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41.
Invertebrates containing endosymbiotic dinoflagellate algae (zooxanthellae) retain excretory nitrogen, and many are able to take up ammonium from the surrounding seawater. However, the site of assimilation and role of nitrogen recycling between symbiont and host remains unclear. In the present study, ammonium uptake by the symbiotic sea anemone Anemonia viridis (Forskål) was examined by following the pathway of assimilation using 15N-enriched ammonium. Since zooxanthellae became enriched with 15N from ammonium at up to 17 times the rate of the host, they appear to be the primary site of assimilation. In the light, the rate of zooxanthellae enrichment at 20?M was twice that at 10?M, whereas the rate of host enrichment was not significantly affected by ammonium concentration. When anemones were incubated with [15N]ammonium in the dark, after 12?h without light the rate of enrichment was lowered in both zooxanthellae and host. However, while the enrichment of the host was significantly reduced when the light level was lowered from 300 to 150?μmol photons m?2?s?1, zooxanthellae enrichment was unchanged. Low molecular weight material from the zooxanthellae became enriched at 20 times the rate of that from the host, and enrichment was detected in the amino acids glutamate, glutamine, aspartate, alanine, glycine, phenylalanine, threonine, valine, tyrosine, and leucine from zooxanthellae. In the zooxanthellae, amino acids accounted for 65% of the total enrichment of low molecular weight material. Of the amino acids detected in zooxanthellae, over 90% of the enrichment was accounted for by glutamate, glutamine and aspartate. The enrichment of the amide group of glutamine was greater than that of the amine group of glutamate or glutamine, consistent with the glutamine synthetase/glutamine 2-oxoglutarate amidotransferase cycle as the mechanism of ammonium assimilation. To examine the flux of 15N from zooxanthellae to host, anemones were pulse-labelled with [15N]ammonium and then transferred to an unlabelled chase. Over a 2?h period there was no evidence for a flux of nitrogen from zooxanthellae to host. However, during the chase period, the enrichment of low molecular weight material declined and that of high molecular weight material increased in both zooxanthellae and host, indicating that protein was synthesized using 15N from ammonium in both components of the symbiosis. Again by using a pulse-chase system, it was found that glutamate was metabolised most rapidly by zooxanthellae, followed by (in order of decreasing rate of turnover) aspartate, alanine, glycine and valine (no data are available for glutamine). Unlike these amino acids, nitrogen was transferred to the essential amino acids phenylalanine and threonine, increasing their enrichment during the chase period. While recycled nitrogen is clearly important to this symbiosis, the mechanism by which it is cycled remains to be resolved. 相似文献
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Carlos Rozas Alberto de la Fuente Hugo Ulloa Peter Davies Yarko Niño 《Environmental Fluid Mechanics》2014,14(4):849-871
Lake Villarrica, located in south central Chile, has a maximum depth of 167 m and a maximum fetch of about 20 km. The lake is monomictic, with a seasonal thermocline located at a depth of approximately 20 m. Field data show the presence of basin-scale internal waves that are forced by daily winds and affected by Coriolis acceleration. A modal linear and non-linear analysis of internal waves has been used, assuming a two-layer system. The numerical simulations show good agreement with the internal wave field observations. The obtained modes were used to study the energy dissipation within the system, which is necessary to control the amplitude growth. Field data and numerical simulations identify (1) the occurrence of a horizontal mode 1 Kelvin wave, with a period of about a day that coincides with the frequency of daily winds, suggesting that this mode of the Kelvin waves is in a resonant state (subject to damping and controlled by frictional effects in the field) and (2) the presence of higher-frequency internal waves, which are excited by non-linear interactions between basin-scale internal waves. The non-linear simulation indicates that only 10 % of the dissipation rate of the Kelvin wave is because of bottom friction, while the rest 90 % represents the energy that is radiated from the Kelvin wave to other modes. Also, this study shows that modes with periods between 5 and 8 h are excited by non-linear interactions between the fundamental Kelvin wave and horizontal Poincaré-type waves. A laboratory study of the resonant interaction between a periodic forcing and the internal wave field response has also been performed, confirming the resonance for the horizontal mode 1 Kelvin wave. 相似文献
46.
Medusahead (Taeniatherum caput-medusae (L.) Nevski) is an exotic annual grass invading rangelands in the western United States. Medusahead is a serious management
concern because it decreases biodiversity, reduces livestock forage production, and degrades the ecological function of rangelands.
Despite the obvious importance of ranchers as partners in preventing and managing medusahead in rangelands, little is known
about their perceptions and behaviors concerning medusahead management. We present the results of a survey of ranchers operating
on sagebrush steppe rangeland in a three-county area in southeast Oregon encompassing over 7.2 million ha. The primary objective
of this research was to determine if the presence of medusahead on a ranch influenced its operator’s perceptions and behaviors
concerning invasive plant control and prevention. Ranchers operating on medusahead-infested rangeland were more likely to
indicate increased awareness and concern about medusahead and the potential for its continued expansion. Ranchers operating
on rangeland invaded by medusahead were also more likely to indicate use of measures to prevent the spread of medusahead and
other invasive plants on rangeland, interest in educational opportunities concerning invasive annual grass management, and
plans for controlling invasive annual grasses in the future. This study revealed an alarming trend in which individuals are
less likely to implement important prevention measures and participate in education opportunities to improve their knowledge
of invasive plants until they directly experience the negative consequences of invasion. Information campaigns on invasive
plants and their impacts may rectify this problem; however, appropriate delivery methods are critical for success. Web- or
computer-based invasive plant information and tools were largely unpopular among ranchers, whereas traditional forms of information
delivery including brochures/pamphlets and face-to-face interaction were preferred. However, in the future web- or computer-based
information may become more popular as ranchers become more familiar with them. 相似文献
47.
This paper describes the application of coastal hydro-informatic modelling (using the TELEMAC Modelling System) to address
management issues arising from projected hydrodynamical and morphological changes within a shallow, sandy estuarine environment.
The model incorporates the complex interaction of ocean, terrestrial and atmospheric processes. The case study of the Dyfi
Estuary, on the west coast of Wales, is highlighted here. As sea levels have risen locally and are predicted to rise further,
a National Nature Reserve (Borth Bog), which has been reclaimed from tidal waters by embankments, will be at increasing risk
from flooding episodes due to overtopping of these embankments at high tide. Present and predicted future tidal-fluvial scenarios
have been modelled in the Dyfi Estuary in order to estimate the potential for flooding. In addition, areas of greatest velocity
change and potential for sediment erosion/accretion have been identified. A further process that has been investigated is
how salt marsh migration is affected by sea-level rise. This case study exemplifies some fundamental and complex physical
processes inherent to estuaries, and shows how different management options can be assessed, before their implementation,
through a modelling approach. 相似文献
48.
Brigitte M. Manship Anthony J. Walker Lucy A. Jones Angela J. Davies 《Marine Biology》2008,153(3):473-482
Juveniles of Paragnathia formica Hesse (Isopoda; Gnathiidae) are haematophagous ectoparasites, feeding on fish blood which supplies the nutrients for their
development through growth and moulting, and the subsequent survival and reproduction of the free-living adults. Little is
known of the mechanisms of digestion in juvenile gnathiids, and biochemical studies on the digestive tract of these interesting
estuarine isopods have not been undertaken previously. Here, functionally active cathepsin-like cysteine proteinases are identified
in the digestive system of juvenile praniza (fed) and zuphea (unfed) forms. The physiological pH of the digestive tract and
the optimum proteolytic activities detected in praniza 3 homogenates using the cathepsin B/L, cathepsin B, and cathepsin H
fluorogenic substrates, N-Carbobenzoxy-Phe-Arg-4-methoxy-2-naphthylamine (Z-phe-arg-MNA), N-Carbobenzoxy-Arg-Arg-4-methoxy-2-naphthylamine (Z-arg-arg-MNA) and Arg-4-methoxy-2-naphthylamine (H-arg-MNA), respectively, are in the acidic range (pH 5.8–6.7). Inhibition profiles against Z-phe-arg-MNA and Z-arg-arg-MNA using the cathepsin B inactivator urea, and cysteine proteinase inhibitors, support the presence of cathepsin
L- and B-like enzymes. These proteolytic activities are 10–50 times higher in homogenates of praniza 3 compared with zuphea
3 forms. Histochemistry of praniza 3 sections reveals that the predominant enzyme activity towards Z-phe-arg-MNA is limited to the digestive glands during early and mid stages of digestion; later, this activity appears in
the lining of the anterior hindgut. Moreover, activity towards Z-arg-arg-MNA is generally restricted to the digestive glands, and only occasionally present in the anterior hindgut. In conclusion,
the digestive glands are the main site of cathepsin-like cysteine proteinase activities in P. formica juveniles; these enzymes appear to be important to the digestion of host fish blood enabling development through to the free-living
adult. 相似文献
49.
R. J. Davies‐Colley D. G. Smith 《Journal of the American Water Resources Association》2001,37(5):1085-1101
ABSTRACT: Suspended sediment causes a range of environmental damage, including benthic smothering, irritation of fish gills, and transport of sorbed contaminants. Much of the impact, while sediment remains suspended, is related to its light attenuation, which reduces visual range in water and light availability for photosynthesis. Thus measurement of the optical attributes of suspended matter in many instances is more relevant than measurement of its mass concentration. Nephelometric turbidity, an index of light scattering by suspended particles, has been widely used as a simple, cheap, instrumental surrogate for suspended sediment, that also relates more directly than mass concentration to optical effects of suspended matter. However, turbidity is only a relative measure of scattering (versus arbitrary standards) that has no intrinsic environmental relevance until calibrated to a ‘proper’ scientific quantity. Visual clarity (measured as Secchi or black disc visibility) is a preferred optical quantity with immediate environmental relevance to aesthetics, contact recreation, and fish habitat. Contrary to common perception, visual clarity measurement is not particularly subjective and is more precise than turbidity measurement. Black disc visibility is inter‐convertible with beam attenuation, a fundamental optical quantity that can be monitored continuously by beam transmissometry. Visual clarity or beam attenuation should supplant nephelometric turbidity in many water quality applications, including environmental standards. 相似文献
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