The Fungicide Tebuconazole Confounds Concentrations of Molecular Biomarkers Estimating Fungal Biomass

Due to their ecological importance, fungi are suitable indicator organisms for anthropogenic stress. To estimate fungal biomass, the fungal membrane molecule ergosterol is often quantified as a proxy. Estimates based on ergosterol may, however, be distorted by exposure to demethylase inhibiting (DMI) fungicides, interfering with sterol synthesis. To test this hypothesis, we exposed ten fungal species to the DMI fungicide tebuconazole and measured concentrations of ergosterol and DNA per unit dry mass of the fungal hyphae. The latter served as alternative biomass proxy that is not specifically targeted by tebuconazole. Effects of tebuconazole on ergosterol concentrations were species-specific, while concentrations were on average reduced by 13%. In contrast, DNA concentrations were on average increased by 13%. We demonstrate that DMI fungicides - at close to field relevant levels - can distort fungal biomass estimation, complicating the use of this endpoint for environmental management.