Relationships between growth and sporulation of aquatic hyphomycetes on decomposing leaf litter

Abstract

The dynamics of changes in microbial biomass (ATP concentrations), respiration rates and sporulation rates of aquatic hyphomycetes associated with tulip poplar leaf disks in two streams with different water chemistry were compared with the activities of a dominant fungal species from each stream growing on sterilized leaf disks in the laboratory. Aquatic hyphomycetes sporulated at maximum rates after 15–19 d in both stream and laboratory studies. Sporulation occurred during periods of increasing biomass and respiration indicating a close relationship between growth and sporulation in these fungi. Leaf disks decomposing in the hardwater stream supported greater biomass, activity and number of species than those decomposing in the softwaer stream. Fungi colonizing leaf disks in the laboratory exhibited higher ATP concentrations and sporulation rates than the communities from either stream. These differences appear to be related to water chemistry, particularly N and P concentrations. Organic matter budgets calculated for the two species grown in the laboratory indicated that growth yield coefficients were 0·15–0·23 g g −1 and net production efficiencies ranged from 24 to 46 %. A significant portion of fungal production was converted into conidia by both fungi.