A comparison of two methods for the estimation of mycelial biomass in leaf litter

The agar-film technique (AF) and hexosamine assay (HA) were compared as methods for measuring the biomass of fungal mycelium in plant litter by application to the growth of Mycena galopus in sterilised leaves of Fraxinus and Betula . The data were statistically analysed and the precision, sources of variation, efficiency (man-hr), sensitivity and potential accuracy compared. Satisfactory precision (coefficient of variation v . 0.14 mg g −1 oven-dry weight, but the efficiency of both methods could be improved. The major sources of variation were the primary litter samples (flasks), the sampling error of AF (microscope fields) and the experimental error of HA (hydrolyses and cation-exchange columns). The biomass values were broadly realistic in terms of the yield efficiency of the fungus and nutrient immobilization (C, N, P, K), but were 2–3 times larger by HA than AF. The AF technique is recommended for mixed mycelia in plant litter, although it is likely to underestimate biomass; HA is probably more accurate, but is limited to monocultures. The accuracy of AF could be greatly increased by optimizing the maceration of litter. Particular importance is placed on the necessity of obtaining more accurate factors for converting the experimental data to biomass, i.e. moisture content (AF), relative density (AF) and hexosamine content (HA) of mycelium of varying age.