The significance of host-fungus combinations in ectomycorrhizal symbioses for the chemical quality of willow foliage

The majority of plants interacts with mycorrhizal fungi, which predominantly provide mutual benefits, but also costs. We tested the hypothesis that specific combinations of host plants (four commercial varieties of Salix spp.) and ectomycorrhizal partners (species of Laccaria, Paxillus, Tricholoma and Hebeloma) differ in their effects on the host foliar chemistry. Twenty specific host - mycorrhiza combinations were pot-grown outdoors under low-N conditions. Foliar concentrations of total phenolics and salicylic acid were decreased by mycorrhizas in S. schwerinii x S. viminalis and S. x dasyclados genotypes, but increased in S. viminalis. Mycorrhiza effects on host biomass production were positive, indifferent or negative, depending on the specific host-mycorrhiza combination. The host plant genotype influenced mainly the direction of mycorrhizal effects on foliar chemistry, whereas the magnitude of mycorrhizal effects varied mostly among the fungal genotypes. The results are relevant with respect to the possible interactions between mycorrhizas, plants and leaf herbivores.