Geology and climate influence rhizobiome composition of the phenotypically diverse tropical tree Tabebuia heterophylla.

Plant-associated microbial communities have diverse phenotypic effects on their hosts that are only beginning to be revealed. We hypothesized that morpho-physiological variations in the tropical tree Tabebuia heterophylla, observed on different geological substrates, arise in part due to microbial processes in the rhizosphere. We characterized the microbiota of the rhizosphere and soil communities associated with T. heterophylla trees in high and low altitude sites (with varying temperature and precipitation) of volcanic, karst and serpentine geologies across Puerto Rico. We sampled 6 areas across the island in three geological materials including volcanic, serpentine and karst soils. Collection was done in 2 elevations (>450m and 0-300m high), that included 3 trees for each site and 4 replicate soil samples per tree of both bulk and rhizosphere. Genomic DNA was extracted from 144 samples, and 16S rRNA V4 sequencing was performed on the Illumina MiSeq platform. Proteobacteria, Actinobacteria, and Verrucomicrobia were the most dominant phyla, and microbiomes clustered by geological substrate and elevation. Volcanic samples were enriched in Verrucomicrobia; karst was dominated by nitrogen-fixing Proteobacteria, and serpentine sites harbored the most diverse communities, with dominant Cyanobacteria. Sites with similar climates but differing geologies showed significant differences on rhizobiota diversity and composition demonstrating the importance of geology in shaping the rhizosphere microbiota, with implications for the plant's phenotype. Our study sheds light on the combined role of geology and climate in the rhizosphere microbial consortia, likely contributing to the phenotypic plasticity of the trees.

Phytotoxic potential of Senna occidentalis (L.) Link extracts on seed germination and oxidative stress of Ipê seedlings.

Senna occidentalis is an invasive plant producing a series of allelochemicals that might inhibit the development of other plants. The objective of this study was to assess the phytotoxic effect of S. occidentalis extracts on the germination, development and antioxidant defence of the native species Tabebuia chrysotricha, T. pentaphylla, T. roseoalba and Handroanthus impetiginosus (Ipê species). We evaluated the effects of chemicals extracted from S. occidentalis on the germination rate, germination speed index (GSI) and biometric parameters of the test species under controlled conditions. The effect of the extracts on the pigment content, amount of H2 O2 and malondialdehyde (MDA), and the activity of the antioxidant enzymes in roots and leaves were also tested. Alkaloids, coumarins, phenols, saponins, free steroids and condensed tannins were present in all extracts of S. occidentalis, while catechins were present only in leaf and stem extracts. Stem and root extracts caused a growth reduction in all Ipê species and total inhibition of seed germination in T. chrysotricha and T. roseoalba. All target species showed an increase in H2 O2 and MDA in radicles and leaves. Oxidative stress contributed strongly to the morphological changes, such as seed blackening, thinning and darkening of radicle tips and reduction of biomass allocation in all Ipê species. Although there was activation of antioxidant defence mechanisms, such as an increase in activity of ascorbate peroxidase (APX) and peroxidase (POD) enzymes, the joint action of the allelochemicals caused phytotoxicity, leading to cell dysfunction in all Ipê species.

Density-dependent adult recruitment in a low-density tropical tree.

The Janzen-Connell hypothesis is a well-known explanation for why tropical forests have large numbers of tree species. A fundamental prediction of the hypothesis is that the probability of adult recruitment is less in regions of high conspecific adult density, a pattern mediated by density-dependent mortality in juvenile life stages. Although there is strong evidence in many tree species that seeds, seedlings, and saplings suffer conspecific density-dependent mortality, no study has shown that adult tree recruitment is negatively density dependent. Density-dependent adult recruitment is necessary for the Janzen-Connell mechanism to regulate tree populations. Here, we report density-dependent adult recruitment in the population of Handroanthus guayacan, a wind-dispersed Neotropical canopy tree species. We use data from high-resolution remote sensing to track individual trees with proven capacity to flower in a lowland moist forest landscape in Panama and analyze these data in a Bayesian framework similar to capture-recapture analysis. We independently quantify probabilities of adult tree recruitment and detection and show that adult recruitment is negatively density dependent. The annualized probability of adult recruitment was 3.03% ⋅ year-1 Despite the detection of negative density dependence in adult recruitment, it was insufficient to stabilize the adult population of H. guayacan, which increased significantly in size over the decade of observation.

Genome assembly of the Pink Ipê (Handroanthus impetiginosus, Bignoniaceae), a highly valued, ecologically keystone Neotropical timber forest tree.

Background: Handroanthus impetiginosus (Mart. ex DC.) Mattos is a keystone Neotropical hardwood tree widely distributed in seasonally dry tropical forests of South and Mesoamerica. Regarded as the "new mahogany," it is the second most expensive timber, the most logged species in Brazil, and currently under significant illegal trading pressure. The plant produces large amounts of quinoids, specialized metabolites with documented antitumorous and antibiotic effects. The development of genomic resources is needed to better understand and conserve the diversity of the species, to empower forensic identification of the origin of timber, and to identify genes for important metabolic compounds. Findings: The genome assembly covers 503.7 Mb (N50 = 81 316 bp), 90.4% of the 557-Mbp genome, with 13 206 scaffolds. A repeat database with 1508 sequences was developed, allowing masking of ∼31% of the assembly. Depth of coverage indicated that consensus determination adequately removed haplotypes assembled separately due to the extensive heterozygosity of the species. Automatic gene prediction provided 31 688 structures and 35 479 messenger RNA transcripts, while external evidence supported a well-curated set of 28 603 high-confidence models (90% of total). Finally, we used the genomic sequence and the comprehensive gene content annotation to identify genes related to the production of specialized metabolites. Conclusions: This genome assembly is the first well-curated resource for a Neotropical forest tree and the first one for a member of the Bignoniaceae family, opening exceptional opportunities to empower molecular, phytochemical, and breeding studies. This work should inspire the development of similar genomic resources for the largely neglected forest trees of the mega-diverse tropical biomes.

Growth and morphological responses of Handroanthus impetiginosus (Mart. ex DC.) Mattos seedlings to nitrogen fertilization / Crescimento e respostas morfológicas de mudas de ipê-roxo Handroanthus impetiginosus (Mart. ex DC.) Mattos à adubação nitrogenada

The use of native tree species for restoration of degraded areas is often hindered by the lack of information about the nutritional requirements of seedlings at the nursery stage. Therefore, this study aimed to evaluate the growth and morphological responses of Handroanthus impetiginosus seedlings to mineral nitrogen fertilization. The experiment was carried out from July to October 2013 in a seedling nursery under 50% shade cloth. Seeds were germinated for 15 days in low density polystyrene trays and then transplanted into 0.9-L polyethylene plastic bags. A complete randomized block design was used, with four replications and four plants per experimental unit. Treatments consisted of five nitrogen levels (0, 50, 150, 300 and 450 mg N dm-3), using ammonium sulfate as the nitrogen source. Two months after transplanting, the following variables were assessed: leaf chlorophyll content; leaf area; specific leaf area; leaf area ratio; root, stem, leaf and total dry mass; shoot dry mass/root dry mass ratio; shoot height/shoot dry mass ratio; and Dickson quality index. Mineral nitrogen fertilization improved seedling growth by promoting higher results of the leaf chlorophyll content, leaf area and shoot dry mass production. Thus, fertilized seedlings significantly expanded their leaves and invested more in shoot growth, improving their hardiness and quality. The nitrogen level of 240 mg dm-3 was considered to be the most effective for production of H. impetiginosus seedlings.

O uso de espécies arbóreas nativas para restauração de áreas degradadas é muitas vezes prejudicada pela falta de informação sobre os requerimentos nutricionais de mudas na fase de viveiro. Portanto, este trabalho objetivou avaliar o crescimento e respostas morfológicas de mudas de ipê-roxo à adubação mineral nitrogenada. O experimento foi conduzido de julho a outubro de 2013, em viveiro de mudas com tela de sombreamento de 50%. As sementes foram postas para germinar por 15 dias em bandejas de poliestireno de baixa densidade, e posteriormente transplantadas para sacos plásticos de polietileno de 0,9 L. Foi utilizado o delineamento de blocos completos ao acaso, com quatro repetições e quatro plantas por unidade experimental. Os tratamentos foram constituídos por cinco níveis de nitrogênio (0, 50, 150, 300 e 450 mg N dm-3), utilizando o sulfato de amônio como fonte. Dois meses após o transplantio, as seguintes variáveis foram avaliadas: conteúdo de clorofila foliar; área foliar; área foliar específica; razão de área foliar; matéria seca da raiz, caule, folhas e total; relação massa seca da parte aérea/massa seca da raiz; relação altura/massa seca da parte aérea; e índice de qualidade de Dickson. A adubação mineral nitrogenada otimizou o crescimento das mudas ao promover resultados mais elevados para o teor de clorofila, área foliar e produção de massa seca da parte aérea. Assim, mudas adubadas expandiram significativamente suas folhas e investiram mais no crescimento da parte aérea, melhorando sua rusticidade e qualidade. O nível de nitrogênio de 240 mg dm-3 foi considerado o mais eficiente para produção de mudas de ipê-roxo.

Two tropical conifers show strong growth and water-use efficiency responses to altered CO2 concentration.

BACKGROUND AND AIMS: Conifers dominated wet lowland tropical forests 100 million years ago (MYA). With a few exceptions in the Podocarpaceae and Araucariaceae, conifers are now absent from this biome. This shift to angiosperm dominance also coincided with a large decline in atmospheric CO2 concentration (ca). We compared growth and physiological performance of two lowland tropical angiosperms and conifers at ca levels representing pre-industrial (280 ppm), ambient (400 ppm) and Eocene (800 ppm) conditions to explore how differences in ca affect the growth and water-use efficiency (WUE) of seedlings from these groups. METHODS: Two conifers (Araucaria heterophylla and Podocarpus guatemalensis) and two angiosperm trees (Tabebuia rosea and Chrysophyllum cainito) were grown in climate-controlled glasshouses in Panama. Growth, photosynthetic rates, nutrient uptake, and nutrient use and water-use efficiencies were measured. KEY RESULTS: Podocarpus seedlings showed a stronger (66 %) increase in relative growth rate with increasing ca relative to Araucaria (19 %) and the angiosperms (no growth enhancement). The response of Podocarpus is consistent with expectations for species with conservative growth traits and low mesophyll diffusion conductance. While previous work has shown limited stomatal response of conifers to ca, we found that the two conifers had significantly greater increases in leaf and whole-plant WUE than the angiosperms, reflecting increased photosynthetic rate and reduced stomatal conductance. Foliar nitrogen isotope ratios (δ15N) and soil nitrate concentrations indicated a preference in Podocarpus for ammonium over nitrate, which may impact nitrogen uptake relative to nitrate assimilators under high ca SIGNIFICANCE: Podocarps colonized tropical forests after angiosperms achieved dominance and are now restricted to infertile soils. Although limited to a single species, our data suggest that higher ca may have been favourable for podocarp colonization of tropical South America 60 MYA, while plasticity in photosynthetic capacity and WUE may help account for their continued persistence under large changes in ca since the Eocene.

Estimation of the distribution of Tabebuia guayacan (Bignoniaceae) using high-resolution remote sensing imagery.

Species identification and characterization in tropical environments is an emerging field in tropical remote sensing. Significant efforts are currently aimed at the detection of tree species, of levels of forest successional stages, and the extent of liana occurrence at the top of canopies. In this paper we describe our use of high resolution imagery from the Quickbird Satellite to estimate the flowering population of Tabebuia guayacan trees at Barro Colorado Island (BCI), in Panama. The imagery was acquired on 29 April 2002 and 21 March 2004. Spectral Angle Mapping via a One-Class Support Vector machine was used to detect the presence of 422 and 557 flowering tress in the April 2002 and March 2004 imagery. Of these, 273 flowering trees are common to both dates. This study presents a new perspective on the effectiveness of high resolution remote sensing for monitoring a phenological response and its use as a tool for potential conservation and management of natural resources in tropical environments.

Understanding strategies for seed dispersal by wind under contrasting atmospheric conditions.

Traits associated with seed dispersal vary tremendously among sympatric wind-dispersed plants. We used two contrasting tropical tree species, seed traps, micrometeorology, and a mechanistic model to evaluate how variation in four key traits affects seed dispersal by wind. The conceptual framework of movement ecology, wherein external factors (wind) interact with internal factors (plant traits) that enable movement and determine when and where movement occurs, fully captures the variable inputs and outputs of wind dispersal models and informs their interpretation. We used model calculations to evaluate the spatial pattern of dispersed seeds for the 16 factorial combinations of four traits. The study species differed dramatically in traits related to the timing of seed release, and a strong species by season interaction affected most aspects of the spatial pattern of dispersed seeds. A rich interplay among plant traits and seasonal differences in atmospheric conditions caused this interaction. Several of the same plant traits are crucial for both seed dispersal and other aspects of life history variation. Observed traits that limit dispersal are likely to be constrained by their life history consequences.

Establecimiento y desarrollo de plántulas de Tabebuia rosea (Bignoniaceae) en una selva subcaducifolia manejada de la costa Pacífica de México / Establishment and development of Tabebuia rosea (Bignoniaceae) seedlings in a semideciduous tropical forest under management, Pacific coast of Mexico

We evaluated the effect of soil "scarification" and vegetation clearing treatments on the natural regeneration and initial development of Tabebuia rosea (Bertold) DC. seedlings in a moderate sized semideciduous tropical forest subjected to wood harvesting on the coast of Jalisco, Mexico. The treatments were applied under "seed" trees, and the number of germinated seedlings and their development were evaluated for nine months. Soil "scarification" promoted seed germination and initial seedling development, while the control of the competing vegetation increased the seedling growth and reduced their mortality. These results should be taken into account for the natural regeneration of this species, after clearing, to improve wood production, and should be incorporated into the silvicultural techniques currently developed in the region.

Evaluamos el efecto de los tratamientos de remoción de suelo y roza de vegetación sobre el establecimiento y desarrollo inicial de la regeneración natural de Tabebuia rosea (Bertold) DC. en una selva mediana subcaducifolia sometida a aprovechamiento maderable en la costa de Jalisco, México. Los tratamientos se aplicaron bajo la copa de árboles “semilleros” y se evaluó el número de plántulas emergidas y su desarrollo durante nueve meses. El tratamiento de remoción de suelo favoreció la emergencia de plántulas y su desarrollo inicial, mientras que el control de la vegetación competidora promovió un mayor crecimiento y menores porcentajes de mortalidad. Estos aspectos deben tomarse en cuenta para la regeneración natural de la especie después de la aplicación de las cortas con fines de aprovechamiento maderable y se sugiere incorporarlos a las técnicas silvícolas que actualmente se desarrollan en la zona.

[Establishment and development of Tabebuia rosea (Bignoniaceae) seedlings in a semideciduous tropical forest under management, Pacific coast of Mexico]. / Establecimiento y desarrollo de plántulas de Tabebuia rosea (Bignoniaceae) en una selva subcaducifolia manejada de la costa Pacífica de México.

We evaluated the effect of soil "scarification" and vegetation clearing treatments on the natural regeneration and initial development of Tabebuia rosea (Bertold) DC. seedlings in a moderate sized semideciduous tropical forest subjected to wood harvesting on the coast of Jalisco, Mexico. The treatments were applied under "seed" trees, and the number of germinated seedlings and their development were evaluated for nine months. Soil "scarification" promoted seed germination and initial seedling development, while the control of the competing vegetation increased the seedling growth and reduced their mortality. These results should be taken into account for the natural regeneration of this species, after clearing, to improve wood production, and should be incorporated into the silvicultural techniques currently developed in the region.

Propagación in vitro de material seleccionado de Tabebuia rosea (Bertol) DC (Ocobo) y Cordia alliodora (Ruiz & Pav) Oken (Nogal Cafetero) / In vitro propagation of Tabebuia rosea (Bertol DC) (large spreading cedar) and Cordia alliodora (Ruiz & Pav) Oken (coffee-shading walnut)

El presente trabajo tuvo por objetivo multiplicar y mantener in vitro plantas de Tabebuia rosea y de Cordia alliodora, a partir de semillas de cinco árboles plus de la primera especie y uno de la segunda. A partir de este material se seleccionaron plantas núcleo (PN), Yemas apicales de las plantas núcleo obtenidas, fueron removidas y cultivadas bajo condiciones in vitro hasta producir 1480 plantas de las dos especies. El proceso de aclimatización del material vegetal se llevó a cabo bajo condiciones de invernadero, en cámaras húmedas ubicadas en la estación experimental "Bambusa" en Pacho, Cundinamarca. Para el manejo de la información, se diseñó una base de datos en el programa Access, Microsoft Office®, con el fin de monitorear y evaluar el comportamiento de cada uno de los individuos durante el desarrollo in vitro, por medio del cálculo de tasas de velocidad de multiplicación (TVM), tasa de pérdida (TP) y tasa de eficiencia del proceso (TE). Este material será entregado a Conif para el establecimiento de la primera plantación de origen in vitro, que será utilizada posteriormente para ensayos de propagación vegetativa, análisis de pruebas clonales y moleculares.

This work was aimed at multiplying and maintaining in vitro plants from seedlings from five Tabebuia rosea (large spreading cedar tree) from and one Cordia alliodora (walnut tree used for providing shade for coffee plantations). Apical leaf buds were excised from mother plants (MP) and cultured in vitro until 1480 plants had been produced from the two species. The hardening process was carried out in greenhouse conditions using humid flow-chambers at Geoambiente Ltda’s Bambusa experimental station in Pacho, Cundinamarca. A database was created using Microsoft Office Access software for handling information required for monitoring and evaluating each plant’s behaviour during the in vitro culture process by calculating the rates of multiplication (RM) and loss(RL). The plants so produced will be used by Conif for field trials and evaluation purposes. This material will then be multiplied by vegetative propagation and used for clone and molecular testing analysis.

Does flood tolerance explain tree species distribution in tropical seasonally flooded habitats?

In the tropics, seasonally flooded forests (SFF) harbor fewer tree species than terra firme (i.e. non-flooded) forests. The low species diversity of tropical flooded forests has been ascribed to the paucity of species with adaptations to tolerate flooding. To test the hypothesis that flooding is the only factor restricting most species from SFF, we compared plant morphological and physiological responses to flooding in 2-month old seedlings of 6 species common to SFF and 12 species common to terra firme forests. Although flooding impaired growth, total biomass, maximum root length and stomatal conductance in most species, responses varied greatly and were species-specific. For example, after 90 days, flooding reduced leaf area growth by 10-50% in all species, except in Tabebuia, a common species from non-flooded habitats. Similarly, flooding had a 5-45% negative effect on total biomass for all species, except in 1 SFF and 1 terra firme species both of which had more biomass under flooding. A principal component analysis, using the above responses to flooding, provided no evidence that SFF and terra firme species differed in their responses to flooding. Flooding also caused reductions in root growth for most species. Rooting depth and root: shoot ratios were significantly less affected by flooding in SFF than in terra firme species. Although flood tolerance is critical for survival in flooded habitats, we hypothesize that responses to post-flooding events such as drought might be equally important in seasonal habitats. Therefore, we suggest that the ability to grow roots under anoxia might be critical in predicting success in inundated habitats that also experience a strong dry season.