Éditeur(s) : HAL CCSD Wiley
Résumé : 1. Trade-offs among functional traits reveal major plant strategies that can give insight into species distributions and ecosystem processes. However, current identification of plant strategies lacks the integration of root structural traits together with leaf and stem traits. 2. We examined correlations among 14 traits representing leaf, stem and woody root tissues. Traits were measured on 1084 individuals representing 758 Neotropical tree species, across 13 sites representative of the environmental variation encompassed by three widespread habitats (seasonally flooded, clay terra firme and white-sand forests) at opposite ends of Amazonia (French Guiana and Peru). 3. Woody root traits were closely aligned with stem traits, but not with leaf traits. Altogether leaf, stem and woody root traits delineated two orthogonal axes of functional trade-offs: a first axis defined by leaf traits, corresponding to a leaf economics spectrum, and a second axis defined by covarying stem and woody root traits, corresponding to a wood economics spectrum. These axes remained consistent when accounting for species evolutionary history with phylogenetically independent contrasts. 4. Despite the strong species turnover across sites, the covariation among root and stem structural traits as well as their orthogonality to leaf traits were strongly consistent across habitats and regions. 5. We conclude that root structural traits mirrored stem traits rather than leaf traits in Neotropical trees. Leaf and wood traits define an integrated whole-plant strategy in lowland South American forests that may contribute to a more complete understanding of plant responses to global changes in both correlative and modelling approaches. We suggest further meta-analyses in expanded environmental and geographic zones to determine the generality of this pattern.
ISSN: 0269-8463

hal-01032415
https://hal.archives-ouvertes.fr/hal-01032415
DOI : 10.1111/j.1365-2435.2012.02020.x

Éditeur(s) : HAL CCSD Nordic Ecological Society
Résumé : Niche differentiation and ecological filtering are primary ecological processes that shape community assembly, but their relative importance remains poorly understood. Analyses of the distributions of functional traits can provide insight into the community structure generated by these processes. We predicted the trait distributions expected under the ecological processes of niche differentiation and environmental filtering, then tested these predictions with a dataset of 4672 trees located in nine 1-ha plots of tropical rain forest in French Guiana. Five traits related to leaf function (foliar N concentration, chlorophyll content, toughness, tissue density and specific leaf area), and three traits related to stem function (trunk sapwood density, branch sapwood density, and trunk bark thickness), as well as laminar surface area, were measured on every individual tree. There was far more evidence for environmental filtering than for niche differentiation in these forests. Furthermore, we contrasted results from species-mean and individual-level trait values. Analyses that took within-species trait variation into account were far more sensitive indicators of niche differentiation and ecological filtering. Species-mean analyses, by contrast, may underestimate the effects of ecological processes on community assembly. Environmental filtering appeared somewhat more intense on leaf traits than on stem traits, whereas niche differentiation affected neither strongly. By accounting for within-species trait variation, we were able to more properly consider the ecological interactions among individual trees and between individual trees and their environment. In so doing, our results suggest that the ecological processes of niche differentiation and environmental filtering may be more pervasive than previously believed.
ISSN: 0030-1299

hal-01032397
https://hal.archives-ouvertes.fr/hal-01032397
DOI : 10.1111/j.1600-0706.2010.19110.x

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Functional aspects of biodiversity were investigated in a lowland tropical rainforest in French Guyana (5°2'N, annual precipitation 2200 mm). We assessed leaf '15N as a presumptive indicator of symbiotic N2 fixation, and leaf and wood cellulose '13C as an indicator of leaf intrinsic water-use efficiency (CO2 assimilation rate/leaf conductance for water vapour) in dominant trees of 21 species selected for their representativeness in the forest cover, their ecological strategy (pioneers or late successional stage species, shade tolerance) or their potential ability for N2 fixation. Similar measurements were made in trees of native species growing in a nearby plantation after severe perturbation (clear cutting, mechanical soil disturbance). Bulk soil '15N was spatially quite uniform in the forest (range 3-5‰), whereas average leaf '15N ranged from m0.3‰ to 3.5‰ in the different species. Three species only, Diplotropis purpurea, Recordoxylon speciosum (Fabaceae), and Sclerolobium melinonii (Caesalpiniaceae), had root bacterial nodules, which was also associated with leaf N concentrations higher than 20 mg gm1. Although nodulated trees displayed significantly lower leaf '15N values than non-nodulated trees, leaf '15N did not prove a straightforward indicator of symbiotic fixation, since there was a clear overlap of '15N values for nodulated and non-nodulated species at the lower end of the '15N range. Perturbation did not markedly affect the difference '15Nsoil m '15Nleaf, and thus the isotopic data provide no evidence of an alteration in the different N acquisition patterns. Extremely large interspecific differences in sunlit leaf '13C were observed in the forest (average values from m31.4 to m26.7‰), corresponding to intrinsic water-use efficiencies (ratio CO2 assimilation rate/leaf conductance for water vapour) varying over a threefold range. Wood cellulose '13C was positively related to total leaf '13C, the former values being 2-3‰ higher than the latter ones. Leaf '13C was not related to leaf '15N at either intraspecific or interspecific levels. '13C of sunlit leaves was highest in shade hemitolerant emergent species and was lower in heliophilic, but also in shade-tolerant species. For a given species, leaf '13C did not differ between the pristine forest and the disturbed plantation conditions. Our results are not in accord with the concept of existence of functional types of species characterized by common suites of traits underlying niche differentiation; rather, they support the hypothesis that each trait leads to a separate grouping of species.
ISSN: 0029-8549

hal-01032378
https://hal.archives-ouvertes.fr/hal-01032378
DOI : 10.1007/s004420050593

Éditeur(s) : HAL CCSD Wiley
Résumé : 1. Functional traits are posited to explain interspecific differences in performance, but these relationships are difficult to describe for long-lived organisms such as trees, which exhibit strong ontogenetic changes in demographic rates. Here, we use a size-dependent model of tree growth to test the extent to which of 17 functional traits related to leaf and stem economics, adult stature and seed size predict the ontogenetic trajectory of tree growth.[br/] 2. We used a Bayesian modelling framework to parameterize and contrast three size-dependent diameter growth models using 16 years of census data from 5524 individuals of 50 rain forest tree species: a size-dependent model, a size-dependent model with species-specific parameters and a size-dependent model based on functional traits.[br/] 3. Most species showed clear hump-shaped ontogenetic growth trajectories and, across species, maximum growth rate varied nearly tenfold, from 0.58 to 5.51 mm year(-1). Most species attained their maximum growth at 60% of their maximum size, whereas the magnitude of ontogenetic changes in growth rate varied widely among species.[br/] 4. The Trait-Model provided the best compromise between explained variance and model parsimony and needed considerably fewer parameters than the model with species terms.[br/] 5. Stem economics and adult stature largely explained interspecific differences in growth strategy. Maximum absolute diameter growth rates increased with increasing adult stature and leaf delta(13)C and decreased with increasing wood density. Species with light wood had the greatest potential to modulate their growth, resulting in hump-shaped ontogenetic growth curves. Seed size and leaf economics, generally thought to be of paramount importance for plant performance, had no significant relationships with the growth parameters.[br/] 6. Synthesis. Our modelling approach offers a promising way to link demographic parameters to their functional determinants and hence to predict growth trajectories in species-rich communities with little parameter inflation, bridging the gap between functional ecology and population demography.
ISSN: 0022-0477

hal-01032387
https://hal.archives-ouvertes.fr/hal-01032387
DOI : 10.1111/j.1365-2745.2011.01883.x

Éditeur(s) : HAL CCSD Wiley
Résumé : [b]1.[/b] Plant functional traits, in particular specific leaf area (SLA), wood density and seed mass, are often good predictors of individual tree growth rates within communities. Individuals and species with high SLA, low wood density and small seeds tend to have faster growth rates.[br/][br/][b]2.[/b] If community-level relationships between traits and growth have general predictive value, then similar relationships should also be observed in analyses that integrate across taxa, biogeographic regions and environments. Such global consistency would imply that traits could serve as valuable proxies for the complex suite of factors that determine growth rate, and, therefore, could underpin a new generation of robust dynamic vegetation models. Alternatively, growth rates may depend more strongly on the local environment or growth–trait relationships may vary along environmental gradients.[br/][br/][b]3.[/b] We tested these alternative hypotheses using data on 27 352 juvenile trees, representing 278 species from 27 sites on all forested continents, and extensive functional trait data, 38% of which were obtained at the same sites at which growth was assessed. Data on potential evapotranspiration (PET), which summarizes the joint ecological effects of temperature and precipitation, were obtained from a global data base.[br/][br/][b]4.[/b] We estimated size-standardized relative height growth rates (SGR) for all species, then related them to functional traits and PET using mixed-effect models for the fastest growing species and for all species together.[br/][br/][b]5.[/b] Both the mean and 95th percentile SGR were more strongly associated with functional traits than with PET. PET was unrelated to SGR at the global scale. SGR increased with increasing SLA and decreased with increasing wood density and seed mass, but these traits explained only 3.1% of the variation in SGR. SGR–trait relationships were consistently weak across families and biogeographic zones, and over a range of tree statures. Thus, the most widely studied functional traits in plant ecology were poor predictors of tree growth over large scales.[br/][br/][b]6.[/b] Synthesis. We conclude that these functional traits alone may be unsuitable for predicting growth of trees over broad scales. Determining the functional traits that predict vital rates under specific environmental conditions may generate more insight than a monolithic global relationship can offer.
ISSN: 0022-0477

hal-01204226
https://hal.archives-ouvertes.fr/hal-01204226
DOI : 10.1111/1365-2745.12401
PRODINRA : 307144

Éditeur(s) : HAL CCSD CSIRO Publishing
Résumé :  
Leaf traits of tropical tree species display an important inter-specific diversity, as detected for instance in the large range of values of leaf mass : area ratio (LMA). They also demonstrate a large irradiance-elicited plasticity, but there is still debate whether this plasticity differs among species. To address this question, leaf traits were recorded on saplings from 12 rainforest tree species in French Guiana, grown under approximately 5, 10 and 20% relative irradiance. Fifteen structural and physiological leaf traits related to photosynthesis were measured. The irradiance-elicited plasticity was quantified using a relative distance plasticity index. A large inter-specific diversity was detected for all leaf traits. A principal component analysis opposed species with a large mass-based photosynthesis, respiration, N content and photosynthetic nitrogen use efficiency, to species with a large leaf mass : area ratio, LMA. The two pioneer species used in this study displayed the largest photosynthetic capacity (and lowest LMA) and ranked at one end of the species continuum. Relative irradiance affected almost all traits with the exception of mass-based photosynthesis.Aweak interaction was found between species and relative irradiance and the species ranking was maintained among relative irradiance treatments for the majority of the traits. A principal component analysis of the values of relative-distance plasticity index failed to reveal any consistent patterns of traits or species.Weconcluded that irradiance-elicited plasticity of leaf traits was similar among species irrespective ofLMA and successional status, despite the occurrence of a large inter-specific diversity for the investigated traits
ISSN: 1445-4408

hal-01032129
https://hal.archives-ouvertes.fr/hal-01032129
DOI : 10.1071/FP09119

Éditeur(s) : HAL CCSD Ecological Society of America
Résumé : Tropical plant diversity is extraordinarily high at both local and regional scales. Many studies have demonstrated that natural enemies maintain local diversity via negative density dependence, but we know little about how natural enemies influence beta-diversity across habitats and/or regions. One way herbivores could influence plant beta-diversity is by driving allocation trade-offs that promote habitat specialization across resource gradients. We therefore predicted that increasing resource availability should be accompanied by increasing herbivory rates and decreasing plant allocation to defense. Second, relative abundances within plant lineages are predicted to reflect patterns of habitat specialization and allocation trade-offs. A phylogenetic context is vital not only to compare homologous plant traits (including defense strategies) across habitat types, but also to connect evolutionary trade-offs to patterns of species diversification in each phylogenetic lineage. We tested these predictions for trees in white-sand, clay terra firme, and seasonally flooded forests in Peru and French Guiana that represent the range of soil fertility, forest structure, and floristic compositions found throughout the Amazon region. We established 74 0.5-ha plots in these habitats and sampled all trees. Within 12 representative plots we marked newly expanding leaves of 394 saplings representing 68 species, including the most abundant species in each plot in addition to species from five focal lineages: Swartzia and Inga (Fabaceae), Protieae (Burseracaeae), Bombacoideae (Malvaceae), and Micropholis (Sapotaceae). We measured total leaf production rates for each sapling and calculated relative herbivory impact as the ratio between herbivory rate and leaf production rate. Herbivory rates averaged 2.1% per month, did not correlate with leaf production rate, and were similar across habitats. Relative herbivore impacts exceeded leaf production rates for most species. Leaf production rate averaged 2.8%, was significantly higher in seasonally flooded forests than the other two habitats, and exhibited significant correlations with specific leaf area. Species with high herbivory rates exhibited significantly lower relative abundances in terra firme forests. Overall, focal species within lineages present contrasting patterns regarding their herbivory rates and leaf production rate within habitats. These results highlight why a lineage-based approach is necessary when attempting to connect hypotheses regarding evolutionary trade-offs to community assembly patterns.
ISSN: 0012-9658

hal-01032418
https://hal.archives-ouvertes.fr/hal-01032418

Éditeur(s) : HAL CCSD Ecological Society of America
Résumé : Herbivory is viewed as a major driver of plant evolution and the mostimportant energy pathway from plants to higher trophic levels. Therefore, understandingpatterns of herbivory on plants remains a key focus in evolution and ecology. Theevolutionary impacts of leaf herbivory include altering plant fitness, local adaptation, theevolution of defenses, and the diversification of plants as well as natural enemies. Leafherbivory also impacts ecological processes such as plant productivity, communitycomposition, and ecosystem nutrient cycling. Understanding the impact of herbivory onthese ecological and evolutionary processes requires species-specific, as opposed tocommunity-level, measures of herbivory. In addition, species-specific data enables the use ofmodern comparative methods to account for phylogenetic non-independence. Althoughhundreds of studies have measured natural rates of leaf consumption, we are unaware of anyaccessible compilation of these data. We created such a data set to provide the raw dataneeded to test general hypotheses relating to plant–herbivore interactions and to test theinfluence of biotic and abiotic factors on herbivory rates across large spatial scales. A largerepository will make this endeavor more efficient and robust. In total, we compiled 2641population-level measures for either annual or daily rates of leaf herbivory across 1145 speciesof vascular plants collected from 189 studies. All damage measures represent naturaloccurrences of herbivory that span numerous angiosperm, gymnosperm, and fern species. Toenable researchers to explore the causes of variation in herbivory and how these mightinteract, we added information about the study sites including: geolocation, climateclassification, habitat descriptions (e.g., seashore, grassland, forest, agricultural fields), andplant trait information concerning growth form and duration (e.g., annual vs. perennial). Wealso included extensive details of the methodology used to measure leaf damage, includingseasons and months of sampling, age of leaves, and the method used to estimate percentagearea missing. We anticipate that these data will make it possible to test important hypothesesin the plant–herbivore literature, including the plant apparency hypothesis, the latitudinalherbivorydefense hypothesis, the resource availability hypothesis, and the macroevolutionaryescalation of defense hypothesis.
ISSN: 0012-9658

hal-01601627
https://hal.archives-ouvertes.fr/hal-01601627
DOI : 10.1890/13-1741.1
PRODINRA : 397136
PUBMED : 24870043

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : In habitat mosaics, plant populations face environmental heterogeneity over short geographical distances. Such steep environmental gradients can induce ecological divergence. Lowland rainforests of the Guiana Shield are characterized by sharp, short-distance environmental variations related to topography and soil characteristics (from waterlogged bottomlands on hydromorphic soils to well-drained terra firme on ferralitic soils). Continuous plant populations distributed along such gradients are an interesting system to study intrapopulation divergence at highly local scales. This study tested (1) whether conspecific populations growing in different habitats diverge at functional traits, and (2) whether they diverge in the same way as congeneric species having different habitat preferences. Phenotypic differentiation was studied within continuous populations occupying different habitats for two congeneric, sympatric, and ecologically divergent tree species (Eperua falcata and E. grandiflora, Fabaceae). Over 3000 seeds collected from three habitats were germinated and grown in a common garden experiment, and 23 morphological, biomass, resource allocation and physiological traits were measured. In both species, seedling populations native of different habitats displayed phenotypic divergence for several traits (including seedling growth, biomass allocation, leaf chemistry, photosynthesis and carbon isotope composition). This may occur through heritable genetic variation or other maternally inherited effects. For a sub-set of traits, the intraspecific divergence associated with environmental variation coincided with interspecific divergence. The results indicate that mother trees from different habitats transmit divergent trait values to their progeny, and suggest that local environmental variation selects for different trait optima even at a very local spatial scale. Traits for which differentiation within species follows the same pattern as differentiation between species indicate that the same ecological processes underlie intra- and interspecific variation.
ISSN: 0305-7364

hal-01032430
https://hal.archives-ouvertes.fr/hal-01032430
DOI : 10.1093/aob/mct176

Éditeur(s) : HAL CCSD Springer Verlag
Résumé :  
Genetic variation for intrinsic water use efficiency (W i) and related traits was estimated in a full-sib family of Quercus robur L. over 3 years. The genetic linkage map available for this F1 family was used to locate quantitative trait loci (QTL) for W i, as estimated by leaf carbon stable isotope composition (δ 13C) or the ratio of net CO2 assimilation rate (A) to stomatal conductance to water vapour (g w) and related leaf traits. Gas exchange measurements were used to standardize estimates of A and g w and to model the sensitivity of g w to leaf-to-air vapour pressure deficit (sgVPD). δ 13C varied by more than 3‰ among the siblings, which is equivalent to 40% variation of W i. Most of the studied traits exhibited high clonal mean repeatabilities (>50%; proportion of clonal mean variability in global variance). Repeatabilities for δ 13C, leaf mass per area (LMA) and leaf nitrogen content were higher than 70%. For δ 13C, ten QTLs were detected, one of which was detected repeatedly for all 3 years and consistently explained more than 20% of measured variance. Four genomic regions were found in which co-localizing traits linked variation in W i to variations in leaf chlorophyll and nitrogen content, LMA and sgVPD. A positive correlation using clonal means between δ 13C and A/g w, as well as a co-localisation of QTL detected for both traits, can be seen as validation of the theoretical model linking the genetic architecture of these two traits.
ISSN: 1614-2942

hal-01032066
https://hal.archives-ouvertes.fr/hal-01032066
DOI : 10.1007/s11295-007-0107-z

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
We assessed the extent of recent environmental changes on leaf morphological (stomatal density, stomatal surface, leaf mass per unit area) and physiological traits (carbon isotope composition, δ(13)C(leaf) , and discrimination, Δ(13)C(leaf) , oxygen isotope composition, δ(18)O(leaf) ) of two tropical rainforest species (Dicorynia guianensis; Humiria balsamifera) that are abundant in the Guiana shield (Northern Amazonia). Leaf samples were collected in different international herbariums to cover a 200 year time-period (1790-2004) and the whole Guiana shield. Using models describing carbon and oxygen isotope fractionations during photosynthesis, different scenarios of change in intercellular CO(2) concentrations inside the leaf (C(i)), stomatal conductance (g), and photosynthesis (A) were tested in order to understand leaf physiological response to increasing air CO(2) concentrations (C(a)). Our results confirmed that both species displayed physiological response to changing C(a) . For both species, we observed a decrease of about 1.7‰ in δ(13)C(leaf) since 1950, without significant change in Δ(13)C(leaf) and leaf morphological traits. Furthermore, there was no clear change in δ(18)O(leaf) for Humiria over this period. Our simulation approach revealed that an increase in A, rather than a decrease in g, explained the observed trends for these tropical rainforest species, allowing them to maintain a constant ratio of C(i)/C(a) .
ISSN: 0140-7791

halsde-00675165
https://hal.archives-ouvertes.fr/halsde-00675165
DOI : 10.1111/j.1365-3040.2011.02333.x
PUBMED : 21486302

Éditeur(s) : HAL CCSD
Résumé : International audience
Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, weconducted a meta-analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the totaltrait variation among communities on average. The relative extent of ITV tended to be greater for whole-plant (e.g. plant height) vs. organ-level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait-based community and ecosystem studies.
Ecology Letters

hal-01237101
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01237101
DOI : 10.1111/ele.12508
PUBMED : 26415616

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
We present a plant trait database covering autecology for rain forest trees of French Guiana. The database comprises more than thirty traits including autecology (e.g., habitat associations and reproductive phenology), wood structure (e.g., density and tension characteristics) and physiology at the whole plant (e.g., carbon and nitrogen isotopes) and leaf level (e.g., specific leaf area, photosynthetic capacity). The current database describes traits for about nine hundred species from three hundred genera in one hundred families. For more than sixty species, data on twelve morphological and ecophysiological traits are provided for individual plants under different environmental conditions and at different ontogenetic stages. The database is thus unique in permitting intraspecific analyses, such as the effects of ontogenetic stages or environmental conditions on trait values and their relationships.
ISSN: 1286-4560

Droits : info:eu-repo/semantics/OpenAccess
hal-00884130
https://hal.archives-ouvertes.fr/hal-00884130
https://hal.archives-ouvertes.fr/hal-00884130/document
https://hal.archives-ouvertes.fr/hal-00884130/file/hal-00884130.pdf

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy B - Oxford Open Option B
Résumé : Variability of leaf traits related to photosynthesis was assessed in seedlings from 14 tree species growing in the tropical rain forest of French Guiana. Leaf photosynthetic capacity (maximum rate of carboxylation and maximum rate of electron transport) was estimated by fitting a biochemical model of photosynthesis to response curves of net CO2 assimilation rate versus intercellular CO2 mole fraction. Leaf morphology described by leaf mass per unit leaf area (LMA), density and thickness, as well as area- and mass-based nitrogen (N) and carbon (C) concentrations, were recorded on the same leaves. Large interspecific variability was detected in photosynthetic capacity as well as in leaf structure and leaf N and C concentrations. No correlation was found between leaf thickness and density. The correlations between area- and massbased leaf N concentration and photosynthetic capacity were poor. Conversely, the species differed greatly in relativeNallocation to carboxylation and bioenergetics. Principal component analysis (PCA) revealed that, of the recorded traits, only the computed fraction of total leafNinvested in photosynthesis was tightly correlated to photosynthetic capacity.We also used PCAto test to what extent species with similar shade tolerances displayed converging leaf traits related to photosynthesis. No clear-cut ranking could be detected among the shade-tolerant groups, as confirmed by a one-way ANOVA.We conclude that the large interspecific diversity in photosynthetic capacity was mostly explained by differences in the relative allocation of N to photosynthesis and not by leafNconcentration, and that leaf traits related to photosynthetic capacity did not discriminate shade-tolerance ranking of these tropical tree species.
ISSN: 0829-318X

hal-01031522
https://hal.archives-ouvertes.fr/hal-01031522

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
1. Despite considerable interest in the application of plant functional traits to questions of community assembly and ecosystem structure and function, there is no consensus on the appropriateness of sampling designs to obtain plot-level estimates in diverse plant communities. 2. We measured 10 plant functional traits describing leaf and stem morphology and ecophysiology for all trees in nine 1-ha plots in terra firme lowland tropical rain forests of French Guiana (N = 4709). 3.We calculated, by simulation, the mean and variance in trait values for each plot and each trait expected under seven sampling methods and a range of sampling intensities. Simulated sampling methods included a variety of spatial designs, as well as the application of existing data base values to all individuals of a given species. 4. For each trait in each plot, we defined a performance index for each sampling design as the proportion of resampling events that resulted in observed means within 5% of the true plot mean, and observed variance within 20%of the true plot variance. 5. The relative performance of sampling designs was consistent for estimations of means and variances. Data base use had consistently poor performance for most traits across all plots, whereas sampling one individual per species per plot resulted in relatively high performance. We found few differences among different spatial sampling strategies; however, for a given strategy, increased intensity of sampling resulted in markedly improved accuracy in estimates of trait mean and variance. 6. We also calculated the financial cost of each sampling design based on data from our 'every individual per plot' strategy and estimated the sampling and botanical effort required. The relative performance of designs was strongly positively correlated with relative financial cost, suggesting that sampling investment returns are relatively constant. 7. Our results suggest that trait sampling for many objectives in species-rich plant communities may require the considerable effort of sampling at least one individual of each species in each plot, and that investment in complete sampling, though great, may be worthwhile for at least some traits.
ISSN: 0269-8463

hal-00594009
https://hal.archives-ouvertes.fr/hal-00594009

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé :  
The maintenance in the long run of a positive carbon balance under very low irradiance is a prerequisite for survival of tree seedlings below the canopy or in small gaps in a tropical rainforest. To provide a quantitative basis for this assumption, experiments were carried out to determine whether construction cost (CC) and payback time for leaves and support structures, as well as leaf life span (i) differ among species and (ii) display an irradiance-elicited plasticity. Experiments were also conducted to determine whether leaf life span correlates to CC and payback time and is close to the optimal longevity derived from an optimization model. Saplings from 13 tropical tree species were grown under three levels of irradiance. Specific-CC was computed, as well as CC scaled to leaf area at the metamer level. Photosynthesis was recorded over the leaf life span. Payback time was derived from CC and a simple photosynthesis model. Specific-CC displayed only little interspecific variability and irradiance-elicited plasticity, in contrast to CC scaled to leaf area. Leaf life span ranged from 4 months to >26 months among species, and was longest in seedlings grown under lowest irradiance. It was always much longer than payback time, even under the lowest irradiance. Leaves were shed when their photosynthesis had reached very low values, in contrast to what was predicted by an optimality model. The species ranking for the different traits was stable across irradiance treatments. The two pioneer species always displayed the smallest CC, leaf life span, and payback time. All species displayed a similar large irradiance-elicited plasticity.
ISSN: 0022-0957

hal-01032198
https://hal.archives-ouvertes.fr/hal-01032198
DOI : 10.1093/jxb/err092

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Cross-species analyses of plant functional traits have shed light on factors contributing to differences in performance and distribution, but to date most studies have focused on either leaves or stems. We extend these tissue-specific analyses of functional strategy towards a whole-plant approach by integrating data on functional traits for 13 448 leaves and wood tissues from 4672 trees representing 668 species of Neotropical trees. Strong correlations amongst traits previously defined as the leaf economics spectrum reflect a tradeoff between investments in productive leaves with rapid turnover vs. costly physical leaf structure with a long revenue stream. A second axis of variation, the 'stem economics spectrum', defines a similar tradeoff at the stem level: dense wood vs. high wood water content and thick bark. Most importantly, these two axes are orthogonal, suggesting that tradeoffs operate independently at the leaf and at the stem levels. By simplifying the multivariate ecological strategies of tropical trees into positions along these two spectra, our results provide a basis to improve global vegetation models predicting responses of tropical forests to global change.
ISSN: 1461-023X

hal-00594040
https://hal.archives-ouvertes.fr/hal-00594040

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
The maintenance in the long run of a positive carbon balance under very low irradiance is a prerequisite for survival of tree seedlings below the canopy or in small gaps in a tropical rainforest. To provide a quantitative basis for this assumption, experiments were carried out to determine whether construction cost (CC) and payback time for leaves and support structures, as well as leaf life span (i) differ among species and (ii) display an irradiance-elicited plasticity. Experiments were also conducted to determine whether leaf life span correlates to CC and payback time and is close to the optimal longevity derived from an optimization model. Saplings from 13 tropical tree species were grown under three levels of irradiance. Specific-CC was computed, as well as CC scaled to leaf area at the metamer level. Photosynthesis was recorded over the leaf life span. Payback time was derived from CC and a simple photosynthesis model. Specific-CC displayed only little interspecific variability and irradiance-elicited plasticity, in contrast to CC scaled to leaf area. Leaf life span ranged from 4 months to >26 months among species, and was longest in seedlings grown under lowest irradiance. It was always much longer than payback time, even under the lowest irradiance. Leaves were shed when their photosynthesis had reached very low values, in contrast to what was predicted by an optimality model. The species ranking for the different traits was stable across irradiance treatments. The two pioneer species always displayed the smallest CC, leaf life span, and payback time. All species displayed a similar large irradiance-elicited plasticity.
ISSN: 1631-0691

hal-01095975
https://hal-agroparistech.archives-ouvertes.fr/hal-01095975
DOI : 10.1016/j.crvi.2011.01.007

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
Irradiance elicits a large plasticity in leaf traits, but little is known about the modulation of this plasticity by ontogeny. Interactive effects of relative irradiance and ontogeny were assessed on leaf traits for two tropical rainforest tree species: Dicorynia guianensis Amshoff and Tachigali melinonii (Harms) Barneby (Fabaceae, Caesalpinioideae). Eleven morphological and physiological leaf traits, relative to photosynthetic performance, were measured on saplings at three different architectural development stages (ASD 1, 2 and 3) and used to derive composite traits like photosynthetic N-use efficiency. Measurements were made along a natural irradiance gradient. The effect of ASD was very visible and differed between the two species. For Dicorynia guianensis, only leaf mass-per-area (LMA) significantly increased with ASDs whereas for Tachigali melinonii, almost all traits were affected by ASD: LMA, leaf N content and photosynthetic capacity increased from ASD 1 to ASD 3. Photosynthetic N-use-efficiency was not affected by ASD in any species. Leaf traits were severely modulated by irradiance, whereas the degree of plasticity was very similar among ASDs. Only few interactions were detected between irradiance and ASD, for leaf thickness, carbon content, and the ratio Chl/N in T. melinonii and for photosynthetic capacity in D. guianensis. We conclude that ontogenic development and irradiance-elicited plasticity modulated leaf traits, with almost no interaction, i.e., the degree of irradiance-elicited plasticity was stable across development stages and independent of ontogeny in these two species, at least in the early stages of development assessed here
ISSN: 1286-4560

halsde-00434378
https://hal.archives-ouvertes.fr/halsde-00434378
DOI : 10.1051/forest/2009062

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé :  
We present a plant trait database covering autecology for rain forest trees of French Guiana. The database comprises more than thirty traits including autecology (e.g., habitat associations and reproductive phenology), wood structure (e.g., density and tension characteristics) and physiology at the whole plant (e.g., carbon and nitrogen isotopes) and leaf level (e.g., specific leaf area, photosynthetic capacity). The current database describes traits for about nine hundred species from three hundred genera in one hundred families. For more than sixty species, data on twelve morphological and ecophysiological traits are provided for individual plants under different environmental conditions and at different ontogenetic stages. The database is thus unique in permitting intraspecific analyses, such as the effects of ontogenetic stages or environmental conditions on trait values and their relationships.
Annals of Forest Science

hal-01032196
https://hal.archives-ouvertes.fr/hal-01032196
DOI : 10.1051/forest:2007058