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121.
Ángeles G. Mayor Sonia Kéfi Susana Bautista Francisco Rodríguez Fabrizio Cartení Max Rietkerk 《Landscape Ecology》2013,28(5):931-942
Conceptual frameworks of dryland degradation commonly include ecohydrological feedbacks between landscape spatial organization and resource loss, so that decreasing cover and size of vegetation patches result in higher water and soil losses, which lead to further vegetation loss. However, the impacts of these feedbacks on dryland dynamics in response to external stress have barely been tested. Using a spatially-explicit model, we represented feedbacks between vegetation pattern and landscape resource loss by establishing a negative dependence of plant establishment on the connectivity of runoff-source areas (e.g., bare soils). We assessed the impact of various feedback strengths on the response of dryland ecosystems to changing external conditions. In general, for a given external pressure, these connectivity-mediated feedbacks decrease vegetation cover at equilibrium, which indicates a decrease in ecosystem resistance. Along a gradient of gradual increase of environmental pressure (e.g., aridity), the connectivity-mediated feedbacks decrease the amount of pressure required to cause a critical shift to a degraded state (ecosystem resilience). If environmental conditions improve, these feedbacks increase the pressure release needed to achieve the ecosystem recovery (restoration potential). The impact of these feedbacks on dryland response to external stress is markedly non-linear, which relies on the non-linear negative relationship between bare-soil connectivity and vegetation cover. Modelling studies on dryland vegetation dynamics not accounting for the connectivity-mediated feedbacks studied here may overestimate the resistance, resilience and restoration potential of drylands in response to environmental and human pressures. Our results also suggest that changes in vegetation pattern and associated hydrological connectivity may be more informative early-warning indicators of dryland degradation than changes in vegetation cover. 相似文献
122.
Land-use and land-cover change processes in the Upper Uruguay Basin: linking environmental and socioeconomic variables 总被引:1,自引:0,他引:1
de Freitas Marcos Wellausen Dias Santos João Roberto dos Alves Diógenes Salas 《Landscape Ecology》2013,28(2):311-327
Landscape Ecology - Land-use and land-cover change affects both ecological and socioeconomic processes, motivating the integration of environmental and socioeconomic data to help understand this... 相似文献
123.
Dueñas M González-Manzano S Surco-Laos F González-Paramas A Santos-Buelga C 《Journal of agricultural and food chemistry》2012,60(14):3592-3598
Different monosulfates of quercetin and epicatechin with metabolic interest were obtained by hemisynthesis and characterized regarding their chromatographic behavior and absorption and mass spectra. Three of these compounds were further isolated, and their structures were elucidated by mass spectrometry and (1)H and (13)C nuclear magnetic resonance using one- and two-dimensional techniques (heteronuclear single-quantum coherence and heteronuclear multiple-bond correlation). The calculation of the proton and carbon shifts caused by sulfation allowed for the assignment of the position of the sulfate group in the flavonoids, so that the compounds were identified as quercetin-3'-O-sulfate, quercetin 4'-O-sulfate, and epicatechin 4'-O-sulfate. It was found that sulfation at position 3' induced a large upfield shift in the carbon bearing the sulfate group and downfield displacements of the adjacent carbons, whereas no significant upfield or downfield shifts were observed with respect to the parent flavonoid when sulfation was produced at position 4'. 相似文献
124.
F Torchio S Giacosa SR Segade F Mattivi V Gerbi L Rolle 《Journal of agricultural and food chemistry》2012,60(36):9006-9016
An instrumental texture analysis method has been optimized for the differentiation of grape ripening stages based on the simultaneous determination of mechanical and acoustic parameters of the seeds. Two factorial central composite design was used to optimize the most influencing operative conditions (speed and deformation) on mechanical and acoustic measurements. This experimental design in combination with response surface methodology showed that the most responsive parameters to changes in seeds during ripening were Young's modulus of elasticity, many acoustic parameters measured with instrumental gain set to 0 (acoustic energy, linear distance, and number of peaks) and others measured at 24 dB gain (linear distance, number of peaks, and average pressure level). However, the optimal operative conditions depended on the texture parameter used. A correlation study between texture parameters and phenolic compounds of the seeds revealed that acoustic parameters like the average pressure level could be proposed as phenolic maturity indices. 相似文献
125.
Maria João Verdasca Ana Sofia Leitão Joana Santana Miguel Porto Susana Dias Pedro Beja 《Biological conservation》2012,146(1):14-23
In cultural landscapes there are often negative biodiversity consequences of agricultural abandonment and subsequent scrub and forest encroachment, due to homogenization and the loss of early-successional habitats. The common forestry practice of removing understory vegetation to prevent fire hazard (fuel management) probably has the side-effect of ameliorating these consequences, but it is uncertain whether it effectively restores habitats for early-successional species. Here we examine the influence of time since fuel management and management frequency on butterfly assemblages, using a chronosequence of cork oak (Quercus suber) stands spanning about 70 years. Overall species richness increased immediately after management and abundances peaked about 2–3 years later, while both declined thereafter for about 10–20 years to pre-disturbance levels. Richness and abundances were also much higher in recurrently managed stands. Most life history groups showed successional trends similar to the overall species richness and abundances, though consistent positive effects of fuel management were only observed for species with univoltine life cycle, herbaceous layer feeding, larval overwintering, and intermediate body size. Individual species were largely associated with recent and recurrent management, though a few specialists occurred most often in undisturbed stands. These findings suggest that fuel management at <10 years intervals is strongly positive for butterfly assemblages in landscapes under land abandonment. However, to maintain the overall forest biodiversity it is critical that patches of undisturbed habitat are also retained at the landscape scale. 相似文献
126.
Susana Peña-Rodríguez Xabier Pontevedra-Pombal David Fernández-Calviño Teresa Taboada Manuel Arias-Estévez Antonio Martínez-Cortizas Juan Carlos Nóvoa-Muñoz Eduardo García-Rodeja 《Journal of Soils and Sediments》2012,12(4):542-555
Purpose
Volcanoes are a natural source of Hg, whose deposition can occur in neighbouring soils. This study examines the role of soil compounds in the geochemical behaviour of total Hg (Hg T ) in volcanic soils. An estimation of Hg from lithological origin is also assessed to ascertain the relevance of other sources in Hg T accumulated in volcanic soils. 相似文献127.
Glanzmann thrombasthenia (GT) is characterized by a defect of platelet aggregation. This autosomal recessive genetic disorder is caused by an abnormality of the platelet glycoprotein receptors alpha IIb or beta III. Recently, we identified a horse with clinical and pathological features of GT. The aim of this study was to describe this case of GT at the molecular level. A point mutation from G to C in exon 2 of ITGA2B causing a substitution of the expected amino acid arginine 72 (Arg(72)) by a proline (Pro(72)) was encountered. This amino acid change may result in abnormal structural conformations that yield an inactive alpha IIb subunit. The genomic DNA analysis showed that this horse was homozygous for the missense mutation. 相似文献
128.
Susana Guill��n Teresa Terrazas Erick De la Barrera Alejandro Casas 《Genetic Resources and Crop Evolution》2011,58(3):409-423
Germination of wild and managed populations of columnar cacti was compared to analyze differences associated to management intensity. The species studied: Polaskia chende, Escontria chiotilla, Myrtillocactus schenckii, Polaskia chichipe, and Stenocereus pruinosus are in a gradient from lower to higher management intensity, respectively. Within each species wild, silvicultural, and cultivated populations also represent a gradient from lower to higher management intensity. We hypothesized that seeds of plants under higher management intensity would require more water to germinate than others since managed environments are relatively wetter than unmanaged environments. Such pattern could be visualized within and among species according to management intensity. We tested germination of seeds from different populations of the different species to the water potentials: 0.0, ?0.2, ?0.4, ?0.6, ?0.8, and ?1.0 MPa. In all species studied seeds of managed populations had significantly more mass than seeds from wild populations. Each species had different susceptibility to water availability decrease, which could be related to particular adaptations to drought resistance. Stenocereus pruinosus and Polaskia chende were the most and least susceptible species, respectively. In control treatments of all species, seeds of managed populations had higher germination rate than seeds from wild populations, but when water availability decreased the pattern was the contrary. Our results suggest that artificial selection for larger fruits and heavier seeds in plants established in wetter environments have affected germination patterns. Although species have particular critical points of water availability for germination, differences in germination patterns are more pronounced according to management and artificial selection intensity. 相似文献
129.
Identification and quantification of major steviol glycosides in Stevia rebaudiana purified extracts by 1H NMR spectroscopy 总被引:1,自引:0,他引:1
Pieri V Belancic A Morales S Stuppner H 《Journal of agricultural and food chemistry》2011,59(9):4378-4384
The use of (1)H NMR spectroscopy for the characterization of Stevia rebaudiana extracts is presented. The developed method allows qualitative and quantitative determination of the major steviol glycosides in purified extracts and fractions obtained from various stages of the purification process. Moreover, it proved to be a powerful tool to differentiate between glycosides which are naturally occurring in the stevia plant and artifacts formed in the course of the manufacturing process. Identification of steviol glycosides was achieved by the use of 2D NMR techniques, whereas quantification is based on qHNMR using anthracene as internal standard. The solvent mixture pyridine-d(5)-DMSO-d(6) (6:1) enabled satisfactory separation of the signals to be integrated. Validation of the method was performed in terms of specificity, precision, accuracy, linearity, robustness, and stability. Quantitative results were compared to those obtained with the JECFA HPLC-UV method and were found to be in reasonable agreement. NMR analysis does not rely on the use of reference compounds and enables significantly faster analysis compared to HPLC-UV. Thus, NMR represents a feasible alternative to HPLC-based methods for the quality control of Stevia rebaudiana extracts. 相似文献
130.
Mar��a Soledad Fuentes Juliana Mar��a S��ez Claudia Susana Benimeli Mar��a Julia Amoroso 《Water, air, and soil pollution》2011,222(1-4):217-231
The current study aimed to compare lindane degradation by pure and mixed cultures of Streptomyces sp. Cell-free extracts were assayed for potentiating dechlorinase activity and, based on these results, consortia of two to six microorganisms were assayed for their growth on and degradation of lindane. Furthermore, the role of bacterial consortia of lindane-degrading strains was examined in lindane decontamination soil assays. Four actinobacteria, previously isolated from a pesticide-contaminated area, were selected because of their tolerance to lindane and their ability to use the pesticide as sole carbon source. These strains as well as Streptomyces sp. M7 and Streptomyces coelicolor A3 were used to study specific dechlorinase activity (SDA) and lindane removal in mixed cultures. Pure cultures presented SDA in the presence of 1.66 mg L-1 lindane as carbon source. SDA was improved by certain mixed cultures until 12 times compared with pure cultures. Mixed cultures with two, three, and four strains showed maximum lindane removal of 46% to 68%, whereas combinations of five and six strains did not efficiently remove the pesticide from the culture medium. The Streptomyces sp. A2, A5, M7, and A11 consortium presented the lowest ratio between residual lindane concentration and SDA and could be a promising tool for lindane biodegradation. 相似文献