Flow-microcalorimetry measurements of aerobic and anaerobic soil microbial activity

Heat output can be used as an indicator of microbial activity and is usually measured in a microcalorimeter with closed ampoules. In long-term experiments particularly, interpretation of the data is hindered by the changing environment in the closed ampoules because of O₂ consumption and CO₂ enrichment. We used a combination of a flow-microcalorimeter and a gas chromatograph to measure the heat flux and CO₂ and N₂O production rates under controlled conditions. Simultaneous detection of the heat output and CO₂ emission allowed calculation of the calorimetric: CO₂ (Cal/CO₂) ratio. A mean ratio of-435 kJ mol^-1 CO₂ was detected in six different soils amended with glucose and incubated under aerobic conditions. This ratio indicated that CO₂ was the end-product of catabolism. In wet 10–12 mm soil aggregates of a gleyic vertisol amended with glucose, values of-285 kJ mol^-1 CO₂ under an aerobic and-141 kJ mol^-1 CO₂ under a N₂ atmosphere was determined. These findings indicated that fermentative metabolism occurred. The Cal/CO₂ ratio was not affected when enough NO _inf3 ^sup- was available and denitrification processes (N₂O production) were possible.     

Holzimpr?gnierung und Forstschulen

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Von Holzkonservierung

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Beobachtungen über Speicherinsekten

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Bioassay and transcuticular movement of systemic fungicides

A sensitive bioassay method was developed using bidirectional diffusion of fungicides in agar bands instead of diffusion through 360°. This method permitted the measurement of fungicide movement through isolated cuticular disks into agar bands underneath. Oil dispersible formulations of oxycarboxin and pyracarbolid penetrated through cuticles of coffee much more efficiently than wettable powder formulations.     

The ultrastructure of sporidia of Ustilago avenae after treatment with the fungicides nuarimol and imazalil nitrate

Ultrastructural changes were observed in sporidia of Ustilago avenue (Pers.) Rostr. after treatment with the fungicides nuarimol and imazalil nitrate. Electron microscopic studies of ultrathin sections, as well as of freeze-fracture replicas, showed that nuarimol caused the following marked changes in the ultrastructure of the cells: increased cell wall thickness and invaginated plasmalemma, with concentrations of extracytoplasmic vesicles in some places between plasmalemma and the cell wall; pores were visible in the septa. Nuarimol-treated sporidia were characterised by vacuolisation and accumulation of lipid bodies. Compared with nuarimol, imazalil nitrate caused small cytological changes; elongation of the sporidia and enlarged cell diameters, as well as an increased thickness of the septa, were observed, and an enhanced number of mitochondria with reduced diameters were found.