Is the decline of soil microbial biomass in late winter coupled to changes in the physical state of cold soils?     

Robert L. Jefferies  Kate A. Edwards  Jack Dainty 《Soil biology & biochemistry》2010,42(2):129-135

During winter when the active layer of Arctic and alpine soils is below 0 °C, soil microbes are alive but metabolizing slowly, presumably in contact with unfrozen water. This unfrozen water is at the same negative chemical potential as the ice. While both the hydrostatic and the osmotic components of the chemical potential will contribute to this negative value, we argue that the osmotic component (osmotic potential) is the significant contributor. Hence, the soil microorganisms need to be at least halotolerant and psychrotolerant to survive in seasonally frozen soils. The low osmotic potential of unfrozen soil water will lead to the withdrawal of cell water, unless balanced by accumulation of compatible solutes. Many microbes appear to survive this dehydration, since microbial biomass in some situations is high, and rising, in winter. In late winter however, before the soil temperature rises above zero, there can be a considerable decline in soil microbial biomass due to the loss of compatible solutes from viable cells or to cell rupture. This decline may be caused by changes in the physical state of the system, specifically by sudden fluxes of melt water down channels in frozen soil, rapidly raising the chemical potential. The dehydrated cells may be unable to accommodate a rapid rise in osmotic potential so that cell membranes rupture and cells lyse. The exhaustion of soluble substrates released from senescing plant and microbial tissues in autumn and winter may also limit microbial growth, while in addition the rising temperatures may terminate a winter bloom of psychrophiles.Climate change is predicted to cause a decline in plant production in these northern soils, due to summer drought and to an increase in freeze-thaw cycles. Both of these may be expected to reduce soil microbial biomass in late winter. After lysis of microbial cells this biomass provides nutrients for plant growth in early spring. These feedbacks, in turn, could affect herbivory and production at higher trophic levels.  相似文献   

Carbon, Nitrogen and Phosphorus Tranformations are Related to Age of a Constructe Wetland     

K. Zemanová  T. Picek  J. Dušek  K. Edwards  H. Šantrůčková 《Water, air, and soil pollution》2010,207(1-4):39-48

Two horizontal constructed wetlands with subsurface flow (CWs) of different age were monitored in a 2-year study. One of the CWs was new, while the second one had been in operation for 5 years in the first year of study. Transformations of C, P, and N were measured in each CW in the substrate of the vegetated bed under both aerobic and anaerobic conditions, and their rates were compared. C was mineralized in both CWs under both aerobic and anaerobic conditions, but mineralization rates differed between the CWs; they were cca ten times higher in the established CW compared to the new CW. Dissolved reactive phosphorus (DRP) was immobilized under aerobic conditions but was mobilized under anaerobic conditions. DRP transformation was cca five times faster in the established CW. Nitrification occurred under aerobic conditions at similar rates in both CWs. NH₄ ⁺ concentration decreased under both aerobic and anaerobic conditions, but there was large variability. The age of the CW affected C mineralization rates and DRP immobilization rates under aerobic conditions and mobilization rates under anaerobic conditions; they increased as the CWs maturated, while no effect of CW age was observed on nitrogen removal rates.  相似文献   

The response of eragrostis curvula (schrad.) nees to fertilizers in the highland sourveld of natal*     

P. J. Edwards  B. D. Mappledoram 《African Journal of Range and Forage Science》2013,30(1):122-125

The effects of five years of application of N, P and K fertilizers at three levels, and of agricultural lime at two levels, on the herbage yield of Eragrostis curvula are discussed. The experiment was carried out on leached soils under an average annual rainfall of 900mm. Significant responses in yield were obtained to N, P and K fertilizers but there was no response to lime.  相似文献   

Fiberoptic endoscopy in bovine infertility     

J E Manspeaker  G H Edwards 《Australian veterinary journal》1985,62(Z1):147-147

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The prevalence of itchmite, Psorergates ovis, among sheep flocks with a history of fleece derangement     

PW JOHNSON  JW PLANT  JC BORAY  SC BLUNT  PJ NICHOLLS 《Australian veterinary journal》1990,67(4):117-120

An investigation of sheep flocks in the main sheep raising areas of New South Wales showed that the itchmite Psorergates ovis was frequently associated with fleece derangement. In 26 of the 41 flocks examined, P. ovis was the only ectoparasite detected. P. ovis and the sheep body louse Damalinia ovis, were found in 5 flocks. No external parasites were found on sheep examined from the 10 remaining flocks. The type of fleece derangement most frequently recorded was rubbing which in some cases was combined with areas of chewed fleece. Among flocks, there were positive relations between the prevalence of fleece derangement and prevalence of itchmite or scurf and between itchmite count and mean scurf score. Within flocks, itchmite infested sheep or sheep with scurf had higher prevalences of fleece derangement than sheep on which no mites or no scurf were found. Itchmite infested sheep had a higher prevalence of scurf than those with no detectable mite infestation. There were no significant differences in itchmite populations or fleece derangement between untreated flocks and flocks treated with synthetic pyrethroids, organophosphates or arsenic and rotenone.  相似文献   

Chlamydiosis in workers at a duck farm and processing plant   总被引：4，自引：0，他引：4  

DG HINTON  A. SHIPLEY†  JW GALVIN‡  JT HARKIN‡  RA BRUNTON† 《Australian veterinary journal》1993,70(5):174-176

SUMMARY An outbreak of chlamydiosis was Investigated in workers at a duck farm and processing plant during winter 1989. Chlamydia psittaci was isolated from ducks, but there was little evidence of clinical chlamydiosis in the ducks. Serological tests showed that 76% of workers had been exposed to Infection, 12% recently, 16% had not been exposed and 8% had inconclusive test results. There was a strong association (P < 0.05) between years of employment and exposure to Infection. Infection appeared to be contracted during the first year of employment. Measures were Implemented to reduce shed contamination and control rodents and wild birds. At the same time, ducks were medicated, the processing plant was modified, work practices were altered and workers were advised about chlamydiosis to reduce the risk of human infection.  相似文献   

Evidence that Cache Valley virus induces congenital malformations in sheep     

S I Chung  C W Livingston  J F Edwards  R W Crandell  R E Shope  M J Shelton  E W Collisson 《Veterinary microbiology》1990,21(4):297-307

An outbreak of congenital abnormalities occurred in sheep at San Angelo, Texas, between December 1986 and February 1987. Of 360 lambs born, 19.2% had arthrogryposis or other musculo-skeletal problems and hydranencephaly (AGH), and the total neonatal loss was 25.6%. In 1987, all ewes that were tested with AGH lambs had antibody to Cache Valley virus (CVV), whereas 62% of the ewes with normal lambs had CVV-specific antibody. Pre-colostral serum samples from AGH lambs had neutralizing antibody to CVV. An increase in prevalence of CVV-specific antibody, from 5% during the spring of 1986 to 63.4% during the winter of 1987, occurred during a time that included the gestation of these affected lambs, as well as a period of increased rainfall. The isolation of a CVV-related strain from a sentinel sheep in October 1987 confirmed the continued presence of this virus in the pasture where this outbreak occurred and provided a recent field strain for future studies.  相似文献   

A study of the predominant genotypes of bovid herpesvirus 1 found in the U.K   总被引：1，自引：0，他引：1  

S Edwards  H White  P Nixon 《Veterinary microbiology》1990,22(2-3):213-223

The genotypic classification of 84 U.K. isolates of bovid herpesvirus 1 was determined by the restriction endonuclease technique. Preliminary studies with six enzymes (EcoRI, HindIII, HpaI, BamHI, PstI and BstEII) showed that the principal genotypic variants, including the live vaccine strains used in the U.K., could be identified from the digestion patterns with just two endonucleases: HindIII and HpaI. Isolates from the 1960s were all categorised as genotype 2b. From 1977 onwards, genotype 1 has predominated in mainland Britain, with occasional type 2b isolates. Type 2b viruses were isolated from both respiratory and genital disease cases. There was no evidence of genotypes 2a or 3 in the U.K.  相似文献   

Suspected non-steroidal anti-inflammatory drug toxicity in a horse     

J M Hunt  P Lees  G B Edwards 《The Veterinary record》1985,117(22):581-582

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Megakaryocytic infection and thrombocytopenia in African swine fever   总被引：1，自引：0，他引：1  

J F Edwards  W J Dodds  D O Slauson 《Veterinary pathology》1985,22(2):171-176

Pigs infected with an African swine fever field isolate of modified virulence became acutely thrombocytopenic four to five days after the onset of fever and viremia. By eight days after inoculation, all pigs were thrombocytopenic. Immunofluorescence microscopy demonstrated that 2 to 10% of the megakaryocytes were infected. By 13 days after inoculation, platelet counts returned to within normal limits, and there was megakaryocytic hyperplasia despite a continued viremia. Secondary complications delayed the return of normal circulating platelet levels in some pigs. The clinical findings of African swine fever are discussed in light of the gross and histologic lesions.  相似文献