Résumé
Nitrogen (N) and phosphorus (P) availability both control microbial decomposers and litter decomposition. However, these two key nutrients show distinct release patterns from decomposing litter and are unlikely available at the same time in most ecosystems. Little is known about how temporal differences in N and P availability affect decomposers and litter decomposition, which may be particularly critical for tropical rainforests growing on old and nutrient-impoverished soils. Here we used three chemically contrasted leaf litter substrates and cellulose paper as a widely accessible substrate containing no nutrients to test the effects of temporal differences in N and P availability in a microcosm experiment under fully controlled conditions. We measured substrate mass loss, microbial activity (by substrate induced respiration, SIR) as well as microbial community structure (using phospholipid fatty acids, PLFAs) in the litter and the underlying soil throughout the initial stages of decomposition. We generally found a stronger stimulation of substrate mass loss and microbial respiration, especially for cellulose, with simultaneous NP addition compared to a temporally separated N and P addition. However, litter types with a relatively high N to P availability responded more to initial P than N addition and vice versa. A third litter species showed no response to fertilization regardless of the sequence of addition, likely due to strong C limitation. Microbial community structure in the litter was strongly influenced by the fertilization sequence. In particular, the fungi to bacteria ratio increased following N addition alone, a shift that was reversed with complementary P addition. Opposite to the litter layer microorganisms, the soil microbial community structure was more strongly influenced by the identity of the decomposing substrate than by fertilization treatments, reinforcing the idea that C availability can strongly constrain decomposer communities. Collectively, our data support the idea that temporal differences in N and P availability are critical for the activity and the structure of microbial decomposer communities. The interplay of N, P, and substrate-specific C availability will strongly determine how nutrient pulses in the environment will affect microbial heterotrophs and the processes they drive.
Auteurs, date et publication :
Auteurs Nicolas Fanin , Stephan Hättenschwiler , Paola F. Chavez Soria , Nathalie Fromin
Publication : Frontiers in Microbiology
Date : 2016
Volume : 6
Pages : 1507
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Developing and improving methods to monitor forest carbon in space and time is a timely challenge, especially for tropical forests. The next European Space Agency Earth Explorer Core Mission BIOMASS will collect synthetic aperture radar (SAR) data globally from employing a multiple baseline orbit during the initial phase of its lifetime. These data will be used for tomographic SAR (TomoSAR) processing, with a vertical resolution of about 20m, a resolution sufficient to decompose the backscatter signal into two to three layers for most closed-canopy tropical forests. A recent study, conducted in the Paracou site, French Guiana, has already shown that TomoSAR significantly improves the retrieval of forest aboveground biomass (AGB) in a high biomass forest, with an error of only 10% at 1.5-ha resolution. However, the degree to which this TomoSAR approach can be transferred from one site to another has not been assessed. We test this approach at the Nouragues site in central French Guiana (ca 100km away from Paracou), and develop a method to retrieve the top-of-canopy height from TomoSAR. We found a high correlation between the backscatter signal and AGB in the upper canopy layer (i.e. 20–40m), while lower layers only showed poor correlations. The relationship between AGB and TomoSAR data was found to be highly similar for forests at Nouragues and Paracou. Cross validation using training plots from Nouragues and validation plots from Paracou, and vice versa, gave an error of 16–18% of AGB using 1-ha plots. Finally, using a high-resolution LiDAR canopy model as a reference, we showed that TomoSAR has the potential to retrieve the top-of-canopy height with an error to within 2.5m. Our analyses show that the TomoSAR-AGB retrieval method is accurate even in hilly and high-biomass forest areas and suggest that our approach may be generalizable to other study sites, having a canopy taller than 30m. These results have strong implications for the tomographic phase of the BIOMASS spaceborne mission.
Auteurs, date et publication :
Auteurs Dinh Ho Tong Minh , Thuy Le Toan , Fabio Rocca , Stefano Tebaldini , Ludovic Villard , Maxime Réjou-Méchain , Oliver L. Phillips , Ted R. Feldpausch , Pascale Dubois-Fernandez , Klaus Scipal , Jérôme Chave
Publication : Remote Sensing of Environment
Date : 2016
Volume : 175
Pages : 138–147
Catégorie(s)
#ANR-Citation #CIRAD #CNRS #FORET NouraguesRésumé
The preparation of tropical wood surface sections for time‐of‐flight secondary ion mass spectrometry imaging is described, and the use of delayed extraction of secondary ions and its interest for the analysis of vegetal surface are shown. The method has been applied to the study by time‐of‐flight secondary ion mass spectrometry imaging with a resolution of less than one micron of a tropical wood species, Dicorynia guianensis, which is one of the most exploited wood in French Guiana for its durable heartwood. The heartwood of this species exhibits an economical importance, but its production is not controlled in forestry. Results show an increase of tryptamine from the transition zone and a concomitant decrease of inorganic ions and starch fragment ions. These experiments lead to a better understanding of the heartwood formation and the origin of the natural durability of D. guianensis.
Auteurs, date et publication :
Auteurs Quentin P. Vanbellingen , Tingting Fu , Claudia Bich , Nadine Amusant , Didier Stien , Serge Della-Negra , David Touboul , Alain Brunelle
Publication : Journal of Mass Spectrometry
Date : 2016
Volume : 51
Issue : 6
Pages : 412–423
Catégorie(s)
#CIRAD #FORET ParacouRésumé
By harvesting scattered large trees, selective logging increases light availability and thereby stimulates growth and crown expansion at early‐life stage among remnant trees. We assessed the effects of logging on total and merchantable bole (i.e., lowest branch at crown base) heights on 952 tropical canopy trees in French Guiana. We observed reductions in both total (mean, −2.3 m) and bole (mean, −2.0 m) heights more than a decade after selective logging. Depending on local logging intensity, height reductions resulted in 2–13 percent decreases in aboveground tree biomass and 3–17 percent decreases in bole volume. These results highlight the adverse effects of logging at both tree and stand levels. This decrease in height is a further threat to future provision of key environmental services, such as timber production and carbon sequestration.
Auteurs, date et publication :
Auteurs Ervan Rutishauser , Bruno Hérault , Pascal Petronelli , Plinio Sist
Publication : Biotropica
Date : 2016
Volume : 48
Issue : 3
Pages : 285–289
Catégorie(s)
#CIRAD #FORET ParacouRésumé
In this study, conducted in French Guiana, a part of the native range of the fire ant Solenopsis saevissima, we compared the cuticular hydrocarbon profiles of media workers with previous results based on intraspecific aggressiveness tests. We noted a strong congruence between the two studies permitting us to delimit 2 supercolonies extending over large distances (up to 54 km), a phenomenon known as unicoloniality. Solenopsis geminata workers, taken as an out‐group for cluster analyses, have a very different cuticular hydrocarbon profile. Because S. saevissima has been reported outside its native range, our conclusion is that this species has the potential to become invasive because unicoloniality (i.e., the main attribute for ants to become invasive) was shown at least for the Guianese population.
Auteurs, date et publication :
Auteurs Alain Lenoir , Séverine Devers , Axel Touchard , Alain Dejean
Publication : Insect Science
Date : 2016
Volume : 23
Issue : 5
Pages : 739–745
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Background and Aims In Costa Rica, coffee (Coffea arabica) plants are often grown in agroforests. However, it is not known if shade-inducing trees reduce coffee plant biomass through root competition, and hence alter overall net primary productivity (NPP). We estimated biomass and NPP at the stand level, taking into account deep roots and the position of plants with regard to trees.Methods Stem growth and root biomass, turnover and decomposition were measured in mixed coffee/tree (Erythrina poeppigiana) plantations. Growth ring width and number at the stem base were estimated along with stem basal area on a range of plant sizes. Root biomass and fine root density were measured in trenches to a depth of 4 m. To take into account the below-ground heterogeneity of the agroforestry system, fine root turnover was measured by sequential soil coring (to a depth of 30 cm) over 1 year and at different locations (in full sun or under trees and in rows/inter-rows). Allometric relationships were used to calculate NPP of perennial components, which was then scaled up to the stand level. Key Results Annual ring width at the stem base increased up to 2·5 mm yr−1 with plant age (over a 44-year period). Nearly all (92 %) coffee root biomass was located in the top 1·5 m, and only 8 % from 1·5 m to a depth of 4 m. Perennial woody root biomass was 16 t ha−1 and NPP of perennial roots was 1·3 t ha−1 yr−1. Fine root biomass (0–30 cm) was two-fold higher in the row compared with between rows. Fine root biomass was 2·29 t ha−1 (12 % of total root biomass) and NPP of fine roots was 2·96 t ha−1 yr−1 (69 % of total root NPP). Fine root turnover was 1·3 yr−1 and lifespan was 0·8 years.Conclusions Coffee root systems comprised 49 % of the total plant biomass; such a high ratio is possibly a consequence of shoot pruning. There was no significant effect of trees on coffee fine root biomass, suggesting that coffee root systems are very competitive in the topsoil.
Auteurs, date et publication :
Auteurs Elsa Defrenet , Olivier Roupsard , Karel Van den Meersche , Fabien Charbonnier , Junior Pastor Pérez-Molina , Emmanuelle Khac , Iván Prieto , Alexia Stokes , Catherine Roumet , Bruno Rapidel , Elias de Melo Virginio Filho , Victor J. Vargas , Diego Robelo , Alejandra Barquero , Christophe Jourdan
Publication : Annals of Botany
Date : 2016
Volume : 118
Issue : 4
Pages : 833-851
Catégorie(s)
#CIRAD #FORET CoffeeFluxAuteurs, date et publication :
Auteurs Clément Stahl , Vincent Freycon , Sébastien Fontaine , Camille Dezécache , Lise Ponchant , Catherine Picon-Cochard , Katja Klumpp , Jean-François Soussana , Vincent Blanfort
Publication : Regional Environmental Change
Date : 2016
Volume : 16
Issue : 7
Pages : 2059–2069
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Although bats are natural reservoirs of many pathogens, few studies have been conducted on the genetic variation and detection of selection in major histocompatibility complex (MHC) genes. These genes are critical for resistance and susceptibility to diseases, and host–pathogen interactions are major determinants of their extensive polymorphism. Here we examined spatial patterns of diversity of the expressed MHC class II DRB gene of three sympatric Neotropical bats, Carollia perspicillata and Desmodus rotundus (Phyllostomidae), and Molossus molossus (Molossidae), all of which use the same environments (e.g., forests, edge habitats, urban areas). Comparison with neutral marker (mtDNA D-loop) diversity was performed at the same time. Twenty-three DRB alleles were identified in 19 C. perspicillata, 30 alleles in 35 D. rotundus and 20 alleles in 28 M. molossus. The occurrence of multiple DRB loci was found for the two Phyllostomidae species. The DRB polymorphism was high in all sampling sites and different signatures of positive selection were detected depending on the environment. The patterns of DRB diversity were similar to those of neutral markers for C. perspicillata and M. molossus. In contrast, these patterns were different for D. rotundus for which a geographical structure was highlighted. A heterozygote advantage was also identified for this species. No recombination or gene conversion event was found and phylogenetic relationships showed a trans-species mode of evolution in the Phyllostomids. This study of MHC diversity demonstrated the strength of the environment and contrasting pathogen pressures in shaping DRB diversity. Differences between positively selected sites identified in bat species highlighted the potential role of gut microbiota in shaping immune responses. Furthermore, multiple geographic origins and/or population admixtures observed in C. perspicillata and M. molossus populations acted as an additional force in shaping DRB diversity. In contrast, DRB diversity of D. rotundus was shaped by environment rather than demographic history.
Auteurs, date et publication :
Auteurs Arielle Salmier , Benoit de Thoisy , Brigitte Crouau-Roy , Vincent Lacoste , Anne Lavergne
Publication : BMC Evolutionary Biology
Date : 2016
Volume : 16
Issue : 1
Pages : 229
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Gérard Dubost, and Olivier Henry (2017) Seasonal changes in tropical forests have been documented in dry and semi-deciduous forests, but not in evergreen ones. Owing to its high level of annual rainfall, French Guiana is considered to be a rainy region, despite a pronounced dry season. French Guiana is therefore appropriate for studying the impact of the dry season on the phenology of rainforest animals. For this purpose, the reproductive characteristics of six terrestrial mammals of the French Guiana rainforest were studied during the four main seasons of the year. Reproduction was more or less continuous in both sexes of all species. Seasonality was not very pronounced and the species were not synchronised, except in terms of births. In all species, the minimum number of litters occurred between August and October. Furthermore, the seasonal birth percentages appeared to be linked to environmental factors such as rainfall and fruiting trees, and to diet as well: the more the diet of one species was composed of fruits, the more seasonal its litters were. Thus, like in many other regions worldwide, most births occur during the most favourable seasons for raising young in this rainforest. This signifies that even in this seemingly aseasonal region, the reproduction of mammals is mainly regulated by environmental factors at the time of birth.
Auteurs, date et publication :
Auteurs Gérard Dubost , Olivier Henry , Benny K K Chan
Publication : Zoological Studies
Date : 2025
Volume : 52
Issue : 2
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Finding suitable models of canopy reflectance in forward simulation mode is a prerequisite for their use in inverse mode to characterize canopy variables of interest, such as leaf area index (LAI) or chlorophyll content. In this study, the accuracy of the three-dimensional reflectance model DART (Discrete Anisotropic Radiative Transfer) was assessed for canopies of different genotypes of Eucalyptus, having distinct biophysical and biochemical characteristics, to improve the knowledge on how these characteristics are influencing the reflectance signal as measured by passive orbital sensors. The first step was to test the model suitability to simulate reflectance images in the visible and near infrared. We parameterized DART model using extensive measurements from Eucalyptus plantations including 16 contrasted genotypes. Forest inventories were conducted and leaf, bark, and forest floor optical properties were measured. Simulation accuracy was evaluated by comparing the mean top of canopy (TOC) bidirectional reflectance of DART with TOC reflectance extracted from a Pleiades very high resolution satellite image. Results showed a good performance of DART with mean reflectance absolute error lower than 2%. Intergenotype reflectance variability was correctly simulated, but the model did not succeed at catching the slight spatial variation for a given genotype, excepted when large gaps appeared due to tree mortality. The second step consisted of sensitivity analysis to explore which biochemical or biophysical characteristics influenced more the canopy reflectance between genotypes. Perspectives for using DART model in inversion mode in these ecosystems were discussed. (Résumé d'auteur)
Auteurs, date et publication :
Auteurs Julianne de Castro Oliveira , Jean Baptiste Feret , Flávio Jorge Ponzoni , Yann Nouvellon , Jean-Philippe Gastellu Etchegorry , Otávio Camargo Campoe , Jose Luiz Stape , Luiz Carlos Estraviz Rodriguez , Guerric Le Maire
Publication : IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Date : 2025
Volume : 10
Issue : 11
Pages : 4844-4852