During desiccation considerable structural changes compensate for the substantial loss of apoplastic and symplastic water. Cytorrhysis occurs in all green algal photobiont cells and in thin-walled fungal hyphae. In thick walled hyphal cells cavitation leads to one symplastic bubble per each cell. The dynamic effects of the formation, growth and the closing of the vapour/gas cavities in liquids are known to be acoustic radiation (AR) sources. Compared to the AR of air-dry lichens desiccating living specimens of Lobaria pulmonaria revealed an increased AR signal over the whole frequency range between 0.2-125 kHz. Fully hydrated specimens revealed only a low AR activity. With ongoing desiccation the AR intensity increased until a maximum was reached after 46 - 49 min when more than 10 pulses per second were measured. This experiment presents the first evidence for the generation of AR in lichen-forming fungi during desiccation. Two major spectral components of the AR signal were discovered, the first low-frequency component at 1 kHz reached a maximum intensity during the desiccation process. We propose that the most likely elementary mechanism of AR over this frequency range is cavitation in cortical and medullary hyphae, a process previously hypothesised from ultrastructural studies.