Lichen Chemical Traits Influence Palatability and can Mediate the Impact of Lichenivores on Nutrient Cycling

Abstract

Lichen functional traits are known to regulate trophic interactions and biogeochemical processes. Consumption of lichens by lichenivorous macrofauna is thought to contribute significantly to the disappearance of lichen litter, and as such lichenivores convert a large amount of lichen biomass into faeces. However, precisely how this conversion influences decomposition rates and nutrient release from lichens remains unknown.

In this thesis, I tested the effect of lichen litter conversion into faeces on decomposition, and investigated the relationship between lichen functional traits, palatability and decomposition. I conducted a no-choice feeding bioassay with the generalist snail Cepaea hortensis on 12 lichen species with natural (control) and reduced (acetone rinsed) concentrations of secondary compounds. I performed a standardized decomposition experiment on both control and acetone rinsed groups of intact lichen thalli as well as faeces produced during grazing by C. hortensis. I measured morphological traits of lichen thalli and chemical traits of lichen thalli and snail faeces to test their effects on palatability and decomposition. Of the measured traits, palatability was significantly correlated only with concentrations of secondary compounds while decomposition rate was predominantly associated with C:N ratio. Given these results, I here show that palatability and decomposition of lichen are driven by different chemical traits and that the effect of lichenivore conversion of lichen litter into faeces on nutrient cycling depends on initial litter quality.