Abstract:
Microbial communities play fundamental roles in ecosystem functioning and are an
essential biological component of soil environments. Therefore, determining the relative
importance of the various factors influencing soil microbial communities and their functional
potential is important. Through amplicon and shotgun metagenomic sequencing, this thesis
examines microbial community interactions with abiotic and biotic elements of their
surrounding environments.
This study encompasses a range of different land uses, including those which have
been subject to recent land use change, to determine the consistency of microbial
biogeographic patterns across spatial and temporal scales. Land use was the dominant driver
of soil bacterial community composition and functional potential. Microbial communities
responded in a somewhat predictable way after land use conversion by shifting from
communities reflecting their former land use towards reflecting their current land use. These
directional changes in soil bacterial community composition after land use conversion were
consistently observed across various land use conversion types and different regions. In
horticultural systems, soil bacterial community composition was more stable than
phyllosphere communities over time, mainly due to the stronger influence of selection in
structuring the soil bacterial communities, suggesting a greater potential for predicting the
responsiveness of soil communities to environmental change. Additionally, while reduced
tree-species diversity did influence soil microbial taxonomic and functional community
profiles, soil environmental conditions and geographic distance had a more important role in
structuring microbial community composition. The soil bacterial communities appeared more
impacted by soil conditions, while the fungal communities displayed stronger spatial
structuring, attributed to differing dispersal capacities between these taxonomic groups.
The results from this thesis emphasise the dominant role anthropogenic land use holds
in structuring soil microbial communities. Importantly, this research highlights the longlasting effects of land use on microbial composition and fundamental soil processes. The
different spatial and temporal scales explored in this thesis, alongside the incorporation of
both taxonomic and functional components of microbial communities, help to better
understand the consistency of microbial community responses to environmental changes.
Improvements in our fundamental understanding of the dynamics of soil microbial
communities will aid in incorporating biotic variables into soil health monitoring systems.