Earth Sciences

Turnover and Availability of Soil Organic Carbon Under Different Mediterranean Land-Uses as Estimated by 13C Natural Abundance

S.C , L.Mantia, , L.VA , N.A , G.L , K.Y


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Summary\ud Soil organic matter (SOM) is an important factor in ecosystem stability and productivity. This is especially the\ud case for Mediterranean soils suffering from the impact of humans and degradation as well as harsh climatic\ud conditions. We used the carbon (C) exchange resulting from C3-C4 and C4-C3 vegetation change under field\ud conditions combined with incubations under controlled conditions to evaluate the turnover and availability of\ud soil organic C under different land-uses. The 40-year succession of Hyparrenia hirta L. (C4 photosynthesis)\ud after more than 85 years of olive (Olea europaea L.) tree (C3 photosynthesis) growth led to the exchange of\ud 54% of soil organic C from C3 to C4 forms. In contrast, 21 years of vine (Vitis vinifera L.) growing after H.\ud hirta decreased the organic C content to 57%. Considering this exchange and decrease as well as the periods\ud after the land-use changes, we calculated the mean residence time (MRT) of soil C of different ages. The\ud MRT of C under grassland dominated by H. hirta was about 19 years, but was 180 years under the vineyard.\ud The rates of C accumulation under the H. hirta grassland were about 0.36MgC ha−1 year−1. In contrast, the\ud rates of C losses after conversion from natural grassland to a vineyard were 1.8 times greater and amounted\ud to 0.65MgC ha−1 year−1. We conclude that changes of land use from natural Mediterranean grassland to a\ud vineyard lead to very large C losses that cannot be compensated for over the same periods

Categorizing chlordecone potential degradation products to explore their environmental fate

D.Patureau , P.Benoit , L.Mamy , R.Servien , Z.Li , E.Latrille , V.Rossard , F.Bessac , F.Martin-Laurent


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Chlordecone has been used extensively as an organochlorine insecticide but is nowadays banned and listed on annex A in The Stockholm Convention on Persistent Organic Pollutants. Although experimental evidences of biodegradation of this compound are scarce, several dechlorination products have been proposed by Dolfing et al. using Gibbs free energy calculations to explore different potential transformation routes. We here present the results of an in silico classification of chlordecone transformation products based on statistical analyses combining several environmental endpoints and structural molecular descriptors. Starting from the list of putative chlordecone TPs and considering available data on degradation routes of other organochlorine compounds, we used different clustering strategies to explore the potential environmental behaviour of putative chlordecone TPs from the knowledge on their molecular descriptors. The method offers the possibility to focus on TPs present in different classes and to infer their environmental fate. Thus, we have deduced some hypothetical trends for the environmental behaviour of TPs of chlordecone assuming that TPs, which were clustered away from chlordecone, would have different environmental fate and ecotoxicological impact compared to chlordecone. Our findings suggest that mono-and di-hydrochlordecone, which are TPs of chlordecone often found in contaminated soils, may have similar environmental behaviour in terms of persistence.

How do biodiversity patterns of river animals emerge from the distributions of common and rare species?

J.Cucherousset , R.Cereghino , F.Santoul , J.Figuerola


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We studied the patterns of commonness and rarity for one vertebrate and four freshwater insect taxa in southwestern France , and we analysed the relationships between the location of sites and the contribution of commonness and rarity to species richness within a large stream system. Richness patterns in fish and aquatic insects were related to the location of sites within the stream system. The number of common and rare fish species increased from up-to downstream areas as a result of downstream additions of species. The number of common insect species peaked in the intermediate section of the river continuum, whereas rarity increased with decreasing elevation. In all taxa, common species gave a closer approximation to overall patterns of species richness than did rare ones. The biodiversity patterns of river animals emerged from convergence in the distributions of common and rare species , or mostly from the distribution of common species. However, in fish, Ephemeroptera and Plecoptera, the rarer species became almost equally, or more strongly correlated with overall species richness when increasing information along the common-to-rare and rare-to-common sequences. These patterns suggested that rarer species show a similar or stronger affinity, on a species-for-species basis, for high richness areas than do the commoner species. These schemes have implications for biodiversity assessments, as studies using common species richness to target important areas for monitoring or conservation efforts within stream systems will not necessarily identify areas important for rare species, and vice versa.

Water and sanitation in the neighborhood of guet ndar-senegal cheikh diop

C.Diop


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The various political regimes that have succeeded Senegal have initiated different projects, programs, strategies and plans in several sectors including "Plan Senegal Emergent " which is the latest to place Senegal in ramps of the emergence or development. The results were more or less satisfactory. Therefore, it seems important, through this study, to mention an important part of water and sanitation in our human settlements: neighborhoods without adequate treatment, may further delay the long awaited emergence/development of our country. One of the major events in recent decades in Senegal is Guet Ndar, a neighborhood located in the Municipality of Saint-Louis in northern Senegal, is a perfect illustration with a high concentration of the population in urban areas consecutive high rate of natural increase. The physical constraints to the expansion of the district, it is densely populated over the years both in terms of habitat and population, reaching a population of more than 16,000 inhabitants on a 16. 9 hectares , making it one of the most densely populated areas of Senegal. In these conditions, access to water and sanitation for that district of populations is complicated by the current lack of planned and operational solution. The town of Saint-Louis, in this context of the policy in support of the people's problems, is considering a number of projects to improve the environment and living conditions of the population. Guet Ndar is characterized by: narrow streets, promiscuity, lack or weakness of networks , amenities and the lack of property titles. Eventually, the living conditions in these areas will be significantly improved with the resolution of the problem of water and sanitation, which are the necessities. Yet the challenge of the emergence and sustainable development of Guet Ndar will be difficult to meet if the area is not properly sanitized. It constitutes a real bottleneck for the City of St. Louis. In this respect, in a context where the emergence is brandished as, lack of sanitation should not find its place in municipalities and cities of Senegal leading to be the locomotive of growth. This study provides some possible solutions to create better living conditions for the residents of Guet Ndar and could assist local authorities in their missions.

Population differentiation or species formation across the indian and the pacific oceans? an example from the brooding marine hydrozoan macrorhynchia phoenicea

M.Pratlong , B.Postaire , P.Gelin , J.Henrich , H.Magalon


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Assessing population connectivity is necessary to construct effective marine protected areas. This connectivity depends, among other parameters, inherently on species dispersal capacities. Isolation by distance is one of the main modes of differentiation in marine species, above all in species presenting low dispersal abilities. This study reports the genetic structuring in the tropical hydrozoan Macrorhynchia phoenicea , a brooding species, from 30 sampling sites in the Western Indian Ocean and the Tropical Southwestern Pacific, using 15 microsatellite loci. At the local scale, genet dispersal relied on asexual propagation at short distance, which was not found at larger scales. Considering one representative per clone, significant positive F-IS values were found within almost all sites. Gene flow was extremely low at all spatial scales, among sites within islands and among islands , with significant pairwise F-ST values. A general pattern of IBD was found at the Indo-Pacific scale, but also within ecoregions in the Western Indian Ocean province. Clustering and network analyses identified each island as a potential independent population, while analysis of molecular variance indicated that population genetic differentiation was significant at small and intermediate spatial scales. As shown by this species, a brooding life cycle might be corollary of the high population differentiation found in some coastal marine species, thwarting regular dispersal at distances more than a few kilometers and probably leading to high cryptic diversity, each island housing independent evolutionary lineages.

Identification of ecological thresholds from variations in phytoplankton communities among lakes: contribution to the definition of environmental standards

V.Roubeix , P.Danis , T.Feret , J.Baudoin


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In aquatic ecosystems, the identification of ecological thresholds may be useful for managers as it can help to diagnose ecosystem health and to identify key levers to enable the success of preservation and restoration measures. A recent statistical method, gradient forest, based on random forests, was used to detect thresholds of phytoplankton community change in lakes along different environmental gradients. It performs exploratory analyses of multivariate biological and environmental data to estimate the location and importance of community thresholds along gradients. The method was applied to a data set of 224 French lakes which were characterized by 29 environmental variables and the mean abundances of 196 phytoplankton species. Results showed the high importance of geographic variables for the prediction of species abundances at the scale of the study. A second analysis was performed on a subset of lakes defined by geographic thresholds and presenting a higher biological homogeneity. Community thresholds were identified for the most important physico-chemical variables including water transparency, total phosphorus, ammonia, nitrates, and dissolved organic carbon. Gradient forest appeared as a powerful method at a first exploratory step, to detect ecological thresholds at large spatial scale. The thresholds that were identified here must be reinforced by the separate analysis of other aquatic communities and may be used then to set protective environmental standards after consideration of natural variability among lakes.

Toward community standards in the quest for orthologs

M.Martin , B.Linard , T.Gabaldon , E.Sonnhammer , C.Dessimoz , D.Roos , J.Herrero , A.Valencia , A.Altenhoff , R.Apweiler , M.Ashburner , J.Blake , B.Boeckmann , A.Bridge , E.Bruford , M.Cherry , M.Conte , D.Dannie , R.Datta , B.Domelevo , I.Ebersberger , M.Galperin , J.Joseph , T.Koestler , E.Kriventseva , O.Lecompte , J.Leunissen , S.Lewis , M.Livstone , H.Lu , R.Mazumder , D.Messina , V.Miele , M.Muffato , G.Perriere , M.Punta , M.Rouard , T.Schmitt , F.Schreiber , A.Silva , K.Sjolander , N.Skunca , E.Stanley , R.Szklarczyk , P.Thomas , I.Uchiyama , M.Van , K.Vandepoele , A.Vilella , A.Yates , E.Zdobnov


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The identification of orthologsgenes pairs descended from a common ancestor through speciation, rather than duplication has emerged as an essential component of many bioinformatics applications, ranging from the annotation of new genomes to experimental target prioritization. Yet, the development and application of orthology inference methods is hampered by the lack of consensus on source proteomes, file formats and benchmarks. The second 'Quest for Orthologs' meeting brought together stakeholders from various communities to address these challenges. We report on achievements and outcomes of this meeting, focusing on topics of particular relevance to the research community at large. The Quest for Orthologs consortium is an open community that welcomes contributions from all researchers interested in orthology research and applications.
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