No allelopathic effect of the dominant forest‐floor lichen Cladonia stellaris on pine seedlings

1 The lichen Cladonia stellaris forms dense mats and dominates the forest-floor vegetation in late-successional oligotrophic boreal forests. This lichen is rich in polyphenolic secondary compounds, and through allelochemical effects of these compounds the dense mat formed by C. stellaris is assumed to have negative effect on forest regeneration and soil microbial functioning. 2 We examined the effect of C. stellaris and its secondary metabolite usnic acid on nutrient uptake and growth of pine (Pinus sylvestris) seedlings in symbiosis with the ectomycorrhizal fungus Suillus variegatus and in non-symbiotic condition. 3 Contrary to our expectations, usnic acid had no effect on nitrogen uptake and growth in pine seedlings. The addition of lichen fragments into the growth substrate significantly increased biomass accumulation in mycorrhizal pine seedlings and needle nitrogen acquisition in non-mycorrhizal seedlings. 4 These results suggest that lichen mats do not have direct allelopathic effects on pine seedling nitrogen acquisition or growth.