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EABIOMEAGROSUP; De par leur structure tridimensionnelle, leur large gamme de porosité, la diversité de leurs caractéristiques physicochimiques et des conditions microclimatiques, les sols abritent un nombre considérable, parfois inestimable d'organismes. Au sein des agroécosystèmes, les enjeux sont de comprendre les relations entre la plante cultivée et son environnement biophysique incluant les interactions biologiques et les effets de la biodiversité des organismes des sols. L’impact de la faune du sol sur la production primaire peut être vu au travers de leur effet sur les fonctions de (i) recyclage des nutriments, (ii) entretien de la stabilité/structure du sol, (iii) contrôle des bioagresseurs et (iv) support de biodiversité. Ces fonctions écosystémiques sont respectivement associées du point de vue des plantes à (i) leur nutrition, (ii) le milieu physique dans lequel les plantes se développent, (iii) leur santé et (iv) les interactions entre plantes. L’effet de la faune du sol sur chaque fonction peut être expliqué par de nombreux processus et mécanismes qui impliquent l’ensemble des organismes des sols. Ces différents processus sont détaillés dans ce chapitre.

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.

This paper presents an overview of a decade (2002-2012) of studies performed on Soil-Plant-Atmosphere processes, in semi-arid areas (Haouz plain, Morocco). In this period, fifteen in-situ experiments on the dominant irrigated crops were performed, controlling the fluxes exchanged between land surface and atmosphere. The results showed that the physically based SVATs (ICARE, SiSPAT and ISBA) provided the best estimates of surface fluxes. For operational purposes, the FAO-56 approach and SAMIR Software (Satellite Monitoring for Irrigation) give a good estimate of evapotranspiration at field and regional scales, respectively. Finally, thermal infrared data were used in conjunction with SVATs to investigate the possibility of estimating the quantity of irrigation water.

Heavy metal-contaminated soils are a major concern for worldwide agricultural production. The main sources of environment pollution by heavy metal are the rapid urbanization and/or industrial growth. These pollutants induce the loss of the structure and the function of soil and microbial community. They affect human health through food chain and water contamination. To rehabilitate lands degraded by heavy metal, some efficiency and low-cost approaches have to be promoted widely. Phytoremediation is a potential tool to clean up pollutants from the contaminated site, implement a ground cover, and improve soil fertility. It is well known that symbiotic microorganisms tolerant to heavy metal increase plant resistance and toxic metal alleviation. So, management of the relationship between hyper-accumulator plants and these microorganisms increases the potential of this biological tool. In this chapter, we discuss (1) the use of actinorhizal plants for remediation of heavy metal-contaminated soils, (2) the impact of mycorrhizal fungi and/or nitrogen-fixing bacteria on plant adaptation and performance in heavy metal-contaminated sites, and (3) the positive effect of actinorhizal plants on soil fertility of heavy metal-contaminated soil.

Owing to their high water retention, the volcanic ash-soils of the Northern Andean highlands (páramos) can be considered as natural 'water storage tanks' for drinking water and for irrigation. Vegetation plays an important role in transferring rain to the soil and in controlling the soil water content. To assess this role, we quantified the stemflow process under rainfall simulations for seven of the main plants along an altitude gradient on the Pichincha volcano in Ecuador. The volume of water transferred into the soil was higher at the lower rainfall intensity than at the higher intensity. The results were compared to the stemflow measured with potato and maize crops growing in the lower altitude range. The results showed that the relative volume of stemflow increased with altitude from 8% in the crop area to 58% in the upper part of the catena. Low values of stemflow were associated with potatoes and maize annual short-cycle crops while high values were associated with the natural vegetation. For cultivated crops rainwater interception by stemflow delayed the soil surface crusting and runoff process. This study shows that rainwater interception by vegetation is of great importance for soil water recharge in these Andisols.

Differences in rates of infestation of root-knot nematode (Meloidogyne spp.) populations by the endospore-forming bacterium Pasteuria penetrans were not entirely due to inter/intra-specific variability of the organisms. Soil conditions, especially texture and chemical characteristics, are also involved. Focusing studies on vegetable crops, interactions between the occurrence of Meloidogyne spp. juveniles encumbered with spores of P. penetrans and some physico-chemical soil characteristics were analysed both between regions (West Africa, e.g. Burkina Faso and Senegal; South America, e.g. Ecuador; the Caribbean, e.g. Trinidad and Tobago; and Mediterranean Europe, e.g. Crete) and within Ecuador, Burkina Faso and Senegal. In Ecuador (clay or silty-clay soils), the mean proportion of infested juveniles was high (41.9%). In the sandiest soils, as in Senegal, there were very few infested juveniles (4.7%). In Crete, Burkina Faso, and Trinidad and Tobago, where the soils are siltier, the mean proportions of infested juveniles range between 14 and 24.4%. Multivariate analysis performed on the data from Senegal and Burkina Faso revealed that a significant increase of the mean clay content (1.4 and 10.5%, respectively) improved the mean proportions of infested juveniles (from 1.6 to 42.2% and from 10.7 to 79.4%, respectively). Influences of the soil texture and structure on the availability of the spores of P. penetrans to infest the juveniles of Meloidogyne spp. are discussed.

To measure nickel (Ni) bioavailability experiments were conducted in the field using ion exchange resin (IER) method. Resin bags were inserted into the upper layer of soils developed on ultramafic rocks in New Caledonia. Their Ni contents were determined after four weeks and compared to those of plant leaves of five species. Significant correlations were obtained so that the IER appeared to be successful for routine applications. Furthermore, the use of chemical reactants such as diethylenetriaminepentaacetic acid (DTPA) and KCl demonstrated to be much less reliable for assessing the bioavailability of Ni.

International audience; Integration of the priming effect (PE) in ecosystem models is crucial to better predict the consequences of global change on ecosystem carbon (C) dynamics and its feedbacks on climate. Over the last decade, many attempts have been made to model PE in soil and its underlying mechanisms. However, PE has not yet been incorporated into any ecosystem models. Here we build plant-soil models to explore how PE and microbial diversity influence soil-plant interactions and ecosystem C and nitrogen (N) dynamics in response to global change (elevated CO2 and increased atmospheric N deposition). Our results show that plant persistence, soil organic matter (SOM) accumulation and low N leaching in undisturbed ecosystems relies on a fine adjustment of microbial N mineralization to plant N uptake. This adjustment can be modeled in the SYMPHONY model by considering the destruction of SOM through PE and the interactions between two distinct microbial functional groups: SOM-decomposers and SOM-builders. After estimation of parameters, SYMPHONYprovided realistic predictions on forage production, soil C storage and N leaching for a permanent grassland. Consistent with recent observations, SYMPHONY predicted a CO2-induced modification of soil microbial communities leading to an intensification of SOM mineralization and a decrease in the soil C stock. SYMPHONY also indicated that atmospheric N deposition may stimulate SOM accumulation via changes in the structure and metabolic activities of microbial communities. Collectively, these results suggest that PE and the functional role of microbial diversity may be incorporated in current ecosystem models with a few additional parameters, improving accuracy of predictions.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; Little is known about how spatial and environmental patterns structure soil microbial activities. We investigated, on 47 soil samples collected in Mediterranean forests, the net and interaction effects of climatic-geographic and edaphic variables as well as vegetation cover and composition on soil microbial community-level physiological profiles (CLPPs) assessed by MicrorespTM. The effects of these variables were also analysed on CLPP response to an experimental drought treatment. CLPPs were shown to be mainly driven by climate-plant-soil and plant-soil interactions; even after drought treatment, there was a decrease in microbial activity but no change in CLPPs. Our findings highlight the robustness of these relationships, which need to be assessed within different ecosystems considering various spatial scales to reliably predict climate change effects on terrestrial ecosystems

International audience; 1. It is important to study how evolution impacts on plant functional traits and to determine how this subsequently determines ecosystem functioning. We tackle this general issue by studying the evolution of plant strategies that affect mineralization through the chemical quality of their own litter and their position on the leaf economic spectrum. This spectrum allows us to classify all plants on single axis ranging from resource-acquisitive to resource-conservative strategies. 2. We build a spatially explicit and individual-based simulation model: individual plants grow in the cells of a lattice and the limiting nutrient is recycled locally in these cells. Individual plants may die and produce seeds that are dispersed. Mutants with different mineralization strategies appear stochastically. A trade-off is implemented between the rate of nutrient loss from plants and litter mineralization. 3. In the spatial-explicit model, plant capacity to increase mineralization evolves and reaches an evolutionary equilibrium in most cases. The evolved mineralization decreases with plant longevity, seed dispersal efficiency, spatial homogenization of mineral nutrient availability and inputs of mineral nutrient to the ecosystem. 4. The evolved mineralization strategies neither maximize plant biomass, nor minimize the availability of mineral nutrient or the stock of dead organic matter. The evolutionary and ecological impacts of nutrient enrichment on the stock of organic matter are different. 5. Synthesis. Our results suggest that plant mineralization strategy may evolve provided that the mineral resource is not fully shared by all individuals. Such an evolution modifies soil capacity to store organic carbon thereby being relevant in the context of the current climate change and global nutrient enrichment. Indeed, our model shows that evolutionary feedbacks of plants to nutrient enrichment are likely to differ from purely ecological feedbacks.

The link between vegetation and soil at a few meter-scale was studied in an old physiognomically homogeneous fallow-land (over 30 years) of anthropic Sudanian savanna with poor tree cover. Sampling was conducted systematically on a 60 m x 60 m surface, following a five-metre grid. Floristic releves were made in quadrats (1 m x 1 m), in each corner of which infiltrability was measured by a method derived from the single-ring infiltrometer. Seventy four herbaceous species are present ; the 156 releves could be classified in seven floristic units, which have a clear link with the soil hydropedological characteristics at a few meter-scale. Among the 18 main species (present in at least 10% of the 156 releves) only four could be considered as indifferent to infiltrability, another eight preferred relatively high infiltrability microsites, and the last six preferred poor infiltrability microsites. The relatively high floristic richness of the site can be partly explained by the aptitude of various species to exploit one or another of the different microsites available. The results also suggest a certain structural and functional redundancy between species. (Résumé d'auteur)

The impact of soil cover organization on the forest community has been studied in a 19-ha tract at Piste de St Elie station in French Guiana. 195 species each represented by at least 10 individuals were chosen from records of the position, diameter at breast height (dbh) and precise identification by botanical sampling of 12104 ligneous plants (dbh ≥ 10 cm).

Results from on-farm measurements of surface overland flow of both runon ( R on ) and runoff ( R off ) are presented for a continuously cultivated pearl millet ( Pennisetum glaucum (L.) R.Br.) field, along a characteristic catena, in the Sahel (Niger). Despite the deep sandy soil along the studied hillslope, classified as a Typic Haplustult, non-negligible depths of R off were measured during two rainy seasons: 12–13% of total rainfall for the upslope position and 6–8% for the downslope position. This was explained by the presence of surface crusts with low infiltrability. Upslope, more than 30% of the soil surface was covered with erosion crusts (runoff coefficient (K r ) = 60 – 70% for moist soil conditions) during 40% of the rainy season. The mean coverage of erosion crust for two rainy seasons was 26% upslope, compared with 11% and 15% midslope and downslope, respectively. Weeding, carried out manually with hand hoes, had a very positive effect on soil infiltrability. The destruction of surface crusts resulted in zero Roff (Kr = 0) for rainstorms directly following weeding operations. However, surface crusts were quickly re-established as a result of the erosive effect of the following storms. Large volumes of runon (Ron) water were measured at the upslope limit of the field (14.4 m 3 m −1 in 1995, corresponding to a rainfall depth of 47.5 mm if redistributed over the 8.5 ha millet field). Small volumes were registered downslope (R on = 0.75 m 3 m −1 ), indicating redistribution of R on along the hillslope. The Ron originated from the upstream degraded fallow zone and the adjacent sparsely vegetated plateau, which in effect functioned as water-harvesting zones. R off was modelled based on field observations of surface coverage of soil crusts, data on hydraulic characteristics for the observed crusts, rainfall data and estimates of antecedent soil moisture. Despite high variance in the observed R off , the model provides a reasonable estimate of R off , indicating the possibility of predicting R off on cultivated fields where crust coverage changes quickly over time. The large volumes of measured overland flow suggest that R on and R off cannot be excluded from on-farm water-balance studies. The findings also indicate the potential of developing water-harvesting systems for protective irrigation during the frequent periods of water stress in the rain-fed Sahelian agriculture.

INTRODUCTION Le deploiement preferentiel des ecosystemes de mangrove sur les estrans argilo-limoneux et le role du regime hydrique valent a cette vegetation specialisee d’etre citee en exemple de vegetation edaphique. De fait, l’etude des sols a ete jusqu’a ces dernieres annees une des entrees thematiques privilegiees de l’etude des mangroves des Rivieres du Sud. Dans le contexte d’aridification qui penalise l’Afrique de l’Ouest depuis la fin des annees 1960, les chercheurs ont attire plus pa...

International audience; While an excess of metals such as zinc, cadmium or nickel (Ni) is toxic for most plants, about 500 plant species called hyperaccumulators are able to accumulate high amounts of these metals. These plants and the underlying mechanisms are receiving an increasing interest because of their potential use in sustainable biotechnologies such as biofortification, phytoremediation, and phytomining. Among hyperaccumulators, about 400 species scattered in 40 families accumulate Ni. Despite this wide diversity, our current knowledge of the mechanisms involved in Ni accumulation is still limited and mostly restricted to temperate herbaceous Brassicaceae. New Caledonia is an archipelago of the tropical southwest pacific with a third of its surface (5500 km 2) covered by Ni-rich soils originating from ultramafic rocks. The rich New Caledonia flora contains 2145 species adapted to these soils, among which 65 are Ni hyperaccumulators, including lianas, shrubs or trees, mostly belonging to the orders Celastrales, Oxalidales, Malpighiales, and Gentianales. We present here our current knowledge on Ni hyperaccumulators from New Caledonia and the latest molecular studies developed to better understand the mechanisms of Ni accumulation in these plants.

La dégradation de l'environnement en particulier la ressource sol ne cesse de s'amplifier, entrainant une diminution de sa fertilité. Face à ce problème, une étude d'interaction plante-vers de terre a été initiée pour déterminer s'il existe un partenariat bénéfique pour la plante, car les vers de terre contribuent beaucoup à l'amélioration de la structure et de la composition physico-chimique du sol. Cette étude a été menée dans le site d'URP-SCRiD à Andranomanelatra en collaboration avec le FOFIFA et l'IRD. L'essai a été conduit sous deux dispositifs sur terrain : i) en mésocosme, vase de végétation (en pots) et ii) au champ. Les traitements testés sont l'apport de Dichogaster saliens dans les pots ou au champ avec un nombre croissant de 0, 4, 8, 12 vers de terre. Le riz et l'éleusine sont les plantes testées. Après 6 mois de culture, le nombre de D.saliens augmente dans la rhizosphère du riz. Par contre, il diminue chez l'éleusine. Les résultats montrent qu'il n'y a pas de différences significatives sur la productivité en grains du riz due à une grande variabilité entre les blocs ainsi que sur la biomasse racinaire des plantes. Cependant, une corrélation positive est obtenue entre le poids de Dichogaster saliens et le poids en grains plein du riz. Des contaminations d'autres vers non étudiés, Pontoscolex corethrurus et Amynthas minimus, ont été observées. Malgré cela, le phénomène de compétitivité entres les espèces n'a pas eu lieu.

Maize was grown under field conditions in the presence and absence of the tropical endogenic earthworm #Millsonia anomala$ (Omodeo and Vaillaud, 1967) in soil of a secondary forest of central Ivory Coast. Experimental units were isolated by PVC sheets to limit earthworm movements. Decomposition and redistribution of nitrogen from maize crop residues incorporated in the soil were monitored using 15N-labelled residues. The density of #M. anomala$ decreased from 50 to 15.9/m2 during the cultivation period (90 days). Activity of #M. anomala$ significantly modified the structure of the soil by increasing the proportion of large aggregates (over 2 mm in diameter). Maize production was increased by 12% for stalks and 18% for grains in the presence of earthworms. Nitrogen contained in the maize residue was more efficiently used by plants grown in the presence of earthworms ; the real coefficient of utilisation of the organic residue increased from 9 to 11% in the presence of #M. anomala$. Nonetheless, total nitrogen exportation was not significantly different between the two treatments. Furthermore, N from the organic residues left after the cultivation period was less easily assimilated by plants in treatments with earthworms. (Résumé d'auteur)

International audience; Les images multispectrales incluant une bande rouge et une bande infrarouge ont prouvé leur efficacité pour la discrimination entre sol et végétation et le suivi cultural en télédétection. Mais elles restent rarement utilisées pour l'imagerie au sol ou par drone, du fait de la non disponibilité de capteurs adaptés. Nous proposons ici une solution originale pour obtenir simultanément les bandes rouge et infrarouge à partir d'un appareil photographique couleur ordinaire, après avoir retiré le filtre interne bloquant l'infrarouge. Nous décrivons d'abord l'approche théorique, ainsi que des résultats simulés sur un jeu de données spectrales, pour deux types d'appareils. Des exemples d'acquisition sur le terrain en conditions réelles sont ensuite présentés, et comparés à une acquisition couleur standard pour la discrimination sol/plantes. Dans la plupart des cas notre approche apporte une amélioration significative, ouvrant de nouvelles opportunités pour les applications de suivi de culture. / Multispectral images including red and near-infrared bands have proved their efficiency for vegetation-soil discrimination and agricultural monitoring in remote sensing applications. But they remain rarely used in ground and UAV imagery, due to a limited availability of adequate 2D imaging devices. In this paper, we propose and evaluate an original solution to obtain simultaneously the near-infrared and red bands from a standard RGB camera, after having removed the near-infrared blocking filter inside. First, the theoretical approach is described, as well as simulated results on a set of soil and vegetation luminance spectra with two different still cameras (Canon 500D and Sigma SD14). Then examples of images obtained in real field conditions are given, and compared with standard colour image acquisition for pixel-based plant/soil discrimination, using an automatic thresholding method. It appears that in most cases our new acquisition procedure brings a significative improvement, opening new opportunities for crop monitoring applications.

International audience; Plant species (exotic invasive vs native non-invasive) colonization pattern and the relation with the soil nutrient availability and AM fungi abundance, was investigated. Soil samples were collected from two sites: one invaded by the exotic plant. Amaranthus viridis, and one uninvaded site for chemical and AM propagules density analyses. Additionally, we grew five Sahelian Acacia species in soil from the two sites, sterilized or not, to test the involvement of soil biota in the invasion process. While nutrient availability was significantly higher in soil samples from the invaded sites, a drastic reduction in AM fungal community density, was observed. Moreover, Acacia seedlings' growth was severely reduced in soils invaded by Amaranthus and this effect was similar to that of sterilized soil of both origins. The observed growth inhibition was accompanied by reduction of AM colonization and nodulation of the roots. Finally, the influence of soil chemistry and AM symbiosis on exotic plants' invasion processes is discussed. (C) 2011 Elsevier Ltd. All rights reserved.

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A fertilisation experiment was started in the French Alps on an acid grassland at 2000 m in 1989 where lime as calcium carbonate (“liming”) and Thomas Slag enriched by potassium chloride (“fertilisation”) were added in a random block design until 1992. Since then, no further amendments were applied. Fifteen years after the last application, we revisited the experiment and observed that soil pH was still significantly higher on limed plots, while nitrogen (N) concentrations were lower. On fertilised plots, soil carbon (C) and N concentrations were lower compared to unfertilised plots. However, litter quality (C and N concentrations, near infrared spectroscopy [NIRS] data) was similar for both treatments. Vegetation composition, but not species richness, nor Shannon–Wiener or evenness differed between limed and unlimed plots, and fertilised and unfertilised plots. Liming explained about 18% and fertilisation about 6% of the variability of the vegetation composition. These changes in the vegetation composition are probably due to lower abundances of former dominant grass species and to an increase in generalist grasses. However, these changes did not influence the total above-ground productivity, which was similar for all treatments. Tissue N and C concentrations and NIRS data indicated a changed chemical composition of the biomass which persisted during time. We conclude that the 3 years of fertilisation and liming did substantially influence the vegetation composition at our site and lead to an increase in the agricultural value of the grassland. These changes are long-lasting as they changed key features of the functioning in the soil of grasslands ecosystems. From an ecological point of view, specialised vegetation was replaced by generalist species leading to a trivialisation of the vegetation.

Lescure, J.-P., Emperaire, L. and Franciscon, C., 1992. Leopoldinia piassaba Wallace (Arecaceae): a few biological and economic data from the Rio Negro region (Brazil). For. Ecol. Manage., 55: 8386. The piacabeira (Leopoldiniapiassaba Wallace) is an endemic palm species of the Rio Negro basin whose biology and ecology are poorly documented. Exploited for the fiber (piacaba), the species is important for rural populations as a source of economic income through extractive activity. Two journeys in the middle Rio Negro region permit us to document more fully the biological and economic aspects of the species. Three populations were observed in the Rio Preto-Rio Negro interfluve (64" 15'-64"28'W, O05'-O"15'S).

In New Caledonia, soils developed on ultramafic rocks (5. 500 km2) are constituted of more than 65 % iron oxi-hydroxide. They present very low contents in nitrogen and phosphor (only 1/10 to 1/100 of average contents); besides their Ca / Mg ratio is unbalanced and they contain very high heavy metals concentrations (nickel, manganese, cobalt, chromium). Nowadays the nickel open mines which exploit such soils must consider both economic interests and ecological preoccupations, as these soils are associated to particularly original and diversified ecosystems. Within these, several endemic pioneer plant species have been identified. Among them, some Costularia (Cyperaceae) are recommended in revegetation programmes of mining sites, after their exploitation. Ecological restoration requires a multidisciplinary approach integrating soil sciences, physiological and microbiological data of ultramafic scrubland ecosystems. Analysis of soils / plant’s relations along a topo-sequence, including various types of scrubland, clearly shows there is a direct relationship between the concentrations of soil available elements and the variety and organization of the vegetation, in particular for the herbaceous stratum. This work, coupled with the creation of an experimental Cyperaceae seed orchard, in association with SIRAS Pacifique Company, indicates that the growth of Costularia comosa answers positively the nitrogenous and phosphated fertilization. The experiment also underlines the fact that vigour, growth speed, rate of mycorhization and fruiting of plants are stimulated by moderate doses of these elements. Other assays enabled to improve our knowledge of the role of the microorganisms associated to Costularia roots. Thus, we shows that nine pioneer species of Cyperaceae, studied in situ, develop arbuscular mycorhizal symbioses. An experiment of controlled mycorhization on Costularia comosa shows that mycorhization by Glomus etunicatum is functional, with an increase of the plants’ biomass of 2,8 times compared to the control. Furthermore, such a mycorhization of C. Comosa reduces the nickel concentration in the plant, suggesting the mycorhize acts as a barrier towards nickel. In this study, we also present a description of the aerobic, heterotrophic and nickel resistant bacterial populations isolated from roots of two Costularia species associated to ultramafic scrublands. The density of these bacterial populations is low and Protéobactéria dominate. Some of the isolated strains present a tolerance to 15 mM of soluble nickel and the capacity to solubilize phosphates. The progresses in both our knowledge of Cyperaceae mineral nutrition and the role of associated microorganisms brought by this study, allow to envisage the implementation of productive seed orchards and the use of the microorganisms associated to Costularia, in the technical routes for optimised ecological restoration plans., En Nouvelle-Calédonie, les sols développés sur roches ultramafiques (5. 500 km2) sont constitués à plus de 65% d’oxy-hydroxyde de fer, ils présentent des teneurs très faibles en azote et en phosphore (1/10 à 1/100 des teneurs moyennes), de surcroît ils sont déséquilibrés pour le rapport Ca/Mg et contiennent des concentrations très élevées en métaux lourds (nickel, manganèse, cobalt, chrome). L’exploitation à ciel ouvert du nickel sur ces sols associés à des écosystèmes particulièrement originaux et diversifiés doit prendre en considération à la fois les intérêts économiques et les préoccupations écologiques. Des espèces endémiques pionnières des sols ultramafiques ou cicatricielles des sites miniers dégradés ont été identifiées. Parmi ces espèces, plusieurs espèces de Costularia (Cyperaceae) sont préconisées pour la revégétalisation des sites miniers après exploitation. Les itinéraires techniques de restauration écologique des sites miniers requièrent une approche pluridisciplinaire intégrant des données pédologiques, physiologiques et microbiologiques des écosystèmes des maquis miniers. L’analyse des relations sols/plantes sur une toposéquence comprenant différents types de maquis a permis de mettre en évidence une relation directe entre les concentrations du sol en éléments disponibles et la diversité et l’organisation des espèces, notamment pour ce qui concerne la structuration de la strate herbacée. Ce travail couplé à la mise en place par la société SIRAS Pacifique d’un champ semencier expérimental de Cyperaceae a permis de montrer que la croissance de Costularia comosa répond positivement à la fertilisation azotée et phosphatée. L’expérimentation a permis également de souligner que la vigueur, la vitesse de développement, le taux de mycorhization et la fructification des plants sont stimulés par des doses modérées de ces éléments. D’autres travaux réalisés ont apporté un approfondissement de nos connaissances sur le rôle des microorganismes associés aux racines des Costularia. Ainsi, nous avons montré que neuf espèces pionnières de Cyperaceae étudiées in situ, développent des symbioses mycorhiziennes arbusculaires. Une expérience de mycorhization contrôlée de Costularia comosa a permis de montrer que la mycorhization par Glomus etunicatum est fonctionnelle, avec une augmentation de la biomasse des plants 2,8 fois supérieure au témoin. De plus, la mycorhization réduit la concentration en nickel dans la plante, suggérant un rôle barrière du champignon mycorhizien vis-à-vis du nickel. Dans cette étude, nous présentons également une description des populations bactériennes aérobies, hétérotrophes et résistantes au nickel, isolées des racines de deux espèces de Costularia inféodées aux maquis. Ces populations bactériennes sont de faible densité et dominées par les Protéobactéries. Certaines des souches isolées présentent une tolérance à 15 mM de nickel soluble et la capacité de solubiliser les phosphates. L’avancement apporté dans les connaissances concernant la nutrition minérale des Cyperaceae et le rôle des microorganismes qui leur sont associés permet d’envisager la mise en place en routine de champs semenciers productifs et l’utilisation des microorganismes associés aux Costularia dans les itinéraires techniques de restauration écologique pour en améliorer la réussite.

Competition between plants for essential resources determines the distribution of biomasses between species as well as the composition of plant communities through effects on species reproductive potentials. Soil organisms influence plant competitive ability and access to resources; thus they should modify plant community composition. The effects of an endogeic (Aporrectodea caliginosa) and an anecic (Lumbricus terrestris) earthworm species on the competition between grass (Poa annua), two forbs (Veronica persica and Cerastium glomeratum) and legume (Trifolium dubium) were investigated in a greenhouse experiment. We established two types of plant communities: monocultures and polycultures of the four species. L. terrestris increased the biomass of P. annua and V. persica (in monocultures as well as in polycultures). However, the presence of L. terrestris allowed the grass to produce the highest biomass in polycultures suggesting that this earthworm species promoted the growth of P. annua against the other plant species. In monocultures as well as in polycultures, the presence of L. terrestris to increased the number of seeds of T. dubium and the total seed mass of V. persica. These results suggest that L. terrestris enhanced the short term competitive ability of P. annua by promoting its growth. The increased number of seeds of T. dubium in the presence of L. terrestris suggests that this earthworm species could enhance the long-term competitive ability of this legume and may increase its number of individuals after several generations.

An attempt is made to assess the relationships between soil conditions and the spatial distribution of two sympa trie species of rain forest trees belonging to genus Eperua (Caesalpiniaceae). The study was carried out at the Paracou study site, French Guiana, on the domed hills of precambrian basement rock, locally schistose or migmatic. The relationships between the distribution of individuals of both species and soil variables (126 samples) were studied using factor analysis and hierarchical classification. Eperua falcata is mostly found on hydromorphic or shallow vertically drained soils, often with a high exchangeable aluminium content. This tree appears to be well adapted to unfavourable soil conditions, but it can also be found in other situations. Eperua grandiflora is also adapted to shallow soils, but it does not withstand hydromorphic conditions as well as E. falcata ; it is also very sensitive to the high aluminium content of the soil. The two Eperua species are therefore complementary to one another, except on shallow soils, thus allowing genus Eperua to fill different edaphic niches., Barthès Bernard. Influence des caractères pédologiques sur la répartition spatiale de deux espèces du genre Eperua (Caesalpiniaceae) en forêt guyanaise. In: Revue d'Écologie (La Terre et La Vie), tome 46, n°4, 1991. pp. 303-320.

Near-surface soil moisture retrieved from Soil Moisture and Ocean Salinity (SMOS)-type data is downscaled and assimilated into a distributed soil–vegetation–atmosphere transfer (SVAT) model with the ensemble Kalman filter. Because satellite-based meteorological data (notably rainfall) are not currently available at finescale, coarse-scale data are used as forcing in both the disaggregation and the assimilation. Synthetic coarse-scale observations are generated from the Monsoon ‘90 data by aggregating the Push Broom Microwave Radiometer (PBMR) pixels covering the eight meteorological and flux (METFLUX) stations and by averaging the meteorological measurements. The performance of the disaggregation/assimilation coupling scheme is then assessed in terms of surface soil moisture and latent heat flux predictions over the 19-day period of METFLUX measurements. It is found that the disaggregation improves the assimilation results, and vice versa, the assimilation of the disaggregated microwave soil moisture improves the spatial distribution of surface soil moisture at the observation time. These results are obtainable regardless of the spatial scale at which solar radiation, air temperature, wind speed, and air humidity are available within the microwave pixel and for an assimilation frequency varying from 1/1 day to 1/5 days.

International audience; Après avoir rappelé comment caractériser une sécheresse pour en évaluer ses conséquences sur le fonctionnement des arbres, l'analyse du bilan hydrique de l'année 2003 en Lorraine est présentée, pour des peuplements feuillus et résineux, et sur des sols à réserve utile moyenne ou forte. La sécheresse 2003 est replacée dans la chronologie des 54 dernières années, avec une comparaison détaillée avec l'année 1976. Le déficit hydrique de l'année 2003 apparaît comme le plus fort des 54 dernières années pour les feuillus. Pour les résineux, 2003 se classe au second rang pour les sols à réserve utile moyenne, et seulement en 5e rang pour les sols profonds. Les conséquences sur la physiologie des arbres sont présentées, et les potentiels hydriques atteints par les arbres en 2003 sont discutés. Cet article compare en particulier un large éventail d'espèces autochtones ou introduites en termes de stratégies de réponses à la sécheresse édaphique (vulnérabilité et risque de cavitation, régulation stomatique, développement du système racinaire).