Éditeur(s) : University of West Indies, Trinidad &Tobago Université des Antilles. Service commun de la documentation
Extrait de : 52e congrès annuel de la Société caribéenne des plantes alimentaires / 52nd annual meeting of the Caribbean food crops society (CFCS), du 10 au 16 juillet 2016. INRA, CFCS
Description : Carbon dioxide (CO2) accounts for the largest proportion (74%) of total greenhouse gas (GHG) emissions globally, with agricultural activities contributing approximately 25% of this gas. Opportunities to reduce the emissions in the sector can therefore contribute significantly to mitigating global climate change. Ag-lime is used extensively to alleviate problems of soil acidity and the potential for this material to contribute to C sequestration in soils is gaining interest among researchers. A laboratory experiment using C-13 isotopic labelling techniques was therefore established to answer the following questions: 1) Is there a potential for sequestering C using ag-lime in Trinidad acid soils? 2) Does enhancing soil microbial respiration by applying labile organic amendments enhance the C sequestration potential of ag-lime? 3) Are lime-derived C (LDC) estimates from non-isotopic difference technique comparable to that from the C- 13 isotopic labelling technique? The results ascertained for the study showed significant (P<0.05) differences between the LDC estimates from the two techniques with the non-isotopic techniques yielding higher estimates. Over the 32- day experiment, between 16.4 to 85.4% of the ag-lime C was released as CO2 with values being lower for the Piarco soil. The LDC in the CO2 was also significantly (P<0.05) lower for the poultry litter treatments comparison to the other organic amendments for the Piarco soil but not the Nariva soil. This effect may not have been as a result of an enhancement of the carbon sequestration potential of the ag-lime due to an elevation in soil microbial respiration since the LDC in the glucose-amended soils did not differ significantly from the no-amendment control soils.
Siècle(s) traité(s) : 21
Droits : CC-BY-NC-ND - Attribution - Pas d'utilisation commerciale - Pas de modification
Permalien : http://www.manioc.org/fichiers/V16308
V16308

Éditeur(s) : HAL CCSD Society for Range Management
Résumé : Grasslands and agroecosystems occupy one-third of the terrestrial area, but their contribution to the global carbon cycle remains uncertain. We used a set of 316 site-years of CO(2) exchange measurements to quantify gross primary productivity, respiration, and light-response parameters of grasslands, shrublands/savanna, wetlands, and cropland ecosystems worldwide. We analyzed data from 72 global flux-tower sites partitioned into gross photosynthesis and ecosystem respiration with the use of the light-response method (Gilmanov, T. G., D. A. Johnson, and N. Z. Saliendra. 2003. Growing season CO(2) fluxes in a sagebrushsteppe ecosystem in Idaho: Bowen ratio/energy balance measurements and modeling. Basic and Applied Ecology 4:167-183) from the RANGEFLUX and WORLDGRASSAGRIFLUX data sets supplemented by 46 sites from the FLUXNET La Thuile data set partitioned with the use of the temperature-response method (Reichstein, M., E. Falge, D. Baldocchi, D. Papale, R. Valentini, M. Aubinet, P. Berbigier, C. Bernhofer, N. Buchmann, M. Falk, T. Gilmanov, A. Granier, T. Grunwald, K. Havrankova, D. Janous, A. Knohl, T. Laurela, A. Lohila, D. Loustau, G. Matteucci, T. Meyers, F. Miglietta, J.M. Ourcival, D. Perrin, J. Pumpanen, S. Rambal, E. Rotenberg, M. Sanz, J. Tenhunen, G. Seufert, F. Vaccari, T. Vesala, and D. Yakir. 2005. On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm. Global Change Biology 11: 1.424-1439). Maximum values of the quantum yield (alpha = 75 mmol.mol(-1)), photosynthetic capacity (A(max) = 3.4 mg CO(2) . m(-2).s-1), gross photosynthesis (P(g,max) = 1.16 g CO(2) . m(-2).d(-1)), and ecological light-use efficiency (epsilon(ecol) = 59 mmol . mol(-1)) of managed grasslands and high-production croplands exceeded those of most forest ecosystems, indicating the potential of nonforest ecosystems for uptake of atmospheric CO(2). Maximum values of gross primary production (8 600 g CO(2) . m(-2).yr(-1)), total ecosystem respiration (7 900 g CO(2) . m(-2).yr(-1)), and net CO(2) exchange (2 400 g CO(2) . m(-2).yr(-1)) were observed for intensively managed grasslands and high-yield crops, and are comparable to or higher than those for forest ecosystems, excluding some tropical forests. On average, 80% of the nonforest sites were apparent sinks for atmospheric CO(2), with mean net uptake of 700 g CO(2) . m(-2).yr(-1) for intensive grasslands and 933 g CO(2) . m(-2).d(-1) for croplands. However, part of these apparent sinks is accumulated in crops and forage, which are carbon pools that are harvested, transported, and decomposed off site. Therefore, although agricultural fields may be predominantly sinks for atmospheric CO(2), this does not imply that they are necessarily increasing their carbon stock.
ISSN: 1550-7424

hal-01190754
https://hal.archives-ouvertes.fr/hal-01190754
DOI : 10.2111/rem-d-09-00072.1
PRODINRA : 214043

Éditeur(s) : HAL CCSD Wiley
Résumé : The allocation and cycling of carbon (C) within forests is an important component of the biospheric C cycle, but is particularly understudied within tropical forests. We synthesise reported and unpublished results from three lowland rainforest sites in Amazonia (in the regions of Manaus, Tapajos and Caxiuana), all major sites of the Large-Scale Biosphere-Atmosphere Programme (LBA). We attempt a comprehensive synthesis of the C stocks, nutrient status and, particularly, the allocation and internal C dynamics of all three sites. The calculated net primary productivities (NPP) are 10.1 +/- 1.4 Mg C ha(-1) yr(-1) (Manaus), 14.4 +/- 1.3 Mg C ha(-1) yr(-1) (Tapajos) and 10.0 +/- 1.2 Mg C ha(-1) yr(-1) (Caxiuana). All errors bars report standard errors. Soil and leaf nutrient analyses indicate that Tapajos has significantly more plant-available phosphorus and calcium. Autotrophic respiration at all three sites (14.9-21.4 Mg C ha yr(-1)) is more challenging to measure, with the largest component and greatest source of uncertainty being leaf dark respiration. Comparison of measured soil respiration with that predicted from C cycling measurements provides an independent constraint. It shows general good agreement at all three sites, with perhaps some evidence for measured soil respiration being less than expected. Twenty to thirty percent of fixed C is allocated belowground. Comparison of gross primary productivity (GPP), derived from ecosystem flux measurements with that derived from component studies (NPP plus autotrophic respiration) provides an additional crosscheck. The two approaches are in good agreement, giving increased confidence in both approaches to estimating GPP. The ecosystem carbon-use efficiency (CUEs), the ratio of NPP to GPP, is similar at Manaus (0.34 +/- 0.10) and Caxiuana (0.32 +/- 0.07), but may be higher at Tapajos (0.49 +/- 0.16), although the difference is not significant. Old growth or infertile tropical forests may have low CUE compared with recently disturbed and/or fertile forests.
ISSN: 1354-1013

hal-01032150
https://hal.archives-ouvertes.fr/hal-01032150
DOI : 10.1111/j.1365-2486.2008.01780.x

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Coarse woody debris (CWD, dead wood sections a parts per thousand yen10 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 (R (cwd)), and investigate the importance of biotic and abiotic factors for predicting the seasonal change of R (cwd) at the ecosystem level. This study presents a 4-month time series of R (cwd) measurements conducted on 42 dead trees (26 species) at the Paracou Research Station in French Guiana. R (cwd) 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 R (cwd) to drop by 20.5 +/- A 5.1% over the wet-dry transition. Changes in woody tissue moisture content explained 41.9% of the measured seasonal variability in R (cwd), but 60% of the seasonal variability in mean forest R (cwd) rates could be modelled using surface soil water content. We estimate that R (cwd) is approximately 5% of annual ecosystem respiration (R (eco)) and that seasonal variations in R (cwd) contribute appreciably to seasonal variations of R (eco), and should be included in functional models simulating the response of tropical rainforest ecosystems to current and future climate.
ISSN: 1432-9840

hal-01032431
https://hal.archives-ouvertes.fr/hal-01032431
DOI : 10.1007/s10021-013-9684-x

Éditeur(s) : HAL CCSD
Résumé : Diffusion du document : INRA Documentation de Centre, Domaine de Duclos, 97170 Petitt-Bourg (Guadeloupe, France) Diplôme : DEA
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
Because soil respiration representes 80% of ecosystem respiration, it is a major flux between biosphere and atmosphere. We examined the effects of root and litter exclusion on soil CO! efflux (Rsu1) using trenching and litter exclusion in a tropical plantation constituted of trees seedlings installed in 16 mono-specific stands 20 years ago near Kourou, French Guyana. Soil CO2 efflux was measured using an infra red gas analyser (PP System,EGM4 ) at 16 randomly distributed plot in each treatment: control, root exclusion, litter exclusion and both root and litter exclusion. in the plantation. We measured R'1l1during four periods, and we have collected soil samples, litter biomass and measured moisture at 5 cm depth in the soil. Soil CO, efflux varied significantly among species from 2,8±O,7f1mo l. m''. s' (mean ± standard deviation) to 7.4± 1.7fLmol. n'-' . s ' for Qualea rosea and Vochys ia tomentosa, respectively. 1'0 significant correlation was found between RSIlI variability and soil moisture, which is mostly related to soil texture in the experimental site. Soil CO2 efflux was significantly reduced in litter exclusion treatment and root exclusion plots (6 months litter and/or root exclusion) during ail measurements period and for ail species, compared to control plots. The reduction of soil CO, efflux was higher in plot without root than in plot without litter of control plot (42% and 25%, respectively). There was an import ant specific diversity in these reductions . We estimated the contribution of roof respiration (Rr) to total Rso1 by calculating the difference between Rso1 control and Rsn l root exclusion plot corrected for the decomposition of root that were killed following t re n e h in ~. Thus the heterotrophic component of soil carbon efflux accounts for 46% of total carbon efflux (1,9f1 mol. rn" . s•') while root respiration accounts for 54% of soil carbon release (2,3 ~t mo l. m-2 S-I) . Because there was a negative and significant correlation between microbial respiration (Rrn) and C/N of mature leaves it seemed to be possible to predict Rm if we known the mature leaves quality. In addition a good estimate theorical R ~, values from R~, measured in different treatments.
La respiration du sol en représentant une part de 80% de la respiration de l'écosystème apparaît être un flux majeur entre la biosphère et l'atmosphère. Nous avons étudié les effets de l'exclusion racinaire et de la litière sur le flux de CO, du sol (R ~ , ) en utilisant la méthode de " Trench-plots" et de suppression de litière dans une plantation d'arbres tropicaux. Ces arbres, âgés de 20 ans ont été plantés sur un sol uniforme, près de Kourou en Guyane française, en 16 placeaux mono-spécifiques. Pour mesurer les flux de CO2 provenant du sol, nous avons utilisé un analyseur différentiel de gaz infrarouge portable muni d'une chambre. Les mesures ont été faites sur 4 traitements différents tels que : le contrôle, l'exclusion racinaire, l'exclusion de litière et l'exclusion de litière et de racine et ce, répétés sur chacune des 16 placettes mono-spécifiques. Cette étude comporte 4 campagnes de mesures. Nous avons également effectué des prélèvements de sol de litière et nous avons fait des mesures d’humidité de sol à une profondeur de 5 cm. Les flux de C01 du sol varient fortement entre espèces de 2.8±O.7 ~t m o 1. m-2. sol à 7 A± 1. 7 ~t m o l. m•1 sol pour Qua/ev rosea ct Vochysto tomentasa, respectivement. Il n'existe pas de corrélation significative entre les variations de Rw l ct celles de l'humidité du sol (indication sur la texture du sol de la plantation ). Nous avons observé que Rso1 était significativement plus faible dans les placeaux sans racines et/ou sans litière (6 mois après la mise en place de l'expérimentation) pour toutes les campagnes de mesures et pour toutes les espèces que dans les placeaux contrôlés. Cette réduction du flux de CO2 du sol est plus forte dans les "trench-plots " que dans les traitement s d'exclusion de litière avec 42 et 25% respectivement. Un effet "traitement " et un effet "espèce" important expliquent 3 1"/.. ct 13% de la variabilité totale de R~. Nous avons cherché à connaître la contribution des racines dans les valeurs de R""I. en comparant le flux de CO2 provenant du sol sur des "trench -plot s'' au flux de COl provenant du sol dans les placeaux contrôlés . Cette estimation a été corrigée pour prendre en compte la décomposition des racines tuées par les tranchées. Ainsi, la composante appartenant aux micro -organismes représente 46% du flux total de carbone provenant du sol (1.9Jlmo l. m-2 S•I ) alors que la respiration des racines représente 54% du dégagement de carbone (2 ,3~lmol. m ol . 5-La respiration des micro-organismes pourrait être estimée en mesurant le C/N des feuilles matures puisqu'il existe une corrélation significative et négative entre les deux. Enfin les résultats obtenus sur les différents traitements permettent d'obtenir une bonne estimation de la respiration du sol avec un RSIlI théorique corrélé à 66% avec les valeurs réelles mesurées.
https://hal.archives-ouvertes.fr/hal-01189239

hal-01189239
https://hal.archives-ouvertes.fr/hal-01189239
PRODINRA : 18212

Éditeur(s) : Université des Antilles. Service commun de la documentation University of West Indies, Barbados
Extrait de : 52e congrès annuel de la Société caribéenne des plantes alimentaires / 52nd annual meeting of the Caribbean food crops society (CFCS), du 10 au 16 juillet 2016. INRA, CFCS
Description : Mulch application of Sargassum seaweed (Sargassum spp.) to soil can help to reduce beach contamination in the Caribbean Region while providing beneficial horticultural effects. This study investigated the effects of fresh Sargassum mulch on soil properties and plant growth in a test crop of tomato (Solanum lycopersicum L. â? ? HA 3019â? TM). Fresh Sargassum material (washed and unwashed) was applied as mulches (0, 5 and 8cm thick) to small field plots one week after transplanting of 3-week-old seedlings. The mulch material was raked away from the plots after three weeks exposure. Observations on soil moisture, electrical conductivity, pH and biological activity, and plant growth were made at 1 to 2-week intervals over a 6-week period with additional soil measurements after 10 weeks. Soil biological activity (respiration) was increased by the Sargassum mulch with values being similar for the 5cm and 8cm mulch layers. Soil moisture content, pH and electrical conductivity (EC) were increased as the mulch layer increased and EC values were only marginally reduced by Sargassum washing. An increase in plant growth compared to the control treatment was noted only in the washed Sargassum treatments. Potential benefits of Sargassum seaweed mulches on soil properties and plant growth can be nullified due to soil salinization effects.
Siècle(s) traité(s) : 21
Droits : CC-BY-NC-ND - Attribution - Pas d'utilisation commerciale - Pas de modification
Permalien : http://www.manioc.org/fichiers/V16269
V16269

Éditeur(s) : HAL CCSD Wiley
Résumé :  
The lack of information on the ways seasonal drought modifies the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEPd) and two main components of this productivity, daily total ecosystem respiration (REd) and daily gross ecosystem productivity (GEPd), were estimated over 2 years at a flux tower site in French Guiana, South America (511605400N, 5215404400W). We compared seasonal variations between wet and dry periods and between dry periods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93-day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 gCm_2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower REd combined with reduced soil respiration associated with low soil water availability. During the mild dry period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 gCm_2. Severe drought conditions resulted in even lower REd, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe dry period was characterized by greater carbon storage (64.6 gCm_2), emphasizing that environmental conditions, such as during a severe drought, modify the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance.
ISSN: 1354-1013

hal-01032067
https://hal.archives-ouvertes.fr/hal-01032067
DOI : 10.1111/j.1365-2486.2008.01610.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : In the context of an ongoing monitoring study on the impacts of gold-mining activities on critical ecosystem processes, we explored the use of soil Denitrifying Enzyme Activity (DEA) and Substrate Induced Respiration (SIR) as ecosystem indicators in tropical rainforests of French Guiana. We also propose DEA/SIR ratio as ecosystem attribute able to describe the state of an ecosystem and to reflect changes in ecological processes. With this purpose, we measured SIR, DEA and DEA/SIR ratio in five gold-mining areas and five surrounding natural reference rainforests. We also measured indicators in two conditions of spontaneous regeneration of vegetation (stratified or not) and two conditions of soil rehabilitation (prior preparation of soils or not). We showed a high variability of DEA, SIR and DEA/SIR ratio in the natural reference forests. This pointed out the necessity to identify relevant reference systems - i.e. proving a close match in all relevant ecological dimensions - to compare with closed perturbed systems in order to assess the levels of alterations after disturbances. Results showed a high impact of gold mine on microbial processes with a strong decrease of DEA (10-fold lower), SIR (2-fold lower) and DEA/SIR ratio (8-fold lower) in perturbed areas in comparison with natural reference forests. The type of spontaneous vegetation (stratified or not) influenced the values of indicators as well as prior rehabilitation of soils, demonstrating the capacity of DEA. SIR and DEA/SIR ratio to respond in proportion to the perturbation (robustness) and to the different levels of restoration (sensitivity). The systematic decrease of the ratio DEA/SIR observed in the studied perturbed situations demonstrates clearly that the structure of microbial communities has been also modified. The ratio DEA/SIR proved to be robust and sensitive, and able to describe in fairly fine way changes of soil microbial communities in terms of structure and function in gold mine areas and during processes of restoration. We propose to use DEA, SIR and DEA/SIR ratio as bioindicators of both structural and functional aspects of C and N cycling in soils. Together with others bioindicators based on key supporting functions in soils, these indicators should accurately evaluate the ecological potential of natural ecosystems and the levels of degradation in case of land-use changes. (C) 2012 Elsevier Ltd. All rights reserved.
ISSN: 1470-160X

hal-01190730
https://hal.archives-ouvertes.fr/hal-01190730
DOI : 10.1016/j.ecolind.2012.01.021
PRODINRA : 213639

Éditeur(s) : HAL CCSD Elsevier
Résumé : Understanding the pattern in spatial distribution of soil microbial processes is critical to understand the environmental factors that regulate them as well as to scale up these processes to ecosystem. Soil samples from a I ha tropical rainforest plot (Paracou, French Guiana) were analyzed according a nested sampling approach using different separation distances ranging from 0.4 to 40 m. The variability of substrate induced respiration (SIR) and of denitrification enzyme activity (DEA) was characterized in relation to various soil properties (total C and N contents, NIRS related index of soil organic matter quality, SOMQ and index of tree influence potential, IP). The variability of SIR and DEA was higher than that of environmental properties. The patterns of accumulated variance as a function of distance varied among the soil properties. The variability of SIR and DEA mainly occurred at small (1 m) scale (and at the 10-40 m-scales for SIR), probably reflecting the quality of litter input that results of the influence of local assemblage of different tree species, though changes in the soil N and C contents. Indeed, total soil C and N contents explained the microbial properties at every scale. Coefficients of codispersion showed that neither SOMQ nor IP did correlate with SIR and DEA, and confirmed that total C and N contents explained microbial properties in a scale dependent and complex manner. Such spatial dependency underlines the importance of soil heterogeneity in this tropical forest with implications for sampling strategies when studying the microbial processes and their response to disturbances. (C) 2012 Elsevier B.V. All rights reserved.
ISSN: 0016-7061

hal-01032409
https://hal.archives-ouvertes.fr/hal-01032409
DOI : 10.1016/j.geoderma.2012.12.009

Éditeur(s) : HAL CCSD
Résumé :  
In tropical rainforests, the origin of the interspecific variability in trunk CO2 efflux (Et) and of seasonal variations in Et have not yet been explained. We conducted a study to test which biotic and abiotic determinants would contribute to these variations. Et and a set of wood anatomical and functional characteristics were measured on trees in two habitats (Terra Firme forest vs. seasonal flooded forest) in a Neotropical rainforest over a 18-months' period including a range of climatic and soil water conditions. The large variability in Et (0.33 to 3.15 μmol CO2 m-2 s-1 in Terra Firme forest) was associated with tree diameter and growth respiration (Eg), although maintenance respiration (Em) was the main component of Et. Neither wood properties nor sapflow density were correlated with trunk CO2 efflux. The large seasonal variations in Et were correlated with diameter growth and surface soil water content (SWC). These data underlined the absence of clearly identified biotic determinants, beside growth, to explain the interspecific variability in Et. We emphasized the fast response of growth and maintenance respiration processes to seasonal variations in SWC that potentially has consequences on the carbon cycle in the ecosystem under upcoming climatic changes.
23. New Phytologist Symposium. Carbon cycling in tropical ecosystems
Guangzhou, China

hal-01032199
https://hal.archives-ouvertes.fr/hal-01032199

Éditeur(s) : HAL CCSD Wiley
Résumé : Seasonal variations in environmental conditions influence the functioning of the whole ecosystem of tropical rain forests, but as yet little is known about how such variations directly influence the leaf gas exchange and transpiration of individual canopy tree species. We examined the influence of seasonal variations in relative extractable water in the upper soil layers on predawn leaf water potential, saturated net photosynthesis, leaf dark respiration, stomatal conductance, and tree transpiration of 13 tropical rain forest canopy trees (eight species) over 2yr in French Guiana. The canopies were accessed by climbing ropes attached to the trees and to a tower. Our results indicate that a small proportion of the studied trees were unaffected by soil water depletion during seasonal dry periods, probably thanks to efficient deep root systems. The trees showing decreased tree water status (i.e., predawn leaf water potential) displayed a wide range of leaf gas exchange responses. Some trees strongly regulated photosynthesis and transpiration when relative extractable water decreased drastically. In contrast, other trees showed little variation, thus indicating good adaptation to soil drought conditions. These results have important applications to modeling approaches: indeed, precise evaluation and grouping of these response patterns are required before any tree-based functional models can efficiently describe the response of tropical rain forest ecosystems to future changes in environmental conditions.
ISSN: 0006-3606

hal-01032411
https://hal.archives-ouvertes.fr/hal-01032411
DOI : 10.1111/j.1744-7429.2012.00902.x

Éditeur(s) : HAL CCSD
Résumé :   Diplôme : Master Recherche
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
Notre étude porte sur la caractérisation à l'échelle de l'hectare de la variabilité spatiale (1) du fonctionnement microbien du sol et (2) de sa stabilité (i.e. de sa réponse à un stress). Elle a été menée sur une forêt tropicale humide (forêt primaire) proche de Kourou en Guyane (site de Paracou). Les indicateurs fonctionnels utilisés sont les potentiels d'activités respiratoires (RP) et dénitrifiantes (OP). La variabilité spatiale du fonctionnement microbien du sol a fait l'objet d'un nombre important d'études mais très peu d'entre elles ont concerné ce type d'écosystème. Un autre aspect novateur réside dans la recherche de la variabilité spatiale de la stabilité du fonctionnement. A notre connaissance, il s'agit de la première étude de ce type en milieu tropical comme en milieu tempéré. Les principales conclusions sont les suivantes : (1) à l'échelle 10m (grille principale) les coefficients de variation (CV) des potentiels de fonction sont similaires pour les 2 processus et élevés (RP : 53% ; OP : 54%) au regard des valeurs de la littérature sur des milieux tempérés, mais RP et OP présentent des variabilités spatiales différentes à des échelles inférieures ; (2) l'utilisation d'un indice de densité locale (ID) des arbres n'a pas permis de mettre en évidence une corrélation entre les répartitions spatiales de la végétation et du fonctionnement microbien du sol. De même, aucun déterminisme clair de l'intensitè des potentiels microbiens n'a pu être dégagé par la prise en compte de la variabilité des caractéristiques physico-chimiques du sol; (3) un stress thermique génère à très court terme (résistance) un accroissement de la spatialisation du potentiel de respiration. A plus long terme, la variabilité inter-échantillons s'atténue pour retrouver ses valeurs initiales et, (4) l'activité originelle (avant stress) n'est pas corrélée avec la résistance et est négativement corrélée aux valeurs observées 15 et 30 jours après le stress. Outre son intérêt intrinsèque, cette étude vise à se doter de données de « cadrage » sur la forêt primaire (non perturbée) qui nous permettront d'accéder à de meilleures évaluations et compréhensions des mécanismes impliqués dans la réponse des écosystèmes tropicaux à l'anthropisation lors de projets en cours. Un exemple de ce type d'application est brièvement décrit.
https://hal.archives-ouvertes.fr/hal-01189259

hal-01189259
https://hal.archives-ouvertes.fr/hal-01189259
PRODINRA : 20250

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Understanding the ability of ecosystem processes to resist to and to recover from disturbances is critical to sustainable land use. However, the spatial variability of the stability has rarely been addressed. Here, we investigated the functional stability of a soil microbial process for 24 soils collected from adjacent locations from a 0.3 ha tropical rainforest plot in Paracou, French Guiana. The 24 locations were characterized regarding soil chemical and biological (microbial diversity) parameters and forest structure. The corresponding soils were submitted to an experimental transient heat disturbance during a microcosm experiment. The response of the respiration process was followed using substrate-induced respiration (SIR). The response of soil SIR to heat disturbance varied widely between samples. The variability of the SIR response increased just after the disturbance, and a global rather homogeneous decrease in SIR rates was observed 15 and 30 days after. The stability of SIR in response to heat disturbance could not be related to either the genetic or the metabolic diversity of the microbial community. The initial level of SIR before the disturbance was the soil variable that best correlated with the impact of the disturbance: the soil locations with the highest initial SIR rates were the most affected 15 and 30 days after the heat disturbance. Such a heterogeneous response suggests that the response of soil processes to a disturbance will be difficult to assess from only local-scale analyses and highlights the need for spatial explicitness in understanding biogeochemical processes.
ISSN: 1439-0108

hal-01204209
https://hal.archives-ouvertes.fr/hal-01204209
DOI : 10.1007/s11368-012-0528-7
PRODINRA : 214444

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Disentangling the autotrophic and heterotrophic components of soil CO2 efflux is critical to understanding the role of soil system in terrestrial carbon (C) cycling. In this study, we combined a stable C-isotope natural abundance approach with the trenched plot method to determine if root exclusion significantly affected the isotopic composition (δ13C) of soil CO2 efflux (RS). This study was performed in different forest ecosystems: a tropical rainforest and two temperate broadleaved forests, where trenched plots had previously been installed. At each site, RS and its δ13C (δ13CRs) tended to be lower in trenched plots than in control plots. Contrary to RS, δ13CRs differences were not significant. This observation is consistent with the small differences in δ13C measured on organic matter from root, litter and soil. The lack of an effect on δ13CRs by root exclusion could be from the small difference in δ13C between autotrophic and heterotrophic soil respirations, but further investigations are needed because of potential artefacts associated with the root exclusion technique.
ISSN: 0032-079X

bioemco-00353850
https://hal-bioemco.ccsd.cnrs.fr/bioemco-00353850
DOI : 10.1007/s11104-008-9844-5

Éditeur(s) : HAL CCSD Elsevier
Résumé :  
Microbial-based indicators, such as C and N contents or microbial functions involved in C and N cycles, are currently used to describe the status of soils in disturbed areas. Microbial functions are more accurate indicators but their measurement for studies at the ecosystem level remains problematical because of the huge spatial variability of these processes and, consequently, of the large number of soil samples which must be analyzed. Our goal was to test the capacity of near-infrared reflectance spectroscopy (NIRS) to predict respiration and denitrification but also carbon and nitrogen contents of soils submitted to various procedures of restoration. To achieve this objective, we took advantage of an experiment conducted on a reforestation system established after open-cast gold mining in French Guiana. In this experimental station, plantations of various ages and various soil textures were at our disposal. Our results showed that both plantations and soil texture had a strong impact on the recovery of soil functioning: carbon and nitrogen contents, respiration and denitrification increased with age of plantation and clay content. Calibrations were performed between spectral data and microbial-based indicators using partial least squares regression (PLS). The results showed that C and N contents were accurately predicted. Microbial functions were less precisely predicted with results more accurate on clayey soils than on sandy soils. In clayey soils, perturbed or restored soils and the year of plantation were discriminated very efficiently through principal component analyses of spectral signatures (over 80% of variance explained on the first two axes). Near-infrared spectroscopy may thus be extended to the prediction of functional soil parameters, but the capacity of this method must be strengthened by expending the databases with other soils in other contexts. The possibility of using NIRS provides many opportunities for understanding both the temporal dynamics and the spatial variability of the recovery of key microbial functions during soil restoration.
ISSN: 0929-1393

hal-01032188
https://hal.archives-ouvertes.fr/hal-01032188
DOI : 10.1016/j.apsoil.2007.07.001

Éditeur(s) : HAL CCSD
Résumé :   Diffusion du document : INRA Antilles-Guyane, UMR ECOFOG, F97387 Kourou, Guyane (France) Diplôme : Master Recherche
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
Worldwide, there is concern regarding the declining quality of ecosystems, their rehabilitation, and their protection. In particular, the recognition that soil is a finite resource has spurred efforts to manage and restore it. In French Guiana, gold mining is a serious social and ecological problem, including the threats it poses to soil quality. The principal goal of this study was to establish a qualitative baseline of impacts of gold mining on soil microbial activity at five previously mined sites. We measured the potential rates of respiration and denitrification in disturbed soils, and compared theses rates with those of soils from adjacent forests, which served as un-disturbed references. Microbial activity, used as a bio-indicator, demonstrated the importance of soil rehabilitation, and the type of soil rehabilitation. We also found that visual observations of plant regeneration were insufficient to infer the rate of microbial activity. These bio-indicators can indicate soil quality, and help to formulate hypotheses about its developmnent. Bio-indicators can be used to obtain reliable indications about the quality of soil and contribute to decision-making in the management and restoration of this valuable resource.
Notre étude s'inscrit dans un contexte mondial de préoccupations environnementales, centrées notamment sur l'évaluation de la qualité des écosystèmes, la mise en place de leur réhabilitation et de leur sauvegarde. En particulier, la prise de conscience que le sol ne constitue pas une ressource inépuisable s'est accompagnée de la nécessité de gérer, voire de restaurer cette ressource. L'étude s'intègre également dans un contexte guyanais où l'exploitation aurifère constitue un problème écologique et sociétal majeur. Notre travail a pour but principal de dresser un bilan qualitatif des impacts de l'exploitation aurifère sur le fonctionnement microbien des sols de cinq sites miniers. Pour cela, nous avons effectué les mesures des activités potentielles de deux fonctions microbiennes, la respiration et la dénitrification, sur les sols des sites perturbés. Nous avons comparé ces valeurs d'activités microbiennes avec celles obtenues pour les sols de forêts naturelles (adjacentes à ces sites) que nous avons considérées comme la référence à atteindre (témoin). Les fonctions microbiennes, utilisées comme bio-indicateurs, ont mis en évidence l'importance de la réhabilitation et du type de réhabilitation sur la reprise du fonctionnement du sol. Nous avons constaté que l'observation de visu de la végétation ne suffit pas à évaluer de façon certaine la reprise de ce fonctionnement. Ces bio-indicateurs sont aptes à traduire l'état d'un sol perturbé et émettre des hypothèses quant à son évolution. Ainsi, les bio-indicateurs peuvent être utilisés afin d'obtenir des indications solides sur la qualité des sols et aider à la prise de décision en matière de gestion et de restauration de cette ressource.
https://hal.archives-ouvertes.fr/hal-01189544

hal-01189544
https://hal.archives-ouvertes.fr/hal-01189544
PRODINRA : 46710

Éditeur(s) : HAL CCSD Wiley
Résumé : 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 (FNEP), 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 ≈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 FNEP 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.
ISSN: 1354-1013

hal-01032076
https://hal.archives-ouvertes.fr/hal-01032076
DOI : 10.1111/j.1365-2486.2009.01991.x

Éditeur(s) : HAL CCSD Wiley
Résumé : 1. 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.
ISSN: 0269-8463

hal-01204229
https://hal.archives-ouvertes.fr/hal-01204229
DOI : 10.1111/1365-2435.12329
PRODINRA : 311389

Éditeur(s) : HAL CCSD
Résumé :   Diplôme : DEA
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
As part of a programme of degraded soils rehabilitation, and in order to follow the biological processes connected with the soils reconstitution, it is a requisite to determine indicators able to account for the evolution of the soil. These indicators can he found on structural and/or functional characteristics of the bacterial communities, such as soil respiration, denitrification or genetic diversity. Theses descriptors are able to characterize the global community or targeted communities chosen for their importance in the ecosystem functioning. In this work, we tried to know whether soil bacteria genetic diversity was able to be a relevant indicator of the soil evolution in a rehabilitated sequence. This diversity is apprehended via a molecular technique: ARISA. A chronosequence situated on a gold mine, already experimented as part of a programme of degraded zones rehabilitation, was at our disposal. Results show that ARISA is a very sensitive technique, able to account for the bacterial community heterogeneity in a soil but unable, at the parcel scale, to discriminate the treatments nor to account for the evolution in lime of planted treatments. Lastly, the advantage of this indicator of genetic diversity may arise from its confrontation to other indicators (functional, for example).
Dans le cadre de la revégétalisation d'un sol dégradé et afin de pouvoir suivre les processus biologiques liés à la reconstitution des sols, il est nécessaire de déterminer des indicateurs pouvant rendre compte de l'évolution de l'état du sol. Ces indicateurs peuvent être fondés sur des caractéristiques fonctionnelles et/ou structurales des communautés bactériennes telles que la respiration, la dénitrification ou la diversité génétique. Ces descripteurs peuvent analyser la communauté globale ou des communautés cibles choisies pour leur importance dans le fonctionnement de l'écosystème. L'objectif de ce stage était de savoir si la diversité génétique des bactéries du sol pouvait être un indicateur de l'évolution des sols au sein d'une séquence de revégétalisation. Cette diversité est appréhendée par une technique de biologie moléculaire : l'ARISA. On dispose d'une chronoséquence située sur une mine d'or étudiée dans le cadre d'un programme de réhabilitation des zones dégradées. Les résultats montrent que l'ARISA est une technique très sensible, qui rend bien compte de l’hétérogénéité des communautés bactériennes présentes dans un sol mais est incapable, à l’échelle de la parcelle, de discriminer ni les traitements ni de rendre compte de l'évolution dans le temps de ces parcelles. Enfin, l'intérêt de cet indicateur de diversité génétique pourra résulter de sa confrontation avec d'autres indicateurs (fonctionnels par exemple).
https://hal.archives-ouvertes.fr/hal-01189155

hal-01189155
https://hal.archives-ouvertes.fr/hal-01189155
PRODINRA : 9464

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Because earthworms sustain soil functioning and fertility, there is a need to advance the knowledge of their adaptation potential to chemicals in anthropogenic landscapes. Our hypothesis is that there is acclimation to organic chemicals (pesticides) in earthworms that durably persist under conventional farming in anthropogenic landscapes. The adaptation capability of two populations of earthworms (Aporectodea caliginosa) having a different chemical exposure history, - one originating from 20 years of organic farming (naïve population) and another from 20 years of conventional farming (pre-exposed population) - to cope with soil organic pollutant (Opus®, epoxiconazole a worldwide used fungicide) were investigated. Several complementary metabolic and energetic endpoints were followed, and cast production was assessed as a behavioural biomarker related to earthworms ecological role for the soil. Basal metabolism reflected by respiration rate was increased in both fungicide-exposed worms compared to controls. Glycogen resources were decreased in the same proportion in the two populations but more rapidly for the naïve (7 days) than for the pre-exposed population (28 days). Soluble protein and most amino-acids contents increased in the pre-exposed population only, suggesting a detoxification mechanism. Metabolomic profiles showed a cut-off between fungicide-exposed and control groups in the pre-exposed earthworms only, with an increase in most of the metabolites. Exposure to a low dose of epoxiconazole increased cast production of pre-exposed earthworms, and this resulted in an increase in pesticide disappearance. As far as we know, this is the first study which evidenced there is an acclimation to an agricultural chemical in earthworms derived from conventional farming that also relates to a change in their burrowing behaviour, and for which larger consequences for the soil ecosystem need to be addressed. This original finding is of major interest in the frame of ecosystem resilience to global changes. Whether this physiological adaptation is a general pattern of response against fungicides or other pesticides would need to be confirmed with other molecules and agricultural contexts.
Soil Biology and Biochemistry

hal-01005821
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01005821
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01005821/document
DOI : 10.1016/j.soilbio.2014.01.032