Differential response of western hemlock from low and high elevations to inoculation with plant growth-promoting Bacillus polymyxa

Abstract

The influence of inoculation with plant growth-promoting Bacillus polymyxa strains L5 and L6-16R was evaluated on the performance of western hemlock [ Tsuga heterophylla (Raf.) Sarg.] using seed that originated from six British Columbia provenances that differed primarily in elevation (from 152 to 1190 m above sea level). Preliminary analysis revealed a tendency for hemlock originating from high and low elevations to respond differently to bacterial inoculation, therefore subsequent analyses were performed after pooling data into two elevational groups: the three hemlock provenances located at the lowest elevations; and the three found at the highest elevations. B. polymyxa strain L6-16R-inoculated seed from the low elevation group produced an average of 2.38-fold ( P < 0.025) more seedlings than uninoculated controls midway through the emergence period, and 1.41-fold ( P < 0.05) more seedlings than uninoculated controls when emergence was complete. Inoculation of low elevation hemlock seed with strain L5 or of high elevation seed with either bacterial strain did not significantly affect seedling emergence. In contrast to the effects observed on emergence, growth of hemlock seedlings in the low elevation group was unaffected by inoculation with either bacterial strain, but strain L6-16R-inoculated high elevation seed produced seedlings that were significantly taller (1.19-fold; P < 0.05) and heavier (1.30-fold; P < 0.05) than uninoculated controls. Strain L5 did not stimulate growth of high elevation seedlings significantly. Hemlock rhizosphere colonization by strain L6-16R was assessed on seedlings that originated from one of the low elevation provenances and was found to be 1.7 × 10 3 cfu g −1 dry root tissue. These results indicate that seed inoculation with B. polymyxa strain L6-16R can result in colonization of western hemlock root systems and in significant increases in seedling emergence, height and biomass accumulation; however, the type of seedling growth response to inoculation with B. polymyxa may depend on the elevation of the provenance from which seed originates.