Biol Fertil Soils (1996) 22:299-304 9 Springer-Verlag 1996 G. Djajakirana - R.G. Joergensen - B. Meyer Ergosterol and microbial biomass relationship in soil Received: 20 June 1994 Abstract Ergosterol and microbial biomass C were mea- sured in 26 arable, 16 grassland and 30 forest soils. The ergosterol content ranged from 0.75 to 12.94 gg g-~ soil. The geometric mean ergosterol content of grassland and forest soils was around 5.5 gg g 1, that of the arable soils 2.14 gg g-1. The ergosterol was significantly correlated with biomass C in the entire group of soils, but not in the subgroups of grassland and forest soils. The geometric mean of the ergosterol:microbial biomass C ratio was 6.0 mg g-l, increasing in the order grassland (5.1), arable land (5.4) and woodland (7.2). The ergosterol:microbial biomass C ratio had a strong negative relationship with the decreasing cation exchange capacity and soil pH, indi- cating that the fungal part of the total microbial biomass in soils increased when the buffer capacity decreased. The average ergosterol concentration calculated from literature data was 5.1 mg g-1 fungal dry weight. Assuming that fungi contain 46% C, the conversion factor from micro- grams ergosterol to micrograms fungal biomass C is 90. For soil samples, neither saponification of the extract nor the more effective direct saponification during extraction seems to be really necessary. Key words Microbial biomass 9 Fungal biomass - Ergosterol 9 Fumigation extraction Introduction As strictly heterotrophic organisms, fungi are very effec- tive decomposers of complex organic material and usually dominate the soil microbial biomass in most soils (Ander- son and Domsch 1975; Parkinson et al. 1978), one excep- G. Djajakirana. R.G. Joergensen ( ~ ) - B. Meyer Institut fttr Bodenwissenschaften,Universit~tG6ttingen, von-Siebold-Strasse4, D-37075 G6ttingen, Germany tion being the rhizosphere (Vancura and Kunc 1977). Sev- eral methods exist for quantifying fungal biomass. Direct microscopic quantification in solid substrates suffers from difficulties in differentiating fungus from mineral soil par- ticles and in separating live and dead fungal tissue. As a consequence, microscopic counts have been reported to overestimate (Schniirer et al. 1985) or underestimate fun- gal biomass (Ingham and Horton 1987). Important indirect methods are the selective inhibition technique (Anderson and Domsch 1973) and the measurement of fungus-specif- ic components such as ergosterol. This predominant fungal sterol is endogenous only to fungi and certain green mi- croalgae (Newell et al. 1987); negligible amounts have been found in higher plants and procaryote organisms (Weete and Weber 1980). Ergosterol is an important con- stituent of cell membranes, controlling their permeability, microviscosity and the activity of membrane-bound en- zymes (Peacock and Goosey 1989). Ergosterol has been used to detect fungal invasion and spoilage of food and cereal grains (Seitz et al. 1977; Schnfirer 1993) and fungal infection of plants (Osswald et al. 1986). The development of ectomycorrhizae (Martin et al. 1990) and vesicular-ar- buscular mycorrhizae (Frey et al. 1992) was monitored by measuring their ergosterol content and ergosterol was also measured as a biomarker for fungi in coastal marine sedi- ments (Newell et al. 1989). Rapid ergosterol losses of more than 95% were ob- served by Davis and Lamar (1992) within 2 weeks after fumigation with methyl bromide. These data imply that er- gosterol decays rapidly after fungal death and will not be accumulated to any great extent in humic material (Nylund and Wallander 1992). Consequently, it can be used to esti- mate fungal biomass in soils (West et al. 1987; Zelles et al. 1987; Davis and Lamar 1992). However, more detailed studies of the relationships between ergosterol and micro- bial biomass are lacking. The major aim in our work was to examine the relationship between ergosterol and micro- bial biomass C in soils and to study the effects of soil properties and land use on this relationship. A subsidiary aim was to see if direct saponification could be omitted for the analysis of ergosterol in soil samples.