Linking root microbiome composition to relative fitness differences that impact plant-plant competition

Thesis

Theoretical and empirical work show that species coexistence depends upon the balance between niche differences (strength of intraspecific vs interspecific competition) and fitness differences (competitive ability). Stable coexistence requires that niche differences are greater than fitness differences. In the absence of niche differences, one species dominates and the rest are competitively excluded at rates relative to the magnitude of fitness differences between species. Soil communities influence both niche and fitness differences in plant communities, thus have impacts on community stability and biodiversity. Here, I test relative fitness differences affected by four local soil communities on ten Arabidopsis thaliana genotypes, grown as individuals, or in communities over five generations. A pilot experiment showed that relative fitness differences among Arabidopsis genotypes changed depending upon the soil community, but that this was not related to known differences in root chemistry (Chapter 1). Over five generations with niche-minimized plant-plant competition, soil communities resulted in communities of Arabidopsis genotypes with differences in genotypic composition (Chapter 2). A second test growing plants as individuals showed again that soil communities determined the relative fitness differences among genotypes, and that relative fitness differences are accompanied by small differences in bacterial root microbiome composition (Chapter 3). I added soil communities to the growing media as inocula made from soils collected at multiple time points from four sites in Oxfordshire. The four soil communities added each generation of the experiment were distinct over sampling time, so plant communities adapted to different soil communities (Chapter 4). This work could be complemented by functional analysis of soil communities and root microbiomes, or the use of synthetic communities to link microbial taxa to plant fitness effects. These results support the importance of soil communities to processes that impact plant species coexistence, and thus the maintenance of biodiversity.

Authors: Norton, CH

• DOI: 10.5287/ora-0o8p2n9yv
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: arabidopsis; root microbiome; relative fitness differences; plant-plant competition; plant ecology
• Subjects: Microbiology; Botany; Ecology; Biology