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Leroy, C., Maes, A. Q. M., Louisanna, E., Schimann, H., & Séjalon-Delmas, N. (2021). Taxonomic, phylogenetic and functional diversity of rootassociated fungi in bromeliads: effects of host identity, life forms and nutritional modes. New Phytologist, 231(3), 1195–1209.
Abstract: Bromeliads represent a major component of neotropical forests and encompass a considerable diversity of life forms and nutritional modes. Bromeliads explore highly stressful habitats and root-associated fungi may play a crucial role in this, but the driving factors and variations in root-associated fungi remain largely unknown.
We explored root-associated fungal communities in 17 bromeliad species and their variations linked to host identity, life forms and nutritional modes by using ITS1 gene-based high-throughput sequencing and by characterizing fungal functional guilds.
We found a dual association of mycorrhizal and nonmycorrhizal fungi. The different species, life forms and nutritional modes among bromeliad hosts had fungal communities that differ in their taxonomic and functional composition. Specifically, roots of epiphytic bromeliads had more endophytic fungi and dark septate endophytes and fewer mycorrhizal fungi than terrestrial bromeliads and lithophytes.
Our results contribute to a fundamental knowledge base on different fungal groups in previously undescribed Bromeliaceae. The diverse root-associated fungal communities in bromeliads may enhance plant fitness in both stressful and nutrient-poor environments and may give more flexibility to the plants to adapt to changing environmental conditions.
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Bréchet, L. M., Daniel Warren, Stahl, C., Burban, B., Goret, J. - Y., Salomon, R. L., et al. (2021). Simultaéneous tree stem and soil greenhouse gas (CO2, CH4, N2O) flux measurements: a novel design for continuous monitoring towards improving flux estimates and temporal resolution. New Phytologist, 230(6), 2487–2500.
Abstract: Tree stems and soils can act as sources and sinks for the greenhouse gases (GHG) carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Since both uptake and emission capacities can be large, especially in tropical rainforests, accurate assessments of the magnitudes and temporal variations of stem and soil GHG fluxes are required. We designed a new flexible stem chamber system for continuously measuring GHG fluxes in a French Guianese rainforest. Here, we describe this new system, which is connected to an automated soil GHG flux system, and discuss measurement uncertainty and potential error sources. In line with findings for soil GHG flux estimates, we demonstrated that lengthening the stem chamber closure time was required for accurate estimates of tree stem CH4 and N2O flux but not tree stem CO2 flux. The instrumented stem was a net source of CO2 and CH4 and a weak sink of N2O. Our experimental setup operated successfully in situ and provided continuous tree and soil GHG measurements at a high temporal resolution over an 11-month period. This automated system is a major step forward in the measurement of GHG fluxes in stems and the atmosphere concurrently with soil GHG fluxes in tropical forest ecosystems.
Keywords: système de chambre automatisé ; efflux de dioxyde de carbone ; flux de méthane ; flux d'oxyde nitreux ; tige d'arbre ; forêt tropicale
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Levionnois, S., Jansen, S., Wandji, R. T., Beauchêne, J., Ziegler, C., Coste, S., et al. (2021). Linking drought-induced xylem embolism resistance to wood anatomical traits in Neotropical trees. New Phytol., 229(3), 1453–1466.
Abstract: Drought-induced xylem embolism is considered to be one of the main factors driving mortality in woody plants worldwide. Although several structure–functional mechanisms have been tested to understand the anatomical determinants of embolism resistance, there is a need to study this topic by integrating anatomical data for many species. We combined optical, laser, and transmission electron microscopy to investigate vessel diameter, vessel grouping, and pit membrane ultrastructure for 26 tropical rainforest tree species across three major clades (magnoliids, rosiids, and asteriids). We then related these anatomical observations to previously published data on drought-induced embolism resistance, with phylogenetic analyses. Vessel diameter, vessel grouping, and pit membrane ultrastructure were all predictive of xylem embolism resistance, but with weak predictive power. While pit membrane thickness was a predictive trait when vestured pits were taken into account, the pit membrane diameter-to-thickness ratio suggests a strong importance of the deflection resistance of the pit membrane. However, phylogenetic analyses weakly support adaptive coevolution. Our results emphasize the functional significance of pit membranes for air-seeding in tropical rainforest trees, highlighting also the need to study their mechanical properties due to the link between embolism resistance and pit membrane diameter-to-thickness ratio. Finding support for adaptive coevolution also remains challenging. © 2020 The Authors New Phytologist © 2020 New Phytologist Foundation
Keywords: bordered pits; drought-induced embolism; pit membrane; transmission electron microscopy; tropical trees; vessel grouping; xylem anatomy
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Schmitt, S., Derroire, G., Tysklind, N., Heuertz, M., & Hérault, B. (2021). Topography shapes the local coexistence of tree species within species complexes of Neotropical forests. Oecologia, 196, 389–398.
Abstract: Forest inventories in Amazonia include around 5000 described tree species belonging to more than 800 genera. Numerous species-rich genera share genetic variation among species because of recent speciation and/or recurrent hybridisation, forming species complexes. Despite the key role that tree species complexes play in understanding Neotropical diversification, and their need to exploit a diversity of niches, little is known about the mechanisms that allow local coexistence of tree species complexes and their species in sympatry. In this study, we explored the fine-scale distribution of five tree species complexes and 22 species within these complexes. Combining forest inventories, botanical determination, and LiDAR-derived topographic data over 120 ha of permanent plots in French Guiana, we used a Bayesian modelling framework to test the role of fine-scale topographic wetness and tree neighbourhood on the occurrence of species complexes and the relative distribution of species within complexes. Species complexes of Neotropical trees were widely spread across the topographic wetness gradient at the local scale. Species within complexes showed pervasive niche differentiation along with topographic wetness and competition gradients. Similar patterns of species-specific habitat preferences were observed within several species complexes: species more tolerant to competition for resources grow in drier and less fertile plateaus and slopes. If supported by partial reproductive isolation of species and adaptive introgression at the species complex level, our results suggest that both species-specific habitat specialisation within species complexes and the broad ecological distribution of species complexes might explain the success of these species complexes at the regional scale.
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Nixon, S. A., Robinson, S. D., Agwa, A., J., Walker, A. A., Choudhay, S., Touchard, A., et al. (2021). Multipurpose peptides: The venoms of Amazonian stinging ants contain anthelmintic ponericins with diverse predatory and defensive activities. Biochemical Pharmacology, 192, 114693.
Abstract: In the face of increasing drug resistance, the development of new anthelmintics is critical for controlling nematodes that parasitise livestock. Although hymenopteran venom toxins have attracted attention for applications in agriculture and medicine, few studies have explored their potential as anthelmintics. Here we assessed hymenopteran venoms as a possible source of new anthelmintic compounds by screening a panel of ten hymenopteran venoms against Haemonchus contortus, a major pathogenic nematode of ruminants. Using bioassay-guided fractionation coupled with liquid chromatography-tandem mass spectrometry, we identified four novel anthelmintic peptides (ponericins) from the venom of the neotropical ant Neoponera commutata and the previously described ponericin M−PONTX−Na1b from Neoponera apicalis venom. These peptides inhibit H. contortus development with IC50 values of 2.8–5.6 μM. Circular dichroism spectropolarimetry indicated that the ponericins are unstructured in aqueous solution but adopt α-helical conformations in lipid mimetic environments. We show that the ponericins induce non-specific membrane perturbation, which confers broad-spectrum antimicrobial, insecticidal, cytotoxic, hemolytic, and algogenic activities, with activity across all assays typically correlated. We also show for the first time that ponericins induce spontaneous pain behaviour when injected in mice. We propose that the broad-spectrum activity of the ponericins enables them to play both a predatory and defensive role in neoponeran ants, consistent with their high abundance in venom. This study reveals a broader functionality for ponericins than previously assumed, and highlights both the opportunities and challenges in pursuing ant venom peptides as potential therapeutics.
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Maggia, M. - E., Decaëns, T., Lapied, E., Dupont, L., Roy, V., Schimann, H., et al. (2021). At each site its diversity: DNA barcoding reveals remarkable earthworm diversity in neotropical rainforests of French Guiana. Applied Soil Ecology, 164, 103932.
Abstract: Despite their recognized essential role in soil, earthworms in tropical environments are still understudied. The aim of this study was to re-evaluate the diversity at the regional scale, as well as to investigate the environmental and spatial drivers of earthworm communities. We sampled earthworm communities across a range of habitats at six localities in French Guiana using three different sampling methods. We generated 1675 DNA barcodes and combined them with data from a previous study. Together, all sequences clustered into 119 MOTUs which were used as proxy to assess species richness. Only two MOTUs were common between the six localities and 20.2% were singletons, showing very high regional species richness and a high number of rare species. A canonical redundancy analysis was used to identify key drivers of the earthworm community composition. The RDA results and beta-diversity calculations both show strong species turnover and a strong spatial effect, resulting from dispersal limitations that are responsible for the current community composition. Sampling in different microhabitats allowed the discovery of 23 MOTUs that are exclusively found in decaying trunks and epiphytes, highlighting hidden diversity of earthworms outside of soil.
Keywords: DNA barcoding Tropical rainforest Community ecology Diversity level Sampling methods
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Diatta, B. D., Niass, O., Diouf, M., Guéye, M., Houel, E., & Boetsch, G. (2021). Diversité et composition phytochimique des bâtonnets frotte-dents (cure-dents) proposés chez les Peul de la commune de Tessékéré (Ferlo Nord, Sénégal). Journal of Applied Biosciences, 158, 16267–16281.
Abstract: Objectifs : Le but de cette étude était de déterminer la composition phytochimique et la teneur en grandes classes chimiques des tiges les plus utilisées comme bâtonnets frotte-dents chez les peul de Widou Thiengoli au Nord Ferlo (Sénégal). Méthodes et résultats : Des entretiens ouverts semi structurés ont permis de recueillir les plantes les plus utilisées. L’indice de fidélité renseigne sur la convergence des usages quant à l’emploi des plantes comme bâtonnets frotte-dent comparé aux autres pratiques cosmétiques. L’étude de la composition phytochimique des tiges a ciblé 8 classes chimiques. Les tanins et les saponines sont très fréquents ; les terpénoïdes et les leuco-anthocyanines presque inexistants. Un dosage des flavonoïdes, alcaloïdes et polyphénols, réalisé chez des extraits aqueux, a porté sur 12 plantes. Les meilleures teneurs en polyphénols et alcaloïdes sont recueillies chez Anogeissus leiocarpa, et la meilleure en flavonoïdes chez Commiphora africana. Conclusion et applicabilité des résultats : Ces résultats permettent de sélectionner à travers la composition phytochimique des plantes, les espèces présentant de potentielles activités antimicrobiennes, car renfermant des composés phytochimique doués de fonctions germicides, au- delà de la fonction mécanique connue des bâtonnets dans l’élimination de la plaque dentaire.
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Dejean, A., Petitclerc, F., Azémar, F., & Rossi, V. (2021). Nutrient provisioning of its host myrmecophytic tree by a temporary social parasite of a plant-ant. Biological Journal of the Linnean Society, 133(3), 744–750.
Abstract: One of the most advanced ant–plant mutualisms is represented by myrmecophytes sheltering colonies of some plant-ant species in hollow structures called domatia. In turn, the myrmecophytes benefit from biotic protection and sometimes nutrient provisioning (myrmecotrophy). Furthermore, over the course of evolution, some ant species have become social parasites of others. In this general context, we studied the relationship between its host trees and Azteca andreae (Dolichoderinae), a temporary social parasite of the plant-ant Azteca ovaticeps, and, as such, obligatorily associated with myrmecophytic Cecropia obtusa trees (Urticaceae). A first experiment showed that the δ15N values of the young leaves of Cecropia sheltering a mature A. andreae colony were very similar to those for trees sheltering Azteca alfari or A. ovaticeps, two typical Cecropia mutualists for which myrmecotrophy is known. In a second experiment, by injecting a 15N-labelled glycine solution into locusts given as prey to A. andreae colonies, we triggered an increase in δ15N in the young leaves of their host Cecropia. Thus, 15N passed from the prey to the host trees, explaining the outcomes of the first experiment. We discuss these results in light of the notion of ‘by-product benefits’.
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Vleminckx, J., Fortunel, C., Valverde-Barrantes, O., Paine, C. E. T., Engel, J., Petronelli, P., et al. (2021). Resolving whole-plant economics from leaf, stem and root traits of 1467 Amazonian tree species. Oikos, 130(7), 1193–1208.
Abstract: It remains unclear how evolutionary and ecological processes have shaped the wide variety of plant life strategies, especially in highly diverse ecosystems like tropical forests. Some evidence suggests that species have diversified across a gradient of ecological strategies, with different plant tissues converging to optimize resource use across environmental gradients. Alternative hypotheses propose that species have diversified following independent selection on different tissues, resulting in a decoupling of trait syndromes across organs. To shed light on the subject, we assembled an unprecedented dataset combining 19 leaf, stem and root traits for 1467 tropical tree species inventoried across 71 0.1-ha plots spanning broad environmental gradients in French Guiana. Nearly 50% of the overall functional heterogeneity was expressed along four orthogonal dimensions, after accounting for phylogenetic dependences among species. The first dimension related to fine root functioning, while the second and third dimensions depicted two decoupled leaf economics spectra, and the fourth dimension encompassed a wood economics spectrum. Traits involved in orthogonal functional strategies, five leaf traits in particular but also trunk bark thickness, were consistently associated with a same gradient of soil texture and nutrient availability. Root traits did not show any significant association with edaphic variation, possibly because of the prevailing influence of other factors (mycorrhizal symbiosis, phylogenetic constraints). Our study emphasises the existence of multiple functional dimensions that allow tropical tree species to optimize their performance in a given environment, bringing new insights into the debate around the presence of a whole plant economic spectrum in tropical forest tree communities. It also emphasizes the key role that soil heterogeneity plays in shaping tree species assembly. The extent to which different organs are decoupled and respond to environmental gradients may also help to improve our predictions of species distribution changes in responses to habitat modification and environmental changes.
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Van Langenhove, L., Depaepe, T., Verryckt, L. T., Vallicrosa, H., Fuchslueger, L., Lugli, L. F., et al. (2021). Impact of Nutrient Additions on Free-Living Nitrogen Fixation in Litter and Soil of Two French-Guianese Lowland Tropical Forests. JGR Biogeosciences, 126(7), e2020JG006023.
Abstract: In tropical forests, free-living Biological nitrogen (N) fixation (BNF) in soil and litter tends to decrease when substrate N concentrations increase, whereas increasing phosphorus (P) and molybdenum (Mo) soil and litter concentrations have been shown to stimulate free-living BNF rates. Yet, very few studies explored the effects of adding N, P, and Mo together in a single large-scale fertilization experiment, which would teach us which of these elements constrain or limit BNF activities. At two distinct forest sites in French Guiana, we performed a 3-year in situ nutrient addition study to explore the effects of N, P, and Mo additions on leaf litter and soil BNF. Additionally, we conducted a short-term laboratory study with the same nutrient addition treatments (+N, +N+P, +P, +Mo, and +P+Mo). We found that N additions alone suppressed litter free-living BNF in the field, but not in the short-term laboratory study, while litter free-living BNF remained unchanged in response to N+P additions. Additionally, we found that P and P+Mo additions stimulated BNF in leaf litter, both in the field and in the lab, while Mo alone yielded no changes. Soil BNF increased with P and P+Mo additions in only one of the field sites, while in the other site soil BNF increased with Mo and P+Mo additions. We concluded that increased substrate N concentrations suppress BNF. Moreover, both P and Mo have the potential to limit free-living BNF in these tropical forests, but the balance between P versus Mo limitation is determined by site-specific characteristics of nutrient supply and demand.
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