Résumé
1. Amazonian droughts are predicted to become increasingly frequent and intense, and the vulnerability of Amazonian trees has become increasingly documented. However, little is known about the physiological mechanisms and the diversity of drought tolerance of tropical trees due to the lack of quantitative measurements. 2. Leaf water potential at wilting or turgor loss point (πtlp) is a determinant of the tolerance of leaves to drought stress, and contributes to plant-level physiological drought tolerance. Recently, it has been demonstrated that leaf osmotic water potential at full hydration (π0) is tightly correlated with πtlp. Estimating πtlp from osmometer measurements of π0 is much faster than the standard pressure-volume curve approach of πtlp determination. We used this technique to estimate πtlp for 165 trees of 71 species, at three sites within forests in French Guiana. Our dataset represents a significant increase in available data for this trait for tropical tree species. 3. Tropical trees showed a wider range of drought tolerance than previously found in the literature, πtlp ranging from -1.4 to -3.2 MPa. This range likely corresponds in part to adaptation and acclimation to occasionally extreme droughts during the dry season. 4. Leaf-level drought tolerance varied across species, in agreement with the available published observations of species variation in drought-induced mortality. On average, species with a more negative πtlp (i.e., with greater leaf-level drought tolerance) occurred less frequently across the region than drought-sensitive species. 5. Across individuals, πtlp correlated positively but weakly with leaf toughness (R2=0.22, Accepted Article P=0.04) and leaf thickness (R2=0.03, P=0.03). No correlation was detected with other functional traits (leaf mass per area, leaf area, nitrogen or carbon concentrations, carbon isotope ratio, sapwood density or bark thickness). 6. The variability in πtlp among species indicates a potential for highly diverse species responses to drought within given forest communities. Given the weak correlations between πtlp and traditionally measured plant functional traits, vegetation models seeking to predict forest response to drought should integrate improved quantification of comparative drought tolerance among tree species
Auteurs, date et publication :
Auteurs Isabelle Maréchaux , Megan K. Bartlett , Lawren Sack , Christopher Baraloto , Julien Engel , Emilie Joetzjer , Jérôme Chave , Kaoru Kitajima
Publication : Functional Ecology
Date : 2015
Volume : 29
Issue : 10
Pages : 1268–1277
Catégorie(s)
#ANR-Citation #CIRAD #CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Laëtitia Bréchet , Stéphane Ponton , Tancrède Alméras , Damien Bonal , Daniel Epron
Publication : Plant and Soil
Date : 2011
Volume : 347
Issue : 1-2
Pages : 293–303
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Tree species-rich tropical rainforests are characterized by a highly variable quality of leaf litter input to the soil at small spatial scales. This diverse plant litter is a major source of energy and nutrients for soil microorganisms, particularly in rainforests developed on old and nutrient-impoverished soils. Here we tested the hypothesis that the variability in leaf litter quality produced by a highly diverse tree community determines the spatial variability of the microbial respiration process in the underlying soil. We analyzed a total of 225 litter-soil pairs from an undisturbed Amazonian rainforest in French Guiana using a hierarchical sampling design. The microbial respiration process was assessed using substrate-induced respiration (SIR) and compared to a wide range of quality parameters of the associated litter layer (litter nutrients, carbon forms, stoichiometry, litter mass and pH). The results show that the variability of both litter quality and SIR rates was more important at large than at small scales. SIR rates varied between 1.1 and 4.0 μg g−1 h−1 and were significantly correlated with litter layer quality (up to 50% of the variability explained by the best mixed linear model). Total litter P content was the individual most important factor explaining the observed spatial variation in soil SIR, with higher rates associated to high litter P. SIR rates also correlated positively with total litter N content and with increasing proportions of labile C compounds. However, contrary to our expectation, SIR rates were not related to litter stoichiometry. These data suggest that in the studied Amazonian rainforest, tree canopy composition is an important driver of the microbial respiration process via leaf litter fall, resulting in potentially strong plant-soil feedbacks.
Auteurs, date et publication :
Auteurs Nicolas Fanin , Stephan Hättenschwiler , Sandra Barantal , Heidy Schimann , Nathalie Fromin
Publication : Soil Biology and Biochemistry
Date : 2011
Volume : 43
Issue : 5
Pages : 1014–1022
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs D. Epron , Laclau JP , Almeida JCR , Gonçalves JLM , Ponton S , Sette Jr CR , Delgado-Rojas JS , Bouillet JP , Y. Nouvellon
Publication : Tree Physiology Advance Access
Date : 2025
Volume : 31
Pages : 1-13
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
White‐sand forests are thought to host many ectomycorrhizal fungi, as demonstrated by the numerous fruiting body collections made by Rolf Singer in the lower Rio Negro in the late 1970s. Despite recognition of the importance of ectomycorrhizal fungi in white‐sand forests, there has not yet been a systematic examination of diversity and taxonomic composition across white‐sand forests, or more widely across lowland Amazonian forests. In an effort to broaden our view of ectomycorrhizal fungal diversity and distribution on white‐sand forests, we collected ectomycorrhizal fruiting bodies in 10 plots of white‐sand forests in Brazil and French Guiana between 2012 and 2014. We collected 221 specimens and 62 morphospecies, from the 10 plots, confirming that all studied white‐sand forests host ectomycorrhizal fungi. Additionally, we searched for taxa associated with white sands among specimens deposited in Brazilian herbaria. We report 1006 unique ectomycorrhizal specimen records in 18 Brazilian herbaria, of which 137 specimens and 64 species are reported from white‐sand forests, mainly in the state of Amazonas, Brazil. Russulaceae and Amanitaceae were frequent in all habitats, and Cortinarius were more frequent on white sands. Our results highlight the high diversity and heterogeneity of ectomycorrhizal communities on white‐sand forests, and the wide distribution of ectomycorrhizal fungi throughout Brazil, irrespective of soil type.
Auteurs, date et publication :
Auteurs Mélanie Roy , Heidy Schimann , Ricardo Braga-Neto , Rosa A. E. Da Silva , Jaime Duque , Dawn Frame , Felipe Wartchow , Maria A. Neves
Publication : Biotropica
Date : 2016
Volume : 48
Issue : 1
Pages : 90–100
Catégorie(s)
#CIRAD #FORET ParacouRésumé
In the current global change context, it is urgent to anticipate the fate of tropical forests. This means understanding tree community response to disturbance and the underlying processes. In that respect, we aim here to clarify taxonomic and functional post-disturbance trajectories, and determine the scope of the Intermediate Disturbance Hypothesis (IDH) that remains debated in tropical forests. We analyzed community trajectories following a disturbance gradient from 10 to 60% of above-ground biomass loss in a Neotropical forest over 30 years. We considered trajectories along time of community taxonomic and functional trajectories in terms of richness, evenness, composition, and redundancy. We based on the annual botanical inventories of 75 ha of a Neotropical forest and on large trait datasets comprising seven leaf, stem, and life-history traits. We identified a decoupling between taxonomic composition, differing among communities, and functional composition, similar among communities and convergent in the functional space. The taxonomic diversity followed humped-shaped trajectories along time after disturbance depending on the initial disturbance intensity, which validated the IDH (Intermediate Disturbance Hypothesis). The functional diversity trajectories, however, were homogeneous among plots and dismissed the IDH. We explained this decoupling by the variations in community functional redundancy that mitigated the functional impact of disturbance. Although consistent, the recovery of community composition, diversity, and redundancy remained divergent from the initial state after 30 years. These results acknowledged the need of decades-long cycles without disturbance to ensure community complete recovery.
Auteurs, date et publication :
Auteurs A. Mirabel , B. Hérault , E. Marcon
Publication : Science of The Total Environment
Date : 2020
Volume : 720
Pages : 137397
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Heidy Schimann , Cyrille Bach , Juliette Lengelle , Eliane Louisanna , Sandra Barantal , Claude Murat , Marc Buée
Publication : Microbial Ecology
Date : 2017
Volume : 73
Issue : 2
Pages : 310–320
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The study of decay resistance in wood is of interest for wood end-users but also for the global carbon balance since wood biodegradation is a key driver of forest ecosystem functioning through its impacts on carbon and nutrient cycling. We studied the density and wood extractive contents in order to understand decay resistance against soil microflora after 90 days exposure of sapwood and heartwood from three Neotropical wood species known for their decay resistance: Bocoa prouacensis, Vouacapoua americana, Inga alba. Decay resistance was correlated with density more than wood extractive content. The results highlighted different decay resistance strategies. In B. prouacensis, both sapwood and heartwood were highly resistant due to the high density and high content of antifungal wood extractives. In V. americana heartwood, decay resistance was due to the high synergistic-acting wood extractive content. Conversely, with the least dense wood species I. alba, we found that decay resistance was due to the antifungal wood extractives synthesized early in the sapwood. In conclusion, we showed that the three wood species with the same level of heartwood decay resistance performance had different decay resistance strategies according to the anatomic and defensive wood traits.
Auteurs, date et publication :
Auteurs N. Amusant , M. Nigg , B. Thibaut , J. Beauchene
Publication : International Biodeterioration & Biodegradation
Date : 2014
Volume : 94
Pages : 103–108
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Human-caused alterations of the carbon and nutrient cycles are expected to impact tropical ecosystems in the near future. Here we evaluated how a combined change in carbon (C), nitrogen (N) and phosphorus (P) availability affects soil and litter microbial respiration and litter decomposition in an undisturbed Amazonian rainforest in French Guiana. In a fully factorial C (as cellulose), N (as urea), and P (as phosphate) fertilization experiment we analyzed a total of 540 litterbag-soil pairs after a 158-day exposure in the field. Rates of substrate-induced respiration (SIR) measured in litter and litter mass loss were similarly affected by fertilization showing the strongest stimulation when N and P were added simultaneously. The stimulating NP effect on litter SIR increased considerably with increasing initial dissolved organic carbon (DOC) concentrations in litter, suggesting that the combined availability of N, P, and a labile C source has a particularly strong effect on microbial activity. Cellulose fertilization, however, did not further stimulate the NP effect. In contrast to litter SIR and litter mass loss, soil SIR was reduced with N fertilization and showed only a positive effect in response to P fertilization that was further enhanced with additional C fertilization. Our data suggest that increased nutrient enrichment in the studied Amazonian rainforest can considerably change microbial activity and litter decomposition, and that these effects differ between the litter layer and the underlying soil. Any resulting change in relative C and nutrient fluxes between the litter layer and the soil can have important consequences for biogeochemical cycles in tropical forest ecosystems.
Auteurs, date et publication :
Auteurs Nicolas Fanin , Sandra Barantal , Nathalie Fromin , Heidy Schimann , Patrick Schevin , Stephan Hättenschwiler , Caroline P. Slomp
Publication : Plos One
Date : 2012
Volume : 7
Issue : 12
Pages : e49990
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Tropical forest mortality is controlled by both biotic and abiotic processes, but how these processes interact to determine forest structure is not well understood. Using long‐term demography data from permanent forest plots at the Paracou Tropical Forest Research Station in French Guiana, we analysed the relative influence of competition and climate on tree mortality. We found that self‐thinning is evident at the stand level, and is associated with clumped mortality at smaller scales (textless2 m) and regular spacing of living trees at intermediate (2.5–7.5 m) scales. A competition index (CI) based on spatial clustering of dead trees was used to build predictive mortality models, which also accounted for climate interactions. The model that most closely fitted observations included both the CI and climatic variables, with climate‐only and competition‐only models less informative than the full model. There was strong evidence for U‐shaped size‐specific mortality, with highest mortality for small and very large trees, as well as sensitivity of trees to drought, especially when temperatures were high, and when soils were water saturated. The effect of the CI was more complex than expected a priori: a higher CI was associated with lower mortality odds, which we hypothesize is caused by gap‐phase dynamics, but there was also evidence for competition‐induced mortality at very high CI values. The strong signature of competition as a control over mortality at the stand and individual scales confirms its important role in determining tropical forest structure. The complexity of the competition‐mortality relationship and its interaction with climate indicates that a thorough consideration of the scale of analysis is needed when inferring the role of competition in tropical forests, but demonstrates that climate‐only mortality models can be significantly improved by including competition effects, even when ignoring species‐specific effects. Synthesis. Empirical models such as the one developed here can help constrain and improve process‐based vegetation models, serving both as a benchmark and as a means to disentangle mortality processes. Tropical vegetation dynamic models would benefit greatly from explicitly considering the role of competition in stand development and self‐thinning while modelling demography, as well as its interaction with climate.
Auteurs, date et publication :
Auteurs Michiel Pillet , Emilie Joetzjer , Camille Belmin , Jérôme Chave , Philippe Ciais , Aurélie Dourdain , Margaret Evans , Bruno Hérault , Sebastiaan Luyssaert , Benjamin Poulter , Shurong Zhou
Publication : Journal of Ecology
Date : 2018
Volume : 106
Issue : 3
Pages : 1165–1179