Fluorescein diacetate hydrolysis as an estimator of microbial biomass on coniferous needle surfaces

Estimating microbial standing crops and microbial production in natural habitats has been difficult for microbial ecologists. The present paper describes a simple spectrophotometric assay based on the hydrolysis of fluorescein diacetate which estimates well the standing crops of microbial cells on coniferous needles and twigs. A technique is also presented for correlating optical density readings with actual dry weights of microbial cells epiphytic on needles, and thus for standardizing the assay. The assay shows promise of broad applicability to other microbial habitats.