Neotropical Tree Species Research Articles

Influence of light intensity on the responses of seedlings of neotropical tree species to nitrogen source

Light intensity plays a crucial role in N uptake and assimilation in plants, but its interaction with different N sources is overlooked. Considering the high energy required for N assimilation, it is hypothesised that low light is critical for the seedling development with both N sources, but with increased light intensity, growing with nitrate (NO3-) becomes favourable in relation to ammonium (NH4+). Seedlings of Cecropia pachystachya (pioneer), Guarea kunthiana (shade-tolerant, understory) and Cariniana estrellensis (shade-tolerant, canopy) were grown in hydroponic medium with NO3- or NH4+ as the sole N source and subjected to low (LL) or high light (HL) for 60 days. All three species showed a decrease in growth when cultivated with NH4+, compared to NO3-, under HL, but not under LL. The decrease in biomass reached 54% in C. pachystachya, 36% in G. kunthiana and 26% in C. estrellensis. Growth reduction was associated with stomatal limitation of photosynthesis and reduced leaf area in C. pachystachya, and with non-stomatal limitation of photosynthesis and oxidative stress in G. kunthiana. Cation uptake was negatively affected by NH4+ in all species. Cariniana estrellensis showed no photosynthetic limitation and showed a higher tolerance to NH4+ under HL in terms of nutrient content. In conclusion, neither N source significantly favors seedling development under LL, while NH4+ is considerably more unfavorable for seedling development than NO3- under HL.

Phylogeography of Coccoloba uvifera (Polygonaceae) Sampled across the Caribbean Basin

Coccoloba uvifera L. (seagrape) is a primarily dioecious neotropical tree species which often grows in the beach–forest transitional ecotone of coastal strand vegetation. We used five maternally inherited non-coding chloroplast regions to characterize the phytogeography of C. uvifera collected across the Caribbean Basin and Florida. Bayesian analysis revealed divergence between the Aruba–Trinidad–Tobago–Antigua–Jamaica island group and the continental Belize–Florida–US Virgin Islands (USVI) group at 1.78 million years before present (mybp), divergence between the Belize and Florida–USVI groups at 1.08 mybp, and a split of Antigua–Jamaica from Aruba–Trinidad–Tobago at 0.217 mybp. Haplotype network analysis supports the three clades, with the island group possessing the oldest haplotype. Based on geology and proximity, these clades correspond to South American (oldest), Central American, and North American (most recent). Coccoloba uvifera demographic expansion occurred during the Pleistocene epoch and peaked near the end of the last glacial maximum (ca. 0.026–0.019 mybp) when the global sea levels were 125 m lower than today. Our findings also reveal that tropical cyclones, which often impact coastal strand vegetation, did not affect genetic diversity. However, there was a positive association between latitude and the average number of substitutions, further enriching our understanding of the species’ phytogeography.

The first record of ants as potential pollinators of a Neotropical tree species (Lomatia hirsuta Diels ex J.F.Macbr., Proteaceae)

AbstractWe provide evidence that Camponotus chilensis (Spinola) visit flowers of the Radal tree (Lomatia hirsuta Diels ex J.F.Macbr.), possibly acting as pollinators of this important tree of the Proteaceae family in the Andean Patagonian forests of Argentina. We found several ant workers transporting pollen from different trees during the blooming season. Pollen transported by workers varied in amount, with some individuals observed fully coated with pollen grains. This note constitutes the first observation of ant activity on the flowers of this plant species and also the first potential example of a tree pollinated by ants in the Neotropics. This note highlights the importance of natural history data in the emergent study field of ant‐pollination.

Influence of plant growth-promoting bacteria on leaf carbon and nitrogen metabolism of two drought-stressed neotropical tree species: a metabolomic approach.

Deforestation of Atlantic Forest has caused prolonged drought events in the last decades. The need for reforestation is growing, and the development of native seedlings that are more tolerant to drought stress is necessary. A biotechnological tool that improves plant tolerance is the use of plant growth-promoting bacteria (PGPB) as inoculants. Two species of PGPB were inoculated in drought-stressed seedlings of two neotropical tree species that have been used in environmental restoration programs: Cecropia pachystachya and Cariniana estrellensis. Biometrical, physiological, and metabolomic parameters from carbon and nitrogen pathways were evaluated. We found that the PGPB positively influenced photosynthesis and growth parameters in both trees under drought. The enzymes activities, the tricarboxylic acid cycle intermediates, the amino acids, and protein contents were also influenced by the PGPB treatments. The results allowed us to find the specific composition of secondary metabolites of each plant species. This study provides evidence that there is not a single mechanism involved in drought tolerance and that the inoculation with PGPB promotes a broad-spectrum tolerance response in Neotropical trees. The inoculation with PGPB appears as an important strategy to improve drought tolerance in Atlantic Forest native trees and enhance environmental restoration programs' success. MAIN CONCLUSION: The association with plant growth-promoting bacteria improved the tolerance to drought in Neotropical trees through biochemical, physiological, and biometrical parameters. This can enhance the success of forest restoration programs.

Andean uplift, climatic events, and rainforest bridges determined the spatiotemporal evolution of the cumaru and tonka beans (Dipterygeae: Leguminosae)

Abstract Historical climatic and geological events are largely known to have impacted biome evolution across the Neotropics and their associated rich biodiversity. However, a clear understanding of dispersal and biome shifts between neotropical biomes over time is still lacking for many ecologically important plant clades. We investigated the timing and ancestral species movements within the early branching papilionoid legume Dipterygeae lineage of neotropical tree species, some of which are among the most ecologically dominant across Amazonian rainforests and Brazilian savannas, to understand how dispersal and evolutionary trajectories in biome predilection have led to their modern distribution. We also estimated the evolution of fruit types and discuss their potential roles in the colonization of non-Amazonian rainforest habitats. To address these questions, we used one nuclear (ITS/5.8S) and two plastid (matK and trnL intron) DNA regions of the Dipterygeae clade to estimate divergence times with a Bayesian relaxed-clock approach, ancestral area distribution, and evolutionary shifts in biome and morphological traits. All currently recognized species of this clade were sampled, covering its full geographical range. Dipterygeae originated in the Amazonia during the Middle Eocene, where it has undergone a long history of in situ diversification, particularly over the last 15 Myr. Dispersal events into the rainforests of the Brazilian Coastal Atlantic Forest and Chocó + Central America, the fire-prone savannas of the Cerrado, and the Caatinga seasonally dry tropical forest occurred independently. Most lineages ecologically associated with rainforests are dispersed by animals (zoochory), whereas shifts to open habitats generally coincide with wind dispersal (anemochory). Our study highlights the significance of geological events, climatic factors, and shifts in fruit type as crucial contributors to the diversification of Dipterygeae.

Trials and tribulations of Neotropical plant taxonomy: Pace of tree species description

Societal Impact StatementGiven the current unprecedented concerns for global biodiversity loss, it is critical to identify best practices for describing new species more efficiently so we can complete the inventory of the Neotropical flora and implement appropriate conservation strategies in a timely manner. This study aims to answer the question of how long it takes to describe a new species of tree in the Neotropics by calculating the time elapsed from collection of the first specimen to the publication of a new species. It demonstrates that enhancing international collaboration and promoting taxonomy training may be the most efficient ways to accelerate species descriptions.Summary One of the main aspects of taxonomic research is the description of new species. Identifying how to describe new species more efficiently is key to completing the inventory of the Neotropical flora in an era of massive biodiversity loss. Here, we calculate the interval between first specimen collection and publication of new species for a group of 2123 Neotropical trees, and discuss the historical context surrounding specimen collection and new species publication events. Our results reveal that on average, it takes almost 16 years from specimen collection to publication of a new Neotropical tree species, which is considerably shorter than previous estimates for other tropical groups. Peru had the longest average time lags by country, while Haiti had the shortest. The average time lags increased until the early 1900s, when a decrease was observed, with the shortest lags between 1941 and 1960. We found that the majority of the species described more rapidly are from plants collected by a field botanist and described by a herbarium‐based researcher as part of ad hoc collaboration, and the ones collected and described by the same researcher. We demonstrate how political instability and conflict can delay or impede the completion of taxonomic research initiatives in the region. We argue that enhancing international collaboration and training opportunities in Latin American countries, as well as ensuring safe plant collection campaigns, are critical to complete the inventory of the Neotropical flora.

Intra-annual stable isotopes in the tree rings of Hymenaea courbaril as a proxy for hydroclimate variations in southern Amazonia

The hydrology of Amazonia is changing due to climate and land-use changes, especially in the southern region, which has warmed and dried faster than other tropical regions. Yet there are no long-term hydrological records to put these changes in a historical perspective. Here we investigate the use of tree-ring carbon (δ13C) and oxygen isotopes (δ18O) to assess the seasonal variation in climate for the southern Amazonia basin. We analysed the intra-annual variation of δ13C and δ18O in 10 segments of each tree ring from 2013 to 2017 from individuals of Hymenaea courbaril, a long-lived and widespread neotropical tree species. We find strong seasonal patterns of tree-ring δ13C supporting previous observations of annual growth rhythms for this species. The intra-annual variation in δ18O shows that the lowest values generally occur just after the middle point of ring formation, corresponding to the peak rainy season. We find strong correlations between the δ18O in the middle of the growth ring and vapour pressure deficit (r = 0.92, P = 0.02) and precipitation (r = −0.93, P = 0.02). We further find associations between the oxygen isotopic series and the discharge of the Araguaia basin’s main rivers during the rainy period. Our results show that these δ18O records are sensitive to fluctuations in rainfall and humidity, and thus to river discharge in the region. Longer reconstructions of based on tree-ring δ18O of Hymenaea courbaril could provide a novel proxy to assess past hydrological changes.

Higher local intra- than interspecific variability in water- and carbon-related leaf traits among Neotropical tree species.

Intraspecific variability in leaf water-related traits remains little explored despite its potential importance in the context of increasing drought frequency and severity. Studies comparing intra- and interspecific variability of leaf traits often rely on inappropriate sampling designs that result in non-robust estimates, mainly owing to an excess of the species/individual ratio in community ecology or, on the contrary, to an excess of the individual/species ratio in population ecology. We carried out virtual testing of three strategies to compare intra- and interspecific trait variability. Guided by the results of our simulations, we carried out field sampling. We measured nine traits related to leaf water and carbon acquisition in 100 individuals from ten Neotropical tree species. We also assessed trait variation among leaves within individuals and among measurements within leaves to control for sources of intraspecific trait variability. The most robust sampling, based on the same number of species and individuals per species, revealed higher intraspecific variability than previously recognized, higher for carbon-related traits (47-92 and 4-33 % of relative and absolute variation, respectively) than for water-related traits (47-60 and 14-44 % of relative and absolute variation, respectively), which remained non-negligible. Nevertheless, part of the intraspecific trait variability was explained by variation of leaves within individuals (12-100 % of relative variation) or measurement variations within leaf (0-19 % of relative variation) and not only by individual ontogenetic stages and environmental conditions. We conclude that robust sampling, based on the same number of species and individuals per species, is needed to explore global or local variation in leaf water- and carbon-related traits within and among tree species, because our study revealed higher intraspecific variation than previously recognized.

Divergent patterns of intraspecific trait variation among floral and vegetative characters in the hyperdominant dioecious Neotropical treeVirola sebifera(Myristicaceae)

AbstractMany Neotropical tree species are widespread at continental and even inter-continental scales, but phenotypic variation across their respective ranges has rarely been quantified. We measured traits in the widespread, unisexual Neotropical tree Virola sebifera (Myristicaceae) across its continental-scale range, and predicted that, given its hyperdominant status, generalist-pollinated flower type, high dispersal capacity and wide ecological amplitude there would be: (1) a weak relationship among and within reproductive and vegetative characters with environmental, spatial and biome correlates; (2) undetectable canalization of reproductive traits; and (3) high phenotypic variation of vegetative characters. We measured five foliar and seven floral traits from 187 male-expressing individuals of V. sebifera in specimens collected from Central to South America. Spatial regression models were employed to test for the importance of distance, elevation, mean annual rainfall and temperature on phenotypic variation. Pairwise correlations of vegetative and reproductive characters were calculated to examine intraspecific trait variation among and within these two classes. We found that most phenotypic variation was weakly explained by spatial predictors such as certain major South American domains like the Andes Cordillera and the Amazon Basin. Within-class comparisons of floral characters were no different than among-class (floral-foliar) correlates, suggesting the absence of canalization of reproductive structures. Greater phenotypic variation in flowers relative to leaves may be due to the generalist pollinator regime and high dispersal capacity thus relaxing divergences in the evolutionary process of its floral morphology. The results of these morphometric analyses (e.g. weak signals of isolation by distance) in combination with the biology of this Neotropical tree suggest that V. sebifera operates as a well-dispersed metapopulation across most of its range.

Relative impact of pollen and seed dispersal on population viability of a neotropical tree species

Relative impact of pollen and seed dispersal on population viability of a neotropical tree species

Broad-scale and long-term forest growth predictions and management for native, mixed species plantations and teak in Costa Rica and Panama

Native tree species and species mixtures are key elements for biodiversity conservation by forest plantations. Yet, introduced species planted in monoculture still dominate plantation forests in many regions around the world and especially in the tropics. In Costa Rica and Panamá, Tectona grandis (teak) is the most planted species, occupying 49% and 64% of the forest plantation area. Here, we analyzed growth performance of four neotropical native species (Dalbergia retusa, Dipteryx oleifera, Hieronyma alchorneoides, Vochysia guatemalensis) in mixture with teak or as an alternative to teak plantations. For the first time, we parametrized a forest growth model for these native, neotropical tree species that was based on a large database which covers different climate, soil and management conditions as well as prolonged monitoring. We parametrized the mixture version of the process-based forest growth model Physiological Principles Predicting Growth (3-PGmix). We then developed management scenarios for pure and mixed plantations, where we simulated mixtures of T. grandis with D. oleifera and D. retusa as well as a mixture of D. oleifera, H. alchorneoides and V. guatemalensis as an alternative to teak plantations. With average 9% of model error, 3-PGmix qualified as a tool for making growth predictions for these native tree species and teak. Except for the very fast growing V. guatemalensis, growth of the native species at harvest age was lower than previously suggested by other studies in pure plantations. With two exceptions, all species showed good growth in mixture and a potential for implementation. Mixture simulations were highly sensitive to the 3-PG fertility rating input parameter. In all our simulated mixtures, we observed a trade-off between volume production and dbh growth, where dbh growth was inversely related to the tree density of the most productive species in the mixture. For mixtures of natives with of a close to baseline thinning T. grandis plantation, diameter growth of the natives was strongly reduced by the presence of teak. When comparing the tree-by-tree mixtures to their respective monocultures, the time of comparison was important, since, in monoculture, fast-growing species can be replanted during the long rotation periods of the slower growing species. This can reverse findings of increased volume production during early ages of plantation development.

Pit characters determine drought-induced embolism resistance of leaf xylem across 18 Neotropical tree species.

Embolism spreading in xylem is an important component of plant drought resistance. Since embolism resistance has been shown to be mechanistically linked to pit membrane characters in stem xylem, we speculate that similar mechanisms account for leaf xylem. We conducted transmission electron microscopy to investigate pit membrane characters in leaf xylem across 18 Neotropical tree species. We also conducted gold perfusion and polar lipid detection experiments on three species covering the full range of leaf embolism resistance. We then related these observations to previously published data on embolism resistance of leaf xylem. We also incorporated previously published data on stem embolism resistance and stem xylem pit membranes to investigate the link between vulnerability segmentation (i.e. difference in embolism resistance) and leaf-stem anatomical variation. Maximum pit membrane thickness (Tpm,max) and the pit membrane thickness-to-diameter ratio (Tpm,max/Dpm) were predictive of leaf embolism resistance, especially when vestured pits were taken into account. Variation in Tpm,max/Dpm was the only trait predictive of vulnerability segmentation between leaves and stems. Gold particles of 5- and 10-nm infiltrated pit membranes in three species, while the entry of 50-nm particles was blocked. Moreover, polar lipids were associated with inner conduit walls and pits. Our results suggest that mechanisms related to embolism spreading are determined by Tpm, pore constrictions (i.e. the narrowest bottlenecks along pore pathways), and lipid surfactants, which are largely similar between leaf and stem xylem and between temperate and tropical trees. However, our mechanistic understanding of embolism propagation and the functional relevance of Tpm,max/Dpm remains elusive.

Leaves of neotropical savanna tree species are more heat-tolerant than leaves of semi-deciduous forest species

Leaves of neotropical savanna tree species are more heat-tolerant than leaves of semi-deciduous forest species

Comparative population genomics in Tabebuia alliance shows evidence of adaptation in Neotropical tree species.

The role of natural selection in shaping spatial patterns of genetic diversity in the Neotropics is still poorly understood. Here, we perform a genome scan with 24,751 probes targeting 11,026 loci in two Neotropical Bignoniaceae tree species: Handroanthus serratifolius from the seasonally dry tropical forest (SDTF) and Tabebuia aurea from savannas, and compared with the population genomics of H. impetiginosus from SDTF. OutFLANK detected 29 loci in 20 genes with selection signal in H. serratifolius and no loci in T. aurea. Using BayPass, we found evidence of selection in 335 loci in 312 genes in H. serratifolius, 101 loci in 92 genes in T. aurea, and 448 loci in 416 genes in H. impetiginosus. All approaches evidenced several genes affecting plant response to environmental stress and primary metabolic processes. The three species shared no SNPs with selection signal, but we found SNPs affecting the same gene in pair of species. Handroanthus serratifolius showed differences in allele frequencies at SNPs with selection signal among ecosystems, mainly between Caatinga/Cerrado and Atlantic Forest, while H. impetiginosus had one allele fixed across all populations, and T. aurea had similar allele frequency distribution among ecosystems and polymorphism across populations. Taken together, our results indicate that natural selection related to environmental stress shaped the spatial pattern of genetic diversity in the three species. However, the three species have different geographical distribution and niches, which may affect tolerances and adaption, and natural selection may lead to different signatures due to the differences in adaptive landscapes in different niches.

How do meteorological factors alter the phenology of a neotropical tree species?

Background: Neotropical species lack autecological information. Among these, are phenological studies, which help to understand forest dynamics and provide important contributions to the collection, restoration, and conservation programs. This research aimed to characterize the vegetative and reproductive phenological behavior of neotropical species Geoffroea spinosa Jacq. in a seasonally dry tropical forest, as well as to verify if there is a correlation between phenophases and environmental parameters. Twenty individuals were accompanied monthly for two years, to detect and tally the presence of floral buds, flowers, immature fruits, ripe fruits, leaf emergence, presence of mature leaves, and defoliation. A semi-quantitative evaluation was carried out with the Fournier method. Results: The results showed that the population had synchrony of reproductive events, with more than 50% of the individuals blooming and fruiting during the same time interval. Furthermore, the circular statistical test indicated a high seasonality for reproductive events (r ≥ 0.50 and p < 0.001). Among the vegetative events, all were classified as non-seasonal (r < 0.5). G. spinosa, showed a significant correlation (p ≤ 0.05) for all meteorological variables evaluated. Conclusion: The reproductive phenophases of G. spinosa showed strongly seasonal behavior, unlike vegetative events. the period between mid-February and the end of March was the most propitious for fruit collection. No seasonality was observed for the vegetative events. The species proved to be sensitive to El niño conditions. Follow-up phenological studies associated with meteorological variables are important for a better understanding of the dynamics of vegetative behavior in response to climate change.

RNA-Seq reveals different responses to drought in Neotropical trees from savannas and seasonally dry forests

BackgroundWater is one of the main limiting factors for plant growth and crop productivity. Plants constantly monitor water availability and can rapidly adjust their metabolism by altering gene expression. This leads to phenotypic plasticity, which aids rapid adaptation to climate changes. Here, we address phenotypic plasticity under drought stress by analyzing differentially expressed genes (DEG) in four phylogenetically related neotropical Bignoniaceae tree species: two from savanna, Handroanthus ochraceus and Tabebuia aurea, and two from seasonally dry tropical forests (SDTF), Handroanthus impetiginosus and Handroanthus serratifolius. To the best of our knowledge, this is the first report of an RNA-Seq study comparing tree species from seasonally dry tropical forest and savanna ecosystems.ResultsUsing a completely randomized block design with 4 species × 2 treatments (drought and wet) × 3 blocks (24 plants) and an RNA-seq approach, we detected a higher number of DEGs between treatments for the SDTF species H. serratifolius (3153 up-regulated and 2821 down-regulated under drought) and H. impetiginosus (332 and 207), than for the savanna species. H. ochraceus showed the lowest number of DEGs, with only five up and nine down-regulated genes, while T. aurea exhibited 242 up- and 96 down-regulated genes. The number of shared DEGs among species was not related to habitat of origin or phylogenetic relationship, since both T. aurea and H impetiginosus shared a similar number of DEGs with H. serratifolius. All four species shared a low number of enriched gene ontology (GO) terms and, in general, exhibited different mechanisms of response to water deficit. We also found 175 down-regulated and 255 up-regulated transcription factors from several families, indicating the importance of these master regulators in drought response.ConclusionOur findings show that phylogenetically related species may respond differently at gene expression level to drought stress. Savanna species seem to be less responsive to drought at the transcriptional level, likely due to morphological and anatomical adaptations to seasonal drought. The species with the largest geographic range and widest edaphic-climatic niche, H. serratifolius, was the most responsive, exhibiting the highest number of DEG and up- and down-regulated transcription factors (TF).

Nanoencapsulation improves the protective effects of a nitric oxide donor on drought-stressed Heliocarpus popayanensis seedlings

Despite the important role played by nitric oxide (NO) in plants subjected to abiotic stress, NO donors application to induce drought tolerance in neotropical tree seedlings has not yet been tested. It is also worth investigating whether NO bioactivity in drought-stressed seedlings could be potentiated by NO donors nanoencapsulation. The aim of the current study is to evaluate the effects of chitosan nanoparticles (NPs) containing S-nitroso-mercaptosuccinic acid (S-nitroso-MSA) on drought-stressed seedlings of neotropical tree species Heliocarpus popayanensis Kunth in comparison to free NO donor and NPs loaded with non-nitrosated MSA. Nanoencapsulation slowed down NO release from S-nitroso-MSA, and nanoencapsulated S-nitroso-MSA yielded 2- and 1.6-fold higher S-nitrosothiol levels in H. popayanensis roots and leaves, respectively, than the free NO donor. S-nitroso-MSA has prevented drought-induced CO2 assimilation inhibition, regardless of nanoencapsulation, but the nanoencapsulated NO donor has induced earlier ameliorative effect. Both NO and MSA have decreased oxidative stress in H. popayanensis roots, but this effect was not associated with antioxidant enzyme induction, with higher seedling biomass, or with proline and glycine betaine accumulation. Nanoencapsulated S-nitroso-MSA was the only formulation capable of increasing leaf relative water content in drought-stressed plants (from 32.3% to 60.5%). In addition, it induced root hair formation (increase by 36.6% in comparison to well-hydrated plants). Overall, results have evidenced that nanoencapsulation was capable of improving the protective effect of S-nitroso-MSA on H. popayanensis seedlings subjected to drought stress, a fact that highlighted the potential application of NO-releasing NPs to obtain drought-tolerant tree seedlings for reforestation programs.

Topography drives microgeographic adaptations of closely related species in two tropical tree species complexes

Closely related tree species that grow in sympatry are abundant in rainforests. However, little is known of the ecoevolutionary processes that govern their niches and local coexistence. We assessed genetic species delimitation in closely related sympatric species belonging to two Neotropical tree species complexes and investigated their genomic adaptation to a fine-scale topographic gradient with associated edaphic and hydrologic features. Combining LiDAR-derived topography, tree inventories, and single nucleotide polymorphisms (SNPs) from gene capture experiments, we explored genome-wide population genetic structure, covariation of environmental variables, and genotype-environment association to assess microgeographic adaptations to topography within the species complexes Symphonia (Clusiaceae), and Eschweilera (Lecythidaceae) with three species per complex and 385 and 257 individuals genotyped, respectively. Within species complexes, closely related tree species had different realized optima for topographic niches defined through the topographic wetness index or the relative elevation, and species displayed genetic signatures of adaptations to these niches. Symphonia species were genetically differentiated along water and nutrient distribution particularly in genes responding to water deprivation, whereas Eschweilera species were genetically differentiated according to soil chemistry. Our results suggest that varied topography represents a powerful driver of processes modulating tropical forest biodiversity with differential adaptations that stabilize local coexistence of closely related tree species.

New cytochalasans from an endophytic Xylaria species associated with Costa Rican Palicourea elata (Rubiaceae)

Four new leucine-derived cytochalasans, possessing a 5,6,5,8-ring (1) and a 5,6,11-ring core (2–4), were isolated from a cultivated endophytic fungus Xylaria sp. strain WH2D4 (Xylariaceae). This fungus was isolated from leaves of the neotropical tree species Palicourea elata (Sw.) Borhidi (Rubiaceae) collected in Costa Rica. The chemical structures were determined by employing IR, MS as well as 1D- and 2D-NMR experiments. The stereochemistry at C-15 of compound 4 was determined by quantum calculations. The isolated compounds did not affect germination and growth of Trichoderma reesei and the opportunistic human fungal pathogen T. longibrachiatum.

Nitrogen use plasticity in response to light intensity in neotropical tree species of distinct functional groups.

Environmental conditions influence the use of different nitrogen (N) sources by plants. We hypothesized that an increase in light intensity favors the use of nitrate (NO3 - ) relative to ammonium (NH4 + ) by seedlings of neotropical tree species from different functional groups, that is, Cecropia pachystachya (a shade-intolerant species), Cariniana estrellensis (a shade-tolerant canopy species), and Guarea kunthiana (a shade-tolerant understory species). We analyzed the growth and N metabolism in seedlings simultaneously provided with NH4 + and NO3 - , under lower (LL) and higher (HL) light intensity. 15 N incorporation into amino acids was monitored after incubation with 15 N-labeled NH4 + or NO3 - . Under HL, all species showed decreased leaf area ratio, and increased growth, nitrate reductase activity and assimilated N content. Cecropia pachystachya increased the use of both N sources under HL, with substantial increases in 15 N-amino acids derived from 15 NO3 - (12.5- and 4.0-fold in roots and leaves, respectively) and 15 NH4 + (4.5- and 3.0-fold in roots and leaves, respectively). Guarea kunthiana showed the greatest plasticity in N use, as the assimilation of 15 NO3 - in roots and leaves increased substantially under HL (11.2- and 17.0-fold, respectively). Cariniana estrellensis increased the assimilation of 15 NH4 + in roots and 15 NO3 - in leaves under HL. Therefore, the responses of N use strategies to light intensity varied with the species according to their ecological characteristics.