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Barantal, S., Schimann, H., Fromin, N., & Hattenschwiler, S. (2012). Nutrient and Carbon Limitation on Decomposition in an Amazonian Moist Forest. Ecosystems, 15(7), 1039–1052.
Abstract: Tropical forests determine global biogeochemical cycles to a large extent, but control factors for key ecosystem processes such as decomposition remain poorly understood. With a full-factorial C (cellulose), N (urea), and P (phosphate) fertilization experiment, we tested the relative importance of C and nutrient limitation on litter decomposition in a mature lowland moist forest of French Guiana. Despite the previously demonstrated litter C quality control over decomposition and the very low soil P content (0. 1 mg g -1 of soil) at our study site, fertilization with C or P alone did not increase the decomposition of a wide range of litter types (N:P ratios between 20 and 80). Nitrogen fertilization alone also had no effect on decomposition. However, the combined fertilization with N and P resulted in up to 33. 5% more initial litter mass lost, with an increasing effect with wider litter N:P ratios. Soil fauna strongly stimulated litter mass loss and enhanced nutrient fertilization effects. Moreover, nutrient effects on decomposition increased with additional C fertilization in the presence of fauna. Our results suggest that increased N availability is required for a positive P effect on decomposition in the studied P-poor tropical forest. Further stimulation of decomposition by C amendment through priming indicates energy limitation of decomposers that is co-determined by nutrient availability. The demonstrated intricate control of the key resources C, N, and P on decomposition calls for an intensified research effort on multiple resource limitation on key processes in tropical forests and how they change under multiple human impacts. © 2012 Springer Science+Business Media, LLC.
Keywords: energy limitation; labile carbon; litter quality; nitrogen; phosphorus; priming effect; soil fauna; tropical forest
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Rey, O., Estoup, A., Vonshak, M., Loiseau, A., Blanchet, S., Calcaterra, L., et al. (2012). Where do adaptive shifts occur during invasion? A multidisciplinary approach to unravelling cold adaptation in a tropical ant species invading the Mediterranean area. Ecol. Lett., 15(11), 1266–1275.
Abstract: Evolution may improve the invasiveness of populations, but it often remains unclear whether key adaptation events occur after introduction into the recipient habitat (i.e. post-introduction adaptation scenario), or before introduction within the native range (i.e. prior-adaptation scenario) or at a primary site of invasion (i.e. bridgehead scenario). We used a multidisciplinary approach to determine which of these three scenarios underlies the invasion of the tropical ant Wasmannia auropunctata in a Mediterranean region (i.e. Israel). Species distribution models (SDM), phylogeographical analyses at a broad geographical scale and laboratory experiments on appropriate native and invasive populations indicated that Israeli populations followed an invasion scenario in which adaptation to cold occurred at the southern limit of the native range before dispersal to Israel. We discuss the usefulness of combining SDM, genetic and experimental approaches for unambiguous determination of eco-evolutionary invasion scenarios. © 2012 Blackwell Publishing Ltd/CNRS.
Keywords: Adaptation; Biological invasion; Climatic niche shift; Cold temperature; Mediterranean zone; Wasmannia auropunctata
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Brousseau, L., Tinaut, A., Duret, C., Lang, T., Garnier-Gere, P., & Scotti, I. (2014). High-throughput transcriptome sequencing and preliminary functional analysis in four Neotropical tree species. BMC Genomics, 15(238), 1–13.
Abstract: Background: The Amazonian rainforest is predicted to suffer from ongoing environmental changes. Despite the need to evaluate the impact of such changes on tree genetic diversity, we almost entirely lack genomic resources. Results: In this study, we analysed the transcriptome of four tropical tree species (Carapa guianensis, Eperua falcata, Symphonia globulifera and Virola michelii) with contrasting ecological features, belonging to four widespread botanical families (respectively Meliaceae, Fabaceae, Clusiaceae and Myristicaceae). We sequenced cDNA libraries from three organs (leaves, stems, and roots) using 454 pyrosequencing. We have developed an R and bioperl-based bioinformatic procedure for de novo assembly, gene functional annotation and marker discovery. Mismatch identification takes into account single-base quality values as well as the likelihood of false variants as a function of contig depth and number of sequenced chromosomes. Between 17103 (for Symphonia globulifera) and 23390 (for Eperua falcata) contigs were assembled. Organs varied in the numbers of unigenes they apparently express, with higher number in roots. Patterns of gene expression were similar across species, with metabolism of aromatic compounds standing out as an overrepresented gene function. Transcripts corresponding to several gene functions were found to be over- or underrepresented in each organ. We identified between 4434 (for Symphonia globulifera) and 9076 (for Virola surinamensis) well-supported mismatches. The resulting overall mismatch density was comprised between 0.89 (S. globulifera) and 1.05 (V. surinamensis) mismatches/100 bp in variation-containing contigs.Conclusion: The relative representation of gene functions in the four transcriptomes suggests that secondary metabolism may be particularly important in tropical trees. The differential representation of transcripts among tissues suggests differential gene expression, which opens the way to functional studies in these non-model, ecologically important species. We found substantial amounts of mismatches in the four species. These newly identified putative variants are a first step towards acquiring much needed genomic resources for tropical tree species. © 2014 Brousseau et al.; licensee BioMed Central Ltd.
Keywords: 454-Pyrosequencing; Polymorphism discovery; Tropical rainforest tree species
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Molina, L., Broquet, G., Imbach, P., Chevallier, F., Poulter, B., Bonal, D., et al. (2015). On the ability of a global atmospheric inversion to constrain variations of CO2 fluxes over Amazonia. Atmospheric Chemistry and Physics, 15(14), 8423–8438.
Abstract: The exchanges of carbon, water and energy between the atmosphere and the Amazon basin have global implications for the current and future climate. Here, the global atmospheric inversion system of the Monitoring of Atmospheric Composition and Climate (MACC) service is used to study the seasonal and interannual variations of biogenic CO<inf>2</inf> fluxes in Amazonia during the period 2002-2010. The system assimilated surface measurements of atmospheric CO<inf>2</inf> mole fractions made at more than 100 sites over the globe into an atmospheric transport model. The present study adds measurements from four surface stations located in tropical South America, a region poorly covered by CO<inf>2</inf> observations. The estimates of net ecosystem exchange (NEE) optimized by the inversion are compared to an independent estimate of NEE upscaled from eddy-covariance flux measurements in Amazonia. They are also qualitatively evaluated against reports on the seasonal and interannual variations of the land sink in South America from the scientific literature. We attempt at assessing the impact on NEE of the strong droughts in 2005 and 2010 (due to severe and longer-than-usual dry seasons) and the extreme rainfall conditions registered in 2009. The spatial variations of the seasonal and interannual variability of optimized NEE are also investigated. While the inversion supports the assumption of strong spatial heterogeneity of these variations, the results reveal critical limitations of the coarse-resolution transport model, the surface observation network in South America during the recent years and the present knowledge of modelling uncertainties in South America that prevent our inversion from capturing the seasonal patterns of fluxes across Amazonia. However, some patterns from the inversion seem consistent with the anomaly of moisture conditions in 2009. © Author(s) 2015.
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Aili, S. R., Touchard, A., Koh, J. M. S., Dejean, A., Orivel, J., Padula, M. P., et al. (2016). Comparisons of Protein and Peptide Complexity in Poneroid and Formicoid Ant Venoms. Journal of Proteome Research, 15(9), 3039–3054.
Abstract: Animal venom peptides are currently being developed as novel drugs and bioinsecticides. Because ants use venoms for defense and predation, venomous ants represent an untapped source of potential bioactive toxins. This study compared the protein and peptide components of the poneroid ants Neoponera commutata, Neoponera apicalis, and Odontomachus hastatus and the formicoid ants Ectatomma tuberculatum, Ectatomma brunneum, and Myrmecia gulosa. 1D and 2D PAGE revealed venom proteins in the mass range <10 to >250 kDa. NanoLC-ESI-QTOF MS/MS analysis of tryptic peptides revealed the presence of common venom proteins and also many undescribed proteins. RP-HPLC separation followed by MALDI-TOF MS of the venom peptides also revealed considerable heterogeneity. It was found that the venoms contained between 144 and 1032 peptides with 5-95% of peptides in the ranges 1-4 and 1-8 kDa for poneroid and formicoid ants, respectively. By employing the reducing MALDI matrix 1,5-diaminonapthalene, up to 28 disulfide-bonded peptides were also identified in each of the venoms. In particular, the mass range of peptides from poneroid ants is lower than peptides from other venoms, indicating possible novel structures and pharmacologies. These results indicate that ant venoms represent an enormous, untapped source of novel therapeutic and bioinsecticide leads. © 2016 American Chemical Society.
Keywords: ant venom; Hymenoptera; Lc-Maldi-Tof Ms; mass spectrometry; nanoLC-ESI-QTOF MS/MS; peptidome; proteomic analysis; toxin
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Schwalm, C. R., Williams, C. A., Schaefer, K., Arneth, A., Bonal, D., Buchmann, N., et al. (2010). Assimilation exceeds respiration sensitivity to drought: A FLUXNET synthesis. Glob. Change Biol., 16(2), 657–670.
Abstract: The intensification of the hydrological cycle, with an observed and modeled increase in drought incidence and severity, underscores the need to quantify drought effects on carbon cycling and the terrestrial sink. FLUXNET, a global network of eddy covariance towers, provides dense data streams of meteorological data, and through flux partitioning and gap filling algorithms, estimates of net ecosystem productivity (F-NEP), gross ecosystem productivity (P), and ecosystem respiration (R). We analyzed the functional relationship of these three carbon fluxes relative to evaporative fraction (EF), an index of drought and site water status, using monthly data records from 238 micrometeorological tower sites distributed globally across 11 biomes. The analysis was based on relative anomalies of both EF and carbon fluxes and focused on drought episodes by biome and climatic season. Globally P was approximate to 50% more sensitive to a drought event than R. Network-wide drought-induced decreases in carbon flux averaged -16.6 and -9.3 g C m-2 month-1 for P and R, i.e., drought events induced a net decline in the terrestrial sink. However, in evergreen forests and wetlands drought was coincident with an increase in P or R during parts of the growing season. The most robust relationships between carbon flux and EF occurred during climatic spring for F-NEP and in climatic summer for P and R. Upscaling flux sensitivities to a global map showed that spatial patterns for all three carbon fluxes were linked to the distribution of croplands. Agricultural areas exhibited the highest sensitivity whereas the tropical region had minimal sensitivity to drought. Combining gridded flux sensitivities with their uncertainties and the spatial grid of FLUXNET revealed that a more robust quantification of carbon flux response to drought requires additional towers in all biomes of Africa and Asia as well as in the cropland, shrubland, savannah, and wetland biomes globally.
Keywords: biome; carbon cycling; drought; eddy covariance; evaporative fraction; FLUXNET; synthesis
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Bandou, E., Lebailly, F., Muller, F., Dulormne, M., Toribio, A., Chabrol, J., et al. (2006). The ectomycorrhizal fungus Scleroderma bermudense alleviates salt stress in seagrape (Coccoloba uvifera L.) seedlings. Mycorrhiza, 16(8), 559–565.
Abstract: The purpose of this study was to test the capacity of the ectomycorrhizal (ECM) fungus, Scleroderma bermudense, to alleviate saline stress in seagrape (Coccoloba uvifera L.) seedlings. Plants were grown over a range (0, 200, 350 and 500 mM) of NaCl levels for 12 weeks, after 4 weeks of non-saline pre-treatment under greenhouse conditions. Growth and mineral nutrition of the seagrape seedlings were stimulated by S. bermudense regardless of salt stress. Although ECM colonization was reduced with increasing NaCl levels, ECM dependency of seagrape seedlings increased. Tissues of ECM plants had significantly increased concentrations of P and K but lower Na and Cl concentrations than those of non-ECM plants. Higher K concentrations in the leaves of ECM plants suggested a higher osmoregulating capacity of these plants. Moreover, the water status of ECM plants was improved despite their higher evaporative leaf surface. The results suggest that the reduction in Na and Cl uptake together with a concomitant increase in P and K absorption and a higher water status in ECM plants may be important salt-alleviating mechanisms for seagrape seedlings growing in saline soils.
Keywords: Coccoloba uvifera; ectomycorrhizal dependency; mineral uptake; salt stress; water status
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Rowland, L., Stahl, C., Bonal, D., Siebicke, L., Williams, M., & Meir, P. (2013). The Response of Tropical Rainforest Dead Wood Respiration to Seasonal Drought. Ecosystems, 16(7), 1294–1309.
Abstract: Coarse woody debris (CWD, dead wood sections ≥10 cm diameter) represents a large store of carbon in tropical forests; however, estimates of the flux of carbon from CWD in these forests remain poorly constrained. The objective of this study was to resolve the dry/wet season response of respiration in CWD (Rcwd), and investigate the importance of biotic and abiotic factors for predicting the seasonal change of Rcwd at the ecosystem level. This study presents a 4-month time series of Rcwd measurements conducted on 42 dead trees (26 species) at the Paracou Research Station in French Guiana. Rcwd measurements were repeated 13 times on each CWD sample from July to November 2011, spanning the transition from wet to dry season, and then from dry season to the following wet season. Seasonal drought caused monthly Rcwd to drop by 20.5 ± 5.1% over the wet-dry transition. Changes in woody tissue moisture content explained 41.9% of the measured seasonal variability in Rcwd, but 60% of the seasonal variability in mean forest Rcwd rates could be modelled using surface soil water content. We estimate that Rcwd is approximately 5% of annual ecosystem respiration (Reco) and that seasonal variations in Rcwd contribute appreciably to seasonal variations of Reco, and should be included in functional models simulating the response of tropical rainforest ecosystems to current and future climate. © 2013 Springer Science+Business Media New York.
Keywords: Amazon rainforest; coarse woody debris; respiration; seasonal drought; soil water content; woody moisture content
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Carrias, J. - F., Céréghino, R., Brouard, O., Pélozuelo, L., Dejean, A., Couté, A., et al. (2014). Two coexisting tank bromeliads host distinct algal communities on a tropical inselberg. Plant Biol., 16(5), 997–1004.
Abstract: The tank bromeliads Aechmea aquilega (Salisb.) and Catopsis berteroniana (Schultes f.) coexist on a sun-exposed Neotropical inselberg in French Guiana, where they permit conspicuous freshwater pools to form that differ in size, complexity and detritus content. We sampled the algal communities (both eukaryotic and cyanobacterial taxa, including colourless forms) inhabiting either A. aquilega (n = 31) or C. berteroniana (n = 30) and examined differences in community composition and biomass patterns in relation to several biotic and abiotic variables. Chlorella sp. and Bumilleriopsis sp. were the most common taxa and dominated the algal biomass in A. aquilega and C. berteroniana, respectively. Using a redundancy analysis, we found that water volume, habitat complexity and the density of phagotrophic protozoa and collector-gatherer invertebrates were the main factors explaining the distribution of the algal taxa among the samples. Hierarchical clustering procedures based on abundance and presence/absence data clearly segregated the samples according to bromeliad species, revealing that the algal communities in the smaller bromeliad species were not a subset of the communities found in the larger bromeliad species. We conclude that, even though two coexisting tank bromeliad populations create adjacent aquatic habitats, each population hosts a distinct algal community. Hence, bromeliad diversity is thought to promote the local diversity of freshwater algae in the Neotropics. © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands.
Keywords: Algae; Bromeliaceae; Inselberg; Neotropics; Phytotelmata; Aechmea; algae; Bromeliaceae; Bumilleriopsis; Catopsis berteroniana; Chlorella (unclassified Chlorophyceae); Chlorella (unclassified Trebouxiophyceae); Chlorella sp.; Cyanobacteria; Eukaryota; Invertebrata; Protozoa
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Stahl, C., Freycon, V., Fontaine, S., Dezecache, C., Ponchant, L., Picon-Cochard, C., et al. (2016). Soil carbon stocks after conversion of Amazonian tropical forest to grazed pasture: importance of deep soil layers. Regional Environmental Change, 16(7), 2059–2069.
Abstract: Recent studies suggest that carbon (C) is stored in the topsoil of pastures established after deforestation. However, little is known about the long-term capacity of tropical pastures to sequester C in different soil layers after deforestation. Deep soil layers are generally not taken into consideration or are underestimated when C storage is calculated. Here we show that in French Guiana, the C stored in the deep soil layers contributes significantly to C stocks down to a depth of 100 cm and that C is sequestered in recalcitrant soil organic matter in the soil below a depth of 20 cm. The contribution of the 50–100 cm soil layer increased from 22 to 31 % with the age of the pasture. We show that long-term C sequestration in C4 tropical pastures is linked to the development of C3 species (legumes and shrubs), which increase both inputs of N into the ecosystem and the C:N ratio of soil organic matter. The deep soil under old pastures contained more C3 carbon than the native forest. If C sequestration in the deep soil is taken into account, our results suggest that the soil C stock in pastures in Amazonia would be higher with sustainable pasture management, in particular by promoting the development of legumes already in place and by introducing new species.
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