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Srivastava, D. S., Céréghino, R., Trzcinski, M. K., MacDonald, A. A. M., Marino, N. A. C., Mercado, D. A., et al. (2020). Ecological response to altered rainfall differs across the Neotropics. Ecology, 101(4), e02984.
Abstract: There is growing recognition that ecosystems may be more impacted by infrequent extreme climatic events than by changes in mean climatic conditions. This has led to calls for experiments that explore the sensitivity of ecosystems over broad ranges of climatic parameter space. However, because such response surface experiments have so far been limited in geographic and biological scope, it is not clear if differences between studies reflect geographic location or the ecosystem component considered. In this study, we manipulated rainfall entering tank bromeliads in seven sites across the Neotropics, and characterized the response of the aquatic ecosystem in terms of invertebrate functional composition, biological stocks (total invertebrate biomass, bacterial density) and ecosystem fluxes (decomposition, carbon, nitrogen). Of these response types, invertebrate functional composition was the most sensitive, even though, in some sites, the species pool had a high proportion of drought-tolerant families. Total invertebrate biomass was universally insensitive to rainfall change because of statistical averaging of divergent responses between functional groups. The response of invertebrate functional composition to rain differed between geographical locations because (1) the effect of rainfall on bromeliad hydrology differed between sites, and invertebrates directly experience hydrology not rainfall and (2) the taxonomic composition of some functional groups differed between sites, and families differed in their response to bromeliad hydrology. These findings suggest that it will be difficult to establish thresholds of “safe ecosystem functioning” when ecosystem components differ in their sensitivity to climatic variables, and such thresholds may not be broadly applicable over geographic space. In particular, ecological forecast horizons for climate change may be spatially restricted in systems where habitat properties mediate climatic impacts, and those, like the tropics, with high spatial turnover in species composition. © 2020 by the Ecological Society of America
Keywords: contingency; distributed experiment; freshwater; global change biology; macroinvertebrates; phytotelmata; precipitation; aquatic ecosystem; climate change; climate conditions; ecosystem response; extreme event; functional group; invertebrate; Neotropical Region; rainfall; species pool; Bacteria (microorganisms); Invertebrata; rain; animal; climate change; drought; ecosystem; invertebrate; Animals; Climate Change; Droughts; Ecosystem; Invertebrates; Rain
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Sullivan, M. J. P., Lewis, S. L., Affum-Baffoe, K., Castilho, C., Costa, F., Sanchez, A. C., et al. (2020). Long-term thermal sensitivity of Earth’s tropical forests. Science, 368(6493), 869–874.
Abstract: A key uncertainty in climate change models is the thermal sensitivity of tropical forests and how this value might influence carbon fluxes. Sullivan et al. measured carbon stocks and fluxes in permanent forest plots distributed globally. This synthesis of plot networks across climatic and biogeographic gradients shows that forest thermal sensitivity is dominated by high daytime temperatures. This extreme condition depresses growth rates and shortens the time that carbon resides in the ecosystem by killing trees under hot, dry conditions. The effect of temperature is worse above 32°C, and a greater magnitude of climate change thus risks greater loss of tropical forest carbon stocks. Nevertheless, forest carbon stocks are likely to remain higher under moderate climate change if they are protected from direct impacts such as clearance, logging, or fires.Science, this issue p. 869The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate controls on forest carbon. Maximum temperature is the most important predictor of aboveground biomass (−9.1 megagrams of carbon per hectare per degree Celsius), primarily by reducing woody productivity, and has a greater impact per °C in the hottest forests (>32.2°C). Our results nevertheless reveal greater thermal resilience than observations of short-term variation imply. To realize the long-term climate adaptation potential of tropical forests requires both protecting them and stabilizing Earth’s climate.
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Svensk, M., Coste, S., Gérard, B., Gril, E., Julien, F., Maillard, P., et al. (2020). Drought effects on resource partition and conservation among leaf ontogenetic stages in epiphytic tank bromeliads. Physiol. Plant., 170(4), 488–507.
Abstract: Studying the response to drought stress of keystone epiphytes such as tank bromeliads is essential to better understand their resistance capacity to future climate change. The objective was to test whether there is any variation in the carbon, water and nutrient status among different leaf ontogenetic stages in a bromeliad rosette subjected to a gradient of drought stress. We used a semi-controlled experiment consisting in a gradient of water shortage in Aechmea aquilega and Lutheria splendens. For each bromeliad and drought treatment, three leaves were collected based on their position in the rosette and several functional traits related to water and nutrient status, and carbon metabolism were measured. We found that water status traits (relative water content, leaf succulence, osmotic and midday water potentials) and carbon metabolism traits (carbon assimilation, maximum quantum yield of photosystem II, chlorophyll and starch contents) decreased with increasing drought stress, while leaf soluble sugars and carbon, nitrogen and phosphorus contents remained unchanged. The different leaf ontogenetic stages showed only marginal variations when subjected to a gradient of drought. Resources were not reallocated between different leaf ontogenetic stages but we found a reallocation of soluble sugars from leaf starch reserves to the root system. Both species were capable of metabolic and physiological adjustments in response to drought. Overall, this study advances our understanding of the resistance of bromeliads faced with increasing drought stress and paves the way for in-depth reflection on their strategies to cope with water shortage. © 2020 Scandinavian Plant Physiology Society
Keywords: chlorophyll; nitrogen; water; Bromeliaceae; drought; metabolism; photosynthesis; plant leaf; Bromeliaceae; Chlorophyll; Droughts; Nitrogen; Photosynthesis; Plant Leaves; Water
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Talaga, S., Dejean, A., Azémar, F., Dumont, Y., & Leroy, C. (2020). Impacts of biotic and abiotic parameters on immature populations of Aedes aegypti. J. Pest Sci., 93(3), 941–952.
Abstract: In recent centuries, the mosquito Aedes aegypti has spread into most urban areas throughout the tropics. This species is considered the main vector of the chikungunya, dengue, yellow fever and Zika viruses and causes major public health issues. The aim of this study is to investigate the relative influence of biotic and abiotic parameters on immature populations of Ae. aegypti. During a one-year-long field experiment, we monitored 108 macroinvertebrate aquatic communities inhabiting four types of water containers across three different urbanized sites in a Neotropical city. A multimodel inference approach revealed that, in addition to abiotic parameters, biotic interactions with aquatic organisms had an important influence on the abundance of Ae. aegypti and that the urbanized site considered influences the outcomes of the interactions. Controphic species other than mosquitoes aided Ae. aegypti development, suggesting a mechanism of facilitation through a chain of processes. However, the abundance of Ae. aegypti was lowered by competition with native mosquito species in the slightly urbanized area and by predation in more urbanized areas. Competitive displacement and reduction, as well as predation by native aquatic organisms, can be considered a form of ecosystem service. The conservation and/or augmentation of natural enemies should improve the short- and long-term success of incompatible and/or sterile insect techniques, thus opening up perspectives for the future of mosquito management. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Keywords: Biocontrol agents; Competition; Ecosystem services; Mosquito control; Mosquito management; Predation; abiotic factor; biotic factor; competitive displacement; disease vector; maturation; mosquito; pest control; Aedes aegypti; Hexapoda; Zika virus
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ter Steege, H., Prado, P. I., Lima, R. A. F., Pos, E., de Souza Coelho, L., de Andrade Lima Filho, D., et al. (2020). Biased-corrected richness estimates for the Amazonian tree flora. Sci. Rep., 10(10130).
Abstract: Amazonian forests are extraordinarily diverse, but the estimated species richness is very much debated. Here, we apply an ensemble of parametric estimators and a novel technique that includes conspecific spatial aggregation to an extended database of forest plots with up-to-date taxonomy. We show that the species abundance distribution of Amazonia is best approximated by a logseries with aggregated individuals, where aggregation increases with rarity. By averaging several methods to estimate total richness, we confirm that over 15,000 tree species are expected to occur in Amazonia. We also show that using ten times the number of plots would result in an increase to just ~50% of those 15,000 estimated species. To get a more complete sample of all tree species, rigorous field campaigns may be needed but the number of trees in Amazonia will remain an estimate for years to come. © 2020, The Author(s).
Keywords: adult; article; averaging; flora; forest; population abundance
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Thomas, H. J. D., Bjorkman, A. D., Myers-Smith, I. H., Elmendorf, S. C., Kattge, J., Diaz, S., et al. (2020). Global plant trait relationships extend to the climatic extremes of the tundra biome. Nat. Commun., 11(1351).
Abstract: The majority of variation in six traits critical to the growth, survival and reproduction of plant species is thought to be organised along just two dimensions, corresponding to strategies of plant size and resource acquisition. However, it is unknown whether global plant trait relationships extend to climatic extremes, and if these interspecific relationships are confounded by trait variation within species. We test whether trait relationships extend to the cold extremes of life on Earth using the largest database of tundra plant traits yet compiled. We show that tundra plants demonstrate remarkably similar resource economic traits, but not size traits, compared to global distributions, and exhibit the same two dimensions of trait variation. Three quarters of trait variation occurs among species, mirroring global estimates of interspecific trait variation. Plant trait relationships are thus generalizable to the edge of global trait-space, informing prediction of plant community change in a warming world. © 2020, Crown.
Keywords: biome; climate change; extreme event; global change; growth; interspecific interaction; plant community; tundra; article; plant community; prediction; tundra; warming; classification; climate; ecosystem; genetics; plant; plant development; Climate; Ecosystem; Plant Development; Plants; Tundra
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Touchard, A., Aili, S. R., Téné, N., Barassé, V., Klopp, C., Dejean, A., et al. (2020). Venom Peptide Repertoire of the European Myrmicine Ant Manica rubida: Identification of Insecticidal Toxins. J. Proteome Res., 19(4), 1800–1811.
Abstract: Using an integrated transcriptomic and proteomic approach, we characterized the venom peptidome of the European red ant, Manica rubida. We identified 13 “myrmicitoxins” that share sequence similarities with previously identified ant venom peptides, one of them being identified as an EGF-like toxin likely resulting from a threonine residue modified by O-fucosylation. Furthermore, we conducted insecticidal assays of reversed-phase HPLC venom fractions on the blowfly Lucilia caesar, permitting us to identify six myrmicitoxins (i.e., U3-, U10-, U13-, U20-MYRTX-Mri1a, U10-MYRTX-Mri1b, and U10-MYRTX-Mri1c) with an insecticidal activity. Chemically synthesized U10-MYRTX-Mri1a, -Mri1b, -Mri1c, and U20-MYRTX-Mri1a irreversibly paralyzed blowflies at the highest doses tested (30-125 nmol·g-1). U13-MYRTX-Mri1a, the most potent neurotoxic peptide at 1 h, had reversible effects after 24 h (150 nmol·g-1). Finally, U3-MYRTX-Mri1a has no insecticidal activity, even at up to 55 nmol·g-1. Thus, M. rubida employs a paralytic venom rich in linear insecticidal peptides, which likely act by disrupting cell membranes.
Keywords: glycosylated toxin; peptidome; polycationic α-helix; predation; pyroglutamate; reversible neurotoxicity
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Tysklind, N., Etienne, M. - P., Scotti-Saintagne, C., Tinaut, A., Casalis, M., Troispoux, V., et al. (2020). Microgeographic local adaptation and ecotype distributions: The role of selective processes on early life-history traits in sympatric, ecologically divergent Symphonia populations. Ecology and Evolution, 10(19), 10735–10753.
Abstract: Trees are characterized by the large number of seeds they produce. Although most of those seeds will never germinate, plenty will. Of those which germinate, many die young, and eventually, only a minute fraction will grow to adult stage and reproduce. Is this just a random process? Do variations in germination and survival at very young stages rely on variations in adaptations to microgeographic heterogeneity? and do these processes matter at all in determining tree species distribution and abundance?. We have studied these questions with the Neotropical Symphonia tree species. In the Guiana shield, Symphonia are represented by at least two sympatric taxa or ecotypes, Symphonia globulifera found almost exclusively in bottomlands, and a yet undescribed more generalist taxon/ecotype, Symphonia sp1. A reciprocal transplantation experiment (510 seeds, 16 conditions) was set up and followed over the course of 6 years to evaluate the survival and performance of individuals from different ecotypes and provenances. Germination, survival, growth, and herbivory showed signs of local adaptation, with some combinations of ecotypes and provenances growing faster and surviving better in their own habitat or provenance region. S. globulifera was strongly penalized when planted outside its home habitat but showed the fastest growth rates when planted in its home habitat, suggesting it is a specialist of a high-risk high-gain strategy. Conversely, S. sp1 behaved as a generalist, performing well in a variety of environments. The differential performance of seeds and seedlings in the different habitats matches the known distribution of both ecotypes, indicating that environmental filtering at the very early stages can be a key determinant of tree species distributions, even at the microgeographic level and among very closely related taxa. Furthermore, such differential performance also contributes to explain, in part, the maintenance of the different Symphonia ecotypes living in intimate sympatry despite occasional gene flow. © 2020 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd
Keywords: determinants of plant community diversity and structure; evolutionary ecology; landscape ecology; local adaptation; Neotropical forest; plant development and life-history traits; reciprocal transplantation experiments; Symphonia
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Urbina, I., Grau, O., Sardans, J., Ninot, J. M., & Peñuelas, J. (2020). Encroachment of shrubs into subalpine grasslands in the Pyrenees changes the plant-soil stoichiometry spectrum. Plant Soil, 448(1-2), 37–53.
Abstract: Aims: Shrub encroachment has been reported over a large proportion of the subalpine grasslands across Europe and is expected to have an important impact on the biogeochemical cycle of these ecosystems. We investigated the stoichiometric changes in the plant-soil system along the succession (e.g. increase in encroachment from unencroached grassland to mature shrubland) at two contrasting sites in the Pyrenees. Methods: We analyzed the chemical composition (C, N,15N, P, K, Ca, Mg and Fe) in the soil and in the aboveground plant compartments (leaves, leaf-litter and stems) of the main herbaceous species and shrubs at three contrasting stages of the succession: unencroached grassland, young shrubland and mature shrubland. Results: The plant-soil stoichiometry spectrum differed between the successional stages. Shrub encroachment generally increased the concentration of C and Ca and the C:N ratio and often reduced to concentrations of N, P and K in the leaves and leaf-litter, while several soil nutrient concentrations (N, P, K Ca and Mg) decreased. The stocks of C, N, P, Ca, and Mg in the total aboveground biomass increased with encroachment. Conclusions: Shrub encroachment favored the dominance of long-lived species with low concentrations of N and P in the plant-soil compartments, high C:nutrient ratios in the aboveground biomass and increase the uptake of N through ericoid or ectomycorrhizal fungi. We highlight the role of shrubs in the sequestration of C and nutrients through the allocation to the aboveground biomass. The changes in plant-soil elemental composition and stocks suggest a slowdown of the biogeochemical cycles in the subalpine mountain areas where shrub encroachment occurred. © 2020, Springer Nature Switzerland AG.
Keywords: Nutrient stocks; Plant strategy; Plant-soil stoichiometry; Shrub encroachment; Subalpine grassland succession; aboveground biomass; biogeochemical cycle; carbon sequestration; ectomycorrhiza; fungus; grass; nitrogen; nutrient uptake; shrub; soil-vegetation interaction; stoichiometry; subalpine environment; succession; Europe; Pyrenees; Fungi
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Van Langenhove, L., Depaepe, T., Vicca, S., van den Berge, J., Stahl, C., Courtois, E., et al. (2020). Regulation of nitrogen fixation from free-living organisms in soil and leaf litter of two tropical forests of the Guiana shield. Plant Soil, 450(1-2), 93–110.
Abstract: Background and aims: Biological fixation of atmospheric nitrogen (N2) is the main pathway for introducing N into unmanaged ecosystems. While recent estimates suggest that free-living N fixation (FLNF) accounts for the majority of N fixed in mature tropical forests, the controls governing this process are not completely understood. The aim of this study was to quantify FLNF rates and determine its drivers in two tropical pristine forests of French Guiana. Methods: We used the acetylene reduction assay to measure FLNF rates at two sites, in two seasons and along three topographical positions, and used regression analyses to identify which edaphic explanatory variables, including carbon (C), nitrogen (N), phosphorus (P) and molybdenum (Mo) content, pH, water and available N and P, explained most of the variation in FLNF rates. Results: Overall, FLNF rates were lower than measured in tropical systems elsewhere. In soils seasonal variability was small and FLNF rates differed among topographies at only one site. Water, P and pH explained 24% of the variation. In leaf litter, FLNF rates differed seasonally, without site or topographical differences. Water, C, N and P explained 46% of the observed variation. We found no regulatory role of Mo at our sites. Conclusions: Rates of FLNF were low in primary rainforest on poor soils on the Guiana shield. Water was the most important rate-regulating factor and FLNF increased with increasing P, but decreased with increasing N. Our results support the general assumption that N fixation in tropical lowland forests is limited by P availability. © 2019, The Author(s).
Keywords: Free-living nitrogen fixation; French Guiana; Molybdenum; Nutrients; Phosphorus; Tropical forest; acetylene; leaf litter; molybdenum; nitrogen fixation; nutrient cycling; phosphorus; rainforest; reduction; soil biota; soil carbon; soil nitrogen; soil water; topographic effect; tropical forest; French Guiana
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