Fungal and bacterial production during the breakdown of yellow poplar leaves in 2 streams

We compared the production and biomass of fungi with that of bacteria during the breakdown of yellow poplar leaves (Liriodendron tulipifera) in 2 streams that differed in water chemistry. The hardwater stream contained higher concentrations of nutrients (N and P) than the softwater stream. Fungal biomass (determined from ergosterol concentrations), production (determined from rates of [C-14]acetate incorporation into ergosterol), and sporulation rates associated with leaves were greater in the hardwater stream than in the softwater stream. Bacterial biomass (determined from direct counts and cell volume estimates) was similar on leaves in both streams, but bacterial production (determined from rates of [H-3]leucine incorporation into protein) was greater on leaves in the hardwater stream than in the softwater stream. Fungal biomass associated with leaves was always much greater than bacterial biomass (385-1236x in the hardwater stream, 32-185x in the softwater stream) during leaf breakdown. Fungal production reached maximum values within the first 2 wk after leaves were submerged in the hardwater stream. In the softwater stream, fungal production was low and remained relatively constant throughout the study with a minimum occurring after 28 d. In both streams, bacterial production increased throughout leaf breakdown. Even so, with the exception of 1 date, production of fungi was greater (2-108x in the hardwater stream and 0.9-35x in the softwater stream) than bacterial production during leaf breakdown. On the basis of both biomass and production, fungi played a greater role than bacteria in the breakdown of yellow poplar leaves in these streams.