Estimation of fungal biomass in forest litter and soil

The contents of fungal biomass markers were analysed in the fruit bodies of dominant basidiomycetes from an ectomycorrhiza-dominated coniferous forest, and used to estimate the fungal biomass content in the litter and soil. The content of ergosterol (3.8 ± 2.0 mg g−1 dry fungal biomass) and the phospholipid fatty acid 18:2ω6,9 (11.6 ± 4.3 mg g−1) showed less variation than the internal transcribed spacer (ITS) copy numbers (375 ± 294 × 109 copies g−1). A high level of variation in the ITS copy numbers (per ng DNA) was also found among fungal taxa. The content of fungal biomass in the litter and soil, calculated using the mean contents, varied between 0.66 and 6.24 mg g−1 fungal biomass in the litter, and 0.22 and 0.68 mg g−1 in the soil. The ratio of fungal biomass in the litter to that in the soil varied greatly among the markers. The estimates of fungal biomass obtained with different biomarkers are not exactly comparable, and caution should be used when analysing taxon abundance using PCR amplification of fungal rDNA.

► Ergosterol and 18:2ω6,9 are less variable fungal biomass markers than rDNA.
► Fungi greatly differ in the rDNA copy numbers in the DNA and in the biomass.
► Various methods of fungal biomass quantification give largely different estimates.