96 research outputs found
Fungi of French Guiana gathered in a taxonomic, environmental and molecular dataset
International audienceIn Amazonia, the knowledge about Fungi remains patchy and biased towards accessible sites. This is particularly the case in French Guiana where the existing collections have been confined to few coastal localities. Here, we aimed at filling the gaps of knowledge in indersampled areas of this region, particularly focusing on the Basidiomycota. From 2011, we comprehensively collected fruiting-bodies with a stratified and reproducible sampling scheme in 126 plots. Sites of sampling reflected the main forest habitats of French Guiana in terms of soil fertility and topography. The dataset of 5219 specimens gathers 245 genera belonging to 75 families, 642 specimens are barcoded. The dataset is not a checklist as only 27% of the specimens are identified at the species level but 96% are identified at the genus level. We found an extraordinary diversity distributed across forest habitats. The dataset is an unprecedented and original collection of Basidiomycota for the region, making specimens available for taxonomists and ecologists. The database is publicly available in the GBIF repository (https://doi.org/10.15468/ymvlrp)
Coordinated community structure among trees, fungi and invertebrate groups in Amazonian rainforests
Little is known regarding how trophic interactions shape community assembly in tropical forests. Here we assess multi-taxonomic community assembly rules using a rare standardized coordinated inventory comprising exhaustive surveys of five highly-diverse taxonomic groups exerting key ecological functions: trees, fungi, earthworms, ants and spiders. We sampled 36 1.9-ha plots from four remote locations in French Guiana including precise soil measurements, and we tested whether species turnover was coordinated among groups across geographic and edaphic gradients. All species group pairs exhibited significant compositional associations that were independent from soil conditions. For some of the pairs, associations were also partly explained by soil properties, especially soil phosphorus availability. Our study provides evidence for coordinated turnover among taxonomic groups beyond simple relationships with environmental factors, thereby refining our understanding regarding the nature of interactions occurring among these ecologically important groups
A costâbenefit analysis of acclimation to low irradiance in tropical rainforest tree seedlings: leaf life span and payback time for leaf deployment
The maintenance in the long run of a positive carbon balance under very low irradiance is a prerequisite for survival of tree seedlings below the canopy or in small gaps in a tropical rainforest. To provide a quantitative basis for this assumption, experiments were carried out to determine whether construction cost (CC) and payback time for leaves and support structures, as well as leaf life span (i) differ among species and (ii) display an irradiance-elicited plasticity. Experiments were also conducted to determine whether leaf life span correlates to CC and payback time and is close to the optimal longevity derived from an optimization model. Saplings from 13 tropical tree species were grown under three levels of irradiance. Specific-CC was computed, as well as CC scaled to leaf area at the metamer level. Photosynthesis was recorded over the leaf life span. Payback time was derived from CC and a simple photosynthesis model. Specific-CC displayed only little interspecific variability and irradiance-elicited plasticity, in contrast to CC scaled to leaf area. Leaf life span ranged from 4 months to >26 months among species, and was longest in seedlings grown under lowest irradiance. It was always much longer than payback time, even under the lowest irradiance. Leaves were shed when their photosynthesis had reached very low values, in contrast to what was predicted by an optimality model. The species ranking for the different traits was stable across irradiance treatments. The two pioneer species always displayed the smallest CC, leaf life span, and payback time. All species displayed a similar large irradiance-elicited plasticity
Ecologie en milieu tropical: Cheminer de l'Ecologie Microbienne à l'Ecologie des Communautés ou comment étudier la Fonge de Guyane
Impacts de perturbations liées à l'orpaillage sur l'évolution des communautés et fonctionnalités microbiennes d'un sol
Ce travail s'intĂšgre dans des problĂ©matiques actuelles cherchant Ă caractĂ©riser l'impact des activitĂ©s humaines sur les Ă©cosystĂšmes. Le sol, et en particulier, les communautĂ©s microbiennes fonctionnelles, abordĂ©es simultanĂ©ment en tant qu'actrices des bio-transformations et en tant que biodescriptrices de l'Ă©tat fonctionnel du systĂšme, ont Ă©tĂ© l'objet d'Ă©tude de ce travail qui s'est articulĂ© autour de deux questions majeures : - Il s'agissait de savoir si des communautĂ©s microbiennes du sol exerçant deux fonctions considĂ©rĂ©es comme reprĂ©sentatives du fonctionnement global (respiration et dĂ©nitrification) pouvaient, sur un sol minier revĂ©gĂ©talisĂ©, rĂ©cupĂ©rer des performances similaires Ă celles d'un sol de forĂȘt. Cette Ă©tude menĂ©e in situ en forĂȘt guyanaise, sur une zone miniĂšre aurifĂšre rĂ©habilitĂ©e a montrĂ© une certaine rĂ©versibilitĂ© des activitĂ©s microbiennes des sols observĂ©es lors d'une telle perturbation. En effet, malgrĂ© une texture extrĂȘmement hĂ©tĂ©rogĂšne, le sol, une fois replantĂ© en lĂ©gumineuses, retrouve un fonctionnement similaire Ă celui de la forĂȘt. Les biodescripteurs utilisĂ©s (ratio respiration rĂ©elle/potentielle et dĂ©nitrification/ respiration) ont permis de caractĂ©rise les diffĂ©rences de fonctionnement le long de la sĂ©quence de reforestation. Ils se sont rĂ©vĂ©lĂ©s pertinents pour dĂ©crire les sols en cours de reconstruction et de stabilisation. La valeur de ratio respiration rĂ©elle/potentielle dans un sol de forĂȘt pourrait ĂȘtre considĂ©rĂ©e comme un indicateur de stabilitĂ©, spĂ©cifique du site et caractĂ©risant l'Ă©tat d'Ă©quilibre Ă atteindre. Enfin, en permettant de dĂ©tecter des variations qualitatives de la matiĂšre organique des sols qui n'avaient pas Ă©tĂ© mises en Ă©vidence par le C/N, l'utilisation de l'analyse NIRS associĂ©e aux analyses d'activitĂ© enzymatiques microbiennes a permis de vĂ©rifier que la dynamique de reconstruction des sols avait Ă©tĂ© accĂ©lĂ©rĂ©e par la plantation. La seconde question majeure de ce travail Ă©tait: quel est l'impact d'une premiĂšre perturbation sur (i) la structure et le fonctionnement microbien du sol et sur (ii) la capacitĂ© du sol Ă rĂ©sister Ă une seconde perturbation ? Pour y rĂ©pondre, une expĂ©rience in vitro menĂ©e sur des microcosmes de sol subissant deux types de perturbations (mercure et chaleur) a Ă©tĂ© Ă©laborĂ©e. Les rĂ©sultats ont montrĂ© que la respiration et la dĂ©nitrification rĂ©pondaient d'une maniĂšre diffĂ©rente avec, parallĂšlement, des modifications durables de la structure des communautĂ©s. La diversitĂ© gĂ©nĂ©tique des communautĂ©s microbiennes du sol a Ă©tĂ© Ă©valuĂ©e Ă l'aide d'une ARISA aprĂšs une extraction directe de l'ADN du sol. Au prĂ©alable, une Ă©tude mĂ©thodologique avait permis d'Ă©valuer les biais engendrĂ©s par diffĂ©rentes mĂ©thodes d'extraction de l'ADN et donc de choisir l'extraction directe de l'ADN. Le maintien, dans certains cas, des fonctions aprĂšs perturbation (respiration inchangĂ©e aprĂšs l'application du mercure; dĂ©nitrification importante malgrĂ© le choc de tempĂ©rature) suggĂšre une redondance fonctionnelle importante parmi les communautĂ©s microbiennes du sol. Pourtant l'application de mercure, semble induire une vulnĂ©rabilitĂ© plus importante des sols face Ă une autre perturbation (chaleur). Cette vulnĂ©rabilitĂ© se traduit par une modification du fonctionnement de la communautĂ© hĂ©tĂ©rotrophe du sol (respiration potentielle) mais aussi par la quasi disparition de la dĂ©nitrification dans ces sols. Cela peut rĂ©vĂ©ler une diminution de la stabilitĂ© des sols qui pourrait ĂȘtre due Ă la modification de diversitĂ© mise en Ă©vidence dĂšs le dĂ©but de l'expĂ©rience. L'ensemble des rĂ©sultats posĂ©s au cours de ce travail doit ĂȘtre analysĂ© au regard des concepts de maintien des cycles biogĂ©ochimiques et d'ingĂ©nierie Ă©cologique. Les expĂ©riences menĂ©es aussi bien sur la Mine Boulanger qu'en microcosmes ont permis de mettre en exergue la nĂ©cessitĂ© de dĂ©finir des biodescripteurs pertinents, capables de dĂ©crire l'Ă©tat du systĂšme mais aussi sa probable Ă©volution. Les indicateurs microbiens fonctionnels utilisĂ©s semblent remplir cette fonction en Ă©tant capables de rendre compte de la "performance" du systĂšme, de sa possibilitĂ© Ă ĂȘtre rĂ©habilitĂ© ou Ă rĂ©sister aux perturbation
Interactive effects of C, N and P fertilization on soil microbial community structure and function in an Amazonian rain forest
International audience1. Resource control over abundance, structure and functional diversity of soil microbial communities is a key determinant of soil processes and related ecosystem functioning. Copiotrophic organisms tend to be found in environments which are rich in nutrients, particularly carbon, in contrast to oligotrophs, which survive in much lower carbon concentrations. We hypothesized that microbial biomass, activity and community structure in nutrient-poor soils of an Amazonian rain forest are limited by multiple elements in interaction. We tested this hypothesis with a fertilization experiment by adding C (as cellulose), N (as urea) and P (as phosphate) in all possible combinations to a total of 40 plots of an undisturbed tropical forest in French Guiana. After 2years of fertilization, we measured a 47% higher biomass, a 21% increase in substrate-induced respiration rate and a 5-fold higher rate of decomposition of cellulose paper discs of soil microbial communities that grew in P-fertilized plots compared to plots without P fertilization. These responses were amplified with a simultaneous C fertilization suggesting P and C colimitation of soil micro-organisms at our study site. Moreover, P fertilization modified microbial community structure (PLFAs) to a more copiotrophic bacterial community indicated by a significant decrease in the Gram-positive:Gram-negative ratio. The Fungi:Bacteria ratio increased in N fertilized plots, suggesting that fungi are relatively more limited by N than bacteria. Changes in microbial community structure did not affect rates of general processes such as glucose mineralization and cellulose paper decomposition. In contrast, community level physiological profiles under P fertilization combined with either C or N fertilization or both differed strongly from all other treatments, indicating functionally different microbial communities. While P appears to be the most critical from the three major elements we manipulated, the strongest effects were observed in combination with either supplementary C or N addition in support of multiple element control on soil microbial functioning and community structure. We conclude that the soil microbial community in the studied tropical rain forest and the processes it drives is finely tuned by the relative availability in C, N and P. Any shifts in the relative abundance of these key elements may affect spatial and temporal heterogeneity in microbial community structure, their associated functions and the dynamics of C and nutrients in tropical ecosystems
Nutrient and Carbon Limitation on Decomposition in an Amazonian Moist Forest
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
C, N and P fertilization in an Amazonian rainforest supports stoichiometric dissimilarity as a driver of litter diversity effects on decomposition
Plant leaf litter generally decomposes faster as a group of different species than when individual species decompose alone, but underlyingmechanisms of these diversity effects remain poorly understood. Because resource C : N: P stoichiometry (i.e. the ratios of these key elements) exhibits strong control on consumers, we supposed that stoichiometric dissimilarity of litter mixtures (i.e. the divergence in C : N: P ratios among species) improves resource complementarity to decomposers leading to faster mixture decomposition. We tested this hypothesis with: (i) a wide range of leaf litter mixtures of neotropical tree species varying in C : N: P dissimilarity, and (ii) a nutrient addition experiment (C, N and P) to create stoichiometric similarity. Litter mixtures decomposed in the field using two different types of litterbags allowing or preventing access to soil fauna. Litter mixture mass loss was higher than expected from species decomposing singly, especially in presence of soil fauna. With fauna, synergistic litter mixture effects increased with increasing stoichiometric dissimilarity of litter mixtures and this positive relationship disappeared with fertilizer addition. Our results indicate that litter stoichiometric dissimilarity drives mixture effects via the nutritional requirements of soil fauna. Incorporating ecological stoichiometry in biodiversity research allows refinement of the underlying mechanisms of how changing biodiversity affects ecosystem functioning
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