2019

Permanent URI for this collectionhttps://hdl.handle.net/1807/92945

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A new species of penzigioid Xylaria (Xylariaceae) from the cloud forest in eastern Mexico revealed through morphological and phylogenetic analyses
(Canadian Science Publishing, 2019-04-06) Chacón, Santiago; González, Dolores
Xylaria subtropicalis, a species new to science, was collected from a montane cloud forest in eastern Mexico. It is described and illustrated, based on detailed macro- and microscopic morphological characteristics, habitat, and DNA sequence data. The distinctive morphological differences between X. subtropicalis and other Xylaria species include: the stromata being significantly erumpent, the size of the ascospores being 23–28 × 13–15 µm, and a straight germ slit as long as the spore. To determine if this was a novel species, ITS sequences were generated and compared with 2478 sequences available for the genus from GenBank using the software USEARCH. Additionally, a phylogenetic reconstruction was performed with Parsimony Ratchet, Maximum Likelihood, and Bayesian Inference, using 122 concatenated ITS sequences, and segments from the 28S rDNA and RPB2. Sequences of this novel species form a strongly supported lineage, clearly separated from other species of Xylaria. Phylogenetic relationships indicate that there have been numerous morphological transformations within the genus.
A novel approach for tracing mycophagous small mammals and documenting their fungal diets
(Canadian Science Publishing, 2019-05-18) Cloutier, Véronique B.; Piché, Yves; Fortin, J.-André; Bérubé, Jean; Glémet, Hélène; Desrochers, André
We developed a method combining passive baiting (animals which are not trapped) with DNA metabarcoding of the feces acquired, to study fungi in the diet of small mammals. Mammal and fungal species were identified using genomic DNA of 596 fecal samples collected in five regions of eastern Canadian boreal forest. For identification of the small mammal species, the cytochrome b region was used. A total of eight species of small mammals displayed hypogeous fungi consumption, with northern flying squirrels (Glaucomys sabrinus) and red-backed voles (Myodes gapperi) as top consumers. For identification of their fungal diets, the ribosomal internal transcribed spacer (ITS) region was used. We recovered 722 Ascomycota, 429 Basidiomycota, 81 Zygomycota, 4 Chytridiomycota, 1 Glomeromycota, and 44 unidentified fungal taxa. Of these, 28 were hypogeous sequestrate fungi (underground fructification) which presumably are dug out by small mammals for consumption. Otherwise, for the remaining fungi, epigeous (above ground fructification) or microscopic fungal species, it is unclear which ones are selected by the animal as a dietary source or result from incidental contamination. Our paper presents a promising approach for tracing mycophagy in small mammals and our results suggest that fungi diversity is important for the diet of some small mammals.
Amino acid composition, protein content and accurate nitrogen-to-protein conversion factor for sheepgrass (Leymus chinensis)
(Canadian Science Publishing, 2019-10-27) Zhang, Qingfen; Qi, Dongmei; Dong, Xiaobing; Li, Xiaoxia; Cheng, Liqin; Liu, Hui; Chen, Shuangyan; Rajora, Om P.; Li, Xiu-Qing; Liu, Gongshe
Protein content of plants is commonly estimated by multiplying total nitrogen content (Kjeldahl; KN) with a nitrogen-to-protein conversion factor of 6.25. This method is based on the incorrect assumption that all nitrogen in ammonia/ammonium and organic substances in plants is protein nitrogen, usually resulting in overestimation of protein content. We have examined amino acid composition, amino acid nitrogen, total nitrogen (KN), and actual protein content (AP) determined from amino acid residues in 16 accessions of perennial sheepgrass (Leymus chinensis). We determined a new nitrogen-to-protein conversion factor, kP, as the ratio of AP to KN, and applied this factor to estimate the total protein content (TP) as KN kP. The non-protein nitrogen accounted for 40.5% to 62.4% of the total nitrogen. The average kP value was 3.17 overall, 3.20 in the accessions sampled at the jointing stage and 3.15 in the accessions sampled at the flowering stage. The TP, calculated as KN 3.17, was about half that of crude protein contents calculated as KN 6.25. Our study suggests that the AP-based kP of 3.17 can be used to more accurately estimate the total protein content in sheepgrass.
An RNA-Seq transcriptome analysis revealing novel insights into fluorine absorption and transportation in the tea plant
(Canadian Science Publishing, 2019-12-17) Huang, Xin; Wang, Pu; Liu, Siyi; Du, Yaru; Ni, Dejiang; Song, Xiaowei; Chen, Yuqiong
The tea plant [Camellia sinensis (L.) O. Kuntze] is a species with a high concentration of fluorine in its leaves, especially in the mature leaves. The physiological mechanisms for fluorine absorption and accumulation have been well studied, but the related molecular mechanisms are poorly understood in the tea plant. In this study, transcriptome analysis by RNA-Seq following exposure to 16 mg/L of fluorine for 0, 3, 6, and 24 h was performed to identify the candidate genes involved in the transmembrane transportation of fluorine. More than 1.23 billion high-quality reads were generated, and 259.84 million unigenes were assembled de novo, with 518 216 of them being annotated in the seven databases used. Meanwhile, a large number of transporters, transcription factors, and heat-shock proteins with differential expression in response to high levels of fluorine (P ≤ 0.05) were identified. Comparative transcriptome analysis showed that the uptake of fluorine is related to photosynthesis, plant hormone signal transduction, and glutathione metabolism. Further systematic analysis of nitrate and potassium transporter genes revealed that many of these genes regulate fluorine transportation in roots and leaves. Gene expression and fluorine content analysis in different cultivars revealed CsNRT1/PTR 3.1 and CsPT 8 as the key genes regulating the transmembrane transportation of fluorine in the tea plant.
Anatomical and ultrastructural studies on gelatinous fibers in the organs of non-woody xerophytic and hydrophytic species
(Canadian Science Publishing, 2019-06-09) Piva, Tayeme Cristina; Machado, Silvia Rodrigues; Scremin-Dias, Edna
Gelatinous fibers (G-layer) occur widely in various organs and plant tissues of both primary and secondary origin, but they are best known in tension wood. Here, we describe the occurrence, distribution patterns, and structural features of G-fibers in non-woody species of xerophytes and hydrophytes in Brazilian Cerrado (dry soil) and Chaco (wet or periodically waterlogged soils). G-fibers were present in all of the studied species, but were more abundant and more developed in xerophytes. They were associated with the phloem of leaves and primary stems and with the xylem of three xerophytic species that exhibited incipient secondary growth. The G-layer was non-lignified and characterized by greater thickness, lower density, and loose appearance in relation to the secondary layers. Under a transmission electron microscope, G-fibers displayed two secondary parietal layers (S1 and S2) in Prosopis rubriflora Hassle. (xerophyte), three secondary layers (S1, S2, and S3) in Eriosema campestre Benth. var. campestre (xerophyte), and a single secondary layer (S1) in Ludwigia leptocarpa Nutt. (hydrophyte). In P. rubriflora, mature G-fibers exhibited a loose-appearing electron-lucent region (transition zone) between G- and S-layers (secondary layers). In addition to mechanical support, this study suggests the involvement of G-fibers in water storage.
Bacillus subtilis-Arabidopsis thaliana: a model interaction system for studying the role of volatile organic compounds in the interchange between plants and bacteria.
(Canadian Science Publishing, 2019-08-04) Li, Fei; Tang, Min; Tang , Xiaoxin; Sun , Wei; Gong, Jiyi; Yi, Yin
Plant–bacteria interactions are known to play important physiological roles in plant growth. Determining the mechanisms behind these interactions has paramount agricultural and ecological importance. Therefore, it is essential to study Plant–bacteria interactions and determine the relevant molecular mechanisms by using model systems. This review summarizes the current knowledge regarding plant–bacteria interactions based on the Arabidopsis thaliana – Bacillus subtilis model system, and highlights future areas for research.
Botryotrichum domesticum sp. nov., a new hyphomycete from an indoor environment
(Canadian Science Publishing, 2019-01-16) Schultes, Neil P.; Strzalkowski, Noelle; Li, De-Wei
Here we report on a fungus that is new to science and was isolated from a swab sample collected in a Massachusetts (USA) residence. Morphological characters of the fungus were studied and DNA sequences generated from ITS, LSU, rpb2, and tub2 ribosomal loci were used to establish a proper phylogenetic relationship with allied genera. The fungus was named Botryotrichum domesticum. The newly named species has thick-walled conidia globose to subglobose, 17.7 ± 2.6 × 17.3 ± 2.5 μm, developing on both aerial and immersed hyphae, with an absence of setae.
Canopy effects on abundance and leaf traits of a spring ephemeral: Erythronium americanum
(Canadian Science Publishing, 2019-09-01) Greco, Danielle A; Schamp, Brandon; Mercer, Kirstin A
Spring ephemerals take advantage of the high light levels available in the spring by completing the aboveground portion of their lifecycle before the canopy develops and while few other understory plant species are growing. The spring is marked by high resource availability, yet spring ephemerals are variably abundant throughout forests. Research indicates that canopy conditions can influence the growth of spring ephemerals; consequently, we tested whether the variation in canopy conditions predicted variation in the abundance of Erythronium americanum Ker Gawl. across 50 forest plots. We also tested whether the specific leaf area (SLA) of E. americanum in plots was predicted by variation in plot-level canopy conditions, reflecting E. americanum‘s ability to adapt to different canopy conditions. The abundance of E. americanum was significantly lower in the plots with greater hard canopy closure (i.e., permanent cover: tree architecture + evergreen leaf cover), and significantly higher under canopies that reached full development earlier. Canopies with greater hard canopy cover at the start of the growing season were associated with significantly higher SLA, quantifying local adaptation by E. americanum to variable canopy conditions. Erythronium americanum takes advantage of the high light levels available in the spring. It is unclear at this time why higher abundance of E. americanum is associated with canopies that close earlier.
Comparative anatomy of the fig wall (Ficus, Moraceae)
(Canadian Science Publishing, 2019-03-24) Fan, Kang-Yu; Bain, Anthony; Tzeng, Hsy-Yu; Chiang, Yun-Peng; Chou, Lien-Siang; Kuo-Huang, Ling-Long
The genus Ficus is unique by its closed inflorescence (fig) holding all flowers inside its cavity, which is isolated from the outside world by a fleshy barrier: the fig wall. The fig wall is the main structure of the fig giving its shape but the wall has also important ecological functions such as protection of fig seeds and fig wasp larvae. Nevertheless, the fig wall anatomy is poorly understood. This study aims to examine the fig wall anatomy of 22 Ficus taxa (21 species, one species having two varieties) in Taiwan in order to reveal the diversity in anatomy of the fig wall. We found that these 21 fig species exhibited a great variety in fig wall anatomy, from the simplest parenchymatic wall to complex fig walls. Fig walls of 12 sampled taxa developed aerenchyma and sclerenchyma formations whereas seven taxa had fig walls containing tanniferous cells. Five anatomical types of fig walls have been identified according to the presence or absence of the different differentiated tissues. These types are distributed among the Ficus subgenera. Further studies on tissue differentiations of the fig wall should investigate other Ficus species as well as the ecological functions of the fig wall.
Continuous monitoring of growth detects photoperiod-dependent oscillations in growth rates in Chlorella vulgaris
(Canadian Science Publishing, 2019-09-23) Hollis, Lauren; Trick, Charles; Hüner, Norman P.A.
The green alga Chlorella vulgaris Beij. exhibits minimal capacity to adjust exponential growth rates in response to photon flux density (PFD) when monitored on a discontinuous basis. We hypothesized that modulation of maximum growth rates in C. vulgaris by PFD is a photoperiod-dependent phenomenon. The use of the photobioreactors to monitor continuous growth allowed us to detect repetitive daily oscillations in growth which were photoperiod-dependent. The rate of change in optical density (OD735) during the daily light period was two-fold greater in cells grown at 28 °C with a PFD of either 2000 or 150 μmol photons·m−2·s−1 when C. vulgaris was grown under a daily light–dark cycle. Concomitantly, oscillations of the chlorophyll fluorescence parameters paralleled the oscillations observed in growth rate. When cultures were shifted from a 12 h photoperiod with low light to continuous light (CL), the growth oscillations disappeared. In contrast, oscillations in the fluorescence parameters persisted even after the shift from a 12 h photoperiod to CL. We suggest that the nocturnal catabolism of starch reserves in conjunction with changes in cellular volume coupled with the diurnal changes in DNA content, as quantified by changes in Vybrant Green fluorescence yield, indicate that these growth oscillations reflect synchronized cellular division in C. vulgaris that is not evident when growth is assayed discontinuously.
Coordination of leaf and stem traits in 25 species of Fagaceae from three biomes of East Asia
(Canadian Science Publishing, 2019-04-13) Kawai, Kiyosada; Okada, Naoki
It has been debated whether leaf and stem economics spectra are coordinated across species as previous studies provide contradictory results. These studies have been restricted to single biomes, and we hypothesize that climate seasonality may determine the strength of coordination between leaf and stem trait combinations. Herein, using 25 Fagaceae species from East Asia, we investigated the coordination of 15 leaf and four stem traits across and within three biomes (cool temperate, warm temperate, and tropical forests). Traits were chosen to reflect multiple aspects of plant adaptive strategies, such as water, carbon, and nutrient use. The leaf and stem traits of species that reflect resource-use strategies for different resources were functionally coordinated, forming a single axis of trait variation across biomes. This axis represented the trade-off between fast and slow resource-use strategies. We found the trend that the coordination between leaf and stem traits was the strongest in cool temperate forests after removing two Fagus species, followed by warm temperate forests but was not observed in tropical forests. Our results support the proposed model that plants vary from slow to fast resource exploitation, using closely related species, and suggest that temperature modulates the coordination of leaf and stem economics spectra.
Coordination of leaf and stem traits in 25 species of Fagaceae from three biomes of East Asia
(Canadian Science Publishing, 2019-04-13) Kawai, Kiyosada; Okada, Naoki
It has been debated whether leaf and stem economics spectra are coordinated across species as previous studies provide contradictory results. These studies have been restricted to single biomes, and we hypothesize that climate seasonality may determine the strength of coordination between leaf and stem trait combinations. Herein, using 25 Fagaceae species from East Asia, we investigated the coordination of 15 leaf and four stem traits across and within three biomes (cool temperate, warm temperate, and tropical forests). Traits were chosen to reflect multiple aspects of plant adaptive strategies, such as water, carbon, and nutrient use. The leaf and stem traits of species that reflect resource-use strategies for different resources were functionally coordinated, forming a single axis of trait variation across biomes. This axis represented the trade-off between fast and slow resource-use strategies. We found the trend that the coordination between leaf and stem traits was the strongest in cool temperate forests after removing two Fagus species, followed by warm temperate forests but was not observed in tropical forests. Our results support the proposed model that plants vary from slow to fast resource exploitation, using closely related species, and suggest that temperature modulates the coordination of leaf and stem economics spectra.
Deformation of a cell monolayer due to osmotic treatment: a case study of onion scale epidermis
(Canadian Science Publishing, 2019-06-25) Natonik-Białoń, Sandra; Borowska-Wykręt, Dorota; Mosca, Gabriella; Grelowski, Michał; Wrzalik, Roman; Smith, Richard S; Kwiatkowska, Dorota
We performed a combination of experiments and mechanical simulations to assess the importance of cell geometry and wall structure in tissue and cell mechanics. Osmotic treatments combined with live imaging were used to quantify deformations at the tissue, cellular and sub-cellular levels. We used the adaxial epidermis of onion scale as a model system. We found that the osmotically-induced surface strain in onion is small as outer periclinal walls are thick and stiff, requiring bending stiffness to be considered in our mechanical models. As expected, the mechanical behaviors of the tissue and its component cells are related. Upon changes in internal pressure, cells embedded in the tissue undergo deformation that is different from isolated cells, while the tissue undergoes a somewhat counterintuitive deformation, e.g. shrinking upon pressurization, that depends on cell geometry. At the sub-cellular level, the amount of deformation and its anisotropy vary within walls of individual cells and are affected by the cell shape and vicinity of three-way wall junctions. When the turgor pressure is lost, the protoplast-facing wall surface wrinkles due to buckling, with the pattern of wrinkles depending on the strain anisotropy and the local wall geometry.
Dimorphic fruit color is associated with differences in germination of Calligonum comosum
(Canadian Science Publishing, 2019-01-28) Bhatt, Arvind; Bhat, N.R.; Carón, María Mercedes; Gallacher, David
Calligonum comosum L’Hér is a perennial evergreen shrub that produces dimorphic fruits of distinctly yellow or red colour. The species is found on sand dunes of the Middle East, is valued as a highly palatable livestock feed that survives extreme drought, and is suitable for desert restoration of non-saline sandy soils. The association of fruit colour with germination was assessed in laboratory conditions under two temperature (15/20 and 20/30 °C) and two light (0 and 12 h per day) treatments. Additionally, the association of fruit colour with emergence and seedling growth up to 90 days from sowing was assessed in shade house conditions. Germination percentage in the laboratory was the only variable that exhibited significant variation by seed colour. Germination was highest for red seeds grown in the dark at the higher temperature but the influence of seed colour on germination was not repeated in the shade house study. The dimorphic fruit colour of C. comosum is thus associated with differing germination rates, but further study is needed to determine whether morphs employ differing recruitment strategies.
DNA barcoding of a complex genus, Aesculus L. (Sapindaceae) reveals lack of species-level resolution
(Canadian Science Publishing, 2019-06-28) Aygoren Uluer, Deniz; Alshamrani, Rahma
Aesculus L. is a small genus of horticulturally important trees and shrubs, comprising 13–19 species. Frequent hybridization among species, particularly in cultivation, has contributed to taxonomic confusion and difficulties in the identification of plants. In this study, we evaluated three widely employed plant DNA barcode loci, matK, and the entire ITS region (ITS1+5.8S+ITS2) as well as subunit ITS2 for 50 individuals representing 13 species of Aesculus, excluding only A. wangii (=A. assamica). In contrast to the plastid matK region, both the ITS and ITS2 loci displayed low levels of species discrimination, especially in our “first hit” BLASTn searches. We also presented the phylogeny of Aesculus based on matK and the entire ITS region, with additional matK and ITS sequences from GenBank. Our results show that Aesculus chinensis, A. flava, A. glabra, A. pavia, and A. sylvatica are probably not monophyletic. Furthermore, with the widest taxon coverage until now, the current study highlights the importance of sampling multiple individuals, not only for DNA barcoding, but also for phylogenetic studies.
Effect of light, temperature, salinity and maternal habitat on seed germination of Aeluropus lagopoides (Poaceae): an economically important halophyte of arid Arabian deserts
(Canadian Science Publishing, 2019-10-27) Bhatt, Arvind; Gairola, Sanjay; Carón, María Mercedes; Santo, Andrea; Murru, Valentina; El-Keblawy, Ali; Mahmoud, Tamer
In this study, salt tolerance during germination of Aeluropus lagopoides (L.) Trin. was tested using fresh seeds collected from three different maternal habitats under three thermoperiods and two light regimes. Additionally, we tested the ability of non-germinated seeds that had been exposed to different concentrations of NaCl to recover their germination in distilled water. The results showed a significant effect of seed source, temperature, and salinity, and some of their two- and three-way interactions on final germination and recovery percentage. The seeds from non-saline provenances had the highest percentages for germination (ca. 79%) under the 35/25 °C temperature regime, whereas the lowest percentages for germination (ca. 21%) was recorded for seeds from saline conditions under the 25/15 °C treatment. Additionally, percent germination was significantly lower for the seeds incubated in the saline solutions (100, 200, 400, and 600 mmol/L NaCl) and germinated under colder conditions (15/25 °C), compared with the seeds incubated in non-saline solutions (control group, 0 mmol/L NaCl) and germinated under warmer conditions (35/25 °C). The highest recovery percentage was recorded for seeds of the hyper-saline habitat incubated at 35/25 °C. Thus, seeds maintained their viability despite experiencing a range of saline conditions and were able to germinate upon the arrival of suitable conditions, which can be an adaptation to its saline arid desert habitat.
Effects of seed age and dormancy-breaking treatments on the viability and germination of the Gulf of Saint Lawrence aster (Symphyotrichum laurentianum)
(Canadian Science Publishing, 2019-08-27) Kelly, Annika; Lacroix, Christian R.
The Gulf of St. Lawrence aster, Symphyotrichum laurentianum, (Asteraceae) is a threatened halophyte found only in parts of Atlantic Canada, and seeds are being stored in the seed bank located at the University of Prince Edward Island. It is important to assess the quality of the seeds in storage to ensure their usefulness in the conservation of the species. We tested the effects of seed age on the viability and germination potential of seeds currently held in the seed bank and the effect of dormancy-breaking treatments on germination. Seeds produced in six different years were tested using the tetrazolium test and standard germination tests. Our results show high viability for seeds from all years but relatively low germination, with no clear relationship between germinability and seed age, indicating that the potential for these seeds to germinate may depend on other factors. To test the usefulness of dormancy-breaking treatments, seeds were subjected to a cold moist treatment or a hormone treatment of gibberellic acid, kinetin, or a combination of the two. All treatments significantly enhanced germination compared to the control, with the combined treatment of gibberellic acid and kinetin being the most effective in stimulating germination.
Evidence and quantitative evaluation of tensile maturation strain in flax phloem through longitudinal splitting
(Canadian Science Publishing, 2019-08-31) Alméras, Tancrède; Petrova, Anna; Kozlova, Liudmila; Gril, Joseph; Gorshkova, Tatyana
The stems of flax (Linum usitatissimum L. cv. ‘Mogilevsky’) contain many gelatinous fibers in their phloem. These fibers are important for the mechanical stability of the plant as well as for industrial applications. Gelatinous fibers are known to have a motor function in the xylem of trees and in many plant organs. This function arises from the so-called maturation strain, i.e., the tendency of the gelatinous layer to shrink during fiber maturation, resulting in a state of residual tensile stress. However, the occurrence of tensile maturation strain in flax phloem fibers remains to be demonstrated, and its magnitude has never been evaluated. Here we present a novel method to highlight and quantify this strain. The method consists in splitting a stem segment longitudinally, and measuring the curvature of the half segments through their opening distance. By using a mechanical model, the maturation strain can be calculated from the curvature, the dimensions of the component tissues, and their elastic properties. The model is validated by the agreement between model predictions and observations. The splitting experiment provides qualitative evidence that flax phloem develops tensile stress during maturation, just as xylem gelatinous fibers do. Calculations enable quantitative estimation of the maturation strain. The magnitude of this strain for the material studied is, on average, –1.5%.
Factors controlling seed dormancy and germination response of Brachypodium hybridum growing in the hot arid mountains of the Arabian Desert
(Canadian Science Publishing, 2019-04-07) Elgabra, Masarra; El-Keblawy, Ali; Mosa, Kareem A.; Soliman, Sameh
Seed dormancy and germination have been studied in the genetic model Brachypodium species complex in cooler, moist higher latitudes. Studying environmental factors in arid mountains affecting dormancy and germination in Brachypodium complex could determine the factors controlling these processes. This study assesses the impacts of temperature during seed maturation, seed after-ripening, drought, photoperiod, and thermoperiod on final germination and germination rate index of B. hybridum in the Arabian Desert. Seeds were germinated in dark and light and under different ratios of red:far red lights at three diurnal thermoperiods. The final germination percentage was significantly greater at 15/25 °C and 20/30 °C than at 25/35 °C and in light rather than in darkness. Seeds that reached maturity at 15/25 °C attained greater and faster germination than those that reached maturity at 20/30 °C. One-year after-ripening enhanced the final germination percentage and reduced photoperiod requirement. Light quality did not affect final germination percentage. Seeds tolerated drought of up to -0.8 MPa polyethylene glycol. The tolerance of B. hybridum seeds produced at higher thermoperiods to moderate levels of osmotic stress and their higher dormancy indicate that this species has the potential to survive the projected global warming in its native and introduced ranges.
Flood disturbance and shade stress shape the population structure of açaí palm Euterpe precatoria, the most abundant Amazon species
(Canadian Science Publishing, 2019-11-21) Brum, Heloisa Dantas; Souza, Alexandre F
Euterpe precatoria Mart. is the most abundant plant species in the Amazon basin, and one of the main non-timber forest products on the continent. A thorough understanding of the ecology of this species is needed to support sustainable management initiatives. Resource availability, disturbance regime, and human management are some of the main factors influencing population structure. We described the species’ life stages, evaluated its allometric relationships, and assessed the effects of habitat type (floodplain and upland) and proximity to human settlements on population size distribution in the Central Amazon near the Purus River. The height:diameter ratio increased from Seedlings to Juvenile 2, but decreased from Juvenile 2 to Reproductive 2, indicating changing height investment for any given diameter along these life stages. There was a marked habitat dependency in both the density and population size distribution, with populations in upland forests dominated by juveniles, whereas populations in the floodplains were dominated by reproductive palms. Proximity to human settlements was not related to population structure parameters. Our results suggest that the disturbance regime may have opposite meanings in várzea forests, where it limits recruitment under increased light levels, and in terra firme forests, where it may stimulate recruitment under limited light conditions.

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