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排序方式: 共有392条查询结果,搜索用时 187 毫秒
41.
Britta Gribsholt Eric Struyf Anton Tramper Maria G. I. Andersson Natacha Brion Loreto De Brabandere Stefan Van Damme Patrick Meire Jack J. Middelburg Frank Dehairs Henricus T. S. Boschker 《Biogeochemistry》2006,80(3):289-298
The fate and transport of watershed-derived ammonium in a tidal freshwater marsh fringing the nutrient rich Scheldt River,
Belgium, was quantified in a whole ecosystem 15N labeling experiment. In late summer (September) we added 15N-NH4+ to the flood water entering a 3477 m2 tidal freshwater marsh area, and traced the ammonium processing and retention in four subsequent tide cycles. In this paper
we present the results for the water-phase components of the marsh system and compare them to a similar experiment conducted
in spring/early summer (May). Changes in concentration and isotopic enrichment of NO3− + NO2−, N2O, N2, NH4+ and suspended particulate nitrogen (SPN) were measured in concert with a mass balance study. All analyzed N-pools were labeled,
and 49% of the added 15NH4+ was retained or transformed. The most important pool for 15N was nitrate, accounting for 17% of 15N-transformation. N2, N2O and SPN accounted for 2.4, 0.02 and 1.4%, respectively. The temporal and spatial patterns of 15N transformation in the water phase component of the system were remarkably similar to those observed in May, indicating good
reproducibility of the whole ecosystem labeling approach, but the absolute ammonium transformation rate was 3 times higher
in May. While the marsh surface area was crucial for nitrification in May this was less pronounced in September. Denitrification,
on the other hand, appeared more important in September compared to May. 相似文献
42.
Gasparini F Andres H Flor PJ Heinrich M Inderbitzin W Lingenhöhl K Müller H Munk VC Omilusik K Stierlin C Stoehr N Vranesic I Kuhn R 《Bioorganic & medicinal chemistry letters》2002,12(3):407-409
The synthesis of a new potent, subtype-selective radioligand [(3)H]-M-MPEP (2-methyl-6-((3-methoxyphenyl)ethynyl)-pyridine) and its in vitro pharmacological characteristics are described. Science Ltd. 相似文献
43.
Bolduc V Baraghis E Duquette N Thorin-Trescases N Lambert J Lesage F Thorin E 《American journal of physiology. Heart and circulatory physiology》2012,302(6):H1330-H1339
Endothelial dysfunction and oxidative stress contribute to the atherosclerotic process that includes stiffening of large peripheral arteries. In contrast, our laboratory previously reported a paradoxical increase in cerebrovascular compliance in LDLr(-/-):hApoB(+/+) atherosclerotic (ATX) mice (7). We hypothesized that prevention of cerebral artery endothelial dysfunction with a chronic dietary antioxidant intake would normalize the changes in cerebral artery wall structure and biomechanics and prevent the decline in basal cerebral blood flow associated with atherosclerosis. Three-month-old ATX mice were treated, or not, for 3 mo with the polyphenol (+)-catechin (CAT; 30 mg·kg(-1)·day(-1)) and compared with wild-type controls. In isolated, pressurized cerebral arteries from ATX mice, CAT prevented endothelial dysfunction (deterioration of endothelium-dependent, flow-mediated dilations; P < 0.05), the inward hypertrophic structural remodeling (increase in the wall-to-lumen ratio; P < 0.05), and the rise in cerebrovascular compliance (rightward shift of the stress-strain curve measured in passive conditions, reflecting mechanical properties of the arterial wall; P < 0.05). Doppler optical coherence tomography imaging in vivo confirmed these findings, showing that cerebral compliance was higher in ATX mice and normalized by CAT (P < 0.05). CAT also prevented basal cerebral hypoperfusion in ATX mice (P < 0.05). Active remodeling of the cerebrovascular wall in ATX mice was further suggested by the increase (P < 0.05) in pro-metalloproteinase-9 activity, which was normalized by CAT. We conclude that, by preserving the endothelial function, a chronic treatment with CAT prevents the deleterious effect of severe dyslipidemia on cerebral artery wall structure and biomechanical properties, contributing to preserving resting cerebral blood flow. 相似文献
44.
45.
Kerzerho J Wunsch D Szely N Meyer HA Lurz L Röse L Wahn U Akbari O Stock P 《Journal of immunology (Baltimore, Md. : 1950)》2012,188(1):470-476
Respiratory exposure to allergen induces T cell tolerance and protection against the development of airway hyperactivity in animal models of asthma. Whereas systemic administration of dexamethasone during the delivery of respiratory Ag has been suggested to prevent the development of mucosal tolerance, the effects of local administration of corticosteroids, first-line treatment for patients with bronchial asthma, on mucosal tolerance remain unknown. To analyze the effects of systemic versus local administration of different types of corticosteroids on the development of mucosal tolerance, mice were exposed to respiratory allergen to induce mucosal tolerance with or without systemic or intranasal application of different doses of dexamethasone or prednisolone. After the induction of mucosal tolerance, proliferation of T cells was inhibited in tolerized mice, whereas systemic applications of corticosteroids restored T cell proliferation and secretion of Th2 cytokines. In contrast, inhaled corticosteroids showed no effect on both T cell proliferation and cytokine secretion. In addition, mice systemically treated with corticosteroids showed an increased airway hyperactivity with a significant lung inflammation, but also an increased T effector cells/regulatory T cells ratio in the second lymphoid organs when compared with mice that receive corticosteroids by inhalation. These results demonstrate that local administration of corticosteroids has no effect on the development of immune tolerance in contrast to systemically applied corticosteroids. Furthermore, although different concentrations of corticosteroids are administered to patients, our results demonstrated that the route of administration rather than the doses affects the effect of corticosteroids on respiratory tolerance induction. Considering the broad application of corticosteroids in patients with allergic disease and asthma, the route of administration of steroid substances seems crucial in terms of treatment and potential side effects. These findings may help elucidate the apparently contradicting results of corticosteroid treatment in allergic diseases. 相似文献
46.
Natacha Coelho Sandra Gonçalves María Elena González-Benito Anabela Romano 《Plant Growth Regulation》2012,66(1):69-74
The aim of this work was to develop an in vitro propagation protocol for the endangered species Thymus lotocephalus using seedlings as explants. Several macronutrient concentrations of Murashige and Skoog medium (MS), cytokinin types and concentrations, and cytokinin/auxin combinations were tested to assess the shoots’ proliferation capacity. Although the best proliferation results were obtained with 6-benzyladenine, high percentages of hyperhidric shoots were observed. Because high proliferation of healthy shoots was observed in MS medium that was free of plant growth regulators, this medium was chosen for proliferation studies. The best rooting results were achieved in ¼MS medium without auxins (92.00 ± 6.11%, 6.54 ± 0.52 and 1.60 ± 0.10 cm regarding rooting frequency, number of roots per shoot and longest roots, respectively) or supplemented with 0.5 mg l?1 indole-3-acetic acid (98.00 ± 2.11%, 11.14 ± 0.75 and 2.40 ± 0.24 cm, respectively). Plantlets were successfully acclimatised to ex vitro conditions with a survival rate of 93.33%. With the development of this micropropagation protocol, an important contribution has been made to the conservation of the endangered species T. lotocephalus. 相似文献
47.
Anatoly Peretyatko Samuel Teissier Sylvia De Backer Ludwig Triest 《Hydrobiologia》2012,689(1):131-146
Nutrient enrichment of aquatic ecosystems caused dramatic increase in the frequency, magnitude and duration of cyanobacterial
blooms. Such blooms may cause fish kills, have adverse health effects on humans and contribute to the loss of biodiversity
in aquatic ecosystems. Some 50 eutrophic to hypereutrophic ponds from the Brussels Capital Region (Belgium) were studied between
2003 and 2009. A number of the ponds studied are prone to persistent cyanobacterial blooms. Because of the related health
concerns and adverse effects on ecological quality of the affected ponds, a tool for assessment of the risk of cyanobacterial
bloom occurrence was needed. The data acquired showed that cyanobacteria have threshold relationships with most of the environmental
factors that control them. This is negatively reflected on the predictive capacity of conventional statistical methods based
on linear relationships. Therefore, classification trees designed for the treatment of complex data and non-linear relationships
were used to assess the risk of cyanobacterial bloom occurrence. The main factors determining cyanobacterial bloom development
appeared to be phytoplankton biomass, pH and, to a lesser degree, nitrogen availability. These results suggest that to outcompete
eukaryotic phytoplankters cyanobacteria need the presence of environmental constraints: carbon limitation, light limitation
and nitrogen limitation, for which they developed a number of adaptations. In the absence of constraints, eukaryotic phytoplankters
appear to be more competitive. Therefore, prior build up of phytoplankton biomass seems to be essential for cyanobacterial
dominance. Classification trees proved to be an efficient tool for the bloom risk assessment and allowed the main factors
controlling bloom development to be identified as well as the risk of bloom occurrence corresponding to the conditions determined
by these factors to be quantified. The results produced by the classification trees are consistent with those obtained earlier
by probabilistic approach to bloom risk assessment. They can facilitate planning management interventions and setting restoration
priorities. 相似文献
48.
Stabilizing the clear-water state in eutrophic ponds after biomanipulation: submerged vegetation versus fish recolonization 总被引:2,自引:0,他引:2
Biomanipulation through fish removal is a tool commonly used to restore a clear-water state in lakes. Biomanipulation of ponds
is, however, less well documented, although their importance for biodiversity conservation and public amenities is undisputed.
In ponds, a more complete fish removal can be carried out as compared to lakes and therefore a stronger response is expected.
Fish recolonization can, however, potentially compromise the longer term success of biomanipulation. Therefore, we investigated
the impact of fish recolonization on zooplankton, phytoplankton, and nutrients for several years after complete drawdown and
fish removal in function of submerged vegetation cover in 12 peri-urban eutrophic ponds situated in Brussels (Belgium). Fish
recolonization after biomanipulation had a considerable impact on zooplankton grazers, reducing their size and density substantially,
independent of the extent of submerged vegetation cover. Only ponds with <30% cover of submerged vegetation shifted back to
a turbid state after fish recolonization, coinciding with an increase in density of small cladocerans, rotifers, and cyclopoid
copepods. In ponds with >30% submerged vegetation cover, macrophytes prevented an increase in phytoplankton growth despite
the disappearance of large zooplankton grazers. Our results suggest that macrophytes, rather than by providing a refuge for
zooplankton grazers, control phytoplankton through other associated mechanisms and confirm that the recovery of submerged
macrophytes is essential for biomanipulation success. Although the longer term effect of biomanipulation is disputable, increased
ecological quality could be maintained for several years, which is particularly interesting in an urban area where nutrient
loading reduction is often not feasible. 相似文献
49.
50.
PA West N Protopopoff MW Rowland MJ Kirby RM Oxborough FW Mosha R Malima I Kleinschmidt 《Malaria journal》2012,11(1):273
ABSTRACT: BACKGROUND: Insecticide-treated nets (ITN) are one of the most effective measures for preventing malaria. Mass distribution campaigns are being used to rapidly increase net coverage in at-risk populations. This study had two purposes: to evaluate the impact of a universal coverage campaign (UCC) of long-lasting insecticidal nets (LLINs) on LLIN ownership and usage, and to identify factors that may be associated with inadequate coverage. METHODS: In 2011 two cross-sectional household surveys were conducted in 50 clusters in Muleba district, north-west Tanzania. Prior to the UCC 3,246 households were surveyed and 2,499 afterwards. Data on bed net ownership and usage, demographics of household members and household characteristics including factors related to socio-economic status were gathered, using an adapted version of the standard Malaria Indicator Survey. Specific questions relating to the UCC process were asked. RESULTS: The proportion of households with at least one ITN increased from 62.6% (95% Confidence Interval (CI) = 60.9-64.2) before the UCC to 90.8% (95% CI = 89.0-92.3) afterwards. ITN usage in all residents rose from 40.8% to 55.7%. After the UCC 58.4% (95% CI = 54.7-62.1) of households had sufficient ITNs to cover all their sleeping places. Households with children under five years (OR = 2.4, 95% CI = 1.9-2.9) and small households (OR = 1.9, 95% CI = 1.5-2.4) were most likely to reach universal coverage. Poverty was not associated with net coverage. Eighty percent of households surveyed received LLINs from the campaign. CONCLUSIONS: The UCC in Muleba district of Tanzania was equitable, greatly improving LLIN ownership and, more moderately, usage. However, the goal of universal coverage in terms of the adequate provision of nets was not achieved. Multiple, continuous delivery systems and education activities are required to maintain and improve bed net ownership and usage. 相似文献