Influencia de la concentración de nutrientes y la herviboría sobre la estructura y la función de una comunidad algal

Un mismo conjunto de algas puede generar diferentes ensamblados finales estables en función del ambiente (lago, laguna, etc.) en que se desarrollen. En este trabajo se pretende averiguar qué mecanismos están afectando simultáneamente al conjunto de especies para que se produzca una selección de ellas apropiada a cada ambiente acuático, y cómo la variabilidad de la respuesta se ve reflejada en la estructura y función de la comunidad (biomasa total, fotosíntesis y respiración). Se ha ensayado la formación de una comunidad algal a partir de la disposición simultánea de 8 especies de algas cosmopolitas de agua dulce de morfología bien distinta (Cosmarium contractum, Cryptomonas ovata, Euglena gracilis, Limnothrix redekei, Monoraphidium contortum, Pediastrum tetras, Planktothrix agardhii y Scenedesmus acutus) en distintos tipos de medio de cultivo. Los tratamientos han sido cuatro: mayor y menor concentración de nutrientes (N y P) y presencia o no de Daphnia magna, Keratella cochlearis y Brachionus calicyflorus. Se han ensayado, además, sistemas de competencia entre algas y se ha averiguado la viabilidad de estas especies como inóculos tras un período de senescencia. La presencia de herbívoros (depredación) y la concentración de nutrientes (competencia), son los mecanismos que aislada o sin enérgicamente afectan al ensamblado de microalgas determinando diferentes estados alternativos desde un mismo conjunto de microalgas. Pero el efecto de estos mecanismos es a su vez diferente en función de las propiedades de las microalgas implicadas como son su tamaño, su tasa de crecimiento y la viabilidad de cada especie como inóculo. La presencia de herbívoros y la oligotrofia reducen la biomasa de productores primarios pero aumentan la diversidad relajando la competencia y aumentando la incertidumbre sobre el final alcanzado. Se demuestra además que las variaciones en la estructura de la comunidad se reflejan directamente en su función, afectando en última instancia a la producción primaria y la respiración.The same pool of algae can generate different final stable assemblages depending on the environment (lake, lagoon, etc.) where they develop. In this work we attempt to ascertain the mechanisms that simultaneously affect the species to appropriately select them for each aquatic environment, and how the variability in the response is reflected in the community structure and function (total biomass, photosynthesis and respiration). An algal community has been formed assembling 8 species of freshwater cosmopolite algae which have quite different morphologies (Cosmarium contractum, Cryptomonas ovata, Euglena gracilis, Limnothrix redekei, Monoraphidium contortum, Pediastrum tetras, Planktothrix agardhii and Scenedesmus acutus) using several kinds of culture media. The treatments were four: low and high nutrient concentrations (N and P) and presence and absence of Daphnia magna, Keratella cochlearis, and Brachionus calicyflorus. The competition between pairs of algae has been studied and also the viability of the species as inoculum after a senescence period. The presence of herbivores (predation) and the nutrient concentration (competition) are the mechanisms that by themselves or sinergically affect the microalgae assemblages originating different alternative states from the same pool of species. But the effect of these mechanisms is different depending on the algal properties such as size, growth rate, and viability as inoculum. The presence of herbivores and the oligotrophic conditions reduce the primary producers' biomass but increase diversity due to relaxation of competition and increase the uncertainty of final states. It is also shown that the variations in the community structure are directly reflected on the function, affecting primary production and respiration

Identification of the meiotic toolkit in diatoms and exploration of meiosis-specific SPO11 and RAD51 homologs in the sexual species Pseudo-nitzschia multistriata and Seminavis robusta (vol 16, 930, 2015)

Following the publication of this article [1], the authors reported that the link to Additionalfile11 linked to the wrong set of data. The correct supplementary data is provided in this Correction article (Additionalfile11)

Biases in the spatial estimation of pesticide loss to groundwater

Prediction of pesticide fate in soils is highly sensitive to parameters describing sorption and degradation processes, namely the Koc partioning coefficient between the soil solution and organic carbon fraction and the half-life DT50 for degradation. This paper explores the impact of getting Koc and DT50 values either from databases or from site-specific measurements on the predicted fate of atrazine, isoproturon and metamitron on the catchment scale. Pesticide fate on the scale of the Bruyères-et-Montbérault catchment, France, was predicted using the SEAMS software that couples a one-dimensional local-scale model of pesticide fate to a geographic information system. The results show that the use of database average values for Koc and DT50 underestimates the average risk of pesticide leaching calculated from site-specific Koc and DT50 values, whereas maximised risk scenarios based on extreme Koc and DT50 values may be overestimated when using database values. Whenever available, site-specific data should be preferred to limit bias in pesticide leaching risk assessments on the catchment scale

Igneous petrology of the Ochiai-Hokubo ultramafic complex,the Sangun zone,western Japan:a preliminary report

Overview of phylogenetic distribution of core meiotic proteins among eukaryotes [11, 72, 133–142]. (DOC 235 kb

A sex-inducing pheromone triggers cell cycle arrest and mate attraction in the diatom Seminavis robusta

Although sexual reproduction is believed to play a major role in the high diversification rates and species richness of diatoms, a mechanistic understanding of diatom life cycle control is virtually lacking. Diatom sexual signalling is controlled by a complex, yet largely unknown, pheromone system. Here, a sex-inducing pheromone (SIP(+)) of the benthic pennate diatom Seminavis robusta was identified by comparative metabolomics, subsequently purified, and physicochemically characterized. Transcriptome analysis revealed that SIP(+) triggers the switch from mitosis-to-meiosis in the opposing mating type, coupled with the transcriptional induction of proline biosynthesis genes, and the release of the proline-derived attraction pheromone. The induction of cell cycle arrest by a pheromone, chemically distinct from the one used to attract the opposite mating type, highlights the existence of a sophisticated mechanism to increase chances of mate finding, while keeping the metabolic losses associated with the release of an attraction pheromone to a minimum

Estimation de la variabilité spatiale des propriétés hydrodynamiques des sols à l'échelle de la parcelle

absen

A sex-inducing pheromone triggers cell cycle arrest and mate attraction in the diatom Seminavis robusta

Although sexual reproduction is believed to play a major role in the high diversification rates and species richness of diatoms, a mechanistic understanding of diatom life cycle control is virtually lacking. Diatom sexual signalling is controlled by a complex, yet largely unknown, pheromone system. Here, a sex-inducing pheromone (SIP(+)) of the benthic pennate diatom Seminavis robusta was identified by comparative metabolomics, subsequently purified, and physicochemically characterized. Transcriptome analysis revealed that SIP(+) triggers the switch from mitosis-to-meiosis in the opposing mating type, coupled with the transcriptional induction of proline biosynthesis genes, and the release of the proline-derived attraction pheromone. The induction of cell cycle arrest by a pheromone, chemically distinct from the one used to attract the opposite mating type, highlights the existence of a sophisticated mechanism to increase chances of mate finding, while keeping the metabolic losses associated with the release of an attraction pheromone to a minimum

Caractérisation du risque de contamination de la nappe de Beauce par les pesticides : Elucidation des mécanismes du transport préférentiel et approche spatiale du risque à l’échelle du bassin hydrologique. Projet de recherche ESHEL « Evaluation et réduction des risques liés à l’utilisation des pesticides »

This report presents the results of the research project ESHEL "Characterization of the risk of contamination of Beauce groundwater by pesticides". The ESHEL project had two main objectives: understanding the mechanisms of pesticide fate in the soils of the Beauce region, and developing a methodological basis for the spatialization of the risk assessment of Beauce groundwater contamination by pesticides. The research considers two spatial scales: the agricultural field, and the hydrological catchment. A detailed pedological study of the selected agricultural field, together with a geophysical prospection of soils, highlighted the strong heterogeneity of the soil cover, in relation to the complexity of the spatial relationships between the various geological materials composing the soil substrate. The strong heterogeneity of the soil cover reflects also in the high spatial variability of the soil water and solute transport properties. Study of the degradation of isoproturon, a cereal herbicide found in the Beauce groundwater, showed that the rate of degradation was highly dependent on soil water content and that isoproturon was highly persistent in subsoil horizons. Mobile /immobile water partitioning was found to play a significant role in solute transport. Isoproturon transp-ort modelling confirmed the importance of this preferential flow process that could explain the contamination levels observed in the Beauce groundwater. The spatial variability of isoproturon fate parameters atthe ouarville catchment scale had characteristics similar to those measured at the field scale. This variability is essentially local (at the metric scale) and does not allow for a geographical definition of risk (i.e. based on soil zoning) at the catchment scale. The spatial variability of isoproturon fate parameters could not be related to the spatial variability of soil characteristics, except the classical relationship between the adsorption coefficient and the organic matter content, which could be spatialised at catchment scale by teledetection. The underdetermined nature of all the other pesticide fate parameters will imply the use of a stochastic risk assessment of the Beauce groundwater contamination by pesticides.Ce rapport présente les principaux résultats du projet de recherches ESHEL "Caractérisation du risque de contamination de la nappe de Beauce par les pesticides". Le projet ESHEL vise deux objectifs : la compréhension des mécanismes de dissipation des pesticides dans les sols de Beauce, et le développement de bases méthodologiques pour la spatialisation de l'évaluation du risque de contamination des eaux souterraines de Beauce par les pesticides. Le travail de recherche est mené à deux échelons spatiaux : celui de la parcelle agricole, et celui du bassin hydrologique. Une étude pédologique approfondie de la parcelle, aidée d'une prospection géophysique des sols, a mis en evidence une forte hétérogénéité des sols, liée à la complexité des relations spatiales entre matériaux superficiels. Cetté hétérogénéité des sols se traduit par une forte variabilité spatiale des propriétés hydriques et de transport des solutés. L'étude de la dégradation de l'isoproturon, herbicide utilisé sur céréales d'hiver et retrouvé parmi les contaminants de la nappe de Beauce, montre une forte dépendance de la vitesse de dégradation vis-à-vis de l'état hydrique du sol et une persistance élevée de l'isoproturon dans les horizons de subsurface. L'existence d'un mode de transport préférentiel des solutés dans les sols de Beauce, impliquant la partition de 1'eau du sol entre une fraction mobile et une autre immobile, a pu être démontrée. La modélisation du transfert de l'isoproturon dans ces sols confirme l'importance de ce transport préférentiel, qui peut expliquer les niveaux de contamination observés en nappe de Beauce. La variabilité spatiale des propriétés de dissipation de l'isoproturon à l'échelle du bassin hydrologique de Ouarville présente les mêmes caractéristiques que celle évaluée à l'échelle intra_parcellaire. Il s'agit essentiellement d'une variabilité à l'échelle locale (métrique) qui ne permet pas d'approche géographique du risque (i.e basée sur un zonage préalable du sol) à l'échelle du bassin hydrologique. La variabilité spatiale des propriétés de dissipation de l'isoproturon n'a pas pu être reliée à celle des caractéristiques de constitution des sols hormis la relation classique entre coefficient d'adsorption et teneur en matière organique, cette dernière pouvant être spatialisée à l'échelle du bassin par télédétection. Le caractère indéterminé de la variabilité spatiale des nombreux autres paramètres intervenant dans la dissipation des pesticides implique donc l'utilisation d'une approche stochastique pour l'évaluation du risque de contamination de la nappe de Beauce

ECoPESt - Evaluation et comparaison des performances environnementales de systèmes de culture innovants conçus pour réduire l’usage des pesticides : lien entre pratiques, pressions et impacts. Rapport final, 130 pp.

Rapport final, 130 p