The interaction between epiphytic algae, a parasitic fungus and <i>Sphagnum</i> as affected by N and P

Abstract

We report the effects of fertilisation with N and P on the infection of Sphagnum by its fungal parasite Lyophyllum palustre, the expansion of epiphytic algae and the interaction between the latter two from 1998 to 2001. We added 40 kg N ha −1 yr −1 or 3 kg P ha −1 yr −1 in a full factorial design at 4 field sites. In a greenhouse experiment we reinoculated Sphagnum to verify the identity of the fungus and its necrotic effect on Sphagnum . Lyophyllum palustre was responsible for the necrosis of Sphagnum in our experiments. Adding N induced complete necrosis of Sphagnum cuspidatum by L. palustre , whereas adding P decreased the area of necrotic tissue. Disease severity was related to the N concentration in the Sphagnum capitula. In Sphagnum magellanicum and S. papillosum , infection with L. palustre resulted in defoliation of stem sections. Adding N stimulated the expansion of algae at all sites, reducing the volume of photosynthetic tissue in Sphagnum. The density of the film of algae in the treatments receiving N was a function of the frequency of defoliated Sphagnum stems. We conclude that infection with parasitic fungi and, in humid environments, the expansion of epiphytic algae, may aggravate the impact of increased N deposition or of other ecosystem disturbances that affect nutrient availability.