Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few 'hyperdominant' species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only ≈1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region.
ISSN: 2041-1723

hal-01204225
https://hal.archives-ouvertes.fr/hal-01204225
DOI : 10.1038/ncomms7857
PRODINRA : 305614
PUBMED : 25919449

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé :  
Modeling soil water availability for tropical trees is a prerequisite to predicting the future impact of climate change on tropical forests. In this paper we develop a discrete-time deterministic water balance model adapted to tropical rainforest climates, and we validate it on a large dataset that includes micrometeorological and soil parameters along a topographic gradient in a lowland forest of French Guiana. The model computes daily water fluxes (rainfall interception, drainage, tree transpiration and soil plus understorey evapotranspiration) and soil water content using three input variables: daily precipitation, potential evapotranspiration and solar radiation. A novel statistical approach is employed that uses Time Domain Reflectometer (TDR) soil moisture data to estimate water content at permanent wilting point and at field capacity, and root distribution. Inaccuracy of the TDR probes and other sources of uncertainty are taken into account by model calibration through a Bayesian framework. Model daily output includes relative extractable water, REW, i.e. the daily available water standardized by potential available water. The model succeeds in capturing temporal variations in REW regardless of topographic context. The low Root Mean Square Error of Predictions suggests that the model captures the most important drivers of soil water dynamics, i.e. water refilling and root water extraction. Our model thus provides a useful tool to explore the response of tropical forests to climate scenarios of changing rainfall regime and intensity.
ISSN: 0168-1923

hal-01032181
https://hal.archives-ouvertes.fr/hal-01032181
DOI : 10.1016/j.agrformet.2011.04.012

Éditeur(s) : HAL CCSD Society of Nuclear Medicine
Résumé : International audience
ISSN: 0161-5505

hal-01117641
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01117641

Éditeur(s) : HAL CCSD Elsevier
Résumé : Eperua falcata (Aublet), a late-successional species in tropical rainforest and one of the most abundant tree in French Guiana, has developed an original strategy concerning N-acquisition by largely preferring nitrate, rather than ammonium (H. Schimann, S. Ponton, S. Hattenschwiler, B. Ferry, R. Lensi, A.M. Domenach, J.C. Roggy, Differing nitrogen use strategies of two tropical rainforest tree species in French Guiana: evidence from N-15 natural abundance and microbial activities, Soil Biol, Biochem. 40 (2008) 487-494). Given the preference of this species for nitrate, we hypothesized that root exudates would promote nitrate availability by (a) enhancing nitrate production by stimulating ammonium oxidation or (b) minimizing nitrate losses by inhibiting denitrification. Root exudates were collected in situ in monospecific planted plots. The phytochemical analysis of these exudates and of several of their corresponding root extracts was achieved using UHPLC/DAD/ESI-QTOF and allowed the identification of diverse secondary metabolites belonging to the flavonoid family. Our results show that (i) the distinct exudation patterns observed are related to distinct root morphologies, and this was associated with a shift in the root flavonoid content, (ii) a root extract representative of the diverse compounds detected in roots showed a significant and selective metabolic inhibition of isolated denitrifiers in vitro, and (iii) in soil plots the abundance of nirK-type denitrifiers was negatively affected in rhizosphere soil compared to bulk. Altogether this led us to formulate hypothesis concerning the ecological role of the identified compounds in relation to N-acquisition strategy of this species. (C) 2013 Elsevier Masson SAS. All rights reserved.
ISSN: 0981-9428

hal-01032437
https://hal.archives-ouvertes.fr/hal-01032437
DOI : 10.1016/j.plaphy.2013.05.003

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : Climate models predict a range of changes in tropical forest regions, including increased average temperatures, decreased total precipitation, reduced soil moisture and alterations in seasonal climate variations. These changes are directly related to the increase in anthropogenic greenhouse gas concentrations, primarily CO2. Assessing seasonal forest growth responses to climate is of utmost importance because woody tissues, produced by photosynthesis from atmospheric CO2, water and light, constitute the main component of carbon sequestration in the forest ecosystem. In this paper, we combine intra-annual tree growth measurements from published tree growth data and the corresponding monthly climate data for 25 pan-tropical forest sites. This meta-analysis is designed to find the shared climate drivers of tree growth and their relative importance across pan-tropical forests in order to improve carbon uptake models in a global change context. Tree growth reveals significant intra-annual seasonality at seasonally dry sites or in wet tropical forests. Of the overall variation in tree growth, 28.7% was explained by the site effect, i.e. the tree growth average per site. The best predictive model included four climate variables: precipitation, solar radiation (estimated with extrasolar radiation reaching the atmosphere), temperature amplitude and relative soil water content. This model explained more than 50% of the tree growth variations across tropical forests. Precipitation and solar radiation are the main seasonal drivers of tree growth, causing 19.8% and 16.3% of the tree growth variations. Both have a significant positive association with tree growth. These findings suggest that forest productivity due to tropical tree growth will be reduced in the future if climate extremes, such as droughts, become more frequent.
ISSN: 1932-6203

hal-01268529
https://hal.archives-ouvertes.fr/hal-01268529
https://hal.archives-ouvertes.fr/hal-01268529/document
https://hal.archives-ouvertes.fr/hal-01268529/file/journal.pone.0092337.PDF
DOI : 10.1371/journal.pone.0092337

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : Climate models for the coming century predict rainfall reduction in the Amazonian region, including change in water availability for tropical rainforests. Here, we test the extent to which climate variables related to water regime, temperature and irradiance shape the growth trajectories of neotropical trees. . We developed a diameter growth model explicitly designed to work with asynchronous climate and growth data. Growth trajectories of 205 individual trees from 54 neotropical species censused every 2 months over a 4-year period were used to rank 9 climate variables and find the best predictive model. . About 9% of the individual variation in tree growth was imputable to the seasonal variation of climate. Relative extractable water was the main predictor and alone explained more than 60% of the climate effect on tree growth, i.e. 5.4% of the individual variation in tree growth. Furthermore, the global annual tree growth was more dependent on the diameter increment at the onset of the rain season than on the duration of dry season. . The best predictive model included 3 climate variables: relative extractable water, minimum temperature and irradiance. The root mean squared error of prediction (0.035 mm.d(-1)) was slightly above the mean value of the growth (0.026 mm.d(-1)). . Amongst climate variables, we highlight the predominant role of water availability in determining seasonal variation in tree growth of neotropical forest trees and the need to include these relationships in forest simulators to test, in silico, the impact of different climate scenarios on the future dynamics of the rainforest.
ISSN: 1932-6203

hal-01268350
https://hal.archives-ouvertes.fr/hal-01268350
DOI : 10.1371/journal.pone.0034074
PRODINRA : 215438
PUBMED : 22506012

Éditeur(s) : HAL CCSD
Résumé : CIRAD, Montpellier, Perspective
In the Brazilian Amazon, degraded forests dominate the landscapes on the agricultural frontiers. This region is now facing a major challenge: halting degradation and sustainably managing these forests. Today, degraded forests represent a class of forest in their own right. They can nevertheless play a key role in combating climate change, and can also help to improve the ecological functioning of the different territories. Implementing public policies with the twin objectives of reducing degradation and promoting these forests implies strong support from research. In this Perspective, we focus on four research priorities: developing methods to characterise and monitor degraded forests; drafting specific forest management plans; understanding the role played by all social actors; and supporting policies at the territorial level.
En Amazonie brésilienne, les forêts dégradées dominent les paysages des fronts pionniers. Un grand défi attend désormais cette région : stopper la dégradation et gérer durablement ces forêts. Les forêts dégradées représentent aujourd’hui une catégorie de forêt à part entière. Elles peuvent néanmoins jouer un rôle majeur pour lutter contre le changement climatique. Elles peuvent aussi contribuer à un meilleur fonctionnement écologique des territoires. Développer des politiques publiques visant le double objectif de réduire la dégradation et de valoriser ces forêts implique un appui fort de la recherche. Dans ce Perspective, nous mettons l’accent sur quatre priorités de recherche : développer des méthodes de caractérisation et de suivi des forêts dégradées, élaborer des plans d’aménagement spécifiques, comprendre le rôle joué par tous les acteurs sociaux et accompagner les politiques à l’échelle territoriale.
Na Amazônia brasileira, as florestas degradadas dominam as paisagens das frentes pioneiras. Atualmente, esta região enfrenta um grande desafio: parar a degradação e fazer a gestão sustentável dessas florestas. As florestas degradadas são atualmente parte integrante de uma categoria de florestas. No entanto, elas podem desempenhar um papel importante na luta contra as mudanças climáticas e podem contribuir para um melhor funcionamento ecológico dos territórios. Desenvolver políticas públicas com o duplo objetivo de reduzir a degradação e melhorar a condição dessas florestas implica um forte apoio da pesquisa. Neste Perspective, nós focalizamos em quatro prioridades de pesquisa: desenvolver os métodos de caracterização e monitoramento das florestas degradadas, elaborar planos específicos de ordenamento do território, compreender o papel desempenhado por todos os atores sociais e acompanhar as politicas em escala territorial.
https://hal.archives-ouvertes.fr/hal-01537653

Droits : http://creativecommons.org/licenses/by-nc-sa/
hal-01537653
https://hal.archives-ouvertes.fr/hal-01537653
https://hal.archives-ouvertes.fr/hal-01537653/document
https://hal.archives-ouvertes.fr/hal-01537653/file/Persp40_LBLanc%20FR.pdf
https://hal.archives-ouvertes.fr/hal-01537653/file/Persp40_LBLanc%20PORT.pdf

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Though the root biomass of tropical rainforest trees is concentrated in the upper soil layers, soil water uptake by deep roots has been shown to contribute to tree transpiration. A precise evaluation of the relationship between tree dimensions and depth of water uptake would be useful in tree-based modelling approaches designed to anticipate the response of tropical rainforest ecosystems to future changes in environmental conditions. We used an innovative dual-isotope labelling approach (deuterium in surface soil and oxygen at 120-cm depth) coupled with a modelling approach to investigate the role of tree dimensions in soil water uptake in a tropical rainforest exposed to seasonal drought. We studied 65 trees of varying diameter and height and with a wide range of predawn leaf water potential (I-pd) values. We confirmed that about half of the studied trees relied on soil water below 100-cm depth during dry periods. I-pd was negatively correlated with depth of water extraction and can be taken as a rough proxy of this depth. Some trees showed considerable plasticity in their depth of water uptake, exhibiting an efficient adaptive strategy for water and nutrient resource acquisition. We did not find a strong relationship between tree dimensions and depth of water uptake. While tall trees preferentially extract water from layers below 100-cm depth, shorter trees show broad variations in mean depth of water uptake. This precludes the use of tree dimensions to parameterize functional models.
ISSN: 0029-8549

hal-01032433
https://hal.archives-ouvertes.fr/hal-01032433
DOI : 10.1007/s00442-013-2724-6

Éditeur(s) : HAL CCSD
Résumé :  
absent
25. International Biometric Conference
Florianopolis, Brazil

hal-01032104
https://hal.archives-ouvertes.fr/hal-01032104

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000 mm yr(-1) (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall < 2000 mm yr(-1).
ISSN: 1726-4170

hal-01557759
https://hal.univ-lorraine.fr/hal-01557759
https://hal.univ-lorraine.fr/hal-01557759/document
https://hal.univ-lorraine.fr/hal-01557759/file/bg-13-2537-2016.pdf
DOI : 10.5194/bg-13-2537-2016

Éditeur(s) : HAL CCSD Hindawi Publishing Corporation
Résumé : International audience
ISSN: 1687-9708

hal-01555344
https://hal.univ-lorraine.fr/hal-01555344
DOI : 10.1155/2014/389409

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : Key messageWe review the recent findings on the influence of drought on tree mortality, growth or ecosystem functioning in tropical rainforests. Drought plays a major role in shaping tropical rainforests and the response mechanisms are highly diverse and complex. The numerous gaps identified here require the international scientific community to combine efforts in order to conduct comprehensive studies in tropical rainforests on the three continents. These results are essential to simulate the future of these ecosystems under diverse climate scenarios and to predict the future of the global earth carbon balance.[br/]ContextTropical rainforest ecosystems are characterized by high annual rainfall. Nevertheless, rainfall regularly fluctuates during the year and seasonal soil droughts do occur. Over the past decades, a number of extreme droughts have hit tropical rainforests, not only in Amazonia but also in Asia and Africa. The influence of drought events on tree mortality and growth or on ecosystem functioning (carbon and water fluxes) in tropical rainforest ecosystems has been studied intensively, but the response mechanisms are complex.[br/]AimsHerein, we review the recent findings related to the response of tropical forest ecosystems to seasonal and extreme droughts and the current knowledge about the future of these ecosystems.[br/]ResultsThis review emphasizes the progress made over recent years and the importance of the studies conducted under extreme drought conditions or in through-fall exclusion experiments in understanding the response of these ecosystems. It also points to the great diversity and complexity of the response of tropical rainforest ecosystems to drought.[br/]ConclusionThe numerous gaps identified here require the international scientific community to combine efforts in order to conduct comprehensive studies in tropical forest regions. These results are essential to simulate the future of these ecosystems under diverse climate scenarios and to predict the future of the global earth carbon balance.
ISSN: 1286-4560

hal-01269438
https://hal.archives-ouvertes.fr/hal-01269438
DOI : 10.1007/s13595-015-0522-5
PRODINRA : 338568

Éditeur(s) : HAL CCSD Landes Bioscience
Résumé : International audience
In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
Autophagy

hal-00735751
https://hal.archives-ouvertes.fr/hal-00735751
PUBMED : 22966490