Unravelling the distribution, structure and function of diverse plant-fungal symbioses

Among the Earth’s most important symbiotic relationships are the associations between mycorrhiza-forming soil fungi and plant roots, where fungal acquired nutrients are exchanged for photosynthetically fixed plant carbon. A distinctive group of mycorrhizal fungi known as Mucoromycotina Fine Root Endophytes (MFRE) have been molecularly identified across land plants over the last decade and have been shown to form nutritional mutualisms with liverworts and the vascular plant Lycopodiella inundata. As interest grows in the potential application of MFRE in agriculture as biofertilisers, it is imperative that we learn more about the ecology and function of these fungi in vascular plants. This thesis is concerned with addressing these knowledge gaps. A third of my investigations were dedicated to evaluating and improving methods for the molecular detection of MFRE in plant roots and for the enrichment of vascular plants with MFRE. I used a cloning with Sanger sequencing approach to detect fungal symbionts in plant specimens from New Zealand and the UK. For the first time, I molecularly confirmed MFRE in the roots of white clover, wheat, barley and the strawberry plant, obtaining 25 new MFRE DNA sequences. I set up two isotope tracing pot experiments to compare fungal transfer of nutrients in plants colonised by two different fungal communities, an MFRE-enriched one and one with only arbuscular mycorrhizal fungi (AMF), under low nutrient conditions and in the presence of other soil microorganisms. I found that co-colonisation of plant roots by MFRE and AMF does not impair the transfer of fungal acquired phosphorus to Trifolium repens and fungal acquired nitrogen from organic and inorganic sources to Holcus lanatus. However, the presence of MFRE stunted plant architecture in both experiments, suggesting that MFRE symbioses occur on a parasitism-mutualism continuum. Bearing these findings in mind, I make recommendations for further MFRE research.