Transformation of Fungal Biomass in Soil.

During this research programme the rate of mineralization of fungal residues in soil was investigated and the effects of various environmental parameters on the process analysed. An open continuous-flow soil perfusion system was designed and used for the investigation. The reactor column was packed with aggregates of a sandy clay loam which was amended in various ways with fungal material (Aspergillus nidulans) and perfused continuously with, defined gas and liquid feeds.

This method was used to study the effects of basic soil conditions such as aeration, anaerobiosis, aggregate size , moisture fluctuations and nutritional status on the processes of mycelial degradation, mineralization and humification. Subsequently the influence of chemical treatments of the soil (glucose, potassium nitrate, ammonium sulphate and ammonium phosphate) on the rates of transformation of native organic matter and added fungal material was assessed. Further the effect of selected pesticides (Dalapon and triphenyltin acetate) on mineralization of fungal material was studied.

Carbon dioxide evolution was taken as the primary measure of carbon mineralization throughout these studies, a decision which facilitates a comparison of the present data with other studies of carbon transformation in soil. A method for determining the total activity of β-1,3 glucanase in soil has been devised and assay of this activity provided a convenient measure of the active mycolytic microflora in the soil. Changes in the microbial population which were induced by soil amendment also were recorded.

Continuous perfusion of soil by water had an appreciable effect on the decomposition of native organic matter and the effect was enhanced under conditions of amendment with fungal mycelia, Continuous water perfusion was more effective in mineralisation than cycles o f soil drying and wetting. The rate of mineralization was more pronounced under aerobic than anaerobic conditions both in control and mycelium-amended soils.

Based on the cumulative production of CO2 from soils amended 14 with C-labelled mycelia it was shown that continuous perfusion with various nutrient solution stimulated fungal mineralization in the decreasing order: potassium nitrate > glucose > ammonium sulphate > ammonium phosphate > water. Treatment with Dalapon for sixty days produced no significant difference in the overall rate of mineralisation compared to the aerobic water perfused condition.

Triphenyltin acetate showed an inhibitory effect on the production of carbon dioxide. Marked inhibition was observed at the highest concentration of the fungicide used (500 ppm) in the mycelium-amended soil and also in unamended control soils at lower concentrations (100 ppm).

Half-lives of readily decomposable and humus material in soil subjected to various treatments were calculated and compared with other studies of carbon mineralization. The enhanced mineralization of the native organic matter (priming effect) following the addition of fungal material to and various treatments of soil was calculated and discussed. Some comparisons with the transformation of higher plant residues in soil have been made.