Diameter distribution in a Brazilian tropical dry forest domain: predictions for the stand and species.

Currently, there is a lack of studies on the correct utilization of continuous distributions for dry tropical forests. Therefore, this work aims to investigate the diameter structure of a brazilian tropical dry forest and to select suitable continuous distributions by means of statistic tools for the stand and the main species. Two subsets were randomly selected from 40 plots. Diameter at base height was obtained. The following functions were tested: log-normal; gamma; Weibull 2P and Burr. The best fits were selected by Akaike's information validation criterion. Overall, the diameter distribution of the dry tropical forest was better described by negative exponential curves and positive skewness. The forest studied showed diameter distributions with decreasing probability for larger trees. This behavior was observed for both the main species and the stand. The generalization of the function fitted for the main species show that the development of individual models is needed. The Burr function showed good flexibility to describe the diameter structure of the stand and the behavior of Mimosa ophthalmocentra and Bauhinia cheilantha species. For Poincianella bracteosa, Aspidosperma pyrifolium and Myracrodum urundeuva better fitting was obtained with the log-normal function.

Diameter distribution in a Brazilian tropical dry forest domain: predictions for the stand and species

ABSTRACT Currently, there is a lack of studies on the correct utilization of continuous distributions for dry tropical forests. Therefore, this work aims to investigate the diameter structure of a brazilian tropical dry forest and to select suitable continuous distributions by means of statistic tools for the stand and the main species. Two subsets were randomly selected from 40 plots. Diameter at base height was obtained. The following functions were tested: log-normal; gamma; Weibull 2P and Burr. The best fits were selected by Akaike's information validation criterion. Overall, the diameter distribution of the dry tropical forest was better described by negative exponential curves and positive skewness. The forest studied showed diameter distributions with decreasing probability for larger trees. This behavior was observed for both the main species and the stand. The generalization of the function fitted for the main species show that the development of individual models is needed. The Burr function showed good flexibility to describe the diameter structure of the stand and the behavior of Mimosa ophthalmocentra and Bauhinia cheilantha species. For Poincianella bracteosa, Aspidosperma pyrifolium and Myracrodum urundeuva better fitting was obtained with the log-normal function.

Gelatinous fibers and variant secondary growth related to stem undulation and contraction in a monkey ladder vine, Bauhinia glabra (Fabaceae).

PREMISE OF THE STUDY: Some of the most striking stem shapes occur in species of Bauhinia (Fabaceae) known as monkey ladder vines. Their mature stems are flattened and develop regular undulations. Although stems have variant (anomalous) secondary growth, the mechanism causing the undulations is unknown. METHODS: We measured stem segments over time (20 mo), described stem development using light microscopy, and correlated the changes in stem shape with anatomy. KEY RESULTS: Growing stems are initially straight and bear tendrils on short axillary branches. The inner secondary xylem has narrow vessels and lignified fibers. As stems age, they become flattened and increasingly undulated with the production of two lobes of outer secondary xylem (OX) with wide vessels and only gelatinous fibers (G-fibers). Similar G-fibers are present in the secondary phloem and the cortical sclerified layer. In transverse sections, the concave side of each undulation has a greater area and quantity of G-fibers than the opposite convex side. Some older stems are not undulated and have less lobing of OX. Undulation causes a shortening of the stem segments: up to 28% of the original length. CONCLUSIONS: Uneven distribution of G-fibers produces tensions that are involved in the protracted development of undulations. While young extending shoots attach by lateral branch tendrils, older stems may maintain their position in the canopy using undulations and persistent branch bases as gripping devices. Flattened and undulated stems with G-fibers produce flexible woody stems.

Relações fisiológicas em mudas de pata-de-vaca (Bauhinia forficata Link) / Physiologic relationships in Brazilian Orchid Tree (Bauhinia forficata Link) seedlings

Os fatores ambientais, tais como: temperatura do ar, umidade relativa do ar e radiação solar, influenciam no comportamento fisiológico dos vegetais refletindo no seu crescimento e desenvolvimento. O objetivo do trabalho foi avaliar o comportamento fisiológico em mudas de pata-de-vaca ao longo do dia e constatar qual o melhor horário para a realização de determinações de trocas gasosas. Para tanto, foram realizadas avaliações de temperatura da folha, radiação fotossinteticamente ativa, resistência estomática e transpiração, utilizando-se um porômetro, das 8:00 às 17:00 horas, em intervalos de uma hora entre as medidas. A espécie apresenta oscilações no seu mecanismo fisiológico em função do horário de avaliação e das condições climáticas, sendo o intervalo mais indicado para a realização de determinações das trocas gasosas das 10:00 às 13:00 horas.

Environmental elements, such as air temperature, relative humidity and solar radiation, affect the physiological behavior of plants, which is reflected in their growth and development. The objective of this study was to evaluate the physiological changes of Brazilian Orchid Tree seedlings over a typical day and find the best time to carry out determinations of gas exchanges. For this end, we evaluated temperature of the leaf, photosynthetically active radiation, stomatal resistance and perspiration, using a porometer, from 8:00 a.m. to 05:00 p.m., in intervals of one hour between measurements. The species presents oscillations in its physiologic mechanism in function of the time of evaluation and climatic conditions, being the most suitable interval to determine gas exchanges from 10:00 a.m. to 01:00 p.m.

Assessment of the potentiality of TDZ on multiple shoot induction in Bauhinia tomentosa L., a woody legume.

An efficient and reproducible protocol for in vitro multiplication of Bauhinia tomentosa L. was developed. Multiple shoots were regenerated from cotyledonary node and stem nodal segments excised from in vitro raised seedlings on Murashige and Skoog (MS) medium supplemented with different concentrations (0.1, 0.3, 0.5, 0.8 and 1.0 µM) of thidiazuron (TDZ). The maximum response (62.6%) was recorded on MS medium amended with 0.8 µM TDZ. A long exposure to TDZ for 8 weeks showed abnormalities such as fasciation and compact shoots formation. To avoid adverse effects of prolonged exposure to TDZ in long-term establishment, the culture were transferred to TDZ free MS medium for further multiplication and elongation. The highest number of shoots and shoot length were recorded at the end of fourth subculture passage. Ex vitro rooting was achieved when the basal cut end of regenerated shoots were dipped in 200 µM indole-3-butyric acid (IBA) for half an hour followed by their transplantation in plastic pots filled with sterile Soilrite™ where 60% plantlets grew well and all expressed normal development.

[Influence of soil moisture, nitrogen and phosphorus contents on Bauhinia faberi seedlings growth characteristics in arid valley of Minjiang River].

To study the influence of resources thresholds on plant growth is a major theme in restoration ecology. Based on the simulation of the natural thresholds of soil moisture, nitrogen (N), and phosphorus (P) under drought condition in the arid valley of Mingjiang River, a full factorial experiment was designed to study the dynamics of Bauhinia faberi seedlings survival rate, growth, biomass production, and resources use efficiency across one growth season. High soil moisture (40% field water capacity), high soil P (24 mg P x kg(-1)), and low N (100 mg N x kg(-1)) increased the seedlings survival rate, and promoted the seedlings growth, biomass production, and water use efficiency. There was a significant coupling effect between soil N and P, but the interactions between soil moisture and soil N and P were not obvious. High N (240 mg N x kg(-1)) restrained the seedlings growth markedly, while high P mitigated the negative effects of high N via increasing root area, root length, and root mass to promote the seedlings N and P uptake. The N and P use efficiency across one growth season kept steady, and had significant positive correlation with root/shoot mass ratio. The combination of high soil moisture, low N, and high P promoted the seedlings growth effectively, while that of low soil moisture, low P, and high N inhibited the seedlings growth markedly.

Effects of light and nutrients on seedlings of tropical Bauhinia lianas and trees.

Lianas differ from trees in many life history characteristics, and we predicted that they are phenotypically more responsive to environmental variation than trees. We analyzed responsiveness to light and nutrient availability of five Bauhinia species (three lianas and two trees). Seedlings were grown in a shade house in two light regimes (5 and 25% of full sunlight) and two nutrient supply regimes (field soil and N fertilization equivalent to 100 kg ha(-1)), and important growth-related physiological and morphological plant parameters were measured. Light availability affected most of the measured variables, whereas N addition had only weak effects. In the four light-demanding species (two lianas and two trees), relative plant biomass growth rate increased and specific leaf area (SLA) decreased with increased light availability, whereas a shade-tolerant liana did not respond. Leaf N concentration and light-saturated photosynthetic rate per unit leaf area increased in response to increased irradiance or soil N in the light-demanding tree species and the shade-tolerant liana, but not in the two light-demanding lianas. The light-demanding lianas also had higher SLA and leaf mass ratio, resulting in a higher leaf area ratio (LAR) in high light, whereas the light-demanding trees did not. Across all treatments, mean plasticity indices of physiological and morphological traits, and all traits combined were similar among the studied species. Plasticity was higher in response to light than to N, indicating that light is the main factor controlling seedling responses of the studied species. Although lianas and trees did not differ in mean plasticity in response to light and N, the light-demanding lianas were phenotypically less plastic in LAR and in photosynthetic rates and biomass allocation than the trees. Light and N interacted in their effects on most physiological variables, but the consequences for relative growth rate differed little among species. We conclude that, contrary to our predictions, lianas were no more responsive to variation in light and N availability than trees.

Seedling growth strategies in Bauhinia species: comparing lianas and trees.

BACKGROUND AND AIMS: Lianas are expected to differ from trees in their growth strategies. As a result these two groups of woody species will have different spatial distributions: lianas are more common in high light environments. This study determines the differences in growth patterns, biomass allocation and leaf traits in five closely related liana and tree species of the genus Bauhinia. METHODS: Seedlings of two light-demanding lianas (Bauhinia tenuiflora and B. claviflora), one shade-tolerant liana (B. aurea), and two light-demanding trees (B. purpurea and B. monandra) were grown in a shadehouse at 25% of full sunlight. A range of physiological, morphological and biomass parameters at the leaf and whole plant level were compared among these five species. KEY RESULTS: The two light-demanding liana species had higher relative growth rate (RGR), allocated more biomass to leaf production [higher leaf mass fraction (LMF) and higher leaf area ratio (LAR)] and stem mass fraction (SMF), and less biomass to the roots [root mass fraction (RMF)] than the two tree species. The shade-tolerant liana had the lowest RGR of all five species, and had a higher RMF, lower SMF and similar LMF than the two light-demanding liana species. The two light-demanding lianas had lower photosynthetic rates per unit area (A(area)) and similar photosynthetic rates per unit mass (A(mass)) than the trees. Across species, RGR was positively related to SLA, but not to LAR and A(area). CONCLUSIONS: It is concluded that the faster growth of light-demanding lianas compared with light-demanding trees is based on morphological parameters (SLA, LMF and LAR), and cannot be attributed to higher photosynthetic rates at the leaf level. The shade-tolerant liana exhibited a slow-growth strategy, compared with the light-demanding species.

Bud composition, branching patterns and leaf phenology in cerrado woody species.

BACKGROUND AND AIMS: Plants have complex mechanisms of aerial biomass exposition, which depend on bud composition, the period of the year in which shoot extension occurs, branching pattern, foliage persistence, herbivory and environmental conditions. METHODS: The influence of water availability and temperature on shoot growth, the bud composition, the leaf phenology, and the relationship between partial leaf fall and branching were evaluated over 3 years in Cerrado woody species Bauhinia rufa (BR), Leandra lacunosa (LL) and Miconia albicans (MA). KEY RESULTS: Deciduous BR preformed organs in buds and leaves flush synchronously at the transition from the dry to the wet season. The expansion time of leaves is <1 month. Main shoots (first-order axis, A1 shoots) extended over 30 d and they did not branch. BR budding and foliage unfolds were brought about independently of inter-annual rainfall variations. By contrast, in LL and MA evergreen species, the shoot extension rate and the neoformation of aerial organs depended on rainfall. Leaf emergence was continuous for 2-6 months and lamina expansion took place over 1-4 months. The leaf life span was 5-20 months and the main A1 shoot extension happened over 122-177 d. Both evergreen species allocated biomass to shoots, leaves or flowers continuously during the year, branching in the middle of the wet season to form second-order (A2 shoots) and third-order (A3 shoots) axis in LL and A2 shoots in MA. Partial shed of A1 shoot leaves would facilitate a higher branching intensity A2 shoot production in LL than in MA. MA presented a longer leaf life span, produced a lower percentage of A2 shoots but had a higher meristem persistence on A1 and A2 shoots than LL. CONCLUSIONS: It was possible to identify different patterns of aerial growth in Cerrado woody species defined by shoot-linked traits such as branching pattern, bud composition, meristem persistence and leaf phenology. These related traits must be considered over and above leaf deciduousness for searching functional guilds in a Cerrado woody community. For the first time a relationship between bud composition, shoot growth and leaf production pattern is found in savanna woody plants.

Mechanical, chemical and X-ray analysis of wood in the two tropical lianas Bauhinia guianensis and Condylocarpon guianense: variations during ontogeny.

Mechanical and chemical properties as well as microfibril angles of wood tissues from different ontogenetic stages are determined for the neotropical lianas Bauhinia guianensis and Condylocarpon guianense. The mechanical properties include the elastic moduli under bending and under dynamic torsion. The chemical analyses cover (i) the content of cellulose, lignin and hemicelluloses fractions, (ii) the monomeric composition of the uncondensed lignin, and (iii) the composition of the hemicelluloses with respect to neutral monosaccharides. By comparing the wood properties of these lianas with the corresponding properties of wood from self-supporting deciduous trees, common characteristics and differences are revealed. Additionally, the changes in the lignin and polysaccharides fractions as well as the variations in microfibril orientation that occur during ontogeny of the two liana species are discussed with regard to their implications for the mechanical properties of wood.