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41.
The benthic invertebrates of the Dolores River in southwest Colorado were sampled during three seasons in an area of historic mine drainage. Benthic density exhibited significantly lower values below the mine drainage. However, the number of species did not decrease significantly, indicating that the effect of the mine drainage was primarily non-selective (i.e. favoring no one taxon). This pattern was seasonal with the least effects evident in summer and the greatest effects found in spring. Diversity indices used to assess the effects of this stress on the invertebrate community were MargalePs, Simpson's, Shannon-Weaver's, Brillouin's, and the Biotic Condition Index. None of the indices tested adequately responded to a decreasing trend in the benthic density when number of species remained constant. The indices did respond to a combination of low density and number of species or to the predominant representation by one species. The Biotic Condition Index actually increased at the stations with the lowest density and number of species. Diversity indices appear to be inadequate in assessing a non-selective stress. 相似文献
42.
Erik S. Button Karina A. Marsden Philip D. Nightingale Elizabeth R. Dixon David R. Chadwick David L. Jones Laura M. Cárdenas 《European Journal of Soil Science》2023,74(2):e13363
Agricultural soils are a major source of the potent greenhouse gas and ozone depleting substance, N2O. To implement management practices that minimize microbial N2O production and maximize its consumption (i.e., complete denitrification), we must understand the interplay between simultaneously occurring biological and physical processes, especially how this changes with soil depth. Meaningfully disentangling of these processes is challenging and typical N2O flux measurement techniques provide little insight into subsurface mechanisms. In addition, denitrification studies are often conducted on sieved soil in altered O2 environments which relate poorly to in situ field conditions. Here, we developed a novel incubation system with headspaces both above and below the soil cores and field-relevant O2 concentrations to better represent in situ conditions. We incubated intact sandy clay loam textured agricultural topsoil (0–10 cm) and subsoil (50–60 cm) cores for 3–4 days at 50% and 70% water-filled pore space, respectively. 15N-N2O pool dilution and an SF6 tracer were injected below the cores to determine the relative diffusivity and the net N2O emission and gross N2O emission and consumption fluxes. The relationship between calculated fluxes from the below and above soil core headspaces confirmed that the system performed well. Relative diffusivity did not vary with depth, likely due to the preservation of preferential flow pathways in the intact cores. Gross N2O emission and uptake also did not differ with depth but were higher in the drier cores, contrary to expectation. We speculate this was due to aerobic denitrification being the primary N2O consuming process and simultaneously occurring denitrification and nitrification both producing N2O in the drier cores. We provide further evidence of substantial N2O consumption in drier soil but without net negative N2O emissions. The results from this study are important for the future application of the 15N-N2O pool dilution method and N budgeting and modelling, as required for improving management to minimize N2O losses. 相似文献
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Robert W. Chadwick Lucy T. Chuang Katherine Williams 《Pesticide biochemistry and physiology》1975,5(6):575-586
This study presents evidence for the dehydrogenation of lindane by a hepatic microsomal mixed-function oxidase system. Preliminary investigation established that the incubation of lindane with rat liver homogenates produces a chlorinated, nonpolar compound identified as hexachlorocyclohexene. Differential centrifugation resulted in the sedimentation of most of the dehydrogenase activity in the microsomal fraction. Optimum in vitro assay conditions were established and it was found that the dehydrogenase system required molecular oxygen and reduced pyridine nucleotide coenzyme for maximum activity. Inhibition by SKF 525-A and CO suggested that the enzyme was cytochrome P-450 dependent. Lack of inhibition by cyanide indicated that the cytochrome b5 desaturase system was probably not involved. Pretreatment of rats with DDT, which stimulates lindane metabolism, also induced significantly higher dehydrogenase activity. Both the in vivo and in vitro metabolism of hexachlorocyclohexene produced previously identified lindane metabolites. The existence of a cytochrome P-450 dependent mixed-function oxidase which catalyzes the dehydrogenation of lindane has not previously been reported and may be of importance in the metabolism of other xenobiotics. 相似文献
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An experiment was conducted to determine chemical composition of raw and treated bitter vetch seed for use in poultry diets.
Processing methods were: soaked in water for 12 h, then autoclaved and dried (SA); coarsely ground, soaked in water for 24 h,
autoclaved and dried (GSA); coarsely ground, soaked in water for 47 h with exchange of water every 12 h, cooked and dried
(GSC); coarsely ground, soaked in solution of 1% acetic acid for 24 h at 60°C and dried (GAA). Raw bitter vetch seed was contained
94.52, 26.56, 0.4, 58.86, 3.38, 5.32, 12.28 and 14.20 percent DM, CP, EE, NFE, Ash, CF, ADF and NDF, respectively. Its GE,
AME, AMEn, TME and TMEn values were 18.10, 13.15, 14.38, 14.10 and 14.69 MJ/kg, respectively. Results indicated that bitter
vetch is a good source of Fe (340 ppm) and Cu (46.7 ppm). It s amino acid profile was suitable and methionine was the first
limiting amino acid when compared with broiler and layer chicks requirements. Its canavanine and tannin content were 0.78
and 6.7 mg/kgDM, respectively. Processing methods improved CP and in some cases AMEn. All processing methods especially GSC
resulted in a significant (P < 0.05) reduction in canavanine and tannin. 相似文献
49.
Chadwick Dearing Oliver E.C. Burkhardt Daniel A. Skojac 《Forest Ecology and Management》2005,210(1-3):393-414
Red oaks – cherrybark oak (Quercus pagoda Raf.), willow oak (Quercus phellos L.), water oak (Quercus nigra L.), and Nuttall oak (Quercus texana Buckley; aka: Quercus nuttallii Palmer) – are not regrowing in Mississippi Delta river floodplain forests in the southeastern United States in sufficient numbers to sustain the former species composition and timber and wildlife values. Even if vigorous red oak reproduction becomes established, partial harvesting that does not remove the taller trees will suppress understory red oak height growth more than it will suppress height growth of such other species as sugarberry (Celtis laevigata Willd.), American elm (Ulmus americana L.), cedar elm (Ulmus crassifolia Nutt.), swamp dogwood (Cornus foemina Mill.), green ash (Fraxinus pennsylvanica Marshall), and sweetgum (Liquidambar styraciflua L.). Consequently, the red oaks in these partially harvested stands become increasingly suppressed and probably die; and there is a shift in species composition to the other species. In addition to ensuring vigorous oak reproduction, silvicultural clearcutting or rapid removal of the residual trees following shelterwood or seed tree harvesting to provide full sunlight is needed to ensure red oaks become a dominant part of these future river floodplain stands. 相似文献
50.
K DYNON A VARRASSO N FICORILLI SA HOLLOWAY GH REUBEL F LI CA HARTLEY MJ STUDDERT HE DRUMMER 《Australian veterinary journal》2001,79(10):695-702
OBJECTIVE: To develop rapid (< 8 hour) tests using polymerase chain reaction (PCR) for the diagnosis of equine herpesvirus 3 (EHV3; equine coital exanthema virus), equine gammaherpesviruses 2 (EHV2) and EHV5, equine adenovirus 1 (EAdV1), EAdV2, equine arteritis virus (EAV), equine rhinitis A virus (ERAV; formerly equine rhinovirus 1) DESIGN: Either single round or second round (seminested) PCRs were developed and validated. METHODS: Oligonucleotide primers were designed that were specific for each virus, PCR conditions were defined and the specificity and sensitivity of the assays were determined. The application of the tests was validated using a number of independent virus isolates for most of the viruses studied. The PCRs were applied directly to clinical samples where samples were available. RESULTS: We developed a single round PCR for the diagnosis of EHV3, a seminested PCR for EHV2 and single round PCRs for EHV5, EAdV1, EAdV2 and RT-PCRs for EAV and ERAV. The PCR primer sets for each virus were designed and shown to be highly specific (did not amplify any recognised non-target template) and sensitive (detection of minimal amounts of virus) and, where multiple virus isolates were available all isolates were detected. CONCLUSION: The development and validation of a comprehensive panel of PCR diagnostic tests, predominantly for viruses causing equine respiratory disease, that can be completed within 8 hours from receipt of clinical samples, provides a major advance in the rapid diagnosis or exclusion diagnosis of these endemic equine virus diseases in Australia. 相似文献