Growth stimulation of young oak plantations inoculated with the ectomycorrhizal fungus Paxillus involutus with special reference to summer drought

Nursery-grown Quercus petraea and Q. robur seedlings were inoculated with the ectomycorrhizal fungi Paxillus involutus, Hebeloma crustuliniforme or Laccaria laccata. At the end of the first growing season, the seedlings with roots colonized with the inoculated fungi were outplanted at two sites in northeastern France in 1985 or 1988. P. involutus was found to be the most competitive and efficient of the three fungi tested; its mycorrhizas were present 7 yrs after outplanting and it markedly improved the growth of both oak species. In the case of Q. robur, the growth stimulation was more marked on years with a dry summer. These results are discussed in terms of water relations and of competitiveness of the introduced versus resident symbiotic fungi.