Éditeur(s) : HAL CCSD Royal Society, The
Résumé : 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.
ISSN: 0962-8452

hal-01204222
https://hal.archives-ouvertes.fr/hal-01204222
DOI : 10.1098/rspb.2014.1682
PRODINRA : 289918

Résumé : During the years 1972-1993, kepone a persistent pesticide has been used in the banana fields of the French West Indies (Martinique and Guadeloupe) to content a weevil. A slow desorption of the molecule from soil induces its transfer to the sea through the rivers from leaching and erosion. This study intended to take stock on the contamination by kepone of the fishery species around the islands fifteen years after the kepone ban. Furthermore other chemical pollutants were sought in fish and shellfish around the Martinique island. The results confirmed persistence of marine fauna contamination by kepone, mainly in the alluvium areas in front of polluted rivers. They shown also that this contamination may spread more widely but with fast decreasing through the marine food webs. For the other pollutants sought, the results were in general lower than the statutory values. Within these substances, only mercury gave a signal close to the prescribed threshold for top predator samples. Finally, on the whole the observed systems appeared preserved from human chemical pollutants, apart from kepone.
Pendant les années 1972-1993 un pesticide persistant, la chlordécone, a été utilisé dans les bananeraies des Antilles françaises (Martinique et Guadeloupe) pour lutter contre un charançon. Une désorption lente de la molécule fixée dans les sols conduit à son transfert progressif dans les milieux aquatiques puis vers le domaine marin au gré du lessivage et de l'érosion des sols contaminés. La présente étude visait à faire le point sur la contamination de la faune halieutique côtière des Antilles françaises quinze ans après l'interdiction d'usage de la molécule. En parallèle, une recherche systématique d'autres polluants chimiques a été effectuée sur des poissons et des crustacés ainsi que dans des sédiments autour de la Martinique. Les résultats confirment la persistance d'une contamination de la faune par la chlordécone, particulièrement dans les zones alluvionnaires des cours d'eau contaminés. Ils montrent également que cette contamination diffuse plus largement en s'atténuant, à travers les réseaux trophiques marins. Parmi les autres substances recherchées, les résultats dans les espèces d'intérêt halieutique se situent en général sous les concentrations maximales admissibles fixées par la réglementation. Parmi ces molécules, seul le mercure donne un signal de contamination proche de ce seuil chez des grands prédateurs. Ce constat souligne l'état de préservation des milieux observés vis-à-vis de la contamination chimique environnementale, hormis bien évidemment le cas de la chlordécone.

Droits : 2010 Onema / Ifremer
http://archimer.ifremer.fr/doc/2009/rapport-6896.pdf
http://archimer.ifremer.fr/doc/00000/6896/

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
In the Caribbean, Pterocarpus officinalis swamp forest, a coastal freshwater wetland, has been locally transformed by human activities into Colocasia esculenta monoculture (under the swamp forest) or pasture (where deforestation has occurred). The aim of this study was to evaluate the impact of three land uses of this tropical wetland (swamp forest, C. esculenta monoculture and pasture) on soil abiotic and biological features. We hypothesized that increasing the level of ecosystem alteration by agricultural intensification would negatively impact soil chemical characteristics, soil fauna diversity and carbon mineralization. As expected, land use significantly affected soil characteristics and changes followed the increasing intensity of land use. The ‘undisturbed system’, that is swamp forest, was characterized by a large soil organic matter content, a high level of soil moisture, a small phosphorus content and a slightly lower pH. These characteristics were correlated with a small faunal abundance and diversity and slow carbon (C) mineralization. The ‘low disturbance system’, that is C. esculenta monoculture, was the closest to swamp forest characteristics and changes between the both systems principally concerned a very slight decrease in organic matter content and very small increase in C mineralization and Coleoptera diversity. By contrast, all parameters (soil chemical characteristics, C mineralization and faunal abundance and diversity) were impacted in the most intensive land-use, pasture. Our study confirmed that agricultural practices have an influence on soil fauna and C mineralization processes in wetlands. Moreover, our study suggested that a C. esculenta traditional agroecosystem under swamp forest cover could be considered as an ‘eco-friendly’ agricultural practice.
ISSN: 0266-0032

hal-01562423
https://hal.archives-ouvertes.fr/hal-01562423
DOI : 10.1111/sum.12273

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The importance of secondary tropical forests regarding the maintenance of soil fauna abundance and diversity is poorly known. The aims of this study were (1) to describe soil fauna abundance and diversity and (2) to assess the determinants of soil fauna abundance and diversity in two stands of a tropical semi-evergreen secondary forest. Soil macrofauna and microarthropod abundance and soil macrofauna diversity were described at two sites developed on different soils and with different site histories: (1) a natural secondary stand (natural forest) under two dominant tree species, Pisonia subcordata and Bursera simaruba, and (2) a planted secondary forest (planted forest) under three tree species, B. simaruba, Swietenia macrophylla, and Tabebuia heterophylla. The effects of both soil and main tree species' litter quality were assessed to explain soil fauna abundance and diversity. The abundance of soil macrofauna was significantly higher in the soil under the planted forest, and soil fauna communities were contrasted between the two sites. In the planted forest, a soil-dwelling macrofauna community developed (mainly consisting of the anecic earthworm Polypheretima elongata). In the natural forest, soil macrofauna and microarthropod communities were located at the soil surface. The effect of plant litter quality varied according to each dominant tree species and was superimposed to soil effect. The lowest macrofauna abundance was associated with B. simaruba in the natural forest. T. heterophylla supported a much greater macrofauna community than the two other tree species studied at the same soil, and it appears likely that this is due to the palatability of its leaves compared with the other trees (low lignin, tannins, soluble phenols).
ISSN: 0178-2762

hal-00495371
https://hal.archives-ouvertes.fr/hal-00495371
https://hal.archives-ouvertes.fr/hal-00495371/document
https://hal.archives-ouvertes.fr/hal-00495371/file/Loranger-Merciris_et_al._2007.pdf
DOI : 10.1007/s00374-007-0199-5

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Decomposition processes in tropical semi-evergreen forests are still poorly understood. The influence of soil properties and litter quality on decomposition rate was studied in two semi-evergreen forests of Guadeloupe, a forest plantation and a secondary forest, located on different soils. Leaf litter of four tree species was enclosed in litterbags for a 14-month period. Nonlinear correlations were calculated between mass loss and the concentration of major leaf components (soluble C, N, lignin, cellulose, tannins, total soluble phenols) in order to determine the best predictor of leaf litter decomposition. Soil physico-chemical properties and ratios between some of the above-mentioned litter quality parameters were also examined as mass loss predictors. In addition, non-linear correlations were calculated between mass loss and litter quality parameters, at successive periods. Litter quality was the main determinant of litter decomposition in the studied forests. Several litter quality parameters were correlated with leaf disappearance, varying according to stages of decomposition. Between 1 month and 2.5 months, the mass loss was correlated negatively with the initial phenol content and with initial lignin:N and (lignin+phenol):N ratios. From 2.5 to 5.5 months, the mass loss was correlated negatively with the initial phenol content and positively with the initial cellulose content. At later stages of decomposition (9-14 months), the mass loss was correlated negatively with the initial tannin content. Differences in soil characteristics and fauna did not seem to be enough to affect decomposition.
ISSN: 0178-2762

hal-00499535
https://hal.archives-ouvertes.fr/hal-00499535
https://hal.archives-ouvertes.fr/hal-00499535/document
https://hal.archives-ouvertes.fr/hal-00499535/file/Article_decomposition.pdf
DOI : 10.1007/s00374-002-0467-3

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Plant litter diversity effects on decomposition rates are frequently reported, but with a strong bias towards temperate ecosystems. Altered decomposition and nutrient recycling with changing litter diversity may be particularly important in tree species-rich tropical rainforests on nutrient-poor soils. Using 28 different mixtures of leaf litter from 16 Amazonian rainforest tree species, we tested the hypothesis that litter mixture effects on decomposition increase with increasing functional litter diversity. Litter mixtures and all single litter species were exposed in the field for 9 months using custom-made microcosms with soil fauna access. In order to test the hypothesis that the long-term presence of tree species contributing to the litter mixtures increases mixture effects on decomposition, microcosms were installed in a plantation at sites including the respective tree species composition and in a nearby natural forest where these tree species are absent. We found that mixture decomposition deviated from predictions based on single species, with predominantly synergistic effects. Functional litter diversity, defined as either richness, evenness, or divergence based on a wide range of chemical traits, did not explain the observed litter mixture effects. However, synergistic effects in litter mixtures increased with the long-term presence of tree species contributing to these mixtures as the home field advantage hypothesis assumes. Our data suggest that complementarity effects on mixed litter decomposition may emerge through long-term interactions between aboveground and belowground biota.
ISSN: 0029-8549

hal-01032393
https://hal.archives-ouvertes.fr/hal-01032393
DOI : 10.1007/s00442-011-1966-4

Éditeur(s) : HAL CCSD Wiley
Résumé : Proper estimates of decomposition are essential for tropical forests, given their key role in the global carbon (C) cycle. However, the current paradigm for litter decomposition is insufficient to account for recent observations and may limit model predictions for highly diverse tropical ecosystems. In light of recent findings from a nutrient-poor Amazonian rainforest, we revisit the commonly held views that: litter traits are a mere legacy of live leaf traits; nitrogen (N) and lignin are the key litter traits controlling decomposition; and favourable climatic conditions result in rapid decomposition in tropical forests. Substantial interspecific variation in litter phosphorus (P) was found to be unrelated to variation in green leaves. Litter nutrients explained no variation in decomposition, which instead was controlled primarily by nonlignin litter C compounds at low concentrations with important soil fauna effects. Despite near-optimal climatic conditions, tropical litter decomposition proceeded more slowly than in a climatically less favourable temperate forest. We suggest that slow decomposition in the studied rainforest results from a syndrome of poor litter C quality beyond a simple lignin control, enforcing energy starvation of decomposers. We hypothesize that the litter trait syndrome in nutrient-poor tropical rainforests may have evolved to increase plant access to limiting nutrients via mycorrhizal associations.
ISSN: 0028-646X

hal-01032400
https://hal.archives-ouvertes.fr/hal-01032400
DOI : 10.1111/j.1469-8137.2010.03483.x

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : 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.
ISSN: 1432-9840

hal-01032414
https://hal.archives-ouvertes.fr/hal-01032414
DOI : 10.1007/s10021-012-9564-9