Abstract: Tree species-rich tropical rainforests are characterized by a highly variable quality of leaf litter input to the soil at small spatial scales. This diverse plant litter is a major source of energy and nutrients for soil microorganisms, particularly in rainforests developed on old and nutrient-impoverished soils. Here we tested the hypothesis that the variability in leaf litter quality produced by a highly diverse tree community determines the spatial variability of the microbial respiration process in the underlying soil. We analyzed a total of 225 litter-soil pairs from an undisturbed Amazonian rainforest in French Guiana using a hierarchical sampling design. The microbial respiration process was assessed using substrate-induced respiration (SIR) and compared to a wide range of quality parameters of the associated litter layer (litter nutrients, carbon forms, stoichiometry, litter mass and pH). The results show that the variability of both litter quality and SIR rates was more important at large than at small scales. SIR rates varied between 1.1 and 4.0 μg h(-1) and were significantly correlated with litter layer quality (up to 50% of the variability explained by the best mixed linear model). Total litter P content was the individual most important factor explaining the observed spatial variation in soil SIR, with higher rates associated to high litter P. SIR rates also correlated positively with total litter N content and with increasing proportions of labile C compounds. However, contrary to our expectation, SIR rates were not related to litter stoichiometry. These data suggest that in the studied Amazonian rainforest, tree canopy composition is an important driver of the microbial respiration process via leaf litter fall, resulting in potentially strong plant-soil feedbacks. (C) 2011 Elsevier Ltd. All rights reserved.

Abstract: Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 degrees C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for.

Abstract: Low coverage MiSeq genome sequencing and restriction associated DNA sequencing (RADseq) were used to identify nuclear and plastid SNP and INDEL genetic markers in Carapa guianensis. 261 genetic markers including 237 nuclear SNPs, 22 plastid SNPs, and 2 plastid INDELs are described based on 96 genotyped individuals from French Guiana, Brazil, Peru, and Bolivia. The best 117 SNPs for identifying population structure and performing individual assignment are assembled into four multiplexes for MassARRAY genotyping.

Abstract: Very high spatial resolution (VHSR) optical satellite imagery has shown good potential to provide non-saturating proxies of tropical forest aboveground biomass (AGB) from the analysis of canopy texture, for instance through the Fourier Transform Textural Ordination method. Empirical case studies however showed that the relationship between Fourier texture features and forest AGB varies across forest types and regions of the world, limiting model transferability. A better understanding of the biophysical mechanisms on which canopy texture – forest AGB relation relies is a prerequisite to move toward broad scale applications. Here we simulated VHSR optical canopy scenes in identical sun-sensor geometry for 279 1-ha tropical forest inventory plots distributed across the tropics. Our aim was to assess the respective merits and complementarity of two types of texture analysis techniques (i.e. Fourier and lacunarity) on a set of forests with contrasted structure and geographical origin, and develop a general texture-based approach for tropical forest AGB mapping. Across forests, Fourier texture captured a gradient of stands mean crown size reflecting well the progressive changes in stand structure throughout forest aggradation phase (e.g. Pearson's r = − 0.42 with basal area) while lacunarity texture captured a gradient of canopy openness (, i.e. Pearson's r = − 0.57 with stand gap fraction). Both types of texture indices were highly complementary for predicting forest AGB at the global level (so-called FL-model). The residual error of the FL-model was structured across sites and could be partially captured with a bioclimatic proxy, further improving the performance of the global model (so-called FLE-model) and reducing site-level biases. The FLE model was tested on a set of real Pleiades images covering a mosaic of high-biomass forests in the Congo basin (mean AGB over 49 field plots: 359 ± 98 Mg ha− 1), leading to a significant relationship (R2 = 0.47 on validation data) with reasonable error levels (< 25% rRMSE). The increasing availability of VHSR optical sensors (such as from constellations of small satellite platforms) raises the possibility of routine repeated imaging of the world's tropical forests and suggests that texture-based analyses could become an essential tool in international efforts to monitor carbon emissions from deforestation and forest degradations (REDD +). © 2017 Elsevier Inc.

Abstract: We investigated performance trade-offs among seedlings of nine tropical tree species during a -five-year field experiment. Seedlings were grown in eight microhabitat types composed of paired gap and shaded understory sites in each of four soil types. We defined performance trade-offs relevant to coexistence as significant pairwise rank reversals for species performance between contrasting situations, of which we characterize three types: microhabitat, fitness component, and ontogenetic. Only 2 of 36 species pairs exhibited microhabitat trade-offs or reversed rankings for survival or relative growth rate (RGR) among microhabitats, and only one species pair reversed performance ranks among soil types. We found stronger evidence for rank reversals between fitness components (survival and RGR), particularly in gap vs. understory environments, suggesting a general trade-off between shade tolerance (survival in shade) and gap establishment (RGR in gaps). Third, the most frequent rank reversals between species pairs occurred between early and later ontogenetic stages, especially between fitness components in contrasting microhabitats. Overall, 15 of 36 pairs of potentially competing species exhibited some type of seedling performance trade-off, two species pairs never outperformed one another, and for 19 species pairs one species was a consistent better performer. We suggest that ontogenetic trade-offs, in concert with microhabitat and fitness component trade-offs, may contribute to species coexistence of long-lived organisms such as tropical trees.