SOURCES OF ERROR IN DIRECT MICROSCOPIC METHODS FOR ESTIMATION OF FUNGAL BIOMASS IN SOIL

Sources of error in direct microscopic measurement of fungal hyphae in soil were examined and fungal biomass estimates and associated variab ility obtained by the direct counting method and the ergosterol techni que were compared. Nested random effects ANOVA indicated that the majo r source of variance in the direct microscopic counting method were th e people examining the prepared microscope slides, accounting for 83% of the total variance. Sampling variability accounted for approximatel y 14% of the total variance. Fungal biomass values calculated from soi l ergosterol concentrations were close to the range of values derived from hyphal length estimates but coefficients of variation were much l ower for soil ergosterol determinations (6-13%) than for hyphal length estimates (16-32%). For one soil sample, we compared total hyphal len gth and fungal biomass estimates from our lab to those of another lab. Values obtained by the other laboratory were outside the range of val ues and 95% confidence intervals reached in our lab. Comparison of fun gal hyphal length estimates from undisturbed prairie soil and an adjac ent cultivated soil indicated that the undisturbed soil contained more than twice as much fungal biomass. Results of our study indicate: (1) extreme caution must be used when comparing hyphal length and fungal biomass estimates made by different laboratories using the direct coun ting method; and (2) soil ergosterol determinations can provide inform ation on fungal biomass that may be useful in comparing direct count e stimates by different labs.