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1.
《Veterinary journal (London, England : 1997)》2015,203(1):44-51
Since phenotypic methods to identify coagulase negative staphylococci (CNS) from the milk of ruminants often yield unreliable results, methods for molecular identification based on gene sequencing or fingerprinting techniques have been developed. In addition to culture-based detection of isolates, culture-independent methods may be of interest. On the basis of molecular studies, the five CNS species commonly causing intramammary infections (IMI) are Staphylococcus chromogenes, Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus simulans and Staphylococcus xylosus. Current knowledge suggests that S. chromogenes is a bovine-adapted species, with most cases of IMI due to this bacterium being opportunistic. S. haemolyticus also appears to be an opportunistic pathogen, but this bacterium occupies a variety of habitats, the importance of which as a source of IMI remains to be elucidated. S. xylosus appears to be a versatile species, but little is known of its epidemiology. S. epidermidis is considered to be a human-adapted species and most cases of IMI appear to arise from human sources, but the organism is capable of residing in other habitats. S. simulans typically causes contagious IMI, but opportunistic cases also occur and the ecology of this bacterium requires further study. Further studies of the ecology and epidemiology of CNS as a cause of IMI in cattle are required, along with careful attention to classification of these bacteria and the diseases they cause. 相似文献
2.
Mapping soil organic carbon (SOC) and establishing any change over time are important because of CO2 fluxes between soil and atmosphere and cropland decreases in SOC. The latter is one of the main causes of soil fertility decline and increased erodibility. As most analytical methods underestimate total SOC content, correction factors are needed to avoid methodological bias when comparing SOC data from sampling campaigns using different analytical procedures. The traditional method for SOC analysis used to be, and in most cases still is wet oxidation in potassium dichromate, better known as the Walkley & Black method. In this study, we aim to estimate correction factors for the classic and modified version of the Walkley & Black method for different land use and soil type combinations for agricultural soils in north Belgium. General correction factors of 1.47 for the classic Walkley & Black method and 1.20 for the modified Walkley & Black method are proposed. The results show that sandy grassland soils are characterised by lower recoveries than silt loam grassland soils. Furthermore, the correction factor appears to increase with soil wetness. 相似文献
3.
4.
《Soil biology & biochemistry》2012,44(12):2473-2479
Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) in combination with sequencing of amplified partial 18S ribosomal DNA was used to assess the effects of transgenic Bt corn 5422Bt1 (event Bt 11) and 5422CBCL (event MON810) on the community structure of a non-target microorganism, namely the arbuscular mycorrhizal fungi (AMF) Glomus in corn roots and rhizosphere soils, relative to their non-Bt isolines 5422 (conventional parent) and 5422wx (conventional hybrid). AMF colonization in roots of different corn genotypes was also assessed using microscopic visualization. No adverse effect was detected on the indigenous AMF colonization of the roots of Bt hybrids 5422Bt1 and 5422CBCL. Two-way indicator species analysis (TWINSPAN®) and detrended correspondence analysis (DCA) of the DGGE data from corn roots presented differences between Bt and non-Bt corn isolines (5422Bt1 vs. 5422wx, and 5422CBCL vs. 5422wx). However, differences were also recognized between the two non-Bt corn cultivars (5422 vs. 5422wx), and between the two Bt corn lines (5422Bt1 vs. 5422CBCL) in roots. Our results suggest that corn genotypes may have a greater influence on the AMF community structure of plant roots and rhizosphere soils than other factors, such as the age of the growing plants. 相似文献
5.
Muhaya Bamba B. M. Leermakers Martine Baeyens Willy 《Water, air, and soil pollution》1998,107(1-4):277-288
Estuarine and riverine sediments from fourlocations showing different sediment structures wereanalysed as fresh, thawed and lyophilised samples fortotal mercury (TotHg) and methylmercury (MeHg)concentrations, and results were compared to addresseffects of sample preservation on Hg speciation. TotHg was measured by cold vapour atomic absorptionspectrometry (CVAAS). MeHg was isolated bydistillation and ion-exchange and analysed by coldvapour atomic fluorescence spectrometry (CVAFS) afterpreconcentration on a gold trap. No loss of TotHg norMeHg due to lyophilisation was found. Concentrationsof TotHg and MeHg respectively ranged from 92 to 267ng g-1 dw and 1.1 to 2.9 ng g-1 dw in freshsamples, from 94 to 215 ng g-1 dw and 1.1 to 2.8ng g-1 dw in thawed samples, and from 100 to 256ng g-1 dw and 1.2 to 3.1 ng g-1 dw inlyophilised samples. Lyophilised samples showedbetter homogeneity and better MeHg analysisreproducibility compared with wet samples. 相似文献
6.
Sandrine Godefroid Dennis Monbaliu Wim Massant Beatrijs Van der Aa Bruno De Vos Vincent Quivy Nico Koedam 《Annals of Forest Science》2007,64(3):321-331
This paper describes the ground floor vegetation that developed four years after tillage implements in an ancient beech forest in central Belgium. The purpose of this study was twofold: (1) to explore whether tillage has a lasting effect on soil compaction and soil moisture as well as on vegetation characteristics; and (2) to analyse whether two distinct tillage treatments (rotary plough vs. disc plough), combined with vegetation control when necessary, have the same effect on soil compaction, soil moisture and plant establishment. Of the 29 species recorded, 15 showed a significant recovery after soil loosening in the studied forest area. Interestingly, different tillage treatments did not have the same influence on plant establishment. Treatment effects on soil structure and/or moisture status can be considered as causing the observed growth response. 相似文献
7.
The relationship between soil redox state, sulphide concentration, salinity and spatial patterns of mangrove species distribution was investigated in the mangrove forest of Gazi Bay (Kenya). Field measurements were conducted to examine the relationship between species distribution along a band transect of 280m and soil redox potential (Eh) and sulphide patterns, as well as the indirectly related (through flooding regimes) soil salinity. Of the three major species Avicenniamarina, Ceriops tagal and Rhizophoramucronata present along the transect, only the distribution of the latter correlated with the measured soil variables, R. mucronata being absent from the lessreduced zone with high salinity. Bruguieragymnorhiza and Heritieralittoralis occur in minor populations, they are restricted to the saline, sulphidepoor and lessreduced substrates. From the results it is concluded that soil redox potential (Eh), sulphide concentration and salinity may contribute to structure mangroves through the distribution of dominant species, however in combination with other environmental conditions and processes of vegetation dynamics. 相似文献
8.
The aim of this study is to clarify the roles of researchers in forest policy development processes. Comparative case studies between Japan and Sweden were conducted. The research–integration–utilisation (RIU) model on scientific knowledge transfer was employed as a framework. Based on the RIU model, ‘scientist’, ‘integrator’, and ‘policy entrepreneur’ were defined as three hypothesised roles of researchers, discussed in conjunction with Pielke's ‘honest broker’ model. It was found that researchers played important roles, both as scientists and integrators in Japan. In Sweden, researchers played only the role of scientist. However, no researchers working as policy entrepreneurs were found in either country. These results indicate that the RIU model could work as a basis for the comparison between countries and the clarification of the roles of researchers in forest policy processes. The case study analysis also specified three additional topics for further discussion: (1) different types of science-based policy advice; (2) the relationship between power allies and consensus building; and (3) the reason why the roles of researchers differ between Japan and Sweden. 相似文献
9.
Urban green spaces are vital for human quality of life and urban avian ecology. In consequence, these areas attract cutting edge research on human/animal relations and the human roles in avian foraging grounds. However, few studies of bird reactions to human presence have included bird adaptation and attraction to human behaviour. More commonly, studies focus on structured, human approaches to subject birds, and consequent avian reactive distances (alert and flight distances and alert periods). This study of green spaces in Nanaimo, Canada, examines the less studied factors for bird reactive behaviour, including the more complex human behaviours such as hand waving, bird anticipation of feeding, passerine and non-passerine bird behaviour and non-feeding human presence. It also tests the hypothesis that bird species size, greater vegetation height, more open vegetation and road and path distance increase avian reactive distances. Consistent with established theory, longer alert and flight distances resulted from larger species size and proximate tree stands, but inconsistent with published hypotheses, taller vegetation, and less dense shrubbery were not sufficient predictors of avian reactive distances. Inconsistent with other findings, larger species were also more attracted to humans than smaller species, and anticipatory perching for human provided food balanced with the alert periods between the alert and flight distances. Most species had shorter reactive distances in human presence and were either significantly more likely to forage in human presence or showed no correlation with human presence or absence. The results of this study contribute to current knowledge of bird reactions to human presence and behavior in variable urban green spaces. 相似文献
10.
Research on mercury (Hg) distribution and speciation was carried out in Lake Baikal, a large, strong-oligotrophic freshwater reservoir in Siberia, Russia, during June 1992 and march 1993. In summer, total Hg in the water column ranged from 0.14 to 0.77 ng Hg/L, with the highest concentrations observed in the central basin of the lake in surface water samples. Labile inorganic Hg was found to be 7 to 20 % of the total Hg content. Highest total Hg concentrations were found in river waters: up to 2 ng Hg/L. Labile methylmercury (MeHg) concentrations ranged from 2 to 38 pg Hg/L in the water column, with the higher concentrations in the central part of the lake, and showing a slight increase in near bottom waters. Labile MeHg makes up 1 to 15 % of the total Hg content in the water column, with larger fractions in deep waters. The slight increase of the MeHg gradient with depth corresponds with the O2 minimum region. Highest MeHg concentrations were observed in river waters (up to 145 pg Hg/L) and in some bays of the lake (up to 160 pg Hg/L). In these high temperature- and phytoplankton-rich water masses, the MeHg-fraction increased up to 35 % of total Hg. Labile MeHg concentrations in water samples taken in winter in the southern basin (under the ice cover), showed slightly higher concentrations than in summer, possibly due to an early spring bloom. In rainwater, total Hg ranged from 3 to 20 ng Hg/L and MeHg from 0.1 to 0.25 ng Hg/L. In snow, a large fraction of total Hg is bound to particulate matter; concentrations of total Hg ranged from 8 to 60 ng Hg/L and labile MeHg from 0.1 to 0.25 ng Hg/L. Atmospheric Hg was found to be 0.73 to 2.31 ng/m3 as gaseous Hg and 0.005 to 0.02 ng/m3 in its particulate form. Spatial distribution patterns of atmospheric Hg show slightly higher concentrations over the central part of the lake and the Selenga river delta. In winter, atmospheric Hg values (measured in the southern region), ranged from 1.2 to 6.1 ng/m3 as total gaseous Hg and 0.02 to 0.09 ng/m3 as total particulate Hg, and are higher than in summer, probably influenced by coal burning and traffic by the local population. MeHg contents in fish ranged from 20 ng Hg/g dry weight in small Cottocomephorus to 300 ng Hg/g dry weight in pike and trout species, which were caught in organic-rich waters. 相似文献