Fluorescein diacetate hydrolysis as a measure of fungal biomass in soil

The fatty acid methyl esters of lipids extracted from an agricultural soil in the preharvest period of soybean or middle growth cycle from wheat were characterized and quantified by gas-liquid chromatography. The fatty acids 18:2 omega6 and 16:1 omega5 were used as markers of saprotrophic and arbusc ular mycorrhizal fungi. In parallel, biomass estimation through plate count s in selective media for cellulolytic and saprotrophic fungi was also perfo rmed all throughout a soybean crop or middle growth cycle of wheat. As an e nzymatic method, the fluorescein diacetate (FDA) hydrolytic activity of the samples was determined. Owing to the high relationship exhibited by FDA hy drolysis with organic carbon and total nitrogen content of soil, the enzyma tic activity was correlated with the microbial biomass estimated through ma rker lipids or plate counts. The results obtained point out that FDA hydrol ysis may be used as a rapid, cheap, and reliable estimator of fungal biomas s.