ECOLOGICAL GROWTH-RESPONSE SPECIFICITY OF 2 DOUGLAS-FIR ECOTYPES INOCULATED WITH COEXISTENT BENEFICIAL RHIZOSPHERE BACTERIA

The influence of inoculation with rhizosphere bacteria on Douglas-fir (Pseudotsuga menziesii (Mirb.) France) seedling emergence in a control led environment and on survival and growth in the field was investigat ed. Seed or seedlings of interior and coastal Douglas-fir ecotypes ori ginating from the vicinity of Williams Lake and Chilliwack, British Co lumbia, Canada, respectively, were inoculated with two strains of rhiz osphere bacteria, Arthrobacter oxydans strain N74 and Pseudomonas aure ofaciens strain K23. These strains were previously isolated from natur ally regenerating Douglas-fir seedlings collected from the Williams La ke and Chilliwack sites, respectively. Seed inoculation with either st rain of bacteria, K23 or N74, stimulated the rate of seedling emergenc e, but these effects were not ecotype specific. While inoculation did not affect germination percentage, ecotype-specific seedling growth re sponses were detected 13 months after field planting. Arthrobacter oxy dans strain N74 significantly stimulated seedling branching and enhanc ed root and shoot dry weight of the Williams Lake ecotype but had no s ignificant stimulatory effect on growth of the Chilliwack ecotype. Pse udomonas aureofaciens strain K23 significantly stimulated shoot branch ing and root dry weight of Chilliwack Douglas-fir but had no significa nt stimulatory effect on growth of that from Williams Lake. When treat ments of Douglas-fir seedlings and rhizosphere bacteria that originate d from the same geographic site were pooled and compared with uninocul ated controls, significant increases in shoot branch number and root d ry weight were also detected. No significant difference in seedling gr owth was detected when treatments of seedlings and bacteria that origi nated from different sites were pooled and compared with uninoculated controls. Based on these results, we hypothesize that plant-microbe sp ecificity may be an important component of Douglas-fir - beneficial rh izosphere bacteria interactions in the field.