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51.
52.
Martin Mkandawire Barbara Taubert E. Gert Dudel 《Water, air, and soil pollution》2005,166(1-4):83-101
Influences of phosphorus and nitrogen on uranium and arsenic accumulation in Lemna gibba L. were investigated in the laboratory hydroponic cultures and in the field pot experiments. The initial uranium and arsenic concentrations in solutions for the hydroponic cultures were 1000 μ g l?1 each, while in situ trials used tailing water containing 198.7 ± 20.0 μ g U l?1 and 75.0 ± 0.4 μ g As l?1 at a former uranium mine in eastern Germany. A test of three PO4 3? concentrations (0.01, 13.6 and 40.0 mg l?1) in the hydroponic cultures, highest uranium accumulated in L. gibba under the culture with highest PO4 3?. Significant differences in uranium accumulation were between 0.01 mg l?1 and 13.6 mg l?1 PO4 3? cultures only (ANOVA p = 0.05). In the field, addition of 40.0 mg l?1 PO4 3? increased the bioaccumulation of uranium significantly. Contrary, high PO4 3? concentrations suppressed the bioaccumulation of arsenic in both the laboratory and the field. The bioaccumulation of both uranium and arsenic increased slightly with the increase of NH4 + concentration. However, high NH4 + concentrations reduced the yield in the control experiments. The concentration of uranium rose temporarily to 856.0 ± 294.0 μ g l?1, while the concentration of arsenic sunk slightly and temporarily immediately after amending the tailing waters with 40 mg l?1 PO4 3?. The speciation of uranium in the tailing water was modelled with geochemical code PhreeqC, which predicted that uranyl carbonate species dominated before addition of phosphates, but after increasing the PO4 3? concentrations, uranyl phosphates species became dominant. Addition of NH4 + to the tailing water had negligible influence on free available uranium and arsenic concentrations. Thus, manipulations to enhance uranium and arsenic attenuation by L. gibba has limitation when the amendments interact with other elements including the contaminants in the milieu, and when the target contaminants have antagonistic behaviour in the tailing water. 相似文献
53.
Short-term patterns of carbon and nitrogen mineralisation in a fallow field amended with green manures from agroforestry trees 总被引:2,自引:0,他引:2
The mineralisation of green manure from agroforestry trees was monitored with the objective to compare the temporal dynamics of mineralisation of litter from different species. Green manures from five agroforestry tree species were used on a fallow field during the long rainy season of 1997 (March-August) and from two species in the following short rainy season (September-January) in western Kenya. Different methods, i.e. measurements of isotopic ratios of C in respired CO2 and of soil organic matter (SOM) fractions, soil inorganic N and mass loss from litterbags, were used in the field to study decomposition and C and N mineralisation. Soil respiration, with the separation of added C from old soil C by using the isotopic ratio of 13C/12C in the respired CO2, correlated well with extractable NH4+ in the soil. Mineralisation was high and very rapid from residues of Sesbania sesban of high quality [e.g. low ratio of (polyphenol+lignin)/N] and low and slow from low quality residues of Grevillea robusta. Ten days after application, 37% and 8% of the added C had been respired from Sesbania and Grevillea, respectively. Apparently, as much as 70-90% of the added C was respired in 40 days from high quality green manure. Weight losses of around 80%, from high quality residues in litterbags, also indicate substantial C losses and that a build-up of SOM is unlikely. For immediate effects on soil fertility, application of high quality green manure may, however, be a viable management option. To achieve synchrony with crop demand, caution is needed in management as large amounts of N are mineralised within a few days after application. 相似文献
54.
Toxicity of aluminium for the earthworm Eisenia andrei was studied in artificial soil at different pH levels. In a range-finding test, effects of three different aluminium salts on earthworm survival were determined. AlCl3 appeared to be most toxic, with LC50 values of 316, 359 and >1000 mg Al/kg dry soil at pHKCl of 3.5, 4.4 and 6.7, respectively in the control soils. Effects of this salt interfered with a strong decrease of soil pH with increasing aluminium concentration. Al2(SO4)3 was less toxic with LC50 values of 457, >4000 and >4000 mg Al/kg dry soil at pH 3.24, 4.86 and 7.22, respectively. Al2O3 did not affect earthworm survival at concentrations of 5000 mg Al/kg and pH levels between 2.4 and 7.1.In the main test, earthworms were exposed for 6 weeks to soils treated with Al2(SO4)3. As in the range-finding test, aluminium sulfate was most toxic at a pH of 3.4 with an LC50 of 589 mg Al/kg dry soil. At this pH, growth and cocoon production of earthworms were significantly reduced at 320 mg Al/kg dry soil, while at 1000 mg Al/kg dry soil all earthworms died. Survival was not affected by 1000 mg Al/kg dry soil at pH 4.3 and 7.3. At pH 4.3, growth was significantly reduced at 1000 mg Al/kg dry soil and cocoon production at 320 and 1000 mg Al/kg dry soil. At pH 7.3, aluminium only affected cocoon production at the two highest exposure levels. At the highest two exposure levels at pH 7.3, growth was significantly increased, suggesting a trade-off between growth and reproduction. These effects of aluminium at the highest soil pH could not be explained from the concentration of extractable, monomeric (labile) aluminium in soil, which decreased with increasing soil pH. 相似文献
55.
Gert N Smit 《BMC ecology》2005,5(1):4
Background
The investigation was conducted in a savanna area covered by what was considered an undesirably dense stand of Colophospermum mopane trees, mainly because such a dense stand of trees often results in the suppression of herbaceous plants. The objectives of this study were to determine the influence of intensity of tree thinning on the dry matter yield of herbaceous plants (notably grasses) and to investigate differences in herbaceous species composition between defined subhabitats (under tree canopies, between tree canopies and where trees have been removed). Seven plots (65 × 180 m) were subjected to different intensities of tree thinning, ranging from a totally cleared plot (0 %) to plots thinned to the equivalent of 10 %, 20%, 35 %, 50% and 75 % of the leaf biomass of a control plot (100 %) with a tree density of 2711 plants ha-1. The establishment of herbaceous plants (grasses and forbs) in response to reduced competition from the woody plants was measured during three full growing seasons following the thinning treatments. 相似文献56.
Ter Haar G Mulder JJ Venker-van Haagen AJ van Sluijs FJ Smoorenburg GF 《Veterinary surgery : VS》2011,40(3):340-346
Objective: To report a surgical implantation of the Vibrant Soundbridge (VSB) middle ear implant in dogs. Study Design: Pilot study. Animals: Dogs (n=3). Methods: A lateral approach to the tympanic bulla was used to insert the floating mass transducer of the VSB into the tympanic bulla. Using microscopic guidance the transducer was moved to and inserted into the round window niche by manipulation through the acoustic bony meatus, after reflection of the tympanic membrane. VSB position was confirmed by computed tomography (CT) imaging. Results: No intraoperative complications occurred and CT images confirmed correct placement of the VSB. Conclusions: A VSB can be safely implanted in the middle of dogs. 相似文献
57.
58.
Joris de Vente Rubia Verduyn Gert Verstraeten Matthias Vanmaercke Jean Poesen 《Journal of Soils and Sediments》2011,11(4):690-707
Purpose
This study aimed to (1) increase understanding of the relation between sediment yield and environmental variables at the catchment scale; (2) test and validate existing and newly developed regression equations for prediction of sediment yield; and (3) identify how better predictions may be obtained. 相似文献59.
Jackson DJ Macis L Reitner J Degnan BM Wörheide G 《Science (New York, N.Y.)》2007,316(5833):1893-1895
Sponges (phylum Porifera) were prolific reef-building organisms during the Paleozoic and Mesozoic approximately 542 to 65 million years ago. These ancient animals inherited components of the first multicellular skeletogenic toolkit from the last common ancestor of the Metazoa. Using a paleogenomics approach, including gene- and protein-expression techniques and phylogenetic reconstruction, we show that a molecular component of this toolkit was the precursor to the alpha-carbonic anhydrases (alpha-CAs), a gene family used by extant animals in a variety of fundamental physiological processes. We used the coralline demosponge Astrosclera willeyana, a "living fossil" that has survived from the Mesozoic, to provide insight into the evolution of the ability to biocalcify, and show that the alpha-CA family expanded from a single ancestral gene through several independent gene-duplication events in sponges and eumetazoans. 相似文献
60.
Pieter M. Verbost Gert Flik James C. Fenwick Anna-Maria Greco Peter K. T. Pang Sjoerd E. Wendelaar Bonga 《Fish physiology and biochemistry》1993,11(1-6):205-215
The branchial Ca2+ uptake by teleost fish is under inhibitory control by the hormone stanniocalcin (STC) which is generated by the corpuscles
of Stannius (CS). Removal of the CS in North American eel, Anguilla rostrata LeSueur, induced a rapid rise in blood calcium levels. Branchial Ca2+ influx following the extirpation of the CS (stanniectomy, STX) increased during the first four days and stayed elevated thereafter
(in agreement with previous studies). The transepithelial potential (TEP) across the gills did not change after STX and this
means that the electrochemical gradient for Ca2+ is less favourable for passive influx of Ca2+ in STX eel. Therefore, the Ca2+ influx in STX eels is a transcellular flux, with Ca2+ crossing the apical and basolateral membrane barrier. The kinetics of ATP-driven Ca2+-transport across basolateral plasma membranes from eel gills did not change after STX. Thus, the increased Ca2+-influx after STX is not correlated with changes in ATP-dependent Ca2+-extrusion across the basolateral membrane, suggesting a regulation at the apical membrane. Moreover, STC did not affect ATP-driven
Ca2+-transport in isolated basolateral membranes (in vitro). STC (0.1 nM) reduced cAMP levels in dispersed eel gill cells. It had no significant effect on the IP3 levels in these cells. We postulate that STC controls the permeability to Ca2+ of the apical membranes of the Ca2+ transporting cells of fish gills by controlling second messenger operated Ca2+ channels in the apical membrane.
Résumé L'entrée de calcium au niveau des branchies est sous le controle inhibiteur de la stanniocalcine (STC) qui est synthétisée au niveau des corpuscules de Stannius (CS). L'ablation des CS chez l'anguille d'Amérique du Nord, Anguilla rostrata LeSueur, induit une augmentation rapide des niveaux de calcium dans le sang. Le flux entrant branchial de calcium consécutif à l'ablation des CS (stanniectomie, STX) augmente pendant les 4 premiers jours et reste élevé au-delà (en accord avec des études antérieures). Le potentiel transépithélial (TEP) à travers les branchies ne change pas après STX, ceci indiquant que le gradient électrochimique du Ca2+ est moins favorable pour le flux entrant passif du Ca2+ chez l'anguille STX. En conséquence, le flux entrant de Ca2+ chez l'anguille STX est un flux transcellulaire, avec le Ca2+ traversant la barrière membranaire apicale et basolatérale. La cinétique du transport de Ca2+ conduit par l'ATP à travers les membranes plasmatiques basolatérales de branches d'anguille n'est pas modifiée après STX. Ainsi, l'augmentation du flux entrant de Ca2+ après STX n'est pas corrlée avec des modifications de l'excrétion de Ca2+ conduit par l'ATP à travers la membrane basolatérale, suggérant donc une régulation au niveau de la membrane apicale. De plus, la STC ne modifie pas le transport de Ca2+ conduit par l'ATP dans des membranes basolatérales isolées (in vitro). La STC (0.1 nM) réduit les niveaux d'AMPc dans des cellules dispersées de branchies d'anguille. Cette hormone n'a pas d'effet significatif sur les niveaux d'IP3 dans ces cellules. Nous suggérons que la STC régule la perméabilité au Ca2+ des membranes apicales des cellules branchiales transporteuses de Ca2+ en controlant un second messager agissant sur les canaux calciques de la membrane apicale.相似文献