Lichen-plant interactions

Controversial data on the pathways and effects of lichen growth on and near bryophytes and vascular plants are reviewed. In most cases, plants which are used as growth substrates positively influence lichen mineral nutrition and are poorly affected by lichen overgrowth, but several reports of negative relationships, including lichen parasitism and allelopathic interferences, prevent generalizations. The allelopathy of terricolous lichens against neighboring plants has been suggested by in vitro investigations, and a multidirectional phytotoxic mode of action has been shown for lichen secondary metabolites. Recent researches on field settings, instead, offer little support of lichen allelopathy, and plant allelopathy against lichens has so far been neglected. A comparison with lichen-rock interactions indicates that a common set of physical and chemical factors can explain the heterogeneous reciprocal effects that exist between lichens and plants, which depend on the species involved, and highlights gaps that need further studies.