. Drought was imposed between 35 and 65 days after sowing (DAS) and root density at 35 cm depth was measured 70 DAS. Leaf rolling, leaf drying and relative water content were recorded as indicators of drought avoidance. Root density correlated with indicators of drought avoidance. Two significant and two putative quantitative trait loci (QTLs) for root density and 28 QTLs for drought avoidance were identified. Most QTLs did not agree between sites. There was also reasonable agreement between leaf-drying QTLs and previously reported root-growth QTLs detected under controlled conditions (in contrast to a previous screen on soil with a higher penetration resistance). These data also reveal QTL × environment interaction, which will need to be understood more clearly if progress towards breeding for drought resistance via alterations of root morphology is to be achieved.

Correspondance auteur: Bravin M.N. CIRAD, UPR Recyclage & Risque 78, F-34398 Montpellier, France E-mail: matthieu.bravin@cirad.fr; International audience; Using a root mat approach, we quantified how root-induced alkalization controlled the establishment of copper (Cu) gradients in the rhizosphere of durum wheat (Triticum turgidum, durum L.) cropped in a strongly acidic, Cu-contaminated soil. Rhizosphere pH increased over 6 mm in soil, reaching up to +2.8 units close to root mat surface. Conversely, free Cu2+ activity decreased by 3 orders of magnitude and total Cu concentration by 3-fold in the rhizosphere solution, while labile Cu assessed by DGT (diffusive gradients in thin films) was halved. The DIFS (DGT-induced flux in soils and sediments) model failed to adequately simulate Cu depletion in the rhizosphere solution, showing that root-induced alkalization almost entirely explained Cu depletion while plant uptake had little impact. We modeled the observed pH gradient to recalculate its radial extension around a single root. The gradient of free Cu2+ activity in solution, deduced from pH modeling, extended over 1-4 mm in the rhizosphere depending on root radius and OH- efflux from root. Rhizosphere alkalization dramatically decreased root exposure to Cu, substantiating that root-induced chemical changes in the rhizosphere should be better accounted for to assess metal bioavailability to plants

L'introduction de biodiversité végétale dans les agroécosystèmes peut modifier la structure des réseaux trophiques du sol et les fonctions écosystémiques qu'ils assurent. Cette thèse fixe les bases d'une démarche expérimentale pour sélectionner des espèces végétales à partir de différents traits fonctionnels et pour évaluer leurs effets sur les réseaux trophiques et le fonctionnement des sols. Nous avons plus particulièrement cherché à sélectionner des plantes de services pouvant induire la régulation des nématodes parasites du bananier Radopholus similis et Pratylenchus coffeae et favoriser la décomposition des matières organiques durant l'interculture dans les bananeraies antillaises. C'est à dire durant la période séparant la destruction d'une ancienne bananeraie et la replantation d'une nouvelle. Au cours de ce travail, les réseaux trophiques du sol ont été appréhendés par une analyse fonctionnelle des communautés de nématodes. Une étude Bibliographique nous a permis de montrer que les traits fonctionnels "statut d'hôtes" vis-à-vis des nématodes phytoparasites, "composition biochimique des litières" et "productivité primaire des espèces végétales" contribuent aux effets des plantes sur les réseaux trophiques du sol et sur les deux services écosystémiques étudiés. Nous avons donc effectué une typologie des plantes de services à partir de ces traits. Puis pour étudier les effets d'apports de litières de composition biochimique contrastée sur les communautés de nématodes du sol, nous avons sélectionné les espèces végétales Paspalum notatum, Crotalaria zanzibarica et Acacia auriculiformis dont les litières présentaient des teneurs variables en hémicellulose, cellulose, azote, et lignine. Une étude en microcosmes a montré que la composition biochimique des litières détermine les successions écologiques au sein des communautés de nématodes et stimule de manière contrastée les voies de décomposition de la matière organique dans les sols. Nous avons discuté des mécanismes de régulation des nématodes parasites du bananier induits par ces apports de litières. Nous avons également montré que la culture de ces trois espèces induit une diminution des populations de R. similis dans les sols. Enfin, nous avons évalué les effets au champ de couverts de P. notatum, de C. zanzibarica et d'un couvert associant ces deux espèces. Pour cela, nous avons cultivé ces couverts durant neuf mois avant de les détruire et de restituer leurs litières à la surface des sols. Nos résultats montrent que ces couverts végétaux influencent différemment l'abondance en nématodes phytoparasites et le potentiel infectieux du sol. Ils induisent également des régulations bottom-up et top down dans leurs communautés. Après la restitution des litières, nous avons observé de fortes abondances de nématodes liées à la décomposition des litières dans la couche de surface du sol. Celle-ci fournit les couches sous-jacentes du sol en azote minéral et favorise le développement des nématodes omnivores et prédateurs. Il en résulte la formation de communautés de nématodes structurées et diversifiées concomitantes à la réduction des populations de R. similis et P. coffeae. Ces résultats étaient plus marqués pour les couverts monospécifiques de C. zanzibarica et les couverts mixtes. Nos travaux confirment que les traits fonctionnels "statut d'hôte", "production primaire", "composition biochimique des litières" sont déterminant pour sélectionner des plantes de services pour l'interculture en bananeraies.

Ammonia exchanges between the atmosphere and terrestrial ecosystems are composed of several pathways including exchange with the soil, the litter, the plant surfaces (cuticle) and through the stomata. In this study, the fate of nitrogen in the different pools (soil and plant) was analyzed with the aim of determining the sources and sink of atmospheric ammonia after slurry application on a wheat canopy. To do this, we measured ammonia exchanges between a winter wheat canopy and the atmosphere following cattle slurry application with a trailing hose. From 12 March to 8 April in Grignon near Paris, France, the ammonia fluxes ranged from an emission peak of 54,300 NH3 ng m−2 s−1 on the day of slurry application (with a median during the first 24 h of 5990 NH3 ng m−2 s−1) to a deposition flux of −600 NH3 ng m−2 s−1 (with a median during the last period of −16 NH3 ng m−2 s−1). The ammonia compensation points were evaluated for apoplasm, foliar bulk, root bulk and litter bulk tissue, as well as for soil surface. Ammonia emission potentials defined by the ratios between the concentration in [NH4+] and [H+] for each N ecosystem pool were in the same order of magnitude for the plant decomposed in apoplastic liquid, green leaf bulk tissue and cuticle, respectively, averaging at 73, 160 and 120; in green leaf bulk tissues, the emission potential decreased gradually from 230 to 78 during the period after slurry application, while in the dead leaf bulk tissues considered as litter, the emission potential reached a maximum of 50,200 after application stabilized at around 20000. The dynamic of the emission potential for roots was similar to the ammonium concentration in the first two centimeters of the soil, with a maximum of 820 reached two days after application and a minimum of 44 reached three weeks later. The surfatm-NH3 model interpreted the emission and deposition fluxes by testing soil surface resistance. We conclude that emission of the first day application was driven by climatic conditions and ammonia concentration at the soil surface, with no surface resistance and with only soil surface emission potential. On the next three days, the ammonia emission originated from the soil surface with the growth of a dry surface layer inducing surface resistance and regulated by slurry infiltration. The following days need a more detailed description of soil surface processes and the integration of vegetation exchanges (stomatal and cuticle pathways), particularly in the last period, in order to explain the ammonia deposition.

This research conducted in the Tougou watershed located in North of Burkina Faso aims at assessing the impact of soil degradation on the water transfer in the soil-plant-atmosphere continuum. Field measurements were performed through an experimental design made of plots measuring 1 m2 each and established on three sites of the watershed: three plots on an erosion crust (PZN), three plots on a desiccation crust supported herbaceous (PZD) and three plots on an area cultivated in sorghum (PZC). Each site was equipped with tensiometric and neutron tubes to measure pressure head and water content of the soil. Results showed that PZN was characterized by a low infiltration capacity enhancing runoff. The water stored during the rain periods is low and remains localized within the first 30 or even 40 cm top of soil, which promoted a quick evaporative recovery in days following the rainy event. PZD and PZC were characterized by a good hydraulic conductivity and a high infiltration speed. The infiltrated water was important and the drainage beyond the depth of 70 cm was observed during important rain events. The real daily average evapotranspiration varied between 3 and 4 mm on the all sites.

Five caesalpinioid legumes, Afzelia africana, Afzelia bella, Anthonotha macrophylla, Cryptosepalum tetraphylum and Paramacrolobium coeruleum, and one Euphorbiaceae species, Uapaca somon, with a consider-able range in seed sizes, exhibited different responses to inoculation by four species of ectomycorrhizal (ECM) fungi, Scleroderma dictyosporum, S. verrucosum, Pisolithus sp. and one thelephoroid sp. in greenhouse conditions. Thelephoroid sp. efficiently colonized seedlings of all of the five caesalpinioid legumes except U. somon, but provided no more growth benefit than the other fungi. Thelephoroid sp. and S. dictyosporum colonized seedlings of U. somon poorly, but stimulated plant growth more than the other fungi. The relative mycorrhizal dependency (RMD) values of the caesalpinioid legumes were never higher than 50%, whilst U. somon had RMD values ranging from 84.6 to 88.6%, irrespective of the fungal species. The RMD values were negatively related to seed mass for all plant species. Potassium concentrations in leaves were more closely related than phosphorus to the stimulation of seedling biomass production by the ECM fungi. Our data support the hypothesis that African caesalpinioid legumes and euphorbe tree species with smaller seeds show higher RMD values than those with the larger seeds.

The arrangement of a plant's roots in the soil determines the ability of the plant to resist uprooting. We have investigated the influence of root morphology on anchorage using simple patterns of root systems and numerical simulation. The form and mechanical properties of roots were derived from results found in the literature. Major parameters determining soil characteristics, root patterns and strength were varied so that their influence could be evaluated. The design of the experimental method we used generated an optimal number of configurations of different root systems, the tensile resistances of which were calculated by two-dimensional finite element analysis. We could quantify the influence of specific parameters, e.g. branching angle, number of lateral roots and soil cohesion, as well as global parameters such as total contact area, basal diameter and volume of the whole root system. We found that the number of roots and the diameter of roots were major components affecting the resistance to uprooting. The combination of topology and biomass explained 70% of the variation of tensile resistance.

International audience; Resource acquisition within the soil is a complex process, which consists of several sub-processes involving both the soil and the plant. A brief analysis of the whole system is presented, first by focusing on the components of the system, and then on the successive events. This analysis stresses the diversity and specificity of the components involved, as well as their interactive roles, at several organisation levels, both in space and time. Therefore, a systemic approach using dynamic models is defended in order to gather available knowledge and gain new insight within the whole system. In comparison to many of the traditional modelling approaches, which tended to over-simplify the plant part of the system, some new and promising attempts are presented. These new models give a good illustration of what can be expected to be gained by associating structural and functional characteristics of the plant components.; Introduction sur l'environnement souterrain et l'acquisition des ressources, avec références particulières aux arbres. Les modèles de simulation devraient inclure la structure et les fonctions de la plante. L'acquisition des ressources du sol est un processus complexe, que l'on peut subdiviser en plusieurs processus plus élémentaires faisant intervenir conjointement la plante et le sol. Nous faisons une brève analyse de ce système, en insistant d'abord sur ses composants, puis sur les événements successifs. Cette analyse révèle la diversité et la spécificité des composants impliqués, ainsi que leurs rôles interactifs, à plusieurs niveaux d'organisation dans le temps et dans l'espace. Aussi, nous défendons une approche systémique, utilisant la modélisation dynamique, pour synthétiser les connaissances disponibles, et obtenir ainsi un nouvel éclairage sur le système pris dans sa globalité. En comparaison avec les approches de modélisation traditionnelles, qui tendent à simplifier outrageusement la partie plante du système, nous présentons quelque démarches nouvelles et prometteuses. Ces derniers modèles illustrent bien les progrès que l'on peut escompter en associant davantage les caractéristiques structurales et fonctionnelles des composants de la plante.

Within plants, sulphur (S), and nitrogen (N) equilibrium is a requisite for their normal development. Pot experiments with oilseed rape and barley fertilized at different N to S ratios were carried out under glasshouse conditions by using the “rhizobag”; technique. The objective was to compare the induced‐influence of rhizosphere and non‐rhizosphere soil on N and S nutrition of the studied plants. Thus, SO4 2‐S, NC3 ‐‐N and NH4 +‐N concentrations, and total N and S taken up by the plants were examined. Barley increased the pH of rhizosphere soil whereas no real change of pH was observed with oilseed rape. Both plants took up all the NO3 ‐ present in the soil solution, but rapeseed took up greater quantities of NH4 +‐N and SO4 2‐ ‐S than barley. Moreover, the ratio values of N to S of the aerial parts of the rapeseed were significantly and positively correlated to those of soil available‐N to ‐S ratios while this correlation was significant but negative with barley. This indicated a clear‐cut diff...

The objective of this study was to evaluate the possibility of using the fraction of transpirable soil water (FTSW) under field conditions, to analyse genotypic differences in plant responses to soil water deficit. Two years of field experiments were carried out on a sandy soil under sub-sahelian conditions in Senegal. Five cotton cultivars (Gossypium hirsutum L.), with similar phenology but different yield responses to drought, were compared under two irrigation treatments differentiated after flowering. Because of differences in the rainfall pattern during the pre-flowering period, the two years resulted in marked differences in soil water hydration and effective rooting depth. Soil water deficit experienced by the plants in each elementary plot was characterized with FTSW, calculated with volumetric soil water content (measured with a neutron probe) from soil surface to the estimated effective rooting depth. Despite large differences of soil water content between years and irrigation treatments, FTSW was closely related to the predawn leaf water potential measured on the same day. Plant responses to soil water deficit were analysed with leaf water potential (ψl), relative water content (RWC), stomatal conductance (gs), and crop water stress index (CWSI) measured during the crop cycle. Genotypic differences for these plant variables were found on some days, but they were frequently associated with genotypic differences in FTSW. The relationships between plant variables and FTSW, over two years of measurements and contrasting soil water profiles, were adjusted to typical logistic functions, previously used in other species. Leaf water status (ψl and RWC), gs and CWSI did not change appreciably until FTSW reached 0.4–0.5. Significant genotypic differences were found in the relationships of RWC and CWSI with FTSW, which allowed the ranking of the five cultivars for dehydration avoidance. The absence of genotypic differences in the relationships between gs and FTSW indicates that the higher dehydration avoidance of one of the cultivars (STAM F) is not linked to stomatal regulation, but probably to osmotic adjustment. Calculation of FTSW from soil water content measurements provided an efficient way to conduct genotypic comparison of plant response to drought in field conditions over two years of contrasted rainfall pattern.

The use of improved germplasm and management to increase rice production in rainfed lowland and upland systems is discussed. Understanding of the mechanisms conferring P efficiency, particularly external efficiency through root-induced changes in the rhizosphere, is reviewed together with evidence for genetic variation in P efficiency in upland and lowland rice germplasm. The following areas for improving resource and input management are considered: P management under alternately wet and dry soil conditions; P fertilizer formulations for banding in highly-weathered soils; cumulative responses to P fertilizer, including interactions with biological N fixation by legumes; amelioration of subsoil acidity, especially by leaching down the effects of surface-applied lime; and the management of soil spatial variability. Areas for future research are given.

This study aims to compare and validate two soil-vegetation-atmosphere-transfer (SVAT) schemes, being TERRA-ML and the Community Land Model. Both SVAT schemes are run in standalone mode (decoupled from an atmospheric model) and forced with meteorological in-situ measurements obtained at several tropical African sites. Model performance is quantified by comparing simulated sensible and latent heat fluxes with eddy-covariance measurements. Our analysis indicates that the Community Land Model corresponds more closely to the micrometeorological observations, reflecting the advantages of the higher model complexity and physical realism. Deficiencies in TERRA-ML are addressed and its performance is improved: i) adjusting input data (root depth) to region-specific values (tropical evergreen forest) resolves dry-season underestimation of evapotranspiration, ii) adjusting the leaf area index and albedo (depending on hard-coded model constants) resolves overestimations of both latent and sensible heat fluxes, and iii) an unrealistic flux partitioning caused by overestimated superficial water contents is reduced by adjusting the hydraulic conductivity parameterization. CLM is by default more versatile in its global application on different vegetation types and climates. On the other hand, with its lower degree of complexity, TERRA-ML is much less computationally demanding which leads to faster calculation times in a coupled climate simulation. ispartof: Journal of Geophysical Research vol:117 issue:G2 status: published

The responses of the soil microbial community features associated to the legume tree Acacia senegal (L.) Willd. including both arbuscular mycorrhizal fungal (AMF) diversity and soil bacterial functions, were investigated under contrasting environmental conditions. Soil samples were collected during dry and rainy seasons in two contrasting rainfall sites of Senegal (Dahra and Goudiry, in arid and semiarid zone, resp.). Soils were taken from the rhizosphere of A. senegal both in plantation and natural stands in comparison to bulk soil. A multiple analysis revealed positive correlations between soil physicochemical properties, mycorrhizal potential and enzyme activities variables. The positive effects of A. senegal trees on soil mycorrhizal potential and enzyme activities indicates that in sahelian regions, AMF spore density and diversity as well as soil microbial functions can be influenced by land-use systems (plantation versus natural population of A. senegal) and environmental conditions such as moisture and soil nutrient contents. Our study underlines the importance of prior natural AMF screening for better combinations of A. senegal seedlings with AMF species to achieve optimum plant growth improvement, and for restoration and reforestation of degraded lands.

International audience; Mycorrhizal symbiosis is a key component of a sustainable soil-plant system, governing the cycles of major plant nutrients and vegetation cover. The mycorrhizosphere includes plants roots, the mycorrhizal fungi, and a complex microbial compartment. A large number of methods have been used to characterize the genetic and functional diversity of these soil microbial communities. We present here a review of the multivariate data analysis methods that have been used in 16 research articles published in the 2005-2009 period. "Descriptive" multivariate data analysis methods have been priviledged over classical "predictive" methods and univariate statistical tests. Data sets, multivariate data analysis methods, graphical outputs and interpretation results are presented and explained in details on several examples coming from some of the 16 articles. These multivariate and graphical methods are available in the ade4 package for the R statistical software. The discussion underlines the importance of using appropriate statistical methods to obtain a good description of soil microbiological and biochemical indicators and a good evaluation of soil quality.

Correspondance auteur: Hinsinger P. philippe.hinsinger@supagro.inra.fr ; In the context of increasing global food demand, ecological intensification of agroecosystems is required to increase nutrient use efficiency in plants while decreasing fertilizer inputs. Better exploration and exploitation of soil resources is a major issue for phosphorus, given that rock phosphate ores are finite resources, which are going to be exhausted in decades from now on. We review the processes governing the acquisition by plants of poorly mobile nutrients in soils, with a particular focus on processes at the root-soil interface. Rhizosphere processes are poorly accounted for in most plant nutrition models. This lack largely explains why present-day models fail at predicting the actual uptake of poorly mobile nutrients such as phosphorus under low input conditions. A first section is dedicated to biophysical processes and the spatial/temporal development of the rhizosphere. A second section concentrates on biochemical/biogeochemical processes, while a third section addresses biological/ecological processes operating in the rhizosphere. New routes for improving soil nutrient efficiency are addressed, with a particular focus on breeding and ecological engineering options. Better mimicking natural ecosystems and exploiting plant diversity appears as an appealing way forward, on this long and winding road towards ecological intensification of agroecosystems.

Dans un contexte de mutation rapide de l'agriculture, la conception de systèmes de culture répondants aux nouvelles exigences des agriculteurs et de la société est une nécessité. L'agriculture doit répondre au double enjeu : être productive et respecter l'environnement. La conception de systèmes de culture innovants repose à la fois sur i) des recherches cognitives, visant à comprendre les processus impliqués dans l'agroécosystème et ii) leur intégration dans des systèmes complexes et l'évaluation multicritère de ces systèmes. J'ai développé une approche de modélisation permettant d'intégrer les connaissances existantes sur le fonctionnement des agroécosystèmes à base de bananiers, d'identifier les connaissances manquantes, et de fournir des outils de pilotage afin de permettre la définition de systèmes de culture durables. Les outils de modélisation développés simulent le fonctionnement biophysique de l'agroécosystème, incluant certaines spécificités, comme la prise en compte d'un peuplement cultivé hétérogène (caractère semi-pérenne des bananiers) et la dynamique des bioagresseurs (nématodes phytoparasites et charançons). Ces modèles ont été couplés à des outils d'évaluation des risques environnementaux (risque de pollution par les pesticides), permettant in fine, d'évaluer systèmes de culture existants ou innovants sur la base de critères de performances agronomiques, économiques et environnementales. Afin d'assister le prototypage de systèmes de culture innovants, ces outils de modélisation ont été utilisés afin de tester un grand nombre de règles de décisions des agriculteurs et d'optimiser les combinaisons les plus prometteuses. Mon projet de recherche traite de la question du rôle de la diversité biologique dans la productivité et la stabilité des systèmes de culture. Je propose de mobiliser des modèles de réseaux trophiques afin de prendre en compte la complexification biologique des systèmes cultivés. Au niveau méthodologique, lier les modèles de culture utilisés par les agronomes, avec les modèles de réseaux trophiques utilisés par les écologues, représente un cadre adapté pour simuler le fonctionnement du continuum sol-plante-atmosphère, la régulation biologique des bioagresseurs, et les feedbacks des différentes communautés sur les propriétés du sol. Ce cadre devrait permettre de faire le lien entre les pratiques culturales des agriculteurs, incluant la composante économique et décisionnelle, avec les propriétés émergentes de ces systèmes complexes. La seconde partie de ce projet de recherche concerne l'étude de la dimension spatiale dans la régulation des bioagresseurs. Il s'agit notamment d'étudier comment l'hétérogénéité spatiale et la diversité des ressources influencent la dispersion et la régulation des bioagresseurs par prédation.