Résumé
Many plant species have dorsiventral leaves that have significant differences in optical properties from one side to the other. Several studies have revealed that ignoring this asymmetry induces significant errors in plant canopy reflectance, and current leaf models simulating leaf dorsiventrality are limited to the 0.4–2.5 μm wavelength range. This article, partly based on two recently collected datasets in the 2.5–14 μm wavelength range, demonstrates that ignoring leaf dorsiventrality induces significant errors in brightness temperature and effective emissivity at the canopy scale. The PROLIB model, which inherits from the PROSPECT-VISIR and LIBERTY models, is the first radiative transfer model to simulate the reflectance and transmittance of both leaf sides from 0.4 to 5.7 μm. The palisade and spongy mesophylls are represented as plate and sphere layers, respectively, to account for the structural asymmetry of leaf cells. The sieve effect that explains the differences in transmittance between the adaxial and abaxial sides of the leaf is successfully incorporated into PROLIB. Evaluation of the model on several leaf datasets shows that: (1) It reproduces well the adaxial and abaxial optical properties of the leaves, with a root mean square error (RMSE) of 0.0109 for reflectance and transmittance. (2) It can be inversed to retrieve leaf traits, with RMSE values for leaf chlorophyll, carotenoid, anthocyanin, water, and dry matter content of 5.519 μg/cm2, 2.344 μg/cm2, 4.219 μg/cm2, 0.0022 g/cm2, and 0.0017 g/cm2, respectively (corresponding normalized RMSE values of 22.0%, 34.0%, 49.4%, 19.6%, and 24.7%). However, better and more complete leaf datasets are needed for leaf dorsiventrality analysis and model calibration.
Auteurs, date et publication :
Auteurs Hanyu Shi , Stéphane Jacquemoud , Jingyi Jiang , Minqiang Zhou , Sophie Fabre , Andrew D. Richardson , Shuang Wang , Xuju Jiang , Zhiqiang Xiao
Publication : Remote Sensing of Environment
Date : 2025
Volume : 306
Pages : 114140
Catégorie(s)
#CNRS #FORET NouraguesRésumé
The fundamental trade-off between current and future reproduction has long been considered to result in a tendency for species that can grow large to begin reproduction at a larger size. Due to the prolonged time required to reach maturity, estimates of tree maturation size remain very rare and we lack a global view on the generality and the shape of this trade-off. Using seed production from five continents, we estimate tree maturation sizes for 486 tree species spanning tropical to boreal climates. Results show that a species' maturation size increases with maximum size, but in a non-proportional way: the largest species begin reproduction at smaller sizes than would be expected if maturation were simply proportional to maximum size. Furthermore, the decrease in relative maturation size is steepest in cold climates. These findings on maturation size drivers are key to accurately represent forests' responses to disturbance and climate change.
Auteurs, date et publication :
Auteurs Valentin Journé , Michał Bogdziewicz , Benoit Courbaud , Georges Kunstler , Tong Qiu , Marie‐Claire Aravena Acuña , Davide Ascoli , Yves Bergeron , Daniel Berveiller , Thomas Boivin , Raul Bonal , Thomas Caignard , Maxime Cailleret , Rafael Calama , J. Julio Camarero , Chia‐Hao Chang‐Yang , Jerome Chave , Francesco Chianucci , Thomas Curt , Andrea Cutini
Publication : Ecology Letters
Date : 2025
Volume : 27
Issue : 9
Pages : e14500
Catégorie(s)
#CNRS #FORET OPTMix #FORET Puechabon #INRAERésumé
The future of tropical forests hinges on the balance between disturbance rates, which are expected to increase with climate change, and tree growth. Whereas tree growth is a slow process, disturbance events occur sporadically and tend to be short-lived. This difference challenges forest monitoring to achieve sufficient resolution to capture tree growth, while covering the necessary scale to characterize disturbance rates. Airborne LiDAR time series can address this challenge by measuring landscape scale changes in canopy height at 1 m resolution. In this study, we present a robust framework for analysing disturbance and recovery processes in LiDAR time series data. We apply this framework to 8000 ha of old-g rowth tropical forests over a 4–5- year time frame, comparing growth and disturbance rates between Borneo, the eastern Amazon and the Guiana shield. Our findings reveal that disturbance was balanced by growth in eastern Amazonia and the Guiana shield, resulting in a relatively stable mean canopy height. In contrast, tall Bornean forests experienced a decrease in canopy height due to numerous small-scale (<0.1 ha) disturbance events outweighing the gains due to growth. Within sites, we found that disturbance rates were weakly related to topography, but significantly increased with maximum canopy height. This could be because taller trees were particularly vulnerable to disturbance agents such as drought, wind and lightning. Consequently, we anticipate that tall forests, which contain substantial carbon stocks, will be disproportionately affected by the increasing severity of extreme weather events driven by climate change.
Auteurs, date et publication :
Auteurs Toby D. Jackson , Fabian J. Fischer , Grégoire Vincent , Eric B. Gorgens , Michael Keller , Jérôme Chave , Tommaso Jucker , David A. Coomes
Publication : Global Change Biology
Date : 2025
Volume : 30
Issue : 9
Pages : e17493
Catégorie(s)
#CNRS #FORET NouraguesRésumé
Understanding the relationship between morphology and movement in biomechanical systems, particularly those composed of multiple complex elements, presents challenges due to the nonlinear nature of the interaction between components. This study focuses on the mandibular closing mechanisms in ants, specifically comparing muscle-driven actuation (MDA) and latch-mediated spring actuation (LaMSA) in the genus Strumigenys. Analyzing 3D structural data from diverse Strumigenys species, we employ mathematical models for both LaMSA and MDA systems. Our findings reveal distinct patterns of mechanical sensitivity between the two models, with sensitivity varying across kinematic output metrics. We explore the performance transition between MDA and LaMSA systems by incorporating biological data and correlations between morphological parameters into the models. In these models tuned specifically to Strumigenys, we find the LaMSA mechanism outperforms MDA at small relative mandible mass. Notably, the location and abruptness of the performance transition differs among various kinematic performance metrics. Overall, this work contributes a novel approach to understanding form-function relationships in complex biomechanical systems. By using morphological data to calibrate a general biomechanical model for a particular group, it strikes a balance between simplicity and specificity and allows for conclusions that are uniquely tuned to the morphological characteristics of the group.Competing Interest StatementThe authors have declared no competing interest.
Auteurs, date et publication :
Auteurs Philip S L Anderson , Justin F Jorge , Stephanie B Crofts , Jackson T Castro , Rosalie L Didcock , Andrés Cook , Fredrick J Larabee , Mark Ilton
Publication : bioRxiv
Date : 2024
Pages : 2024.02.15.580213
Catégorie(s)
#CNRS #FORET NouraguesRésumé
In the context of current climate change, municipalities tend to plant more trees in order to benefit from services they provide in urban areas, such as reducing heat islands. However, in cities, trees are subject to severe abiotic constraints, the main ones being soil contamination and the lack of water due to soil compaction and droughts. This can negatively impact the ecological services provided by trees. Our study aims to help managers in monitoring the phytosanitary status of trees in order to be able to react promptly. In a controlled condition experiment, different plant compounds were analyzed (proline, malondialdehyde-MDA, photosynthetic pigments) in the leaves of young linden trees conventionally grown for planting by the City of Paris, France. They were grown on a trace element (TE) contamination soil gradient, and under different water regimes (well-hydrated/no water stress (Ct), dehydration (Dh), rehydration (Rh)) to see if tested compounds could be early stress markers in trees. Chlorophylls (Chl) could be considered as water and TE-mediated stress markers. Indeed Chl a and b concentrations significantly decreased with dehydration (e.g. respectively -34 % and -24 %) and increasing lead concentration in leaves (respectively, correlation coefficients were -1.08; -0.64 (p < 0.001)). On the contrary, Chl concentrations increased with increasing copper concentration in optimal physiological ranges (correlation coefficients for Chla and Chb were respectively 1.3 and 1.08 (p < 0.05)). Proline and malondialdehyde seemed to be good complementary markers of water stress in the Tilia genus. Indeed, proline concentration increased during the dehydration period (early water stress marker) (mean concentration for Ct, Dh and Rh trees were respectively 3.6, 29.6 and 51.3 mu mol.g(-1) DW), while MDA increased during the rehydration process (marker for stress accumulation over time) (mean concentration for Ct, Dh, and Rh were respectively 461.8, 313.9 and 493.5 nmol.g(-1) DW). In order to reinforce the diagnoses of urban tree managers, these stress indicators should be tested in situ.
Auteurs, date et publication :
Auteurs Iry Andrianjara , Cecile Cabassa , Jean-Christophe Lata , Amandine Hansart , Xavier Raynaud , Mathilde Renard , Francois Nold , Patricia Genet , Severine Planchais
Publication : ECOLOGICAL INDICATORS
Date : 2024
Volume : 158
Catégorie(s)
#ANR-Citation #CEREEP #CNRS #ENSRésumé
In some angiosperm species, especially in the Malvaceae family, postural control and directional growth of the stem are enabled by the mechanical interaction between the growing cambium and the secondary phloem. A key feature of this motor mechanism is the ability to redirect the tangential stress induced in secondary phloem into a longitudinal stress enabling the control of stem orientation. Here we studied how the microstructure of the secondary phloem is optimized for this function. We measured the longitudinal-tangential Poisson’s ratio and the longitudinal modulus of elasticity of secondary phloem in 22 tree species including Malvaceae and other families. We modeled the microstructure of Malvaceae secondary phloem using finite elements. The Poisson’s ratio of secondary phloem from Malvaceae trees was found one to two orders of magnitude higher than for other species, reaching the highest values ever reported for a natural material. Mechanical modeling confirmed these results and showed that parameters of the microstructure of secondary phloem are set at value optimizing this Poisson’s ratio. This highlights that the specific microstructure of Malvaceae secondary phloem is designed to maximize the conversion of cambial growth pressure into a longitudinal mechanical stress enabling the directional growth.
Auteurs, date et publication :
Auteurs Tancrède Alméras , Stéphane Corn , Anne Baranger , Arnaud Regazzi , Jonathan Barés , Romain Lehnebach , Bruno Clair
Publication : Trees
Date : 2025
Volume : 38
Issue : 6
Pages : 1379-1390
Catégorie(s)
#CNRS #FORET NouraguesRésumé
One foundational assumption of trait-based ecology is that traits can predict species demography. However, the links between traits and demographic rates are, in general, not as strong as expected. These weak associations may be due to the use of traits that are distantly related to performance, and/or the lack of consideration of size-related variations in both traits and demographic rates. Here, we examined how wood traits were related to demographic rates in 19 tree species from a lowland forest in eastern Amazonia. We measured 11 wood traits (i.e. structural, anatomical and chemical traits) in sapling, juvenile and adult wood; and related them to growth and mortality rates (MR) at different ontogenetic stages. The links between wood traits and demographic rates changed during tree development. At the sapling stage, relative growth rates (RGR) were negatively related to wood specific gravity (WSG) and total parenchyma fractions, while MR decreased with radial parenchyma fractions, but increased with vessel lumen area (VA). Juvenile RGR were unrelated to wood traits, whereas juvenile MR were negatively related to WSG and axial parenchyma fractions. At the adult stage, RGR scaled with VA and wood potassium concentrations. Adult MR were not predicted by any trait. Overall, the strength of the trait-demography associations decreased at later ontogenetic stages. Our results indicate that the associations between traits and demographic rates can change as trees age. Also, wood chemical or anatomical traits may be better predictors of growth and MR than WSG. Our findings are important to expand our knowledge on tree life-history variations and community dynamics in tropical forests, by broadening our understanding on the links between wood traits and demography during tree development.
Auteurs, date et publication :
Auteurs Andrés González-Melo , Juan Manuel Posada , Jacques Beauchêne , Romain Lehnebach , Sébastian Levionnois , Géraldine Derroire , Bruno Clair , Juliana Medeiros
Publication : AoB PLANTS
Date : 2024
Volume : 16
Issue : 1
Pages : plad090
Catégorie(s)
#CIRAD #CNRS #FORET Nouragues #FORET ParacouRésumé
Maintaining a healthy gut microbiome plays a critical role in avoiding gut-related pathologies. Bacterial adherence to the intestinal epithelium plays a vital role in niche establishment in the gut, as in vitro experiments and mathematical modeling suggest that adherence provides a strong competitive advantage over free-floating planktonic microbes. Currently, we lack the ability to study gut microbiome adherence in an in vivo model system. Through sampling natural populations of Caenorhabditis, we discovered three bacterial species that adhere to the intestinal epithelium of several wild Caenorhabditis isolates. When transferred to C. elegans, all three bacterial species colonized the entire anterior to posterior length of the intestine lumen. We isolated these bacterial species via in vitro growth or selective enrichment in the nematode gut and identified them as Lelliottia jeotgali, Candidatus Lumenectis limosiae, and Candidatus Enterosymbion pterelaium, the latter two representing new species. Adherent Ca. L. limosiae negatively affects host fitness, while Lelliottia jeotgali and Ca. E. pterelaium exhibited a neutral effect in our assays. We demonstrated that two of these species can actively proliferate in the intestine throughout the host lifespan, with Lelliottia jeotgali colonizing throughout the lumen simultaneously and Candidatus Lumenectis limosiae showing anterior-to-posterior directionality. In competition assays, animals pre-colonized with L. jeotgali significantly reduced colonization by pathogenic Ca. L. limosiae, but this effect was not seen when animals were colonized by both bacteria simultaneously. Strikingly, regardless of the colonization paradigm, populations exposed to both bacteria showed a near-identical mitigation of the pathogenic effects of Ca. L. limosiae. Altogether, these strains illustrate the capacity of microbiome bacteria to adhere, replicate, and establish a niche across the entire intestinal lumen in C. elegans and they present an opportunity to study bacterial adherence in the context of a whole, intact and transparent animal.Competing Interest StatementThe authors have declared no competing interest.
Auteurs, date et publication :
Auteurs Dalaena E Rivera , Kayla Poirier , Samuel Moore , Ophélie Nicolle , Emily Morgan , Jonah-Faye Longares , Anupama Singh , Grégoire Michaux , Marie-Anne Félix , Robert J Luallen
Publication : bioRxiv
Date : 2024
Pages : 2024.10.24.620080
Catégorie(s)
#CNRS #FORET NouraguesRésumé
Understanding the relative importance of biotic interactions, multiple environmental drivers, and neutral processes in shaping community diversity and composition is a central question for both theoretical and applied ecology. We analysed a dataset describing 125 earthworm communities sampled in 10 localities in French Guiana. DNA barcodes were used to delimit operational taxonomic units (OTUs) that we considered as species surrogates to avoid the taxonomic deficit and calculate community-scale species richness and pair-wise Sørensen beta-diversity. We used log-ratio and generalised linear models to highlight the effects of biotic interactions and environment as drivers of alpha diversity, and generalised dissimilarity models to figure out the relative contribution of space and environment to beta-diversity at different spatial extents. Community-scale alpha diversity was mainly explained by habitat filtering (soil texture) and interspecific competition that limit the number of locally co-existing species. Beta diversity between pairs of communities was mainly explained by distance when comparing communities in similar habitats, by topography and available soil phosphorus when comparing communities in different habitats, and by distance, elevation and climate when comparing all possible pairs of communities. While community composition is determined locally by neutral processes and environmental filtering, biogeographic processes linked to dispersal limitation and adaptation to local environment are the most influential on a regional scale. This highlights the complex interplay of dispersal limitation, biotic interactions and environmental filtering during the process of community assembly.
Auteurs, date et publication :
Auteurs Arnaud Goulpeau , Mickaël Hedde , Pierre Ganault , Emmanuel Lapied , Marie-Eugénie Maggia , Eric Marcon , Thibaud Decaëns
Publication : Oecologia
Date : 2025
Volume : 207
Issue : 9
Pages : 151
Catégorie(s)
#CNRS #FORET NouraguesRésumé
Parent-offspring interactions constitute the first contact of many newborns with their environment, priming community assembly of microbes through priority effects and shaping host health and disease. Microbe acquisition during parental care is well studied in humans and agriculturally relevant species but remains poorly understood in other vertebrate groups, such as amphibians. Here, we investigate vertical transmission of skin microbiota in poison frogs (Dendrobatidae), where fathers transport tadpoles piggyback-style from terrestrial clutches to aquatic nurseries. We found that substantial bacterial colonization of embryos begins after hatching, suggesting that the vitelline envelope acts as a microbial barrier. A cross-foster experiment demonstrated that poison frogs performing tadpole transport serve as a source of skin microbes for tadpoles on their back. To study how transport impacts skin communities of tadpoles in an ecologically relevant setting, we sampled sympatric species that do or do not exhibit tadpole transport in their natural habitat. We did not find a higher degree of similarity between microbial communities of tadpoles and adults in species that transport their offspring compared to those that do not. Similarly, communities of tadpoles were no more similar to their caregiver than to unrelated adults, indicating that most caregiver-associated microbes do not remain in tadpole communities long-term. Nonetheless, some taxa persisted on tadpoles over development. This study is the first to demonstrate that offspring transport facilitates transmission of parental skin microbes in anurans.
Auteurs, date et publication :
Auteurs Marie-Therese Fischer , Katherine S Xue , Elizabeth K Costello , Mai Dvorak , Gaelle Raboisson , Anna Robaczewska , Stephanie N Caty , David A Relman , Lauren A O'Connell , Jenny Tung , Sergio Rasmann
Publication : eLife
Date : 2025
Volume : 14
Pages : RP103331