Rosana Marta Kolb

Gochnatia polymorpha (Less.) Cabrera (Asteraceae) changes in leaf structure due to differences in light and edaphic conditions

Gochnatia polymorpha (Less.) Cabrera is a widespread Asteraceae species found in different physiognomies of cerrado (Neotropical savanna) and in forest formations of southeast Brazil. This study describes some leaf anatomy characteristics of this species and quantitatively evaluates them in relation to different environments, as well as under different light conditions. We found quantitative differences in all anatomical parameters analyzed. The results demonstrate that high leaf anatomy plasticity is an adaptive advantage that allows this species to occur in diverse cerrado conditions.

Fractal analysis of leaf-texture properties as a tool for taxonomic and identification purposes: a case study with species from Neotropical Melastomataceae (Miconieae tribe)

Melastomataceae is a common and dominant family in Neotropical vegetation, with high species diversity which leads to a large variation in some morphological structures. Despite this, some species of Melastomataceae are very similar in their external leaf morphology, leading to difficulties in their identification without the presence of reproductive organs. Here we have proposed and tested a computer-aided texture-based approach used to correctly identify and distinguish leaves of some species of Melastomataceae that occur in a region of Neotropical savanna in Southeastern Brazil, also comparing it with other previously proposed approaches. The results demonstrated that our approach may clearly separate the studied species, analyzing the patterns of leaf texture (both adaxial and abaxial surfaces), and achieving better accuracy (100%) than other methods. Our work has suggested that leaf texture properties can be used as a new characteristic for identification, and as an additional source of information in taxonomic and systematic studies. As the method may be supervised by experts, it is also suitable for discrimination of species with high morphological plasticity, improving the automated discrimination task. This approach can be very useful for identification of species in the absence of reproductive material, and is a rapid and powerful tool for plant identification.

Plant Identification Based on Leaf Midrib Cross-Section Images Using Fractal Descriptors

The correct identification of plants is a common necessity not only to researchers but also to the lay public. Recently, computational methods have been employed to facilitate this task, however, there are few studies front of the wide diversity of plants occurring in the world. This study proposes to analyse images obtained from cross-sections of leaf midrib using fractal descriptors. These descriptors are obtained from the fractal dimension of the object computed at a range of scales. In this way, they provide rich information regarding the spatial distribution of the analysed structure and, as a consequence, they measure the multiscale morphology of the object of interest. In Biology, such morphology is of great importance because it is related to evolutionary aspects and is successfully employed to characterize and discriminate among different biological structures. Here, the fractal descriptors are used to identify the species of plants based on the image of their leaves. A large number of samples are examined, being 606 leaf samples of 50 species from Brazilian flora. The results are compared to other imaging methods in the literature and demonstrate that fractal descriptors are precise and reliable in the taxonomic process of plant species identification.

An evergreen neotropical savanna tree (Gochnatia polymorpha, Asteraceae) produces different dry- and wet-season leaf types

Gochnatia polymorpha (Less.) Cabrera is a widespread tree species found in different physiognomies of neotropical savanna (cerrado) formations of south-eastern Brazil. The present study describes some leaf anatomical characteristics of this species as a function of the time of leaf flush, during dry or wet seasons. This species presents anatomical plasticity in the cuticle, palisade parenchyma and abaxial epidermis as well as in stomatal size and stomatal and trichome density, which are leaf structures linked with water-status control. Leaf structure changed to suit the particular environmental conditions during dry and wet seasons. The production of different wet- and dry-season leaf types in G. polymorpha could be a response to drought and an adaptation to environmental constraints in the cerrado.

Leaf anatomical traits corroborate the leaf economic spectrum: a case study with deciduous forest tree species

Deciduous forests are seasonal systems that occur scattered throughout the Neotropics. Many aspects about these ecosystems have been studied. However, there is a lack of information about leaf structure and its possible functional and adaptive aspects. Here we examined leaf anatomy and specific leaf area (SLA) in 13 dominant tree species of dry forests in central Brazil, identifying structural patterns of these species. As the system is seasonal, with species presenting a deciduous behavior, we expect to find tree species with a set of mesomorphic leaf traits. The studied dry forest trees share similar leaf structure, with one-layered adaxial and abaxial epidermis and a well-developed mesophyll, high values of SLA, and the presence of calcium crystals and mucilaginous cells. Higher values of SLA and the high investment achieved in the mesophyll (especially in parenchyma tissue) are probably related to the accomplishment of a high performance of carbon and nutrients gain during the limited wet season.

A computer vision approach to quantify leaf anatomical plasticity: A case study on gochnatia polymorpha (less.) cabrera

Abstract Inferences about leaf anatomical characteristics had largely been made by manually measuring diverse leaf regions, such as cuticle, epidermis and parenchyma to evaluate differences caused by environmental variables. Here we tested an approach for data acquisition and analysis in ecological quantitative leaf anatomy studies based on computer vision and pattern recognition methods. A case study was conducted on Gochnatia polymorpha (Less.) Cabrera (Asteraceae), a Neotropical savanna tree species that has high phenotypic plasticity. We obtained digital images of cross-sections of its leaves developed under different light conditions (sun vs. shade), different seasons (dry vs. wet) and in different soil types (oxysoil vs. hydromorphic soil), and analyzed several visual attributes, such as color, texture and tissues thickness in a perpendicular plane from microscopic images. The experimental results demonstrated that computational analysis is capable of distinguishing anatomical alterations in microscope images obtained from individuals growing in different environmental conditions. The methods presented here offer an alternative way to determine leaf anatomical differences.

Germinação de Pyrostegia venusta (Bignoniaceae), viabilidade de sementes e desenvolvimento pós-seminal

The effect of light and temperature on the germination of Pyrostegia venusta (Ker Gawl.) Miers was studied by isothermic incubations. The seeds of this species do not present photoblastism, and can germinate equally in the presence and absence of light. The minimum temperature for germination is between 10 and 15 °C and the maximum between 35 and 40 °C. The germination rate was higher at 35 °C, despite the fact that no statistically significant differences in the germinability were observed at 25, 30 and 35 °C. At 25 °C, germination initiates at the 7th day, while the development of the first pair of leaves occurs after 22 days of experiment. The seeds viability is better maintained when these are stored in glass containers at low temperatures. Germination in a wide range of temperature, and the absence of photoblastism allow the species to germinate in open areas and under the canopy, favoring its distribution in the different physiognomies of the Cerrado biome.

Fractal descriptors for discrimination of microscopy images of plant leaves

This study proposes the application of fractal descriptors method to the discrimination of microscopy images of plant leaves. Fractal descriptors have demonstrated to be a powerful discriminative method in image analysis, mainly for the discrimination of natural objects. In fact, these descriptors express the spatial arrangement of pixels inside the texture under different scales and such arrangements are directly related to physical properties inherent to the material depicted in the image. Here, we employ the Bouligand-Minkowski descriptors. These are obtained by the dilation of a surface mapping the gray-level texture. The classification of the microscopy images is performed by the well-known Support Vector Machine (SVM) method and we compare the success rate with other literature texture analysis methods. The proposed method achieved a correctness rate of 89%, while the second best solution, the Co-occurrence descriptors, yielded only 78%. This clear advantage of fractal descriptors demonstrates the potential of such approach in the analysis of the plant microscopy images.

Changes in irradiance and soil properties explain why typical non-arboreal savanna species disappear under tree encroachment

Savanna vegetation maintains its openness and its diverse plant composition because of frequent fire events; however, when these are suppressed, encroachment is caused by increases in the tree density. In the neotropical savanna (cerrado of Brazil), typical forest trees are invading savanna areas, altering abiotic conditions and affecting the persistence of their exclusive species. Here we studied changes in abiotic conditions, species richness and diversity of a non-arboreal community (herbs, vines, grasses, subshrubs and shrubs) in a gradient of encroachment at a site where fire has been suppressed for more than 50 years in south-eastern Brazil. Encroached communities were more shaded and possessed a wetter and richer soil (higher contents of organic matter and P) compared with the typical savanna. These abiotic changes were related to a less rich and less diverse plant community in encroached savanna compared with typical savanna. The most important abiotic variables driving such changes were photosynthetically active radiation (PAR) reaching the understorey and soil P content: communities with lower species richness and diversity had lower PAR incidence and higher soil P content. Our results suggest that non-arboreal savanna species may be under serious threat of extinction given the expected ecological changes caused by the widespread expansion of forest on the savannas in the absence of fire.

Avaliação do potencial alelopático, atividade antimicrobiana e antioxidante dos extratos orgânicos das folhas de Pyrostegia venusta (Ker Gawl.) Miers (Bignoniaceae)

This paper presents the results of allelopathic, antimicrobial and antioxidant activities of organic extracts (hexane, ethyl acetate and methanol) from the leaves of Pyrostegia venusta (Ker Gawl.) Miers (Bignoniaceae). Allelopathic activity was assessed based on Cucumis sativus (cucumber) development for the parameters main root length, number of secondary roots and hypocotyl length. All tested extracts affected the first two parameters, while the hypocotyl length was not affected only by the ethyl acetate extract. For antimicrobial activity, assessed by MIC assay, hexane extract showed moderate inhibition for Staphylococcus aureus (0.9 mg mL-1) and strong inhibition for Enterococcus hirae (0.5 mg mL-1). Ethyl acetate extract showed strong activity against Candida albicans (0.3 mg mL-1), whereas methanolic extract was not active against the tested microorganisms. On the other hand, methanol extract showed the most promising radical scavenging capacity (Effective Concentration 50% - EC50 = 102.0 ± 56.9 mg mL-1, with TEC50 = 30 min) in DPPH assay (2,2-diphenyl-1-picryl-hidrazil) and the highest level of phenolic compounds (116.2 ± 83.0 mg acid garlic g sample-1), as indicated by Folin-Ciocalteau assay.