A method to detect metabolically-active microorganisms in leaf litter habitats

Autoradiographic procedures are described to detect metabolically-active hyphae in litter habitats. Experiments with Sclerotium rolfsii and with hyphae present on the surfaces of leaf litter of beech showed that active hyphae could be detected after exposure for 2 hr to 10 μCi/ml of uniformly-labelled ¹⁴C-glucose followed by film exposure for 2 days. Controls indicated that there was negligible background radioactivity and that there was no adsorption or non-metabolic (passive) uptake of radionuclide by hyphae. Liquid photographic emulsion was superior to stripping film because closer contact could be obtained between the hyphae and the emulsion. Use of photographic emulsion was facilitated by removing hyphae from leaf litter surfaces in polystyrene peels and then covering the polystyrene peels with emulsion. The use of these techniques in other habitats in soil is discussed.