Exploring drivers of spatial and temporal trends in soil microbial communities

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.