Rafael Silva Oliveira - Academia.edu (original) (raw)
Papers by Rafael Silva Oliveira
Journal of Power Sources, 2009
The effect of adding a non-ionic surfactant to disperse oxide particles on the electrochemical pe... more The effect of adding a non-ionic surfactant to disperse oxide particles on the electrochemical performance of PAni/LiMnNiO4 composites is evaluated by using cyclic voltammetry (CV), impedance measurements and constant-current charge/discharge cycling techniques. Three surfactants based on ethoxylated (EO) and propoxylated (PO) lauryl alcohols (3EO/6PO, L306; 4EO/5PO, L405; and 6EO/3PO, L603) were investigated. For comparative purposes, the oxide and polyaniline were prepared by sol–gel and chemical methods and were also investigated for their physical and electrochemical performances. By galvanostatic charge–discharge tests, the PAni/LiMnNiO4 L306 composite showed a better electrochemical performance than each single component and other composites (PAni/LiMnNiO4 L405 and PAni/LiMnNiO4 L603). The electrical conductivity of this composite reached 21.7 S cm−1, and an initial discharge capacity of 198 mAh g−1 was obtained. After 21 cycles, the retention capacity was 91%. These results indicate a synergistic effect among the materials in the composite.Analytical techniques, such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) were also used to characterize the composite materials.
Key message Relationship between sap flow and functional traits changes with altitude and changes... more Key message Relationship between sap flow and functional traits changes with altitude and changes in water availability can impose a conservative water use in woody species of tropical rainforest. Abstract Using a trait-based approach, we have identified that tropical trees are vulnerable to decreases in water availability, especially in montane areas, where higher radiation and vapor pressure deficits lead to higher water loss from trees. Changes to functional traits are useful descriptors of the response of species to variation in resource availability and environmental conditions. However, how these trait-environment relationships change with altitude remains unclear. We investigated changes in xylem sap flow along an altitudinal variation and evaluated the contribution of morphological traits to total plant water use. We hypothesize that (1) at the Montane forest, plant species will show a more conservative water use and seasonally, there will be a much greater increase in conservative water use during the dry season at the Lowland site, since the climate conditions in the Montane site impose constraints to water use throughout the year. Remarkably, although water is assumed to be a non-limiting resource for Atlantic rainforest in general, we observed ecophysiological adjustments for more conservative water use in Montane forest. Our findings demonstrate that changes to water supply and demand as determined by rainfall, VPD and soil water storage can impose restrictions to water loss which differ across spatio-temporal scales. We suggest that the next steps for research in Montane forest should focus on traits related to hydraulic failure and carbon starvation to address the question whether the higher conservative water use observed at the Montane Forest translates into a higher or lower susceptibility to intensification of drought which might arise due to climate change.
Climate change is predicted to affect the water balance of several ecosystems mostly through chan... more Climate change is predicted to affect the water balance of several ecosystems mostly through changes in the energy budget and hydrological input (rainfall frequency, intensity, and timing). Changes in rainfall patterns and cloudiness directly affect incoming radiation, atmospheric water vapor saturation deficit and soil water availability, the main variables controlling the rates of water uptake and transport along the soil-plant-atmosphere continuum (SPAC). Developing a predictive framework about vegetation responses to a changing climate is challenging because it involves complex non-linear interactions between these environmental variables and species-specific responses. By examining the hydraulic traits of functional groups within plant communities we can better predict the impacts of changes in rainfall regimes within functional groups and therefore, generate more realistic predictions of ecosystem carbon and water balance changes due to local and regional changes in precipitation regimes. In this review, we discuss several aspects of plant hydraulic functioning and then explore how predicted changes in precipitation regimes may affect tree water and carbon balance. We examine the impacts of changes in rainfall patterns on the SPAC and also explore the multiple ways that plants can absorb and transport water. Finally, we explore the diversity of hydraulic traits and potential mechanisms causing large-scale drought-induced mortality recently observed in several ecosystems.
Understanding the environmental factors shaping savannah and tropical forest boundaries is import... more Understanding the environmental factors shaping savannah and tropical forest boundaries is important to predict tropical vegetation responses to climate change and other human-mediated disturbances. To better understand the soil characteristics affecting the distribution of Cerradão (Brazilian woodland savannah) and seasonally dry forest (SDF), two vegetation types occurring next to each other in a similar seasonal climate in south-eastern Brazil, we compared several leaf chemical and morphological traits associated with soil pH and resource availability of Cerradão and SDF woody species. Leaf functional traits were measured for 25 Cerradão and 27 SDF species. We performed between-site comparisons with either all species pooled using phylogenetically independent contrasts or species shared between Cerradão and SDF, as well as congeneric pairs. We found higher specific leaf area and leaf nitrogen, potassium, calcium and sulfur concentrations for SDF species. We did not find higher concentrations for leaf phosphorus and manganese (Mn) for SDF species, despite a higher concentration of these nutrients in SDF soil. Cerradão plants had higher leaf iron (Fe), Mn and aluminium (Al) concentrations. For most of the traits assessed, variance was higher among species and genera than between sites. Nutrients with greater availability in the SDF soil did not invariably exhibit higher concentrations in the leaves of SDF species, indicating that these were not limiting for plant productivity. Higher concentrations in the leaves of Cerradão species for Al, Fe and Mn are probably a consequence of lower soil pH, which increases the availability of these elements. In spite of the differences in belowground resources and the divergence for some traits between Cerradão and SDF, our results show high diversity in leaf functional traits within communities and a similarity of leaf functional traits in closely related species in the contrasting habitats. Besides, we surmise that soil pH is an important factor affecting Cerradão and SDF species distribution, excluding SDF species from more acidic soils, because of the toxic effects of Al, and possibly also Mn and Fe.
Foliar water uptake (FWU) is a common water acquisition mechanism for plants inhabiting temperate... more Foliar water uptake (FWU) is a common water acquisition mechanism for plants inhabiting temperate fog-affected ecosystems, but the prevalence and consequences of this process for the water and carbon balance of tropical cloud forest species are unknown.
Water is a key resource in tropical savannas. Changes in vegetation structure due to land-use cha... more Water is a key resource in tropical savannas. Changes in vegetation structure due to land-use change and increased fire frequency may affect the availability of water and the flux of water through these ecosystems. 2. We compared the seasonal soil moisture dynamics of two adjacent savanna ecosystems with contrasting tree densities in central Brazil. Our goal was to investigate the influence of tree density on deep water uptake, soil water dynamics and evapotranspiration. 3. Soil water was measured using a depth of 7·5 m beneath the tree-dominated cerrado denso ecosystem and to 4 m beneath the grass-dominated campo sujo ecosystem. Plantavailable water (PAW) throughout the cerrado denso soil profile ranged from 293 mm at the end of the dry season to 689 mm during the wet season. In the grass-dominated site, PAW in the profile ranged from 155 to 362 mm. 4. During the dry season, ≈ 82% of the water used in cerrado denso and 67% in campo sujo was extracted from the profile below 1 m. The tree-dominated cerrado denso used 137 mm more water than the grass-dominated campo sujo . Significant deep soil water uptake was also observed during the wet season of 1998, when rainfall was below average. 5. Evapotranspiration (ET) rates (estimated as change in soil moisture over time) were higher in cerrado denso than in campo sujo during both seasons. Estimated ET ranged from 1·4 mm day − 1 during the dry season to 5·8 mm day − 1 for the wet season in cerrado denso , and from 0·9 mm day − 1 in the dry season to 4·5 mm day − 1 in early wet season in campo sujo . The differences in PAW and ET rates between the two ecosystems are associated not only with differences in root distribution, but also with differences in tree densities and the phenology of full-leaf canopies. 6. Our results suggest that deep-rooted plants may contribute significantly to the water balance of cerrado ecosystems, and that the hydrological cycle of this biome could change as woody vegetation is replaced by exotic grasses and agricultural crops.
© springer-Verlag Berlin heidelberg 2013 the S. involucrata individuals. Our results demonstrate ... more © springer-Verlag Berlin heidelberg 2013 the S. involucrata individuals. Our results demonstrate that intraspecific competition was stronger than interspecific competition for S. involucrata, but not for B. attenuata. We conclude that cluster roots of B. attenuata facilitate the acquisition of nutrients by neighbouring shrubs by making P and Mn more available for their neighbours.
O diagnóstico laboratorial da raiva é de suma importância para o controle e prevenção da doença, ... more O diagnóstico laboratorial da raiva é de suma importância para o controle e prevenção da doença, uma vez que os diagnósticos clínicos não são precisos. A imunofluorescência direta (IFD) é o teste mais utilizado e mesmo sendo altamente sensível, acurado e relativamente rápido, pode gerar resultados falsos negativos. Desta forma, recomenda-se o isolamento do vírus da raiva em camundongos (IVC) em amostras de Sistema Nervoso Central (SNC) de animais suspeitos de estarem infectados, teste que atualmente vem sendo substituído em vários laboratórios pelo isolamento viral em cultura de células (IVCC). O objetivo do presente estudo foi comparar a sensibilidade do teste de isolamento do vírus em cultura de células de neuroblastoma de camundongos (N2A), com o teste de IVC e com a IFD, bem como avaliar os resultados obtidos na rotina de diagnóstico do Instituto Pasteur, em relação à redução de custo, tempo e trabalho. Foram analisadas 105 amostras de SNC de diferentes espécies de animais pela IFD, pelo IVC e pelo IVCC: 50 de morcegos, 32 de cães, 13 de raposas e 10 de bovinos. Todas as amostras de morcegos e de bovinos apresentaram resultados concordantes para os três testes, enquanto que as de cães e raposas apresentaram concordância em somente 24 amostras (69%). Com base nestes resultados, a partir de 2004 estabeleceu-se que todas as amostras de morcegos enviadas ao Laboratório do Instituto Pasteur, após o diagnóstico por IFD, seriam submetidas ao IVCC, substituindo o uso de camundongos. No período de janeiro de 2004 a setembro de 2007, foram analisadas 11.298 amostras de morcegos. Um total de 67 amostras positivas por IFD e/ou IVCC foram também submetidas ao IVC e 61 amostras apresentaram resultados concordantes nos três testes, mostrando que o uso de células N2A é mais sensível para o isolamento de "vírus de rua" em uma rotina laboratorial para amostras de morcegos, sendo rápido e de menor custo do que o IVC.
concentrations. We conclude that the sand-binding root specialization in this nonmycorrhizal cact... more concentrations. We conclude that the sand-binding root specialization in this nonmycorrhizal cactus functions similar to that of cluster roots, which efficiently enhance P acquisition in other habitats with very low P availability.
Measurement, 2000
In a hand-operated torque primary standard machine, many parameters are very peculiar and can rea... more In a hand-operated torque primary standard machine, many parameters are very peculiar and can really influence the final results of a calibration. The paper presents studies to quantify how these parameters act and are able to influence the main operations of this type of machine. In conclusion, it is demonstrated that only an initial characterisation of the system is not
Acta Oecologica-international Journal of Ecology, 2010
Environmental conditions can have major influences in shaping biophysical properties of leaf surf... more Environmental conditions can have major influences in shaping biophysical properties of leaf surfaces. In moist environments, high leaf water repellency (LWR) is expected because the presence of a water film on leaf surfaces can block stomatal pores, reduce the diffusion of CO 2 , ...
Terrestrial Ecology, 2007
Annals of botany, 2014
† Background Tropical montane cloud forests (TMCFs) are characterized by a unique set of biologic... more † Background Tropical montane cloud forests (TMCFs) are characterized by a unique set of biological and hydroclimatic features, including frequent and/or persistent fog, cool temperatures, and high biodiversity and endemism. These forests are one of the most vulnerable ecosystems to climate change given their small geographic range, high endemism and dependence on a rare microclimatic envelope. The frequency of atmospheric water deficits for some TMCFs is likely to increase in the future, but the consequences for the integrity and distribution of these ecosystems are uncertain. In order to investigate plant and ecosystem responses to climate change, we need to know how TMCF species function in response to current climate, which factors shape function and ecology most and how these will change into the future. † Scope This review focuses on recent advances in ecophysiological research of TMCF plants to establish a link between TMCF hydrometeorological conditions and vegetation distribution, functioning and survival. The hydraulic characteristics of TMCF trees are discussed, together with the prevalence and ecological consequences of foliar uptake of fog water (FWU) in TMCFs, a key process that allows efficient acquisition of water during cloud immersion periods, minimizing water deficits and favouring survival of species prone to drought-induced hydraulic failure. † Conclusions Fog occurrence is the single most important microclimatic feature affecting the distribution and function of TMCF plants. Plants in TMCFs are very vulnerable to drought ( possessing a small hydraulic safety margin), and the presence of fog and FWU minimizes the occurrence of tree water deficits and thus favours the survival of TMCF trees where such deficits may occur. Characterizing the interplay between microclimatic dynamics and plant water relations is key to foster more realistic projections about climate change effects on TMCF functioning and distribution.
The New phytologist, 2015
In Brazil, the campos rupestres occur over the Brazilian shield, and are characterized by acidic ... more In Brazil, the campos rupestres occur over the Brazilian shield, and are characterized by acidic nutrient-impoverished soils, which are particularly low in phosphorus (P). Despite recognition of the campos rupestres as a global biodiversity hotspot, little is known about the diversity of P-acquisition strategies and other aspects of plant mineral nutrition in this region. To explore nutrient-acquisition strategies and assess aspects of plant P nutrition, we measured leaf P and nitrogen (N) concentrations, characterized root morphology and determined the percentage arbuscular mycorrhizal (AM) colonization of 50 dominant species in six communities, representing a gradient of soil P availability. Leaf manganese (Mn) concentration was measured as a proxy for carboxylate-releasing strategies. Communities on the most P-impoverished soils had the highest proportion of nonmycorrhizal (NM) species, the lowest percentage of mycorrhizal colonization, and the greatest diversity of root specializations. The large spectrum of leaf P concentration and variation in root morphologies show high functional diversity for nutritional strategies. Higher leaf Mn concentrations were observed in NM compared with AM species, indicating that carboxylate-releasing P-mobilizing strategies are likely to be present in NM species. The soils of the campos rupestres are similar to the most P-impoverished soils in the world. The prevalence of NM strategies indicates a strong global functional convergence in plant mineral nutrition strategies among severely P-impoverished ecosystems.
Journal of Power Sources, 2009
The effect of adding a non-ionic surfactant to disperse oxide particles on the electrochemical pe... more The effect of adding a non-ionic surfactant to disperse oxide particles on the electrochemical performance of PAni/LiMnNiO4 composites is evaluated by using cyclic voltammetry (CV), impedance measurements and constant-current charge/discharge cycling techniques. Three surfactants based on ethoxylated (EO) and propoxylated (PO) lauryl alcohols (3EO/6PO, L306; 4EO/5PO, L405; and 6EO/3PO, L603) were investigated. For comparative purposes, the oxide and polyaniline were prepared by sol–gel and chemical methods and were also investigated for their physical and electrochemical performances. By galvanostatic charge–discharge tests, the PAni/LiMnNiO4 L306 composite showed a better electrochemical performance than each single component and other composites (PAni/LiMnNiO4 L405 and PAni/LiMnNiO4 L603). The electrical conductivity of this composite reached 21.7 S cm−1, and an initial discharge capacity of 198 mAh g−1 was obtained. After 21 cycles, the retention capacity was 91%. These results indicate a synergistic effect among the materials in the composite.Analytical techniques, such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) were also used to characterize the composite materials.
Key message Relationship between sap flow and functional traits changes with altitude and changes... more Key message Relationship between sap flow and functional traits changes with altitude and changes in water availability can impose a conservative water use in woody species of tropical rainforest. Abstract Using a trait-based approach, we have identified that tropical trees are vulnerable to decreases in water availability, especially in montane areas, where higher radiation and vapor pressure deficits lead to higher water loss from trees. Changes to functional traits are useful descriptors of the response of species to variation in resource availability and environmental conditions. However, how these trait-environment relationships change with altitude remains unclear. We investigated changes in xylem sap flow along an altitudinal variation and evaluated the contribution of morphological traits to total plant water use. We hypothesize that (1) at the Montane forest, plant species will show a more conservative water use and seasonally, there will be a much greater increase in conservative water use during the dry season at the Lowland site, since the climate conditions in the Montane site impose constraints to water use throughout the year. Remarkably, although water is assumed to be a non-limiting resource for Atlantic rainforest in general, we observed ecophysiological adjustments for more conservative water use in Montane forest. Our findings demonstrate that changes to water supply and demand as determined by rainfall, VPD and soil water storage can impose restrictions to water loss which differ across spatio-temporal scales. We suggest that the next steps for research in Montane forest should focus on traits related to hydraulic failure and carbon starvation to address the question whether the higher conservative water use observed at the Montane Forest translates into a higher or lower susceptibility to intensification of drought which might arise due to climate change.
Climate change is predicted to affect the water balance of several ecosystems mostly through chan... more Climate change is predicted to affect the water balance of several ecosystems mostly through changes in the energy budget and hydrological input (rainfall frequency, intensity, and timing). Changes in rainfall patterns and cloudiness directly affect incoming radiation, atmospheric water vapor saturation deficit and soil water availability, the main variables controlling the rates of water uptake and transport along the soil-plant-atmosphere continuum (SPAC). Developing a predictive framework about vegetation responses to a changing climate is challenging because it involves complex non-linear interactions between these environmental variables and species-specific responses. By examining the hydraulic traits of functional groups within plant communities we can better predict the impacts of changes in rainfall regimes within functional groups and therefore, generate more realistic predictions of ecosystem carbon and water balance changes due to local and regional changes in precipitation regimes. In this review, we discuss several aspects of plant hydraulic functioning and then explore how predicted changes in precipitation regimes may affect tree water and carbon balance. We examine the impacts of changes in rainfall patterns on the SPAC and also explore the multiple ways that plants can absorb and transport water. Finally, we explore the diversity of hydraulic traits and potential mechanisms causing large-scale drought-induced mortality recently observed in several ecosystems.
Understanding the environmental factors shaping savannah and tropical forest boundaries is import... more Understanding the environmental factors shaping savannah and tropical forest boundaries is important to predict tropical vegetation responses to climate change and other human-mediated disturbances. To better understand the soil characteristics affecting the distribution of Cerradão (Brazilian woodland savannah) and seasonally dry forest (SDF), two vegetation types occurring next to each other in a similar seasonal climate in south-eastern Brazil, we compared several leaf chemical and morphological traits associated with soil pH and resource availability of Cerradão and SDF woody species. Leaf functional traits were measured for 25 Cerradão and 27 SDF species. We performed between-site comparisons with either all species pooled using phylogenetically independent contrasts or species shared between Cerradão and SDF, as well as congeneric pairs. We found higher specific leaf area and leaf nitrogen, potassium, calcium and sulfur concentrations for SDF species. We did not find higher concentrations for leaf phosphorus and manganese (Mn) for SDF species, despite a higher concentration of these nutrients in SDF soil. Cerradão plants had higher leaf iron (Fe), Mn and aluminium (Al) concentrations. For most of the traits assessed, variance was higher among species and genera than between sites. Nutrients with greater availability in the SDF soil did not invariably exhibit higher concentrations in the leaves of SDF species, indicating that these were not limiting for plant productivity. Higher concentrations in the leaves of Cerradão species for Al, Fe and Mn are probably a consequence of lower soil pH, which increases the availability of these elements. In spite of the differences in belowground resources and the divergence for some traits between Cerradão and SDF, our results show high diversity in leaf functional traits within communities and a similarity of leaf functional traits in closely related species in the contrasting habitats. Besides, we surmise that soil pH is an important factor affecting Cerradão and SDF species distribution, excluding SDF species from more acidic soils, because of the toxic effects of Al, and possibly also Mn and Fe.
Foliar water uptake (FWU) is a common water acquisition mechanism for plants inhabiting temperate... more Foliar water uptake (FWU) is a common water acquisition mechanism for plants inhabiting temperate fog-affected ecosystems, but the prevalence and consequences of this process for the water and carbon balance of tropical cloud forest species are unknown.
Water is a key resource in tropical savannas. Changes in vegetation structure due to land-use cha... more Water is a key resource in tropical savannas. Changes in vegetation structure due to land-use change and increased fire frequency may affect the availability of water and the flux of water through these ecosystems. 2. We compared the seasonal soil moisture dynamics of two adjacent savanna ecosystems with contrasting tree densities in central Brazil. Our goal was to investigate the influence of tree density on deep water uptake, soil water dynamics and evapotranspiration. 3. Soil water was measured using a depth of 7·5 m beneath the tree-dominated cerrado denso ecosystem and to 4 m beneath the grass-dominated campo sujo ecosystem. Plantavailable water (PAW) throughout the cerrado denso soil profile ranged from 293 mm at the end of the dry season to 689 mm during the wet season. In the grass-dominated site, PAW in the profile ranged from 155 to 362 mm. 4. During the dry season, ≈ 82% of the water used in cerrado denso and 67% in campo sujo was extracted from the profile below 1 m. The tree-dominated cerrado denso used 137 mm more water than the grass-dominated campo sujo . Significant deep soil water uptake was also observed during the wet season of 1998, when rainfall was below average. 5. Evapotranspiration (ET) rates (estimated as change in soil moisture over time) were higher in cerrado denso than in campo sujo during both seasons. Estimated ET ranged from 1·4 mm day − 1 during the dry season to 5·8 mm day − 1 for the wet season in cerrado denso , and from 0·9 mm day − 1 in the dry season to 4·5 mm day − 1 in early wet season in campo sujo . The differences in PAW and ET rates between the two ecosystems are associated not only with differences in root distribution, but also with differences in tree densities and the phenology of full-leaf canopies. 6. Our results suggest that deep-rooted plants may contribute significantly to the water balance of cerrado ecosystems, and that the hydrological cycle of this biome could change as woody vegetation is replaced by exotic grasses and agricultural crops.
© springer-Verlag Berlin heidelberg 2013 the S. involucrata individuals. Our results demonstrate ... more © springer-Verlag Berlin heidelberg 2013 the S. involucrata individuals. Our results demonstrate that intraspecific competition was stronger than interspecific competition for S. involucrata, but not for B. attenuata. We conclude that cluster roots of B. attenuata facilitate the acquisition of nutrients by neighbouring shrubs by making P and Mn more available for their neighbours.
O diagnóstico laboratorial da raiva é de suma importância para o controle e prevenção da doença, ... more O diagnóstico laboratorial da raiva é de suma importância para o controle e prevenção da doença, uma vez que os diagnósticos clínicos não são precisos. A imunofluorescência direta (IFD) é o teste mais utilizado e mesmo sendo altamente sensível, acurado e relativamente rápido, pode gerar resultados falsos negativos. Desta forma, recomenda-se o isolamento do vírus da raiva em camundongos (IVC) em amostras de Sistema Nervoso Central (SNC) de animais suspeitos de estarem infectados, teste que atualmente vem sendo substituído em vários laboratórios pelo isolamento viral em cultura de células (IVCC). O objetivo do presente estudo foi comparar a sensibilidade do teste de isolamento do vírus em cultura de células de neuroblastoma de camundongos (N2A), com o teste de IVC e com a IFD, bem como avaliar os resultados obtidos na rotina de diagnóstico do Instituto Pasteur, em relação à redução de custo, tempo e trabalho. Foram analisadas 105 amostras de SNC de diferentes espécies de animais pela IFD, pelo IVC e pelo IVCC: 50 de morcegos, 32 de cães, 13 de raposas e 10 de bovinos. Todas as amostras de morcegos e de bovinos apresentaram resultados concordantes para os três testes, enquanto que as de cães e raposas apresentaram concordância em somente 24 amostras (69%). Com base nestes resultados, a partir de 2004 estabeleceu-se que todas as amostras de morcegos enviadas ao Laboratório do Instituto Pasteur, após o diagnóstico por IFD, seriam submetidas ao IVCC, substituindo o uso de camundongos. No período de janeiro de 2004 a setembro de 2007, foram analisadas 11.298 amostras de morcegos. Um total de 67 amostras positivas por IFD e/ou IVCC foram também submetidas ao IVC e 61 amostras apresentaram resultados concordantes nos três testes, mostrando que o uso de células N2A é mais sensível para o isolamento de "vírus de rua" em uma rotina laboratorial para amostras de morcegos, sendo rápido e de menor custo do que o IVC.
concentrations. We conclude that the sand-binding root specialization in this nonmycorrhizal cact... more concentrations. We conclude that the sand-binding root specialization in this nonmycorrhizal cactus functions similar to that of cluster roots, which efficiently enhance P acquisition in other habitats with very low P availability.
Measurement, 2000
In a hand-operated torque primary standard machine, many parameters are very peculiar and can rea... more In a hand-operated torque primary standard machine, many parameters are very peculiar and can really influence the final results of a calibration. The paper presents studies to quantify how these parameters act and are able to influence the main operations of this type of machine. In conclusion, it is demonstrated that only an initial characterisation of the system is not
Acta Oecologica-international Journal of Ecology, 2010
Environmental conditions can have major influences in shaping biophysical properties of leaf surf... more Environmental conditions can have major influences in shaping biophysical properties of leaf surfaces. In moist environments, high leaf water repellency (LWR) is expected because the presence of a water film on leaf surfaces can block stomatal pores, reduce the diffusion of CO 2 , ...
Terrestrial Ecology, 2007
Annals of botany, 2014
† Background Tropical montane cloud forests (TMCFs) are characterized by a unique set of biologic... more † Background Tropical montane cloud forests (TMCFs) are characterized by a unique set of biological and hydroclimatic features, including frequent and/or persistent fog, cool temperatures, and high biodiversity and endemism. These forests are one of the most vulnerable ecosystems to climate change given their small geographic range, high endemism and dependence on a rare microclimatic envelope. The frequency of atmospheric water deficits for some TMCFs is likely to increase in the future, but the consequences for the integrity and distribution of these ecosystems are uncertain. In order to investigate plant and ecosystem responses to climate change, we need to know how TMCF species function in response to current climate, which factors shape function and ecology most and how these will change into the future. † Scope This review focuses on recent advances in ecophysiological research of TMCF plants to establish a link between TMCF hydrometeorological conditions and vegetation distribution, functioning and survival. The hydraulic characteristics of TMCF trees are discussed, together with the prevalence and ecological consequences of foliar uptake of fog water (FWU) in TMCFs, a key process that allows efficient acquisition of water during cloud immersion periods, minimizing water deficits and favouring survival of species prone to drought-induced hydraulic failure. † Conclusions Fog occurrence is the single most important microclimatic feature affecting the distribution and function of TMCF plants. Plants in TMCFs are very vulnerable to drought ( possessing a small hydraulic safety margin), and the presence of fog and FWU minimizes the occurrence of tree water deficits and thus favours the survival of TMCF trees where such deficits may occur. Characterizing the interplay between microclimatic dynamics and plant water relations is key to foster more realistic projections about climate change effects on TMCF functioning and distribution.
The New phytologist, 2015
In Brazil, the campos rupestres occur over the Brazilian shield, and are characterized by acidic ... more In Brazil, the campos rupestres occur over the Brazilian shield, and are characterized by acidic nutrient-impoverished soils, which are particularly low in phosphorus (P). Despite recognition of the campos rupestres as a global biodiversity hotspot, little is known about the diversity of P-acquisition strategies and other aspects of plant mineral nutrition in this region. To explore nutrient-acquisition strategies and assess aspects of plant P nutrition, we measured leaf P and nitrogen (N) concentrations, characterized root morphology and determined the percentage arbuscular mycorrhizal (AM) colonization of 50 dominant species in six communities, representing a gradient of soil P availability. Leaf manganese (Mn) concentration was measured as a proxy for carboxylate-releasing strategies. Communities on the most P-impoverished soils had the highest proportion of nonmycorrhizal (NM) species, the lowest percentage of mycorrhizal colonization, and the greatest diversity of root specializations. The large spectrum of leaf P concentration and variation in root morphologies show high functional diversity for nutritional strategies. Higher leaf Mn concentrations were observed in NM compared with AM species, indicating that carboxylate-releasing P-mobilizing strategies are likely to be present in NM species. The soils of the campos rupestres are similar to the most P-impoverished soils in the world. The prevalence of NM strategies indicates a strong global functional convergence in plant mineral nutrition strategies among severely P-impoverished ecosystems.