Growth and production of aquatic hyphomycetes in decomposing leaf litter

Abstract

The acetate-to-ergosterol technique was used to estimate fungal productivity of three species of aquatic hyphomycetes growing in decomposing ash leaves in stream microcosms. Following a lag of 20-88 min, incorporation of acetate into ergosterol was linear for at least 10 h. Substrate saturation was reached in the mM range, and there was no indication of isotope dilution. For one species, Articulospora tetracladia, a conversion factor of 5.5 mg mycelial dry mass produced per pmol acetate incorporated was deter-mined. This was similar to the theoretical conversion factor (6.6 mg p,mol-I) deduced from pathways OF ergosterol synthesis in fungi. Thus, the acetate-toergosterol assay appears to be suitable for estimating the productivity of aquatic hyphomycetes growing in leaf litter in streams. Estimated growth rates of A. tetracladia in microcosms changed markedly over time, with the maximum being as high as 0.72 d-l at an early growth stage. After 23 d when 58% of the initial leaf mass was degraded, the fungus had produced 89 mg biomass per g of initial leaf mass. Almost half of this production was allocated to conidia. Assuming an average growth efficiency of 0.35, this would be equivalent to a fungal assimilation of 25% of initial leaf mass and account for 44% of the observed leaf mass loss. In an experiment with leaf litter colonized by fungi in a stream, acetate incorporation was linear for 6 h, but the estimated growth rate was only 0.017 d-l.

Autumnal Biomass and Potential Productivity of Salt Marsh Fungi from 29° to 43° North Latitude along the United States Atlantic Coast

“…This relationship has been observed previously with smooth cordgrass (44) and with riparian leaves decaying in streams (18,55). This relationship probably occurs because the amount of living fungal matter increases until any additional increase in the living fungal matter content of decaying leaves is hindered by limited substrate availability or limited access to one or more nutrients, at which point the growth rate decreases and translocation of fungal organic compounds to points where spores are produced becomes the dominant fungal activity (8).…”

“…The rates of acetate incorporation (fungal membrane synthesis) were used as an index of fungal productivity (16,18,19,56). Pieces (1.5 cm) were cut from the nonligule end of each of the four air-dried blades obtained from a site for each height (upper or mid) on the shoots and were pooled to obtain one 6-cm sample, which was used for a fungal productivity assay, as described by Newell (36) and Newell et al (44).…”

Comparison of Fungal Activities on Wood and Leaf Litter in Unaltered and Nutrient-Enriched Headwater Streams

“…Fungal biomass of plant litter was calculated using the conversion factor of 5.5 mg ergosterol g Ϫ1 fungal dry mass (15). Instantaneous fungal growth rates were calculated assuming an exponential growth model as described previously (16). Empirical conversion factors of 19.3 g fungal biomass nmol Ϫ1 acetate incorporated for leaf litter (49) and 27.0 g nmol Ϫ1 for wood sticks (V. Gulis, unpublished data) were used.…”

Benthic Bacterial and Fungal Productivity and Carbon Turnover in a Freshwater Marsh

“…Fungal biomass, growth rate, and production were estimated by determining ergosterol concentrations and rates of [ 14 C]acetate incorporation into ergosterol (28). Samples were incubated for 5 h at ambient lake temperatures in 4 ml of filtered lake water containing sodium [ 14 C]acetate (Amersham, Little Chalfont, Buckinghamshire, United Kingdom); the specific activity of added acetate was 3.7 10 7 Bq mmol Ϫ1 (27). The total added acetate concentration was 5 mM.…”