Fungal biomass of 3 leaf litter species during decay in an Appalachian stream

Leaf decay and fungal biomass accrual was measured for maple (Acer rubrum), tulip-poplar (Liriodendron tulipifera), and rhododendron (Rhododendron maximum) leaf packs in an Appalachian stream over 8 mo. Fades were placed in 2 stream sites along a longitudinal gradient at the Coweeta Hydrologic Laboratory in North Carolina: a 1st-order headwater stream and a 4th-order stream. Decay was measured as percent mass loss over time, and fungal biomass was estimated using ergosterol. Tulip-poplar decayed faster than maple, and rhododendron decayed the slowest of the 3 in both sites. Decay was faster in the 4th-order stream for tulip-poplar and rhododendron leaves, largely because of differences in stream geomorphology. Fungal biomass showed no trend along the longitudinal gradient. Average fungal biomass (as dry mass [DM] per ash free DM [AFDM]) of aquatic hyphomycetes during the study period was 42 mg DM/g AFDM on tulip-poplar and 11 mg DM/g AFDM on maple leaves in these streams. These estimates are on the lower end of the range for the few fungal biomass estimates from streams and are attributed to low nitrogen and phosphorus concentrations (2-4 mu g NH4/L, 2-18 mu g NO3/L and 1-2 mu g P/L). Peak fungal biomass for tulip-poplar and maple leaves occurred on the Ist through 7th days (120 mg DM/g AFDM and 40 mg DM/g AFDM respectively). This biomass was not correlated with aquatic hyphomycete sporulation on tulip-poplar and was attributed to terrestrial fungi within the senescent leaves. Rhododendron leaves had little or no ergosterol associated with them, yet decayed to less than 20% initial mass after 8 mo. The decay of this species during the 1st 8 mo is therefore probably due to physical abrasion, shredding activity, or oomycete and bacterial decomposition. A model of fungal biomass dynamics in a Ist-order stream is presented and suggests that fungal carbon accrual can reach as much as 0.05 g C m(-2) d(-1) which would adequately meet the carbon ingestion demand of shredding invertebrates in this stream from October to January (0.05 g C m(-2) d(-1)).