ATP and Ergosterol as Indicators of Fungal Biomass during Leaf Decomposition in Streams: a Comparative Study

Abstract

Ergosterol and ATP concentrations, microbial respiration and sporulation rates of aquatic hyphomycetes associated with leaves of Castanea sativa decomposing in a 5 th order stream were determined periodically over a period of 102 days in order to compare ergosterol and ATP as indicators of fungal biomass. ATP and ergosterol concentrations exhibited a significant positive correlation (F = 4.459, DF = 28, P < 0.001) during the first stages of leaf breakdown (until day 39), i.e., during periods of increasing fungal biomass. No correlation was found between ATP and ergosterol concentrations during later stages of decomposition (days 39 to 102). Respiration rates increased rapidly up to 0.525 mg O 2 h -1 g -1 AFDM during the first month and remained high until the end of the experiment. Sporulation rates peaked at day 9 (1069 conidia day -1 mg -1 AFDM) and decreased during later stages of decomposition. ATP-to-biomass conversion factors were determined for both fungi (0.59 μmol ATP g -1 dry mass) and bacteria (1.30 μmol ATP g -1 dry mass) collected from the stream and grown in the laboratory. Estimates of fungal biomass based on ATP concentrations were similar to those calculated from ergosterol concentrations during the first 39 days of breakdown. The results here presented suggest that ATP is a reliable method to quantify microbial biomass in streams and that the relative importance of bacteria increases at later stages of decomposition.

Fungi in freshwaters: ecology, physiology and biochemical potential

“…Ideally, ergosterol levels should strictly correlate with fungal biomass, but, depending on species and environmental conditions, the ratio of ergosterol to biomass in pure cultures can vary by a factor of up to 14 (Gessner & Chauvet, 1993; Charcosset & Chauvet, 2001; Raviraja et al , 2004). Estimates of fungal biomass based on ergosterol were up to three times higher than those calculated from ATP concentrations (Suberkropp et al , 1993); with other conversion factors, the discrepancy was less severe (Abelho, 2009). Clearly, ergosterol measurements from environmental samples have to be interpreted with caution.…”

“…Selected taxonomic surveys of aquatic hyphomycetees with keys Petersen (1962, 1963a, b) Nilsson (1964) Ingold (1975) Brathen (1982, 1984 Nawawi (1985) Goh (1997) Marvanová (1997) Santos-Flores & Betancourt-López (1997) Gulis et al (2005) vary by a factor of up to 14 (Gessner & Chauvet, 1993;Charcosset & Chauvet, 2001;Raviraja et al, 2004). Estimates of fungal biomass based on ergosterol were up to three times higher than those calculated from ATP concentrations (Suberkropp et al, 1993); with other conversion factors, the discrepancy was less severe (Abelho, 2009). Clearly, ergosterol measurements from environmental samples have to be interpreted with caution.…”

Leaf-litter breakdown in urban streams of Central Amazonia: direct and indirect effects of physical, chemical, and biological factors

“…ATP values can represent the biomass of various microorganisms, including fungi. Several investigators have used the relationship between ATP and ergosterol to obtain fungal participation in microbial biomass (Suberkropp et al 1993, Ruzicka et al 2000, Abelho 2009). We recorded a low association between ATP and ergosterol concentrations (r < 0.1) for both plant species.…”

Leaf decomposition of the macrophyte Eichhornia azurea and associated microorganisms and invertebrates

“…Colonization by the microbial community during the decomposition of detritus of leaves from the riparian zone of a tropical stream showed that fungi predominate in the initial stages of decomposition and that bacteria are more abundant when the leaves are already fragmented and soft (Abelho et al 2005). Abelho (2009) also reported that bacteria become gradually more important in the degradation of plant organic matter as the detritus particles become smaller. However, other studies have shown that in the initial stages of decomposition, the density of bacteria is greater than that of fungi, which become more abundant in intermediate and final stages of decomposition (Gonçalves et al 2007).…”

“…Also, studies on fungi biomass quantification during macrophyte decomposition in subtropical lakes are scarce and equally needed (Carvalho et al 2015). The role played by fungi in plant decomposition has been more commonly investigated in lotic environments (e.g., Abelho et al 2005, Graça and Canhoto 2006, Gonçalves et al 2007, Abelho 2009, Sales et al 2015. In aquatic environments, fungi and bacteria are considered the main heterotrophic organisms that feed by osmotrophy from degraded plant detritus during colonization.…”