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UBC Theses and Dissertations

Long-term effects of timber harvesting on hemicellulolytic microbial communities in North American coniferous forest soils Leung, Hilary


Forests are essential for maintaining global climate and biodiversity, with industrial applications vital to the world economy. Forest soils are inhabited by a highly diverse community of macro- and microorganisms which are responsible for a variety of fundamental ecosystem services such as decomposition, and nutrient cycling. The effects of forest disturbance on soil microorganisms specific to these key processes have yet to be studied thoroughly. Bearing in mind the importance of forest soil organisms, I have identified and investigated the long-term effects of forest disturbance by timber harvesting on bacterial and fungal populations that degrade hemicellulose using molecular techniques coupled to stable-isotope probing (SIP) with ¹³C-hemicellulose. I identified 104 putatively hemicellulolytic bacterial operational taxonomic units (OTUs) and 52 putatively hemicellulolytic fungal OTUs. Based on analysis of ¹³C-enriched phospholipid fatty acids and DNA, harvesting resulted in long-term changes in relative abundances of putatively hemicellulolytic bacterial and fungal populations. Although harvesting resulted in long-term changes in these populations, no statistically significant differences in potential hemicellulolytic activity of the soils was observed, suggesting functional redundancy in this fundamental ecosystem process. Additionally, I identified Methylibium, a genus of facultative methylotrophs as a novel putative hemicellulose degrader. This study is the first to extensively survey both bacterial and fungal soil microorganisms specific to hemicellulose degradation using stable-isotope probing, and to provide evidence for long-term effects of timber harvesting on these populations. These results contribute towards the strategic management of forest ecosystems, and the identification of novel hemicellulolytic organisms in this study will pave new roads for industrial applications of cellulolytic and hemicellulolytic enzymes.

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