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

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.     

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

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.     

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

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.     

Amoebic meningoencephalitis caused by Balamuthia mandrillaris in an orang utan

Objective
To describe a case of meningoencephalitis caused by Balamuthia mandrillaris in an orang utan.
Design
A pathological case report.
Animal
A 20 years old male orang utan (Pongo pygmaeus).
Procedure
The disease process was investigated by clinical pathology, necropsy, histopathology and immunofluorescence labelling.
Results
The orang utan developed sudden onset of depression, lethargy, inappetence and apparent head pain. The condition was considered to be related to a 2 year history of upper and lower respiratory disease, and the animal was placed on antibiotics after extensive testing. By the seventh day the animal had become ataxic and disoriented and a brain abscess was suspected. He died on the ninth day of illness. At necropsy, and subsequent sectioning, the brain showed multiple circular, soft, white to grey brown areas of varying size, the largest being in the left temporal (3.5 cm diameter) and right occipital (2.5 cm diameter) regions of the cerebrum. Histological examination of these regions revealed many amoebic trophozoites and occasional cysts associated with areas of haemorrhage and inflammatory necrosis. The trophozoites were packed in perivascular spaces and their nuclei often contained two or more prominent nucleoli. Immunofluorescent labelling of histological sections suggested that the agent was B mandrillaris.
Clinical implications
This report provides further evidence that B mandrillaris , a free living amoeba, can act as a pathogen in animals as well as people, and cause fatal meningoencephalitis. Along with Naegleria and Acanthamoeba spp, B mandrillaris should be considered amongst the causes of acute onset meningoencephalitis in animals.     

Evidence that Cache Valley virus induces congenital malformations in sheep

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.     

A study of the predominant genotypes of bovid herpesvirus 1 found in the U.K

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.     

Megakaryocytic infection and thrombocytopenia in African swine fever

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.