Rates and quantities of carbon flux to ectomycorrhizal mycelium following 14C pulse labeling of Pinus sylvestris seedlings: effects of litter patches and interaction with a wood-decomposer fungus

We used a novel digital autoradiographic technique that enabled, for the first time, simultaneous visualization and quantification of spatial and temporal changes in carbon allocation patterns in ectomycorrhizal mycelia. Mycorrhizal plants of Pinus sylvestris L. were grown in microcosms containing non-sterile peat. The time course and spatial distribution of carbon allocation by P. sylvestris to mycelia of its mycorrhizal partners, Paxillus involutus (Batsch) Fr. and Suillus bovinus (L.): Kuntze, were quantified following 14C pulse labeling of the plants. Litter patches were used to investigate the effects of nutrient resource quality on carbon allocation. The wood-decomposer fungus Phanerochaete velutina (D.C.: Pers.) Parmasto was introduced to evaluate competitive and territorial interactions between its mycelial cords and the mycelial system of S. bovinus. Growth of ectomycorrhizal mycelium was stimulated in the litter patches. Nearly 60% of the C transferred from host plant to external mycorrhizal mycelium (> 2 mm from root surfaces) was allocated to mycelium in the patches, which comprised only 12% of the soil area available for mycelial colonization. Mycelia in the litter patch most recently colonized by mycorrhizal mycelium received the largest investment of carbon, amounting to 27 to 50% of the total 14C in external mycorrhizal mycelium. The amount of C transfer to external mycelium of S. bovinus following pulse labeling was reduced from a maximum of 167 nmol in systems with no saprotroph to a maximum of 61 nmol in systems interacting with P. velutina. The 14C content of S. bovinus mycelium reached a maximum 24-36 h after labeling in control microcosms, but allocation did not reach a peak until 56 h after labeling, when S. bovinus interacted with mycelium of P. velutina. The mycelium of S. bovinus contained 9% of the total 14C in the plants (including mycorrhizae) at the end of the experiment, but this was reduced to 4% in the presence of P. velutina. The results demonstrate the dynamic manner in which mycorrhizal mycelia deploy C when foraging for nutrients. The inhibitory effect of the wood-decomposer fungus P. velutina on C allocation to external mycorrhizal mycelium has important implications for nutrient cycling in forest ecosystems.     

INTRA- AND INTEROBSERVER VARIABILITY OF ULTRASONOGRAPHIC MEASUREMENTS OF THE THYROID GLAND IN HEALTHY BEAGLES

The repeatability of ultrasonographic measurements of the canine thyroid gland was evaluated. The variability of three different parameters (the maximal length, width, and height) within observer, between observer and between dogs was assessed based on three different measurements made by each of three observers infive healthy beagle dogs. From the three parameters, the volume of the gland was estimated using a formula of a rotation ellipse. The height and the volume had the lowest intra- and interobserver variability, while measurements of the length had the biggest intra- and interobserver variability. The mean values, with their 90% confidence interval were: height = 0.53cm [0.33-0.73], length = 2.45cm [2.04-2.85], width = 0.62cm [0.46- 0.78], volume = 0.38 cm3 [0.20-0.55].     

Resolution of chylothorax after resection of rib chondroma in a dog

A six-year-old, male dobermann was presented with a history of dyspnoea and bouts of coughing. Radiography and computed tomography of the thorax showed pleural effusion and a well-circumscribed, calcified mass of 10 cm in diameter, appearing to originate from the left first rib. Thoracocentesis revealed that the pleural fluid was chylous in nature. An incisional biopsy was performed, which gave a histological diagnosis of chondroma. Resolution of the chylothorax after en-bloc surgical removal of the tumour suggested that the rib tumour was the initiating cause of the chylothorax. Seventeen months later, rib neoplasia recurred without pleural effusion, and was removed successfully. To the authors' knowledge, rib chondroma, which is an unusual tumour in dogs, has not been previously documented as a cause of chylothorax.     

Temporal patterns and quantification of excretion of Mycobacterium avium subsp paratuberculosis in sheep with Johne's disease

OBJECTIVES: To determine the frequency of excretion of Mycobacterium avium subsp paratuberculosis in Merino sheep with Johne's disease and to quantify excretion in a group of Merino sheep. DESIGN: A pen and laboratory experiment. PROCEDURE: Seven sheep selected from an affected flock on the basis of acid-fast bacilli in the sheep's faeces were housed and total daily faecal output was collected, weighed and subjected to culture for M avium subsp paratuberculosis. An end-point titration method was used to enumerate viable M avium subsp paratuberculosis in a 15 day pooled sample from five sheep that had acid-fast bacilli in their faeces while housed. RESULTS: Four sheep with subclinical multibacillary Johne's disease excreted M avium subsp paratuberculosis each day for 11 days of cultural observation. A further three sheep were intermittent excreters but lacked other evidence of infection with M avium subsp paratuberculosis. The average number of viable bacteria excreted was 1.09 x 10(8) per gram of faeces while total daily excretion was 8.36 x 10(10) viable M avium subsp paratuberculosis per sheep. Examination of faecal smears stained with Ziehl Neelsen was an unreliable means of assessing daily excretion in individual animals except in those with severe lesions. CONCLUSION: Excretion of M avium subsp paratuberculosis in Merino sheep with multibacillary Johne's disease occurred daily, proving that environmental contamination can be continuous on farms with endemic ovine Johne's disease. Faecal culture is a useful method for detecting infection as it does not appear to be affected by the timing of collection of a sample from sheep with multibacillary disease however, to maximise the sensitivity of disease surveillance using faecal culture, sampling rates should be adjusted to take account of the proportions of multibacillary and paucibacillary cases.