Title: Serendipita diversity in Australia: Biogeography and specificity of Serendipita across the Australian continent
Applicant: Fitria Tisa Okalita
Institution: The Australian National University
This project will investigate biogeographical patterns in Serendipita on a continental scale. We are targeting four Australian orchid genera associate with Serendipita; Caladenia, Eriochilus, Microtis and Cyrtostylis. Although one study has shown some Serendipita lineages have a continent-wide distribution (Davis et al., 2015), most fungi surprisingly appear to be geographically restricted. Geographic restriction could however, be an artefact of sampling. Therefore targeting phylogenetically related orchids (which should associate with similar OMF) as well as species that are widespread (which usually means they associate with a large number of OMF lineages – increasing the possibility of finding similar Serendipita lineages in eastern and western Australia) should elucidate whether an east-western Australia distribution is more common than previously thought. Also, this will maximise our chances of finding OMF that have wide geographic distributions. The investigation of germination ability of studied orchid in utilizing a range of given fungi during germination may facilitate improvement in the knowledge for ex situ conservation to enable informed assessment of the suitability of mycorrhizae for translocation/restoration of endangered orchid species. Therefore, this approach will contribute in retaining biodiversity by conserving endangered orchid species as well as fungal lineages they associate with. Lastly, by providing biogeographical pattern of distribution of Serendipita on a continental scale will contribute to understanding Australian biodiversity in a cryptic and ecologically important group of soil fungi.
We investigated whether Serendipita fungi in Australia are broadly distributed at the continental scale, whether Serendipita Operational Taxonomic Units (OTUs) are shared between southwest (SWA) and southeast Australia (SEA) and whether SWA, which has high floristic diversity, also have a higher Serendipita diversity. Fungal symbiont diversity of species-pair comparisons of five orchid genera (Eriochillus – Eriochilidinae, Caladenia, Elythranthera, Glossodia, – Caladeniinae, Cyrtostylis – Acianthinae), one species of each genus occurring in either SWA or SEA, were investigated. In total, 35 OTUs of Serendipita were identified with ITS sequencing from the roots of eight orchid species pairs. Depending on the subtribe of orchids studied, some subtribes were highly specialised in their fungal associations, while orchids in the Eriochilidinae are true generalists associating with 30 OTUs. This study shows that a widespread orchid distribution may be achieved by forming an association with a range of mycorrhizal partners or with a few widespread fungi and potentially not limiting orchid distribution. In total, 14 of the 35 OTUs were found on both sides of the continent, suggesting either long-distance dispersal or historic step-wise dispersal on a continuous landscape. Elucidating fungal distribution patterns have important consequences for future conservation studies, potentially highlighting recruitment sites with specific fungi for endangered orchids. The number of Serendipita OTUs, Shannon’s diversity and phylogenetic diversity of Serendipita did not differ significantly between geographic regions. Therefore, higher plant diversity in SWA does not result in a higher apparent Serendipita diversity.
Further, we investigated whether symbiotic orchid seed germination always exhibits lower fungal specificity during in vitro germination as previously thought, employing multiple Australian common sebacinoid orchid species. While some species showed similar mycorrhizal specificity in both germination and adulthood, the other studied orchid species could be germinated by more Serendipita OTUs than those found in adult plants, suggesting lower mycorrhizal specificity during germination. No significant difference in the mean of the number of OTUs could germinate orchid seeds and OTUs found in adult roots. Serendipita OTUs which germinated seeds in the in vitro germination trials occur on both sides of the Australian continent, suggesting there likely are new potential recruitment sites for the orchids which do not match the fungal distribution.