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A comparison of soil microbial communities in adjacent forest types that differ in nutrient cycling rates Leckie, Sara Elizabeth


Soil microorganisms have fundamental roles in terrestrial ecosystems yet little is known about the composition, activity, and dynamics of these communities. I investigated the soil microbial communities in two common coniferous forest types of northern Vancouver Island, British Columbia. These two ecosystem types occur adjacently and are similar as coastal temperate coniferous forests with the same types of processes occurring. They differ, however, in nutrient availability and productivity. They thus provide an interesting contrast for exploring variability in forest soil communities and potential links between the organisms and soil processes. Microbial community composition was measured using several cultivation-independent approaches: denaturing gradient gel electrophoresis (DGGE), ribosomal intergenic spacer analysis (RISA), internal transcribed spacer (ITS) and phospholipid fatty acid (PLFA) analyses. Although the communities in each forest type were found to be largely similar using DGGE, RISA, and PLFA analyses, differences were detected using the ITS analysis of the fungal communities. PLFA analysis also detected subtle differences between the forest types in overall composition as well as within particular groups of organisms. Fungal PLFAs were more abundant in the nutrient-poor CH forests. Bacteria were proportionally more abundant in HA forests than CH in the lower humus layer, and Gram-positive bacteria were proportionally more abundant in HA forests irrespective of layer. Bacterial and fungal communities were distinct in the F, upper humus, and lower humus layers of the forest floor and total biomass decreased in deeper layers. These results suggest that the microbial communities in these two forest types are similar but that they do differ in detectable ways. These differences may relate to differences in ecosystem process rates, although, in this study, it was not possible to determine cause and effect.

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