On 8 November at 9:15 Jane Oja will defend her doctoral thesis „Temporal and spatial patterns of orchid mycorrhizal fungi in forest and grassland ecosystems“.
Prof. Urmas Kõljalg, University of Tartu institute of ecology and earth sciences, University of Tartu
Prof. Tiiu Kull, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences
Dr. Melissa K. McCormick, Smithsonian Environmental
Research Center, USA
Orchids represent one of the largest plant families and display tight associations with pollinators and mycorrhizal fungi. Orchid mycorrhizal (OrM) symbiosis is unique anatomically, taxonomically as well as functionally. Mycorrhizal fungi play a vital role for the orchids during their germination by providing essential nutrients to the dust-like orchid seeds that are almost devoid of their own food reserves. Even after orchids have developed green leaves and start photosynthesizing, their roots remain colonized by mycorrhizal fungi. However, the abundance of fungal colonization as well as the fungal community composition presumably change in the roots of the mature orchids during the vegetation period. Typically, photosynthetic, autotrophic orchids associate with saprotrophic fungi from the Ceratobasidiaceae, Tulasnellaceae and Sebacinales. So far, the distribution and ecological requirements of these fungi remain poorly explored. The aim of this thesis was therefore to study the temporal and spatial patterns of orchid mycorrhizal fungi in forest and grassland ecosystems. The thesis was particularly focused on 1) how the community composition of the putative OrM fungal taxa changes over the vegetation period in relation to the developmental phases of the host orchid species, 2) how the community composition of the putative OrM fungal taxa varies across different habitats as well as within the same habitat and on 3) how the richness of putative OrM fungi changes with the increasing distance from the orchid patches and 4) whether the putative OrM fungi form spatial patterns along the distance from the orchid patches. In addition, we extended annotations of publicly available OrM fungal ITS sequences. The main results of the thesis can be summarized as follows: 1) the community composition of the OrM fungi in roots was primarily host dependent and only secondarily affected by habitat and even to a lesser degree by the developmental phase and 2) in semi-natural grasslands, OrM fungi were randomly distributed and showed little evidence of a distance-dependent decline away from the adult orchids. We detected a number of insufficiently annotated OrM fungal sequences deposited in public databases, as well as sequences which suffered from low read quality and/or chimeras.