Résumé
Changes in terrestrial tropical carbon stocks have an important role in the global carbon budget. However, current observational tools do not allow accurate and large-scale monitoring of the spatial distribution and dynamics of carbon stocks'. Here, we used low-frequency L-band passive microwave observations to compute a direct and spatially explicit quantification of annual aboveground carbon (AGC) fluxes and show that the tropical net AGC budget was approximately in balance during 2010 to 2017, the net budget being composed of gross losses of -2.86 PgC yr(-1) offset by gross gains of -2.97 PgC yr(-1) between continents. Large interannual and spatial fluctuations of tropical AGC were quantified during the wet 2011 La Nina year and throughout the extreme dry and warm 2015-2016 El Nino episode. These interannual fluctuations, controlled predominantly by semiarid biomes, were shown to be closely related to independent global atmospheric CO2 growth-rate anomalies (Pearson's r = 0.86), highlighting the pivotal role of tropical AGC in the global carbon budget.
Auteurs, date et publication :
Auteurs Lei Fan , Jean-Pierre Wigneron , Philippe Ciais , Jerome Chave , Martin Brandt , Rasmus Fensholt , Sassan S. Saatchi , Ana Bastos , Amen Al-Yaari , Koen Hufkens , Yuanwei Qin , Xiangming Xiao , Chi Chen , Ranga B. Myneni , Roberto Fernandez-Moran , Arnaud Mialon , N. J. Rodriguez-Fernandez , Yann Kerr , Feng Tian , Josep Penuelas
Publication : NATURE PLANTS
Date : 2019
Volume : 5
Issue : 9
Pages : 944-951
Catégorie(s)
#ANR-Citation #CNRS #FORET NouraguesRésumé
Continental relative humidity (RH) is a key climate parameter, but there is a lack of quantitative RH proxies suitable for climate model-data comparisons. Recently, a combination of climate chamber and natural transect calibrations have laid the groundwork for examining the robustness of the triple oxygen isotope composition (delta O-'18 and O-17-excess) of phytoliths, that can preserve in sediments, as a new proxy for past changes in RH. However, it was recommended that besides RH, additional factors that may impact delta'O-18 and O-17-excess of plant water and phytoliths be examined. Here, the effects of grass leaf length, leaf development stage and day-night alternations are addressed from growth chamber experiments. The triple oxygen isotope compositions of leaf water and phytoliths of the grass species F. arundinacea are analysed. Evolution of the leaf water delta'O-18 and O-17-excess along the leaf length can be modelled using a string-of-lakes approach to which an unevaporated-evaporated mixing equation must be added. We show that for phytoliths to record this evolution, a kinetic fractionation between leaf water and silica, increasing from the base to the apex, must be assumed. Despite the isotope heterogeneity of leaf water along the leaf length, the bulk leaf phytolith delta'O-18 and O-17-excess values can be estimated from the Craig and Gordon model and a mean leaf water-phytolith fractionation exponent (lambda(Phyto-LW)) of 0.521. In addition to not being leaf length dependent, delta'O-18 and O-17-excess of grass phytoliths are expected to be impacted only very slightly by the stem vs. leaf biomass ratio. Our experiment additionally shows that because a lot of silica polymerises in grasses when the leaf reaches senescence (58 % of leaf phytoliths in mass), RH prevailing during the start of senescence should be considered in addition to RH prevailing during leaf growth when interpreting the O-17-excess of grass bulk phytoliths. Although under the study conditions O-17-excess(Phyto) do not vary significantly from constant day to day-night conditions, additional monitoring at low RH conditions should be done before drawing any generalisable conclusions. Overall, this study strengthens the reliability of the O-17-excess of phytoliths to be used as a proxy of RH. If future studies show that the mean value of 0.521 used for the grass leaf water-phytolith fractionation exponent lambda(Phyto-LW) is not climate dependent, then grassland leaf water O-17-excess obtained from grassland phytolith O-17-excess would inform on isotope signals of several soil-plant-atmosphere processes.
Auteurs, date et publication :
Auteurs Anne Alexandre , Elizabeth Webb , Amaelle Landais , Clement Piel , Sebastien Devidal , Corinne Sonzogni , Martine Couapel , Jean-Charles Mazur , Monique Pierre , Frederic Prie , Christine Vallet-Coulomb , Clement Outrequin , Jacques Roy
Publication : BIOGEOSCIENCES
Date : 2019
Volume : 16
Issue : 23
Pages : 4613-4625
Catégorie(s)
#ANR-Citation #CNRS #Ecotron de MontpellierRésumé
Prolonged and complex courtship behaviors, involving tactile, acoustic, and visual signals, are common in Neotropical poison frogs (Dendrobatidae). Courtship is an important precursor to mating, but courtship components vary across species. In Brilliant-Thighed Poison Frogs (Allobates femorlis [Boulanger 1883]), males guide females to oviposition sites in a so-called “courtship march.” The courtship duration in A. femorlis is among the longest known in poison frogs. To gain insights into the functions of courtship, we observed 29 courtship events in an A. femorlis population in French Guiana. In addition, we observed multiple courtships of 7 males to assess intra- and interindividual variations in courtship behavior. We recorded temporal, spatial, and behavioral characteristics of courtship and searched for previously deposited clutches in the males' territories. Courtships started in the afternoon and ended on the following morning. During courtship, pairs moved an average of 19 m within an area of about 6 m(2). Twenty-seven out of 29 courtships (93.1%) resulted in successful oviposition, indicating that females rarely reject males once engaged in courtship. Contrary to previous studies of A. femoralis, the spatial and temporal extent of the courtship march did not correlate with the size of a male's territory. Our results indicate that females do not evaluate male quality during courtship but might need an extended courtship phase to verify territory ownership of the courting male and to stimulate ovulation. The prolonged courtship might also be beneficial for spatial learning by females, allowing them to find clutches again in cases of mate loss. Temporal and spatial characteristics vary considerably within and among individuals, and males do not use the same routes in consecutive courtships. However, they probably show females previous clutches. Several courtship traits in our study population differ from A. femoralis courtship previously described from Peru and Brazil, indicating that dendrobatid courtship is variable among populations.
Auteurs, date et publication :
Auteurs Susanna Stueckler , Max Ringler , Andrius Pasukonis , Steffen Weinlein , Walter Hoedl , Eva Ringler
Publication : HERPETOLOGICA
Date : 2019
Volume : 75
Issue : 4
Pages : 268-279
Catégorie(s)
#ANR-Citation #CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Sruthi M Krishna Moorthy , Pasi Raumonen , Jan Van den Bulcke , Kim Calders , Hans Verbeeck
Publication : Forest Ecology and Management
Date : 2025
Volume : 456
Pages : 117751
Catégorie(s)
#CNRS #FORET NouraguesRésumé
Leaf-inhabiting fungal and bacterial endophytes are at their most diverse in tropical rainforest plant hosts, with some influencing host plant fitness as either symbionts or pathogens. Endophyte activity and community composition is thought to depend on competition amongst co-occurring species for resources. Here, we reveal the strength of competitive interactions between endophytes by combining e-DNA metabarcoding to characterize the community with culturing assays to ascertain their potential activity. The endophyte community associated with the understory palm Astrocaryum sciophilum was determined by extracting eDNA from 120 leaflets of eight plants located in a lowland rainforest in French Guiana. This revealed 516 fungal and 606 bacterial Operational Taxonomic Units (OTUs). Co-occurrence analysis of the most abundant OTUs revealed that direct fungal-fungal interactions were overall more negative than bacterial-bacterial interactions. This was confirmed by C-score calculations for the whole endophyte community, revealing significantly greater levels of species segregation for fungi but not bacteria when compared with simulated random communities. Following the culturing of 131 fungal, and 66 bacterial Astrocaryum endophytes collected from the same leaves, Minimal Inhibitory Concentrations of ethyl acetate culture extracts were evaluated against the fungus Trichophyton rubrum and the bacterium Staphylococcus aureus. Overall, a minority of extracts demonstrated antipathogen activity, with greater antifungal activity expression for both fungi and bacteria when compared with antibacterial activity. In order to explore whether this activity translated into competitive structuring of the community, a BLAST was conducted to match metabarcoding sequences with Sanger derived culture sequences. This demonstrated that cultures displaying antipathogen activity were significantly more likely to co-occur with fungi if they were bacteria, and bacteria if they were fungi. Nevertheless, overall correlation values averaged around zero. These results indicate that for Astrocaryum palms, fungal endophytes are likely to play a greater role in determining colonization success of subsequent endophytes whether these be fungal or bacterial, but that overall endophyte communities do not display strong patterns of community structuring through competition. Endophyte communities are thus likely to reach relative stasis in mature leaves, where the diverse community of fungi and bacteria amongst other factors prevent the subsequent establishment of pathogens.
Auteurs, date et publication :
Auteurs Julian Donald , Morgane Barthelemy , Nina Gazal , Yannick Eveno , Sophie Manzi , Veronique Eparvier , Didier Stien , Melanie Roy
Publication : FRONTIERS IN FORESTS AND GLOBAL CHANGE
Date : 2019
Volume : 2
Catégorie(s)
#ANR-Citation #CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Stephanie C Bodin , Jean-François Molino , Guillaume Odonne , Laurent Bremond
Publication : Vegetation History and Archaeobotany
Date : 2025
Pages : 1-14
Catégorie(s)
#CNRS #FORET NouraguesRésumé
Anthropogenic perturbations such as harvesting often select against a large body size and are predicted to induce rapid evolution toward smaller body sizes and earlier maturation. However, body-size evolvability and, hence, adaptability to anthropogenic perturbations remain seldom evaluated in wild populations. Here, we use a laboratory experiment over 6 generations to measure the ability of wild-caught medaka fish (Oryzias latipes) to evolve in response to bidirectional size-dependent selection mimicking opposite harvest regimes. Specifically, we imposed selection against a small body size (Large line), against a large body size (Small line) or random selection (Control line), and measured correlated responses across multiple phenotypic, life-history, and endocrine traits. As expected, the Large line evolved faster somatic growth and delayed maturation, but also evolved smaller body sizes at hatch, with no change in average levels of pituitary gene expressions of luteinizing, follicle-stimulating, or growth hormones (GH). In contrast, the Small medaka line was unable to evolve smaller body sizes or earlier maturation, but evolved smaller body sizes at hatch and showed marginally significant signs of increased reproductive investment, including larger egg sizes and elevated pituitary GH production. Natural selection on medaka body size was too weak to significantly hinder the effect of artificial selection, indicating that the asymmetric body-size response to size-dependent selection reflected an asymmetry in body-size evolvability. Our results show that trait evolvability may be contingent upon the direction of selection and that a detailed knowledge of trait evolutionary potential is needed to forecast population response to anthropogenic change.
Auteurs, date et publication :
Auteurs Clémentine Renneville , Alexis Millot , Simon Agostini , David Carmignac , Gersende Maugars , Sylvie Dufour , Arnaud Le Rouzic , Eric Edeline
Publication : Ecology and Evolution
Date : 2025
Volume : 10
Issue : 19
Pages : 10571-10592
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
Anthropogenic change in the abundance or identity of dominant top predators may induce reorganizations in whole food webs. Predicting these reorganizations requires identifying the biological rules that govern trophic niches. However, we still lack a detailed understanding of the respective contributions of body size, behaviour (e.g. match between predator hunting mode and prey antipredator strategy), phylogeny and/or ontogeny in determining both the presence and strength of trophic interactions. Here, we address this question by measuring zooplankton numerical response to fish predators in lake enclosures. We compared the fit to zooplankton count data of models grouping zooplankters based either on 1) body sizes, 2) antipredator behaviour, 3) body size combined with antipredator behaviour, or on 4) phylogeny combined with ontogeny (i.e. different life stages of copepods). Body size was a better predictor of zooplankton numerical response to fish than antipredator behaviour, but combining body size and behaviour provided even better predictions. Models based on phylogeny combined with ontogeny clearly outperformed those based on other zooplankton grouping rules, except when phylogeny was poorly resolved. Removing ontogenetic information plagued the predictive power of the highly-resolved (genus-level) phylogenetic grouping but not of medium-resolved or poorly-resolved phylogenetic grouping. Our results support the recent use of phylogeny as a superior surrogate for traits controlling trophic niches, and further highlight the added value of combining phylogeny with ontogenetic traits. Further improvements in our mechanistic understanding of how trophic networks are shaped are bound to uncovering the trophic traits captured by phylogeny and ontogeny, but that currently remain hidden to us. This article is protected by copyright. All rights reserved.
Auteurs, date et publication :
Auteurs Florian Vincent , Andrea Bertolo , Gérard Lacroix , Maud Mouchet , Eric Edeline
Publication : Oikos
Date : 2025
Volume : n/a
Issue : n/a
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
The leaf economics spectrum (LES) is based on a suite of leaf traits related to plant functioning and ranges from resource-conservative to resource-acquisitive strategies. However, the relationships with root traits, and the associated belowground plant functioning such as N uptake, including nitrate (NO3−) and ammonium (NH4+), is still poorly known. Additionally, environmental variations occurring both in time and in space could uncouple LES from root traits. We explored, in subalpine grasslands, the relationships between leaf and root morphological traits for three dominant perennial grass species, and to what extent they contribute to the whole-plant economics spectrum. We also investigated the link between this spectrum and NO3− and NH4+ uptake rates, as well as the variations of uptake across four grasslands differing by the land-use history at peak biomass and in autumn. Although poorly correlated with leaf traits, root traits contributed to an economic spectrum at the whole plant level. Higher NH4+ and NO3− uptake abilities were associated with the resource-acquisitive strategy. Nonetheless, NH4+ and NO3−-uptake within species varied between land-uses and with sampling time, suggesting that LES and plant traits are good, but still incomplete, descriptors of plant functioning. Although the NH4+:NO3− uptake ratio was different between plant species in our study, they all showed a preference for NH4+, and particularly the most conservative species. Soil environmental variations between grasslands and sampling times may also drive to some extent the NH4+ and NO3− uptake ability of species. Our results support the current efforts to build a more general framework including above- and below-ground processes when studying plant community functioning.
Auteurs, date et publication :
Auteurs Nicolas Legay , Fabrice Grassein , Cindy Arnoldi , Raphael Segura , Philippe Laîné , Sandra Lavorel , Jean-Christophe Clément
Publication : Oikos
Date : 2025
Volume : 129
Issue : 6
Pages : 830-841
Catégorie(s)
#CNRS #Lautaret #UGARésumé
In the processes controlling ecosystem fertility, fungi are increasingly acknowledged as key drivers. However, our understanding of the rules behind fungal community assembly regarding the effect of soil fertility level remains limited. Using soil samples from typical tea plantations spanning c. 2167 km north-east to south-west across China, we investigated the assemblage complexity and assembly processes of 140 fungal communities along a soil fertility gradient. The community dissimilarities of total fungi and fungal functional guilds increased with increasing soil fertility index dissimilarity. The symbiotrophs were more sensitive to variations in soil fertility compared with pathotrophs and saprotrophs. Fungal networks were larger and showed higher connectivity as well as greater potential for inter-module connection in more fertile soils. Environmental factors had a slightly greater influence on fungal community composition than spatial factors. Species abundance fitted the Zipf–Mandelbrot distribution (niche-based mechanisms), which provided evidence for deterministic-based processes. Overall, the soil fungal communities in tea plantations responded in a deterministic manner to soil fertility, with high fertility correlated with complex fungal community assemblages. This study provides new insights that might contribute to predictions of fungal community complexity.
Auteurs, date et publication :
Auteurs Junjie Guo , Ning Ling , Zhaojie Chen , Chao Xue , Ling Li , Lisheng Liu , Limin Gao , Min Wang , Jianyun Ruan , Shiwei Guo , Philippe Vandenkoornhuyse , Qirong Shen
Publication : New Phytologist
Date : 2025
Volume : 226
Issue : 1
Pages : 232-243