QUANTIFYING THE EXTENT FUNGAL MYCORRHIZAL COMMUNITIES AFFECT ORCHID NICHE BREADTH AND GEOGRAPHICAL DISTRIBUTION

Periodic Reporting for period 1 - MYCRONICHE (QUANTIFYING THE EXTENT FUNGAL MYCORRHIZAL COMMUNITIES AFFECT ORCHID NICHE BREADTH AND GEOGRAPHICAL DISTRIBUTION)

Periodo di rendicontazione: 2015-09-01 al 2017-08-31

As a consequence of increasing human influence on the natural environment, there has been a decrease in the abundance of plant populations in Europe over the last 50 years. In addition, there has been a reduction in the abundance of important plant mutualists (e.g. mycorrhizas) in the soil, and such decreases in mutualists are expected to negatively impact on important life-history stages in certain plant groups e.g. seed germination of orchids. However, we do not know how soil mycorrhizas vary across a range of different habitats. One salient example of such declines are members of the genus Spiranthes. Spiranthes populations are known to be in decline and of conservation concern. A combination of both habitat and mycorrhizal limitation may underlie the decline of Spiranthes populations and impede their ability to colonise novel habitats in the future. The overall aim of MYCRONICHE was to quantify the extent to which plant populations over a large geographical range rely on fungal (mycorrhizal) mutualists and to test whether interactions between plants, specifically orchids, and their associated mycorrhizas vary geographically. Specifically, this project aimed to; (i) provide a European-wide quantification of the distribution of orchid mycorrhizas using state-of-the-art genetic sequencing methods, (ii) show the extent to which this single biotic factor can affect the potential for orchid populations to adapt to novel or heterogeneous environmental conditions, and (iii) demonstrate the potential extent-of-occurrence of declining orchid populations, amidst rapid habitat fragmentation and shifting species distributions due to climate change.
The general conclusions of MYCRONICHE are:
1. That mycorrhizal communities associated with Spiranthes spiralis differ over the geographical range and according to habitat type, but that similar mycorrhizal fungi are associated with S. spiralis populations throughout the range of S. spiralis.
2. That seeds of S. spiralis from different regions can germinate in different populations in its range.
3. That future climate change scenarios will have a strong impact on species ranges, particularly their ecological and geographical isolation.

MYCRONICHE consisted of three Work Packages (WPs) that investigated the following three hypotheses:
1. There is spatial variation in the European distribution of fungal mycorrhizas associated with Spiranthes populations.
2. Spiranthes populations are locally adapted to particular fungal mycorrhizas that vary over the European range
3. Spiranthes utilise different mycorrhizas at different life-stages (e.g. germination, seedling establishment) and mycorrhizas may limit individual growth.
WP1: Spatial variation in mycorrhizal taxa associated with Spiranthes populations
For this, up five individuals were sampled from 50 populations across the entire range of S. spiralis. This included sampling across population over a ~2,500 km latitude. Root material was collected from each individual and we amplified the fungal ITS 3/4OF gene region to identify mycorrhizal taxa associated with each orchid. For this, we used Illumina Miseq amplicon sequencing. In total, we have mycorrhizal data from >100 individual S. spiralis plants from 39 populations, representing all regions of its distribution. This is the largest database of mycorrhizal taxa associated across the geographical range of one orchid species that we know of. Our initial results show that two most abundant mycorrhizal families that associate with S. spiralis across Europe are the Ceratobasidiaceae and Thelephoraceae.

WP2: Quantifying whether Spiranthes populations are adapted to their local mycorrhizal communities
We performed reciprocal translocation experiments between populations in Ireland, France, and Greece. This involved collecting seeds from each region and placing seeds from each region in seed packets and placing these in marked locations in the soil in each of the three regions. These seed packets are enclosed in algae mesh which allows the seeds to remain in place in the soil, while simultaneously allowing mycorrhizal fungi to penetrate the seeds. 20 seed packets from each region was placed in each region (60 seed packets in total). These seed packets were left in the field for 15 months to allow seeds to germinate. At the end of this period, seed packets were dug out of the soil and microscopically examined to see if germination had taken place. We found that there was evidence for early stages of seed germination of all seeds in all regions, indicating that Spiranthes seeds can germinate in any region, provided suitable mycorrhizas are present.

WP3: Extent to which mycorrhizas limit establishment from seeds and seedlings.
For this WP, we needed to cultivate mycorrhizal fungi in laboratory conditions and present orchid seeds to the fungi. However, we could not culture mycorrhizas under controlled conditions in the lab. Therefore, for this WP, we took the opportunity to shift the research focus slightly to understand biogeography of a different plant genus, Pulmonaria (Boraginaceae) under various climate change scenarios. Pulmonaria is a taxonomically complex genus, containing between 10 and 18 species. Members of Pulmonaria tend to lack pre-zygotic barriers to mating as they have strong overlapping distributions, share pollinators (mostly bumblebees and bees), and many produce hybrids. We tested whether an important pre-mating barrier – ecogeographical isolation would change under future climate scenarios. In that way, we tested whether anthropogenic climate change may indirectly shape the potential for plant evolution through hybridisation. We calculated ecogeographic isolation under dispersal limitation, we found that there was an overall increase in ecogeographic isolation. These results highlight the potential of climate change will have a direct effect on the distributions of plants in the near future.

These results have been presented at the International Botanical Congress in Shenzhen, China in July 2017. We are currently analysing and assembling our database of mycorrhizas associated with S. spiralis. Once the papers have been published, as outlined in our Data Management Plan, we will provide all published data via open source platforms – GenBank for gene sequences of mycorrhizal taxa and DRYAD for climate and mycorrhizal taxon distribution data so other scientists can access our data. We will also make a database for the distribution of mycorrhizas in Europe associated with S. spiralis which will be available on DRYAD for researchers.

MYCRONICHE progressed beyond the state of the art, with the expected results to be of broad importance to society. This is because MYCRONICHE provided a large-scale test of how a mutualist varies between populations over a large geographical scale. The approach to be taken by this project was novel, as it; (i) provides a European-wide examination of the distribution of mycorrhizas using Illumina Miseq amplicon sequencing methods, (ii) showed the extent to which a single biotic factor (mycorrhizal communities) can affect the potential for orchid populations to adapt to novel conditions, and (iii) demonstrated the potential of ecogeographic isolation and shifting species distributions due to climate change. The datasets and results will be of benefit to scientists working to predict how species and habitats will shift in an increasingly human-dominated environment.

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Periodic Reporting for period 1 - MYCRONICHE (QUANTIFYING THE EXTENT FUNGAL MYCORRHIZAL COMMUNITIES AFFECT ORCHID NICHE BREADTH AND GEOGRAPHICAL DISTRIBUTION)

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