VESICULAR MYCORRHIZAL COLONIZATION OF SEEDLINGS OF PINACEAE AND BETULACEAE AFTER SPORE INOCULATION WITH GLOMUS INTRARADICES

Although Pinaceae and Betulaceae have been reported to contain Glomus- type root endophytes, its ecological importance and the conditions inf luencing this symbiosis are poorly understood. Seedlings of Abies lasi ocarpa, Alnus rubra, Pinus contorta, Pinus ponderosa, Pseudotsuga merz iesii, and Tsuga heterophylla were inoculated with Glomus intraradices to determine the vesicular-arbuscular mycorrhizae (VAM) development a nd responsiveness of these hosts. The role of companion VAM host plant s on mycorrhizal colonization and nutrient uptake by Pseudotsuga menzi esii was also examined by growing seedlings of Pseudotsuga menziesii i n dual culture with VAM hosts Thuja plicata or Calamagrostis rubescens . After 8 weeks, no seedlings were colonized. At 16 weeks, 8 of 17 Thu ja plicata seedlings grown with Pseudotsuga menziesii and all 18 inocu lated Thuja plicata seedlings grown alone were colonized with vesicles and hyphae. Two of 17 inoculated Pseudotsuga menziesii seedlings grow n in dual culture with Thuja plicata were colonized with abundant vesi cles and hyphae. No ectomycorrhizal seedlings grown in monoculture wer e colonized. At 9 months, all 10 Calamagrostis rubescens and all 10 in oculated Pseudotsuga menziesii seedlings grown in dual culture were co lonized by vesicles and hyphae. Two of 10 inoculated Pseudotsuga menzi esii and 1 of 10 inoculated Pinus ponderosa seedlings grown in monocul ture were similarly colonized. The mean phosphorus content in the need les of colonized Pseudotsuga menziesii seedlings grown with Calamagros tis rubescens was about twice as high as in noncolonized Pseudotsuga m erziesiiseedlings grown with Calamagrostis rubescens. Tissue nitrogen did not differ between these treatments. The results show that Glomus intraradices colonization of Pinaceae is most successful when a VAM ho st is present, although some vesicular colonization of Pinaceae occurr ed in the absence of a VAM host.