COMPARISON OF ATP AND ERGOSTEROL AS INDICATORS OF FUNGAL BIOMASS ASSOCIATED WITH DECOMPOSING LEAVES IN STREAMS

ATP and ergosterol were compared as indicators of fungal biomass assoc iated with leaves decomposing in laboratory microcosms and streams. In all studies, the sporulation rates of the fungi colonizing leaves wer e also determined to compare patterns of fungal reproductive activity with patterns of mycelial growth. During leaf degradation, ATP concent rations exhibited significant, positive correlations with ergosterol c oncentrations in the laboratory and when leaves had been air dried pri or to being submerged in a stream. However, when freshly shed leaves w ere submerged in a stream, concentrations of ATP and ergosterol were n egatively correlated during degradation. This appeared to be due to th e persistence of leaf-derived ATP in freshly shed leaves during the fi rst 1 to 2 weeks in the stream. Estimates of fungal biomass from ergos terol concentrations of leaf litter were one to three times those calc ulated from ATP concentrations. ATP, ergosterol, and sporulation data generally provided similar information about the fungi associated with decomposing leaves in streams during periods when fungi were growing. Ergosterol concentrations provide a more accurate indication of funga l biomass in situations in which other organisms make significant cont ributions to ATP pools.