Modelling spectral reflectance of open cork oak woodland: a simulation analysis of the effects of vegetation structure and background

This study analyses the influence of vegetation structure (i.e. leaf area index and canopy cover) and seasonal background changes on moderate-resolution imaging spectrometer (MODIS)-simulated reflectance data in open woodland. Approximately monthly spectral reflectance and transmittance field measurements (May 2011 to October 2013) of cork oak tree leaves (Quercus suber) and of the herbaceous understorey were recorded in the region of Ribatejo, Portugal. The geometric-optical and radiative transfer (GORT) model was used to simulate MODIS response (red, near-infrared) and to calculate vegetation indices, investigating their response to changes in the structure of the overstorey vegetation and to seasonal changes in the understorey using scenarios corresponding to contrasting phenological status (dry season vs. wet season). The performance of normalized difference vegetation index (NDVI), soil-adjusted vegetation index (SAVI), and enhanced vegetation index (EVI) is discussed. Results showed that SAVI and EVI were very sensitive to the emergence of background vegetation in the wet season compared to NDVI and that shading effects lead to an opposing trend in the vegetation indices. The information provided by this research can be useful to improve our understanding of the temporal dynamic of vegetation, monitored by vegetation indices.

An improved estimate of leaf area index based on the histogram analysis of hemispherical photographs

Leaf area index (LAI) is a key parameter that affects the surface fluxes of energy, mass, and momentum over vegetated lands, but observational measurements are scarce, especially in remote areas with complex canopy structure. In this paper we present an indirect method to calculate the LAI based on the analyses of histograms of hemispherical photographs. The optimal threshold value (OTV), the gray-level required to separate the background (sky) and the foreground (leaves), was analytically calculated using the entropy crossover method (Sahoo, P.K., Slaaf, D.W., Albert, T.A., 1997. Threshold selection using a minimal histogram entropy difference. Optical Engineering 36(7) 1976-1981). The OTV was used to calculate the LAI using the well-known gap fraction method. This methodology was tested in two different ecosystems, including Amazon forest and pasturelands in Brazil. In general, the error between observed and calculated LAI was similar to 6%. The methodology presented is suitable for the calculation of LAI since it is responsive to sky conditions, automatic, easy to implement, faster than commercially available software, and requires less data storage. (C) 2008 Elsevier B.V. All rights reserved.

Specific leaf areas of the tank bromeliad Guzmania monostachia perform distinct functions in response to water shortage

Leaves comprise most of the vegetative body of tank bromeliads and are usually subjected to strong longitudinal gradients. For instance, while the leaf base is in contact with the water accumulated in the tank, the more light-exposed middle and upper leaf sections have no direct access to this water reservoir. Therefore, the present study attempted to investigate whether different leaf portions of Guzmania monostachia, a tank-forming C(3)-CAM bromeliad, play distinct physiological roles in response to water shortage, which is a major abiotic constraint in the epiphytic habitat. Internal and external morphological features, relative water content, pigment composition and the degree of CAM expression were evaluated in basal, middle and apical leaf portions in order to allow the establishment of correlations between the structure and the functional importance of each leaf region. Results indicated that besides marked structural differences, a high level of functional specialization is also present along the leaves of this bromeliad. When the tank water was depleted, the abundant hydrenchyma of basal leaf portions was the main reservoir for maintaining a stable water status in the photosynthetic tissues of the apical region. In contrast, the CAM pathway was intensified specifically in the upper leaf section, which is in agreement with the presence of features more suitable for the occurrence of photosynthesis at this portion. Gas exchange data indicated that internal recycling of respiratory CO(2) accounted for virtually all nighttime acid accumulation, characterizing a typical CAM-idling pathway in the drought-exposed plants. Altogether, these data reveal a remarkable physiological complexity along the leaves of G. monostachia, which might be a key adaptation to the intermittent water supply of the epiphytic niche. (C) 2009 Elsevier GmbH. All rights reserved.

Dispersion of Seeds of Tree Species by the Leaf-Cutting Ant Acromyrmex subterraneus molestans (Hymenoptera: Formicidae) in Vicosa, Minas Gerais State, Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structural characteristics and forage mass of Tifton 85 pastures managed under three post-grazing residual leaf areas

The experiment was carried out on Cynodon spp cv. Tifton 85 pastures grazed by sheep under rotational stocking, with the objective of evaluating the structural characteristics as well as the forage mass of the pastures subjected to three grazing intensities in successive cycles. Treatments were composed of three residual leaf area indices (rLAI; 2.4; 1.6 and 0.8), allocated in completely randomized blocks with seven replications, totaling 21 experimental units. Tiller population density, pasture height, leaf area index, forage morphological composition and pasture forage mass were evaluated. The rLAI modified the tiller population density, which increased linearly with decrease in the rLAI of the pastures. Dry masses of leaf blade, stem and dead material were inferior when the rLAI imposed were lower, which resulted in differentiated forage production among the treatments. Tifton 85 pastures grazed by sheep in rotational stocking under tropical conditions with different rLAI show a modified sward structure over successive grazing cycles, mainly by alteration in the height and LAI of the plants at pre-grazing and by light interception post-grazing, which change the tiller population density. The residual leaf area index of 1.6 is the most suitable for pasture management for being equivalent to the heights of entrance and exit of animals on and from paddocks of 33 and 19 cm, respectively, which avoid great accumulation of dead material and excessive stem elongation, in addition to ensuring tillering in the sward.

Cellulose nanocomposites with nanofibres isolated from pineapple leaf fibers for medical applications

Nanocellulose is the crystalline domains obtained from renewable cellulosic sources, used to increase mechanical properties and biodegrability in polymer composites. This work has been to study how high pressure defibrillation and chemical purification affect the PALF fibre morphology from micro to nanoscale. Microscopy techniques and X-ray diffraction were used to study the structure and properties of the prepared nanofibers and composites. Microscopy studies showed that the used individualization processes lead to a unique morphology of interconnected web-like structure of PALF fibers. The produced nanofibers were bundles of cellulose fibers of widths ranging between 5 and 15 nm and estimated lengths of several micrometers. Percentage yield and aspect ratio of the nanofiber obtained by this technique is found to be very high in comparison with other conventional methods. The nanocomposites were prepared by means of compression moulding, by stacking the nanocellulose fibre mats between polyurethane films. The results showed that the nanofibrils reinforced the polyurethane efficiently. The addition of 5 wt% of cellulose nanofibrils to PU increased the strength nearly 300% and the stiffness by 2600%. The developed composites were utilized to fabricate various versatile medical implants. (C) 2011 Elsevier Ltd. All rights reserved.

Nest Digging by Leaf-Cutting Ants: Effect of Group Size and Functional Structures.

Leaf-cutting ant workers dig underground chambers, for housing their symbiotic fungus, interconnected by a vast quantity of tunnels whose function is to permit the entrance of food (leaves), gaseous exchanges, andmovement of workers, offspring, and the queen. Digging is a task executed by a group of workers, but little is known about the group effect and group-constructed functional structures. Thus, we analyzed the structures formed by worker groups (5, 10, 20, and 40 individuals) of the leaf-cutting ant, Atta sexdens rubropilosa, for 2 days of excavation. The digging arena was the same for the 4 groups, with each group corresponding to a different density. Our results verified a pattern of tunneling by the workers, but no chamber was constructed. The group effect is well known, since the 40-worker group dug significantly more than the groups of 5, 10, and 20. These groups did not differ statistically from each other. Analysis of load/worker verified that workers of the smallest group carried the greatest load. Our paper demonstrates the group effect on the digging of nests, namely, that excavation is proportional to group size, but without emergence of a functional structure such as a chamber.

The pulvinus endodermal cells and their relation to leaf movement in legumes of the Brazilian cerrado

Legume pulvini have a clearly delimited endodermis, whose variable content has been associated with the velocity and type of leaf movement: pulvini in leaves with fast nastic movement contain starch grains; pulvini in leaves with slow nastic movements have calcium oxalate crystals as well as starch grains in the endodermis. However, the studies carried out to date have involved few legume species. This study therefore purported to examine the consistency of this hypothesis in other legumes. Thus, the structure and content of the pulvinus endodermal cells of nine legumes of the Brazilian cerrado, with different types and velocities of leaf movement, were investigated: slow nyctinastic and heliotropic movements (Bauhinia rufa, Copaifera langsdorffii, Senna rugosa - Caesalpinioideae; Andira humilis and Dalbergia miscolobium - Faboideae; Stryphnodendron polyphyllum - Mimosoideae), slow heliotropic movement (Zornia diphylla - Faboideae), and fast seismonastic and slow nyctinastic and heliotropic movements (Mimosa rixosa and Mimosa flexuosa - Mimosoideae). Samples were prepared following standard plant anatomy and ultrastructure techniques. The endodermis of all the species contains starch grains. In the species displaying only slow movements, calcium oxalate prismatic crystals were observed in addition to starch grains, except in Zornia diphylla. in conclusion, oxalate crystals occur only in endodermal cells of pulvini that display slow movements, while starch grains are always present in pulvinus endodermal cells of plants with any kind of movement.

Bulliform cells in Loudetiopsis chrysothrix (Nees) Conert and Tristachya leiostachya Nees (Poaceae): structure in relation to function

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Pulvinus functional traits in relation to leaf movements: A light and transmission electron microscopy study of the vascular system

Previous studies on legume pulvini suggest that the vascular system plays an important role in the redistribution of ions and transmission of stimuli during leaf's movements. However, the number of anatomical and ultrastructural studies is limited to few species. The aim of this paper is to investigate the structure and cellular features of the pulvinus vascular system of nine legume species from Brazilian cerrado, looking for structural traits pointing to its participation in the leaf's movements. Samples were excised from the medial region of opened pulvinus of Bauhinia rufa, Copaifera langsdorffii, Senna rugosa (Caesalpinioideae), Andira humilis, Dalbergia miscolobium, Zornia dilphylla (Faboideae), Mimosa rixosa, Mimosa flexuosa and Stryphnodendron polyphyllum (Mimosoideae), and were prepared following light microscopy, transmission electron microscopy and histochemical standard techniques. The vascular system occupies a central position, comprises phloem and xylem and is delimited by a living sheath of septate fibers in all the species studied. This living cells sheath connects the cortex to the vascular tissues via numerous plasmodesmata. The absence of fibers and sclereids, the presence of phenolic idioblasts and the abundance and diversity of protein inclusions in the sieve tube members are remarkable features of the phloem. Pitted vessel elements, parenchyma cells with abundant cytoplasm and living fibriform elements characterize the xylem. The lack of lignified tissues and extensive symplastic continuity by plasmodesmata are remarkable features of the vascular system of pulvini of the all studied species. (c) 2007 Elsevier Ltd. All rights reserved.

Leaf emergences in Microlepis oleaefolia (DC.) Triana (Melastomataceae) and their probable function: An anatomical and ultrastructural study

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Yeasts and filamentous fungi carried by the gynes of leaf-cutting ants

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

On the taxonomic value of the anatomical structure of vegetative organs and inflorescence axis of Abolboda species (Xyridaceae - Poales)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Biological Activity of Quinoline Alkaloids from Raulinoa echinata and X-ray Structure of Flindersiamine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Comparison of leaf morphology and anatomy among Malva sylvestris (gerânio-aromático), Pelargonium graveolens (falsa-malva) and Pelargonium odoratissimum (gerânio-de-cheiro)

Malva sylvestris é comumente confundida com Pelargonium graveolens e Pelargonium odoratissimum devido às semelhanças na morfologia foliar. As folhas de M. sylvestris possuem antocianinas com propriedades citotóxicas, antiinflamatória, antitumoral e antioxidante já comprovadas cientificamente. As folhas de P. odoratissimum apresentam óleo essencial com propriedades antibacteriana e espasmolítica, e o óleo essencial da folha de P. graveolens possui atividade antimicrobiana e antifúngica. O objetivo deste estudo foi analisar morfo-anatomicamente as folhas destas espécies, apontando diferenças que possam ser utilizadas para esclarecer controvérsias na sua utilização como planta medicinal. Com a finalidade de se comparar anatomicamente a estrutura de cada planta, as amostras foram observadas por Microscopia de Luz e Microscopia Eletrônica de Varredura (MEV). A anatomia foliar entre as espécies foi bem distinta. Malva sylvestris apresentou tricomas do tipo capitado, estrelado e tector, além de drusas e células mucilaginosas. A distinção entre P. graveolens e P. odoratissimum foi observada em relação aos tricomas. Ambas as espécies apresentaram tricomas glandulares e tectores, sendo que P. graveolens se diferencia pela maior altura dos tricomas tectores e menor quantidade destes em relação ao P. odoratissimum. Este trabalho permitiu constatar diferenças anatômicas, auxiliando na taxonomia e classificação entre estas espécies.