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Levionnois, S., Salmon, C., Alméras, T., Clair, B., Ziegler, C., Coste, S., et al. (2021). Anatomies, vascular architectures, and mechanics underlying the leaf size-stem size spectrum in 42 Neotropical tree species. Journal of Experimental Botany, 72(22), 7957–7969.
Abstract: The leaf size-stem size spectrum is one of the main dimensions of plant ecological strategies. Yet the anatomical, mechanical, and hydraulic implications of small vs. large shoots are still poorly understood. We investigated 42 tropical rainforest tree species in French Guiana, with a wide range of leaf areas at the shoot level. We quantified the scaling of hydraulic and mechanical constraints with shoot size estimated as the water potential difference ΔΨ and the bending angle ΔΦ, respectively. We investigated how anatomical tissue area, flexural stiffness and xylem vascular architecture affect such scaling by deviating (or not) from theoretical isometry with shoot size variation. Vessel diameter and conductive path length were found to be allometrically related to shoot size, thereby explaining the independence between ΔΨ and shoot size. Leaf mass per area, stem length, and the modulus of elasticity were allometrically related with shoot size, explaining the independence between ΔΦ and shoot size. Our study also shows that the maintenance of both water supply and mechanical stability across the shoot size range are not in conflict.
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Levionnois, S., Ziegler, C., Heuret, P., Jansen, S., Stahl, C., Calvet, E., et al. (2021). Is vulnerability segmentation at the leaf‑stem transition a drought resistance mechanism? A theoretical test with a trait‑based model for Neotropical canopy tree species. Annals of Forest Science, 78(4), 78–87.
Abstract: Leaf-stem vulnerability segmentation predicts lower xylem embolism resistance in leaves than stem. However, although it has been intensively investigated these past decades, the extent to which vulnerability segmentation promotes drought resistance is not well understood. Based on a trait-based model, this study theoretically supports that vulnerability segmentation enhances shoot desiccation time across 18 Neotropical tree species. CONTEXT: Leaf-stem vulnerability segmentation predicts lower xylem embolism resistance in leaves than stems thereby preserving expensive organs such as branches or the trunk. Although vulnerability segmentation has been intensively investigated these past decades to test its consistency across species, the extent to which vulnerability segmentation promotes drought resistance is not well understood. AIMS: We investigated the theoretical impact of the degree of vulnerability segmentation on shoot desiccation time estimated with a simple trait-based model. METHODS: We combined data from 18 tropical rainforest canopy tree species on embolism resistance of stem xylem (flow-centrifugation technique) and leaves (optical visualisation method). Measured water loss under minimum leaf and bark conductance, leaf and stem capacitance, and leaf-to-bark area ratio allowed us to calculate a theoretical shoot desiccation time (tcᵣᵢₜ). RESULTS: Large degrees of vulnerability segmentation strongly enhanced the theoretical shoot desiccation time, suggesting vulnerability segmentation to be an efficient drought resistance mechanism for half of the studied species. The difference between leaf and bark area, rather than the minimum leaf and bark conductance, determined the drastic reduction of total transpiration by segmentation during severe drought. CONCLUSION: Our study strongly suggests that vulnerability segmentation is an important drought resistance mechanism that should be better taken into account when investigating plant drought resistance and modelling vegetation. We discuss future directions for improving model assumptions with empirical measures, such as changes in total shoot transpiration after leaf xylem embolism.
Keywords: Neotropics, bark, canopy, capacitance, drought, drought tolerance, embolism, leaves, models, transpiration, trees, tropical rain forests, xylem
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Li, L., Preece, C., Lin, Q., Bréchet, L. M., Stahl, C., Courtois, E. A., et al. (2021). Resistance and resilience of soil prokaryotic communities in response to prolonged drought in a tropical forest. FEMS Microbiology Ecology, 97(9).
Abstract: Global climate changes such as prolonged duration and intensity of drought can lead to adverse ecological consequences in forests. Currently little is known about soil microbial community responses to such drought regimes in tropical forests. In this study, we examined the resistance and resilience of topsoil prokaryotic communities to a prolongation of the dry season in terms of diversity, community structure and co-occurrence patterns in a French Guianan tropical forest. Through excluding rainfall during and after the dry season, a simulated prolongation of the dry season by five months was compared to controls. Our results show that prokaryotic communities increasingly diverged from controls with the progression of rain exclusion. Furthermore, prolonged drought significantly affected microbial co-occurrence networks. However, both the composition and co-occurrence networks of soil prokaryotic communities immediately ceased to differ from controls when precipitation throughfall returned. This study thus suggests modest resistance but high resilience of microbial communities to a prolonged drought in tropical rainforest soils.
Keywords: drought, microbial communities, microbial network, tropical forest, resistance, resilience
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Llusia, J., Asensio, D., Sardans, J., Filella, I., Peguero, G., Grau, O., et al. (2021). Contrasting nitrogen and phosphorus fertilization effects on soil terpene exchanges in a tropical forest. Science of the Total Environment, 802, 149769.
Abstract: Production, emission, and absorption of biogenic volatile organic compounds (BVOCs) in ecosystem soils and associated impacts of nutrient availability are unclear; thus, predictions of effects of global change on source-sink dynamic under increased atmospheric N deposition and nutrition imbalances are limited. Here, we report the dynamics of soil BVOCs under field conditions from two undisturbed tropical rainforests from French Guiana. We analyzed effects of experimental soil applications of nitrogen (N), phosphorus (P), and N + P on soil BVOC exchanges (in particular of total terpenes, monoterpenes, and sesquiterpenes), to determine source and sink dynamics between seasons (dry and wet) and elevations (upper and lower elevations corresponding to top of the hills (30 m high) and bottom of the valley). We identified 45 soil terpenoids compounds emitted to the atmosphere, comprising 26 monoterpenes and 19 sesquiterpenes; of these, it was possible to identify 13 and 7 compounds, respectively. Under ambient conditions, soils acted as sinks of these BVOCs, with greatest soil uptake recorded for sesquiterpenes at upper elevations during the wet season (-282 μg m-2 h-1). Fertilization shifted soils from a sink to source, with greatest levels of terpene emissions recorded at upper elevations during the wet season, following the addition of N (monoterpenes: 406 μg m-2 h-1) and P (sesquiterpenes: 210 μg m-2 h-1). Total soil terpene emission rates were negatively correlated with total atmospheric terpene concentrations. These results indicate likely shifts in tropical soils from sink to source of atmospheric terpenes under projected increases in N deposition under global change, with potential impacts on regional-scale atmospheric chemistry balance and ecosystem function.
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Lormée, H., Berzins, R., Rocheteau, V., De Coster, F., Denis, T., & Richard-Hanssen, C. (2021). Seasonal Variation in the Home Ranges of Black Curassow, Crax alector, in French Guiana. Tropical Conservation Science, 14(1), 1–10.
Abstract: Cracidae is the most threatened avian family in the Neotropics, mainly because of habitat destruction, heavy hunting pressure and poaching. In French Guiana, Black Curassows are heavily hunted, although basic knowledge of the ecological and demographical traits of the species remains limited. Such a gap prevents any attempt to assess the impact of hunting and to help stakeholders to develop proposals ensuring hunting sustainability. The spatial relationship between animals and their habitat is important for conservation management, being related to population densities through complex patterns. Here, we report on a radio-tracking study of Black Curassows in tropical primary rainforest, in Nouragues National Reserve, French Guiana. The aims of the study were to estimate home range size and its variation across seasons, and to quantify movement patterns of the birds. We captured and fitted VHF tags to four adults, and tracked them for 10 to 21.5 months. Daily movements were recorded, and home ranges estimated using the Kernel Density method, for two consecutive wet seasons and one dry season. Using 95% and 50% Kernel densities, the average annual home range and core area were 96.3± 32.6 ha (SE) and 22.8 ± 2.8 ha respectively. Home ranges appeared spatially stable over the two years, and overlapped between neighbouring groups. During the dry season, Black Curassows did not migrate but tended to enlarge their home range, with greater daily movements and higher home range overlap. Although additional data are still needed, our results can help to improve the knowledge and management of this poorly studied species
Keywords: spatial ecology, Cracids, tracking, Kernel method, Home range, movement pattern
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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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Migliavacca, M., Musavi, T., Mahecha, M. D., Nelson, J. A., Knauer, J., Baldocchi, D. D., et al. (2021). The three major axes of terrestrial ecosystem function. Nature, 598(7881), 468–472.
Abstract: The leaf economics spectrum1,2 and the global spectrum of plant forms and functions3 revealed fundamental axes of variation in plant traits, which represent different ecological strategies that are shaped by the evolutionary development of plant species2. Ecosystem functions depend on environmental conditions and the traits of species that comprise the ecological communities4. However, the axes of variation of ecosystem functions are largely unknown, which limits our understanding of how ecosystems respond as a whole to anthropogenic drivers, climate and environmental variability4,5. Here we derive a set of ecosystem functions6 from a dataset of surface gas exchange measurements across major terrestrial biomes. We find that most of the variability within ecosystem functions (71.8%) is captured by three key axes. The first axis reflects maximum ecosystem productivity and is mostly explained by vegetation structure. The second axis reflects ecosystem water-use strategies and is jointly explained by variation in vegetation height and climate. The third axis, which represents ecosystem carbon-use efficiency, features a gradient related to aridity, and is explained primarily by variation in vegetation structure. We show that two state-of-the-art land surface models reproduce the first and most important axis of ecosystem functions. However, the models tend to simulate more strongly correlated functions than those observed, which limits their ability to accurately predict the full range o
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Mirabel, A., Marcon, E., & Hérault, B. (2021). 30 Years of postdisturbance recruitment in a Neotropical forest. Ecology and Evolution, 11(21), 14448–14458.
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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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Peguero, G., Ferrin, M., Sardans, J., Verbruggen, E., Ramirez-Rojas, I., Van Langenhove, L., et al. (2021). Decay of similitary across tropical forest communities: integrating spatial distance with soil nutrients. Ecology, 103(2), e03599.
Abstract: Understanding the mechanisms that drive the change of biotic assemblages over space and time is the main quest of community ecology. Assessing the relative importance of dispersal and environmental species selection in a range of organismic sizes and motilities has been a fruitful strategy. A consensus for whether spatial and environmental distances operate similarly across spatial scales and taxa, however, has yet to emerge. We used censuses of four major groups of organisms (soil bacteria, fungi, ground insects, and trees) at two observation scales (1-m2 sampling point vs. 2,500-m2 plots) in a topographically standardized sampling design replicated in two tropical rainforests with contrasting relationships between spatial distance and nutrient availability. We modeled the decay of assemblage similarity for each taxon set and site to assess the relative contributions of spatial distance and nutrient availability distance. Then, we evaluated the potentially structuring effect of tree composition over all other taxa. The similarity of nutrient content in the litter and topsoil had a stronger and more consistent selective effect than did dispersal limitation, particularly for bacteria, fungi, and trees at the plot level. Ground insects, the only group assessed with the capacity of active dispersal, had the highest species turnover and the flattest nonsignificant distance−decay relationship, suggesting that neither dispersal limitation nor nutrient availability were fundamental drivers of their community assembly at this scale of analysis. Only the fungal communities at one of our study sites were clearly coordinated with tree composition. The spatial distance at the smallest scale was more important than nutrient selection for the bacteria, fungi, and insects. The lower initial similarity and the moderate variation in composition identified by these distance-decay models, however, suggested that the effects of stochastic sampling were important at this smaller spatial scale. Our results highlight the importance of nutrients as one of the main environmental drivers of rainforest communities irrespective of organismic or propagule size and how the overriding effect of the analytical scale influences the interpretation, leading to the perception of greater importance of dispersal limitation and ecological drift over selection associated with environmental niches at decreasing observation scales.
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