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991.
Leila J. Hamdan Robert B. Jonas 《Journal of experimental marine biology and ecology》2007,342(2):242-252
Phytoplankton production and accumulation of extracellular organic carbon (EOC) was tracked during diel intervals in microcosms by inhibiting bacterioplankton assimilation of EOC with streptomycin and kanamycin. Bacterioplankton production (3H-thymidine incorporation) and metabolism (14C-glucose incorporation) were monitored in samples collected from the Potomac River estuary to determine the effect of the antibiotics. Particulate (i.e., raw water) primary production and EOC (i.e., water passing through 1.0 μm glass fiber filter) production rates were monitored to determine the impact of antibiotics on phytoplankton. In preliminary experiments, neither streptomycin nor kanamycin alone significantly inhibited bacterioplankton activity compared to controls, but when both were present secondary production and metabolism were reduced up to 90%, and remained as such for 45 h. During field evaluations using a streptomycin and kanamycin mixture (50 μM each) particulate primary production and EOC production were not statistically different in control and antibiotic treated samples indicating that the antibiotics did not negatively influence phytoplankton production rates. In the presence of antibiotics dissolved free amino acids (DFAA) and, to a lesser extent, monosaccharides were significantly elevated compared to controls. This study demonstrates that streptomycin and kanamycin are capable of inhibiting bacterioplankton metabolism and uptake of dissolved organic carbon (DOC) in the samples tested so that the contribution of EOC to the DOC pool and to bacterioplankton metabolism could be measured and assessed. 相似文献
992.
M.S. Koch S. Schopmeyer C.J. Madden 《Journal of experimental marine biology and ecology》2007,341(1):91-101
To examine the synergism of high temperature and sulfide on two dominant tropical seagrass species, a large-scale mesocosm experiment was conducted in which sulfide accumulation rates (SAR) were increased by adding labile carbon (glucose) to intact seagrass sediment cores across a range of temperatures. During the initial 10 d of the 38 d experiment, porewater SAR in cores increased 2- to 3-fold from 44 and 136 μmol L− 1 d− 1 at 28-29 °C to 80 and 308 μmol L− 1 d− 1 at 34-35 °C in Halodule wrightii and Thalassia testudinum cores, respectively. Labile C additions to the sediment resulted in SAR of 443 and 601 μmol L− 1 d− 1 at 28-29 °C and 758 to 1,557 μmol L− 1 d− 1 at 34-35 °C in H. wrightii and T. testudinum cores, respectively. Both T. testudinum and H. wrightii were highly thermal tolerant, demonstrating their tropical affinities and potential to adapt to high temperatures. While plants survived the 38 d temperature treatments, there was a clear thermal threshold above 33 °C where T. testudinum growth declined and leaf quantum efficiencies (Fv/Fm) fell below 0.7. At this threshold temperature, H. wrightii maintained shoot densities and leaf quantum efficiencies. Although H. wrightii showed a greater tolerance to high temperature, T. testudinum had a greater capacity to sustain biomass and short shoots under thermal stress with labile C enrichment, regardless of the fact that sulfide levels in the T. testudinum cores were 2 times higher than in the H. wrightii cores. Tropical seagrass tolerance to elevated temperatures, predicted in the future with global warming, should be considered in the context of the sediment-plant complex which incorporates the synergism of plant physiological responses and shifts in sulfur biogeochemistry leading to increased plant exposure to sulfides, a known toxin. 相似文献
993.
ABSTRACT Band-recovery and wing-collection survey data have the potential to provide information on American woodcock (Scolopax minor) fall migration ecology in the Central Region of the United States, yet researchers have not recently analyzed these extensive data sets. We analyzed all direct recoveries of woodcock banded in Michigan, Minnesota, and Wisconsin, USA, as well as wing-collection survey data, to determine the progression of fall migration, the migration direction, and the final destination of woodcock migrating from these states. We did not observe migration initiation based on band recoveries until late October and early November, with most migration occurring during November. Wing-receipt data showed a similar trend, with most change in mean receipt latitude occurring from 1 November to 5 December. During November, wing receipts were spread through the entire Central Region. By 15–31 December, 92% (n = 26) of band recoveries were on the wintering grounds (south of latitude 33°N). Most banded woodcock from Michigan, Minnesota, and Wisconsin wintered in Louisiana, USA. Woodcock banded in these states will be exposed to harvest for most of the hunting season because they remain in these states through November. If the population status of local birds is a concern, managers should consider this migration pattern when setting season dates. 相似文献
994.
Water use efficiency in C3 cereals under Mediterranean conditions: a review of physiological aspects
In this review, we will discuss physiological traits of C3 cereals related to water use efficiency (WUE) in Mediterranean environments, from leaf (WUEinstantaneous) to crop level (WUEyield or ‘water productivity’). First, we analyse the WUEinstantaneous and the possible trade‐off between improving this parameter and growth/yield performance. Ways to ameliorate WUE without penalties are discussed. We also analyse in what cases breeding by high or low WUEinstantaneous is a suitable criterion to maintain grain yield under drought (Mediterranean) conditions. This question is approached in the framework of carbon isotope discrimination, (Δ13C), the main indirect parameter used to integrate (at time and space scale) the WUEinstantaneous in C3 plants. A negative correlation between these two parameters has been confirmed by several studies. The relationship between Δ13C and grain yield, however, is more complex, and may differ from one environment to another. In Mediterranean conditions with moderate or no water stress, a positive correlation between Δ13C and grain yield is found in barley and wheat, whereas in ‘stored‐water’ crops (such as in some regions of Australia), lower Δ13C (i.e. higher WUEinstantaneous) is associated with higher grain yield, particularly in more stressful conditions. These apparent inconsistencies and their possible implications for plant breeding are discussed. One physiological trait that has received minor attention in attempts to improve WUEinstantaneous is the role of ear photosynthesis. Ears of barley and durum wheat have a higher WUEinstantaneous than the flag leaf, both in well‐watered and in drought conditions. The underlying causes of the higher WUEinstantaneous of ears are not fully understood, but their refixation capacity (i.e. the capacity to re‐assimilate respired carbon dioxide) could be important. Although the genotypic variability of this trait has not been extensively studied, some data support the idea that variation in refixation capacity may be attributable to genetic factors. At the crop level, decreasing soil evaporation is a crucial factor in efforts to improve the WUEyield in Mediterranean conditions, and fast initial growth of the crop (i.e. early vigour) seems to be relevant. In wheat, modern varieties with dwarfing genes (giberellic acid – insensitive) have higher yields but, concomitantly, they have lower initial growth performance. Recently, semi‐dwarf cultivars (giberellic acid – sensitive) with high grain yield and simultaneously high early vigour were found, opening new avenues to increase WUEyield in wheat. The negative effects of futile water loss by cuticular and nocturnal transpiration are also commented. Finally, we discuss some agronomic practices (in particular, ‘deficit irrigation’ systems) linked to physiological traits that confer higher WUEyield,, in particular, in the cases of Mediterranean regions. 相似文献
995.
Kenichi Fujisawa Masakazu Takahata 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2007,193(1):127-140
We investigated how the physiological characteristics and synaptic activities of nonspiking giant interneurons (NGIs), which
integrate sensory inputs in the brain and send synaptic outputs to oculomotor neurons innervating eyestalk muscles, changed
after unilateral ablation of the statocyst in order to clarify neuronal mechanisms underlying the central compensation process
in crayfish. The input resistance and membrane time constant in recovered animals that restored the original symmetrical eyestalk
posture 2 weeks after operation were significantly greater than those immediately after operation on the operated side whereas
in non-recovered animals only the membrane time constant showed a significant increase. On the intact side, both recovered
and non-recovered animals showed no difference. The frequency of synaptic activity showed a complex pattern of change on both
sides depending on the polarity of the synaptic potential. The synaptic activity returned to the bilaterally symmetrical level
in recovered animals while bilateral asymmetry remained in non-recovered ones. These results suggest that the central compensation
of eyestalk posture following unilateral impairment of the statocyst is subserved by not only changes in the physiological
characteristics of the NGI membrane but also the activity of neuronal circuits presynaptic to NGIs. 相似文献
996.
本文通过选用特定的吸附柱层析活性炭纯化油茶皂苷。以总皂苷的得率及纯度为考察指标,确定活性炭吸附柱层析富集油茶总皂苷的性能、洗脱参数及再生使用情况。结果表明,水洗之后再以90%乙醇洗脱较好;香草醛.浓硫酸为检测方法检测下,总皂苷解吸得率为62.9%,总洗脱率为92.4%,纯度为50.1%以上;该类柱层析活性炭在分离纯化及脱色方面作用较显著,工艺简便、成本低,适合工业化生产。 相似文献
997.
Layer-by-layer assembly of glucose oxidase (GOx) with single-wall carbon nanotubes (SWCNTs) is achieved on the electrode surface based on the electrostatic attraction between positively charged GOx in pH 3.8 buffer and negatively charged carboxylic groups of CNTs. The cyclic voltammetry and electrochemical impedance spectroscopy are used to characterize the formation of multilayer films. In deaerated buffer solutions, the cyclic voltammetry of the multilayer films of {GOx/CNT}n shows two pairs of well-behaved redox peaks that are assigned to the redox reactions of CNTs and GOx, respectively, confirming the effective immobilization of GOx on CNTs using the layer-by-layer technique. The redox peak currents of GOx increase linearly with the increased number of layers indicating the uniform growth of GOx in multilayer films. The dependence of the cyclic voltammetric response of GOx in multilayer films on the scan rate and pH is also studied. A linear decrease of the reduction current of oxygen at the {GOx/CNT}-modified electrodes with the addition of glucose suggests that such multilayer films of GOx retain the bioactivity and can be used as reagentless glucose biosensors. 相似文献
998.
Jutta Stadler Annette Trefflich Roland Brandl Stefan Klotz 《Biodiversity and Conservation》2007,16(3):621-630
Dry grasslands are among the most threatened plant communities of Central Europe. We explore the time scale of spontaneous
regeneration of dry grasslands on abandoned fields in an area of Central Europe, where also ancient grassland communities
occur (Saxony-Anhalt, Germany). On three permanent plots with shallow soils we monitored during 10 years change of species
composition and analysed whether spontaneous succession leads to assemblages similar to the ancient dry grassland communities
in the direct surroundings. We found that dry grassland species are able to invade the permanent plots and during the 10 years
of succession the number of dry grassland species increased. But even after 10 years there was a clear difference between
ancient dry grassland communities and the assemblages on the permanent plots. Our findings suggest two important conclusions:
First, spontaneous succession on abandoned fields is a cheap possibility for the conservation of some dry grassland species,
at least on shallow soils. Second, the time scale of the regeneration process, however, is rather long. Hence, conservation
of remnants of ancient grassland communities needs special attention. 相似文献
999.
1000.
Douroumis D Fatouros DG Bouropoulos N Papagelis K Tasis D 《International journal of nanomedicine》2007,2(4):761-766
Within the family of nanomaterials, carbon nanotubes (CNTs) have emerged as a new efficient scaffold for studying molecular interactions at interfaces. Poor dispersability of CNTs in any solvent presents a considerable drawback for the development of novel functional composite structures. Previous studies have demonstrated that the solubility of CNTs can be greatly enhanced by employing appropriate surfactants, some of them being biological molecules. In this work, we study the noncovalent wrapping of lipid chains onto the graphitic surface of single-walled material (SWCNTs) by electron microscopy and Raman spectroscopy. Stable and homogenous aqueous suspensions of SWCNTs in the presence of lipids have been prepared, whereas their electrophoretic mobility was confirmed by zeta-potential measurements. Raman measurements revealed that smaller diameter SWCNTs are preferentially dispersed by lipid molecules in the aqueous supernatant part of the prepared suspension. 相似文献