Annual production of leaf‐decaying fungi in a woodland stream

Abstract

1. Fungi are thought to be important mediators of energy flow in the detritus‐based food webs of woodland streams. However, until recently, quantitative methods to assess their contribution have been lacking. Growth rates of leaf‐decaying fungi can be estimated from rates of acetate incorporation into ergosterol which, together with estimates of fungal biomass from ergosterol concentrations, enables calculation of fungal production. In this study, I used this method to estimate total production of leaf‐decaying fungi over an annual cycle in a small woodland stream, Walker Branch, Tennessee, U.S.A. To calculate fungal biomass and production on an areal basis, I determined the amount of leaf litter occurring in the stream by sampling transects randomly selected in each of ten 10‐m sections every 20–50 days. Subsamples of leaves chosen from five of the transects were used to determine ergosterol concentrations 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 less 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 basis 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 leaf 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 ranged from 0.49 g m–2 in November, when the amount of leaf litter was at its maximum, to 0.006 g m–2 during the summer when the amount of leaf 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. Fungal spore concentrations in the stream were also seasonal and were correlated with amount of leaf litter m–2 and fungal biomass m–2. Spore concentrations varied between one and four spores ml–1 throughout most of the year, but increased to eighteen spores ml–1 shortly after the greatest amount of leaf litter was present in the stream during November.