Toward A Method For Measuring Instantaneous Fungal Growth Rates In Field Samples

Methods are available in the literature for the measurement of instantaneous growth rates in field samples of photosynthetic microbes and procaryotic saprotrophic microbes, but there has been no such method for eucaryotic saprotrophic microbes (members of the kingdom Fungi). We have devised a technique for estimating instantaneous growth rates for ergosterol—containing fungi in field material, and preliminarily applied the technique to estimation of fungal productivities and throughputs in two types of standing—dead grass (one saltwater, one freshwater), obtaining plausible values (e.g., conversion efficiencies, total fungal production ° leaf mass loss, were calculated to be 36—64%). This method is based on measuring rates of radiolabeled acetate incorporation into ergosterol. We examined several potential problem areas for use of radiolabeled precursors in measurement of microbial molecular syntheses, and its extrapolation to microbial productivity. Key findings were: (a)5 mmol/L added acetate (required for maximization of detection of change in rates) had positive or neutral impact on 48—h fungal growth, and no shift—up (sudden upward change in rate) or lag in incorporation of acetate into ergosterol occurred between 0.25 and 1.25 h of incubation of naturally decaying leaf (Spartina alteriflora) samples with 5 mmol/L acetate; (b) bacterial assemblages on leaves did not contribute radioactivity to the ergosterol fraction after incubation with radioacetate (as opposed to > 30 Bq per centimetre length of leaf containing fungal mycelium); (c) the average empirical factor for conversion from nanomoles 1 4 C—acetate incorporated to micrograms organic fungal mass produced was 8.2 mg/nmol (coefficient of variation, 27%). We tentatively conclude that the acetate—to—ergosterol method is tenable for measurement of natural fungal productivity.