Effect of Laccaria bicolor strains inoculated on Douglas-fir (Pseudotsuga menziesii) several years after nursery inoculation

In the Saint-Brisson experiment conducted in central France, the American strain of the ectomycorrhizal fungus Laccaria bicolor (Maire) P.D. Orton S238N and the French strain L. bicolor 81306 inoculated on containerized Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings increased by 60% the total volume of wood produced 8 years after outplanting as compared with uninoculated but naturally mycorrhizaltrees. The two strains introduced 10 years before in the inoculated plots are still present and dominant; they did not prevent the colonization of Douglas-fir roots by naturally occurring ectomycorrhizal fungi but allowed for the establishment of a very diversified symbioticmicroflora. Eight to 12 years after outplanting, all the Douglas-firplots were colonized by Laccaria laccata (Scop.:Fr.) Cooke or L. bicolor strains, as well as some other species, independently of the nursery treatments. With one exception in one plot, the presence of indigenous genets in the control treatments may have prevented the vegetative colonization of the inside of the noninoculated plots by the twointroduced strains. [ABSTRACT FROM AUTHOR]