ANNUAL PRODUCTION OF LEAF DECAYING FUNGI IN A WOODLAND STREAM

1. Fungi are thought to be important mediators of energy flow in the d etritus-based food webs of woodland streams. However, until recently q uantitative methods to assess their contribution have been lacking. Gr owth rates of leaf-decaying fungi can be estimated from rates of aceta te incorporation into ergosterol which, together with estimates of fun gal biomass from ergosterol concentrations, enables calculation of fun gal production. In this study, I used this method to estimate total pr oduction of leaf-decaying fungi over an annual cycle in a small woodla nd stream, Walker Branch, Tennessee, U.S.A. To calculate fungal biomas s and production on an areal basis, I determined the amount of leaf li tter occurring in the stream by sampling transects randomly selected i n each of ten 10-m sections every 20-50 days. Subsamples of leaves cho sen from five of the transects were used to determine ergosterol conce ntrations and in situ rates of acetate incorporation into ergosterol. 2. Leaf litter, fungal biomass m(-2), and fungal production m(-2) were highly seasonal. Leaf litter ranged from 249 g m(-2) in November to l ess than 5 g m(-2) during the summer. Fungal biomass as percentage of leaf litter ranged from 4.4 to 8.8% during the year, but on an areal b asis ranged from 11 to 13 g m(-2) during November to January to 0.25 g m(-2) in June, primarily due to the seasonal variation in amount of l eaf litter present. Fungal growth rates averaged 2.6% day(-1) (0.9-7.0 % day(-1)) during the year. Daily production of leaf-decaying fungi ra nged from 0.49 g m(-2) in November, when the amount of leaf litter was at its maximum, to 0.006 m(-2) during the summer when the amount of l eaf litter was low. Annual production of leaf-decaying fungi was 34 g m(-2), with an annual production to biomass ratio (P/B) of 8.2. 3. Fun gal spore concentrations in the stream were also seasonal and were cor related with amount of leaf litter m(-2) and fungal biomass m(-2). Spo re concentrations varied between one and four spores ml(-1) throughout most of the year, but increased to eighteen spores ml(-1) shortly aft er the greatest amount of leaf litter was present in the stream during November.