The effect of the saprotrophic ascomycete Chalara longipes on the decomposition of humic acids was determined in a cultivation experiment. The fungus was incubated in liquid cultures in a full-strength (F system) and an organic nitrogen-free medium (F-N system), both amended with pure humic acids isolated from spruce forest litter. Fungal biomass production was highest in the F system with humic acids and lowest in the F-N system, the effect of organic nitrogen and humic acids being significant (p < 0.05). The presence of organic nitrogen seems to be essential for growth. The fungus utilized humic acids; molar mass distribution in media obtained by gel-permeation chromatography showed decrease in the humic acids fraction. Decolorization of the media reached 75 and 64 % in the F and F-N systems, respectively. The molar mass of humic acids probably also decreased as estimated from the increase in the absorbance A465/A665 (A4/A6) ratio. It is assumed that the utilization of humic acids may be mediated by the production of organic acids (as their components) and production of some oxidative enzymes.

Institute of Botany Academy of Sciences of the Czech Republic 252 43 Průhonice Czechia

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