Methods for determination of carbon loss from fungal propagules incubated in soil

Abstract

Losses of C from fungal propagules exposed in soil were determined by incubating 14C-labelled fungal propagules enclosed in membrane filter envelopes in 4 g soil in planchets in a closed chamber. 14CO 2 evolved was recovered daily by passing air through the headspace and collecting CO 2 in ethanolamine scintillation cocktail. Dissolved 14CO 2 in soil was recovered by bubbling air through an acidified aqueous soil suspension and collecting the CO 2 evolved. Residual 14C in soil was determined, after removal of membrane filters containing conidia, by oxidizing the soil with acid dichromate and collecting the CO 2, evolved. The amount of dissolved 14CO 2 was negligible (0.1 to 0.2% of total label). The amount of residual 14C, as percentage of total label, was 20.6% from conidia of Cochliobolus sativus after 18 days in soil and 2.3% from sclerotia of Sclerotium rolfsii after 26 days in soil. 14CO 2 evolved from the soil with added conidia during 18 days was 31.2%, and with added sclerotia during 26 days was 16.4%. The relative contribution of fungal respiration to total 14CO 2 evolved from soil was estimated to be 57–60% for conidia and 65–72% for sclerotia. Propagule respiration may play a greater role in 14C loss from fungal propagules in soil than assumed previously.