Caracterização por XPS de filmes passivos formados sobre aços de baixa liga em meio de bicarbonato

Passive films formed in bicarbonate solutions on carbon steel, chromium steel and high speed steel have been characterized by XPS. The passive films formed on chromium and high speed steels showed superior protective properties than those formed on carbon steel. It was confirmed by XPS that the steel composition influences the passive film composition. Chromium oxide and hydroxide, as well as molybdenum and tungsten oxides and hydroxides are present in the passive film of chromium steel and high speed steel, respectively, besides iron oxide and hydroxide. The more complex composition of the oxide film on high speed steel explains its electrochemical behaviour and highest corrosion resistance.

SEASONAL CHEMICAL COMPOSITIONS OF THE ESSENTIAL OILS OF TWOEugenia SPECIES AND THEIR ACARICIDAL PROPERTIES

The leaf essential oils of Eugenia lutescens Cambess andEugenia langsdorffii O. Berg, collected in the rainy (RS) and dry seasons (DS), were extracted by hydrodistillation and then characterized by a gas chromatography-flame ionization detector and a gas chromatography-mass spectrometer. The potential acaricidal activity and oviposition deterrence of these oils were evaluated against Tetranychus urticae . The oil yields were higher in the RS for E. lutescens, while those forE. langsdorffii were higher in the DS. α-Pinene and β-pinene were determined to be the major constituents of the oils fromE. lutescens, while bicyclogermacrene, spathulenol, and β-caryophyllene predominated in E. langsdorffii . Seasonal variations in the oils were primarily related to chemical diversity, and E. lutescens was more affected than was E. langsdorffii . The E. langsdorffii oil collected in the DS was most toxic to the spider mite, while the oils of E. lutescens and E. langsdorffii collected in the RS drastically reduced its egg quantities. This study successfully determined the periods of greater oil production and acaricidal activity.

Resistência à corrosão das fases presentes em amálgamas dentários

Neste trabalho avaliou-se a resistência à corrosão em solução salina das fases presentes na microestrutura de amálgamas dentários comerciais: gama1-Ag2Hg3, o eutético Ag-Cu e gama2-Sn7-8Hg, empregando-se técnicas eletroquímicas de potencial a circuito aberto com o tempo, de polarização potenciodinâmica e de espectroscopia de impedância eletroquímica. As ligas metálicas em estudo já foram caracterizadas em um trabalho prévio, por meio de microscopia eletrônica de varredura e difratometria de raios X. A resistência à corrosão se origina da formação de filmes passivos na superfície metálica e parece estar determinada pela natureza rugosa e porosa das superfícies.

Etiology and epidemiology of Pythium root rot in hydroponic crops: current knowledge and perspectives

The etiology and epidemiology of Pythium root rot in hydroponically-grown crops are reviewed with emphasis on knowledge and concepts considered important for managing the disease in commercial greenhouses. Pythium root rot continually threatens the productivity of numerous kinds of crops in hydroponic systems around the world including cucumber, tomato, sweet pepper, spinach, lettuce, nasturtium, arugula, rose, and chrysanthemum. Principal causal agents include Pythium aphanidermatum, Pythium dissotocum, members of Pythium group F, and Pythium ultimum var. ultimum. Perspectives are given of sources of initial inoculum of Pythium spp. in hydroponic systems, of infection and colonization of roots by the pathogens, symptom development and inoculum production in host roots, and inoculum dispersal in nutrient solutions. Recent findings that a specific elicitor produced by P. aphanidermatum may trigger necrosis (browning) of the roots and the transition from biotrophic to necrotrophic infection are considered. Effects on root rot epidemics of host factors (disease susceptibility, phenological growth stage, root exudates and phenolic substances), the root environment (rooting media, concentrations of dissolved oxygen and phenolic substances in the nutrient solution, microbial communities and temperature) and human interferences (cropping practices and control measures) are reviewed. Recent findings on predisposition of roots to Pythium attack by environmental stress factors are highlighted. The commonly minor impact on epidemics of measures to disinfest nutrient solution as it recirculates outside the crop is contrasted with the impact of treatments that suppress Pythium in the roots and root zone of the crop. New discoveries that infection of roots by P. aphanidermatum markedly slows the increase in leaf area and whole-plant carbon gain without significant effect on the efficiency of photosynthesis per unit area of leaf are noted. The platform of knowledge and understanding of the etiology and epidemiology of root rot, and its effects on the physiology of the whole plant, are discussed in relation to new research directions and development of better practices to manage the disease in hydroponic crops. Focus is on methods and technologies for tracking Pythium and root rot, and on developing, integrating, and optimizing treatments to suppress the pathogen in the root zone and progress of root rot.

Avaliação do plantio homogêneo de mogno, Swietenia macrophylla King, em comparação com o plantio consorciado com Eucalyptus urophylla S. T. Blake, após 40 meses de idade

Na Amazônia, plantios de mogno têm sido limitados por ataques de Hypsiphylla grandella Zeller. No entanto, plantios em áreas urbanas em Brasília vêm apresentando bom desenvolvimento. O objetivo deste trabalho foi observar o comportamento do mogno em plantios homogêneo e consorciado. Para isso foi instalado um experimento na Fazenda Água Limpa, da Universidade de Brasília (UnB), Distrito Federal, com dois tratamentos: plantio homogêneo e plantio misto com eucalipto. O primeiro consistiu no plantio homogêneo de mogno e o segundo, consorciado com eucalipto. Foram medidas as variáveis altura aos 7, 12, 15, 24, 28, 36 e 40 meses de idade e diâmetro aos 7, 24, 28, 36 e 40 meses. O delineamento utilizado foi inteiramente ao acaso, em esquema de parcelas subdivididas, sendo os tratamentos as parcelas e o tempo, as subparcelas. A altura média aos 40 meses do consórcio foi de 2,28 m e do homogêneo, de 3,45 m, sendo as alturas máximas, respectivamente, de 4,15 e 5,17 m. O diâmetro médio também foi maior no tratamento homogêneo do que no consórcio (4,08 e 6,92 cm, respectivamente). A mortalidade situou-se em torno de 20%, tanto no plantio homogêneo quanto no consorciado, não havendo diferenças significativas. O ataque das larvas de H. grandella foi menor no plantio consorciado, indicando que o eucalipto serve como barreira física, diminuindo o ataque da praga, porém a competição de ambos ocasionou menor crescimento do mogno.

Canopy openness and lai estimates in two seasonally deciduous forests on limestone outcrops in central Brazil using hemispherical photographs

Patches of seasonally dry tropical forests occur on limestone outcrops in Central Brazil surrounded by the dominant savanna vegetation. They contain valuable timber species but are threatened by farming and mining activities. The objective of this study was to describe canopy opening and light relations in two seasonally deciduous dry forests on slopes and limestone outcrops, in the Paranã valley at the northeastern region of the Goiás state, Brazil. The studied forests were in the Fazenda Sabonete in Iaciara-Go and Fazenda Forquilha in Guarani-GO. Woody plants were sampled in 25 (20 x 20 m) plots in each forest. In the Sabonete forest 40 species, 705 ind./ha-1 with a basal area of 15.78 m²/ha-1 were found, while in Forquilha there were 55 species, 956 ind./ha-1 with a basal area of 24.76 m²/ha-1. Using hemispherical photographic techniques, 25 black and white photographs were taken at each site, during the dry season, totaling 50 photographs. These were taken at the beginning of each vegetation-sampling plot. The photographs were scanned in grey tones and saved as 'Bitmap'. The canopy opening and leaf area index (LAI) were calculated using the software Winphot. The mean canopy opening was 54.0% (±9.36) for Fazenda Sabonete and 64.6% (±11.8) in Fazenda Forquilha, with both sites presenting significant differences in the opening estimates (P < 0.05). Their floristic richness and structure also differed with the more open canopy forest, Forquilha, being richer and denser, suggesting the need for further studies on species-environment relationships in these forests.

Avaliação temporal da regeneração natural em uma floresta estacional semidecídua secundária, em Pirenópolis, Goiás

A regeneração natural em ambientes florestais é dinâmica, variável no espaço e no tempo, e integra o ciclo de desenvolvimento das florestas. Em florestas estacionais tropicais, devido à sazonalidade climática, a regeneração natural depende principalmente da disponibilidade de umidade no solo, que afeta tanto os padrões de produção de sementes quanto a germinação, a sobrevivência e o desenvolvimento das plântulas. O objetivo deste estudo foi analisar a dinâmica da regeneração natural em uma floresta estacional semidecídua secundária, em Pirenópolis, Goiás, verificando as mudanças na composição florística de plântulas e arvoretas ao longo do tempo, e relacionando-as a fatores ambientais das parcelas por Análises de Correspondência Canônica (CCA). Os resultados indicaram plântulas mais dinâmicas do que arvoretas, em função principalmente do clima. Isso ocorreu devido à maior susceptibilidade das plântulas com relação ao estresse hídrico do solo e ao aumento da incidência de radiação solar e da temperatura na estação seca. Foi encontrada alta similaridade florística (±50%) entre as populações da regeneração natural e a comunidade adulta, indicando estágio avançado de regeneração da floresta, com Índices de Diversidade superiores a 3,0 nats.indv-¹. A CCA agrupou as espécies em função do gradiente ambiental de umidade e sombreamento versus cobertura do solo, posicionando próximas as espécies preferenciais de ambientes úmidos versus as preferenciais de ambientes mais secos de cerrado típico.

Regime de luz em uma floresta estacional semidecídua sob manejo, em Pirenópolis, Goiás

Esta pesquisa foi realizada em um fragmento de floresta estacional semidecídua, localizada em Pirenópolis, Goiás, e investigou as alterações no regime de luz, medida pela densidade de fluxo de fótons, associadas a intervenções silviculturais que visaram, sobretudo, aumentar o crescimento de espécies arbóreas, sem permitir a invasão por espécies oportunistas que poderiam influenciar negativamente a dinâmica da regeneração natural. O delineamento foi em blocos casualizados, em esquema fatorial, testando as diferenças entre tratamentos silviculturais, estações climáticas e alturas de medida no sub-bosque (1,30 m e ao nível do solo). Foram testadas duas intensidades de corte seletivo de indivíduos arbóreos e de cipós na floresta. Os tratamentos foram suficientes para alterar o regime de luz, tanto na estação seca como na estação chuvosa, em acordo com a hipótese testada. O sombreamento na área controle foi de 97% na estação chuvosa e de 86% na estação seca, apresentando diferenças significativas com o sombreamento associado aos tratamentos silviculturais, que variaram de 93% a 94% na chuva e de 77% a 80% na seca. Esse estudo pode auxiliar na validação deste sistema de manejo florestal proposto para as florestas estacionais semidecíduas no Brasil Central, devendo ser associado aos estudos populacionais e de comunidade, preservando os fragmentos florestais encontrados na região e gerando benefícios ambientais e renda extra para a população rural.

Intracellular and intercellular compartmentation of carbohydrate metabolism in leaves of temperate gramineae

This review considers the importance of compartmentation in the regulation of carbohydrate metabolism in leaves. We draw particular attention to the role of the vacuole as a site for storage of soluble sugars based on sucrose, and discuss briefly their characteristic metabolism. We also point out inconsistencies between the observed properties of vacuoles and the behaviour in vitro of the enzymes of fructan biosynthesis that do not support the hypothesis that the vacuole is the site of synthesis as well as of storage. We also consider compartmentation of carbohydrate metabolism between different cell types, using mainly our studies on leaves of temperate C3 gramineae. Here we present evidence of significant differences in carbon metabolism between epidermis, mesophyll, bundle sheath and vasculature based upon both single-cell sampling and immunolocalisation. The implications of these differences for the control of metabolism in leaves are discussed.

Floristic composition, diversity and structure of the "cerrado" sensu stricto on rocky soils in northern Goiás and southern Tocantins, Brazil

The "cerrado" sensu stricto is a savanna woodland physiognomy which occupies most of central Brazil, with the degree of canopy cover varying from 10% to 60% at a site with trees reaching up to seven meters high. It occurs mostly on deep and well-drained soils but can also be found on shallower ones. The diversity and structure of the "cerrado" sensu stricto on shallow and rocky Cambisols and Litosols were studied here. Sixteen 20 x 50 m² plots were sampled in a random design over patches of this vegetation in northern Goiás State and southern Tocantins. All stems from 5 cm diameter at 30 cm from the ground level were measured. Vouchers were collected and deposited at the IBGE herbarium. A total of 87 species in 65 genera and 33 families were found. Diversity index was 2.87 nats ind-1, density was 836 stems ha-1 with a basal area of 8.4374 m² ha-1. Sørensen's index indicated higher similarities between plots at the same site indicating a geographical gradient influencing the floristic composition of the "cerrado" sensu stricto on rocky soils. Czekanowski's index confirmed this trend. TWINSPAN classification final groups were defined by preferential species of more fertile soils, in opposition to those typical of dystrophic soils and to common species to gallery forests occurring on sloping terrains with gullies.

Floristic composition and community structure of a seasonally deciduous forest on limestone outcrops in Central Brazil

The objective of this study was to analyze the floristic composition and structure of the tree component in a seasonally deciduous forest on limestone outcrops, located in the northeast region of Goiás State, Brazil. A sample composed of 25 randomly sampled plots of 20 x 20 m (400 m²) within a 50 ha forest, was measured. All woody individuals > 5 cm diameter at breast height (DBH) had their diameter and height measured. The tree community was composed of 39 species with a density of 734 individuals ha-1; the richest families were Leguminosae (11 species), Bignoniaceae (4 species) and Apocynaceae (4 species). The forest had a basal area of 16.37 m² ha-1, with the most important species Cavanillesia arborea (3.26 m² ha-1), Pseudobombax tomentosum (2.35 m² ha-1), Dilodendron bipinnatum (1.84 m² ha-1), Tabebuia impetiginosa (1.36 m² ha-1) and Myracrodruon urundeuva (1.26 m² ha-1) occupying 61.5% of the total basal area of the forest. Several species grew on rocks, or in rock fissures or in places with a shallow layer of soil or even in litter over rocky layers. The floristic composition showed links with the "Caatinga" flora, with other patches of seasonal forests in Central Brazil and in the Pantanal, and with the Chiquitano forests of Bolivia too, containing even two species considered as endemic to the "Caatinga".