Bryophyte-microbe interactions on the remote oceanic island of St. Helena

Bryophytes (mosses, liverworts and hornworts) are major contributors to the functioning and biodiversity of many terrestrial ecosystems. Together with their associated microbial communities (microbiomes), bryophytes play key roles in nutrient cycling; however, many aspects of these communities are poorly understood or completely ignored. The composition of bryophyte microbiomes is thought to vary across species but is also influenced by habitat and may vary across disturbance gradients. Bryophyte microbiomes may comprise a wide range of organisms including nitrogen-fixing cyanobacteria, methanotrophic bacteria and fungi, with associations occurring both below and above ground and ranging from intimate endosymbioses through to more loose epiphytic associations. Interactions between plants and microbes can have a significant effect on the host phenotype, mediating processes such as pathogen resistance, stress tolerance, nutrient acquisition, growth and reproduction. To date, most research on plant-microbe interactions has focused almost exclusively on 'higher' vascular plants and comparatively little is known about the microbiomes of bryophytes and how bryophytes are influenced by their associated microbial communities and vice versa.
St Helena is a tiny (121.7 km2) and isolated volcanic island in the South Atlantic Ocean with a mild tropical climate tempered by the ocean that is part of the UK Overseas Territory of St. Helena, Ascension and Tristan da Cunha. It has a unique flora and fauna with an exceptionally high level of endemism. However, biodiversity is severely threatened by anthropogenic pressures such as habitat destruction and invasive species. Mosses, liverworts and hornworts are an important component of the flora, with most of their diversity found in the remnant fragments of St. Helena native and highly threatened cloud forest in the Peaks National Park.
The aims of the PhD project are to characterise for the first time the microbiome community composition of bryophytes on St. Helena, test for interactions between microbes and fungi, and determine how microbiomes and interactions vary across species, host genotype, habitat type and along disturbance gradients.
This project will take an integrative approach, combining extensive field work on St. Helena with laboratory-based methodologies including state-of-the-art sequencing and imaging techniques and in vitro studies. The PhD student will characterise the microbiomes (bacteria and fungi) using DNA sequencing, bioinformatics, statistical and microbial community structure analysis techniques. The plant-microbe interactions will be studied and documented using in vivo laboratory-based cultivation experiments and scanning electron and light microscopy. The PhD student will collaborate with a multi-disciplinary team at the Natural History Museum and Imperial Collage London as well as work directly with the St. Helena's Government, CASE partner on the project.