MICROBIOLOGY OF ORNITHOGENIC SOILS FROM THE WINDMILL ISLANDS, BUDD COAST, CONTINENTAL ANTARCTICA - SOME OBSERVATIONS ON METHODS FOR MEASURING SOIL BIOMASS IN ORNITHOGENIC SOILS

A range of measures of microbial biomass were compared for their effectiveness and internal consistency in characterizing omithogenic soils. Excellent correspondences (r = 0.86-0.94, slope = 0.84-1.12) were found between four measures of total biomass (ATP, fluorescein diacetate hydrolysis rate, substrate induced respiration rate and algal + bacterial biomass) when they were compared using regression analysis. Bacterial numbers, estimated from agar plate counts, were found to be highly correlated with microscopy counts and total biomass measurements, though the best-fit relationship was curvilinear rather than linear. Measurement of the procaryotic and eucaryotic components of the soil microbiota by selective antibiotic inhibition was found to be unreliable. Other problems were noted when assay units were converted into microbial C using multiplication factors published in the literature. The substrate-induced-respiration method overestimated the bacterial biomass of occupied penguin colony soil by at least 4-fold when the standard conversion factor (1 mg C = 25 mul CO2 h-1) was used. Total biomass was also overestimated when fluorescein-diacetate-hydrolysis rates were converted to microbial C. While all four approaches could provide relative measures of the biomass of the Antarctic microbiota, it was concluded that they should not be employed in isolation but always in parallel when such soils are initially analysed.