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UBC Theses and Dissertations

Phytobiomes and soil communities : assessing natural communities and the impact of anthropogenic change on plants, soils and their associated organisms Super, Laura


Biodiversity on Earth is under immense threat and we must increase our understanding across systems to help research, conserve, manage and protect biodiversity for its own sake and human livelihoods worldwide. This thesis examined plant and microbial biodiversity across scales in three study systems: study system 1, a growth chamber experiment; study system 2, a field experiment with experimental nitrogen deposition and open top chamber warming in clear-cuts (CC) and forests edges (FE) at the subplot and plot scale, in a research forest in Canada; and study system 3, data mining across ecosystems in the continental United States of America. This thesis aimed to assess phytobiomes, plant performance, associated phytobiome communities (prokaryotic, fungal, nematode), and relationships (organism-pH, cross-taxon) to quantify richness and stochasticity and to use richness and stochasticity theory for synthesis across systems and scales. In study system 1, soil refugia treatments (bare soil vs. soil amended with plant roots of Arctostaphylos uva-ursi, Calamagrostis rubescens, or Pseudotsuga menziesii) did not impact P. menziesii seedling performance, but nematode abundance increased and root and shoot mycobiome stochasticity differed. In study system 2, simulated nitrogen deposition did not impact planted tree seedlings and associated understory vascular plant cover and there was no nitrogen and warming interaction effect, but warming increased plant growth in clear-cuts and the microenvironment impacted growth in both clear-cuts and forest edges. Plant and nematode richness and stochasticity were higher in clear-cuts than forest edges, but prokaryotic and fungal communities showed no trend. Stochasticity, not richness, had organism-pH and cross-taxon associations. In study system 3, plant and prokaryotic richness showed a linear organism-pH relationship across forests, but across different ecosystems only plant variables had a unimodal relationship with pH. Overall, this thesis finds that stochasticity and richness tend to be positively correlated. Stochasticity relationships were more common than richness relationships. For plants, lower stochasticity related to lower richness, local disturbance increased stochasticity and high determinism appeared with different ecosystem comparisons. Plant and nematode communities showed similar trends. Fungal communities generally showed higher stochasticity.

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