18 minute read
Feature interview - Nathan Emery: fighting the extinction battle seed-by-seed
Rebecca Harcourt interviews Nathan Emery, Manager of the Seedbank & Conservation Collections in the Australian PlantBank, based at the Australian Botanic Garden Mount Annan.
Nathan’s interest in plants started during his many childhood cicada hunting adventures in the bush with his father. While he still hunts cicadas in his spare time, his day job revolves around the seedbank, and includes both lab work and fieldwork. I chatted to Nathan about his work as a seed scientist and ecologist, which involves seed collection and research, plant monitoring, threatened species translocation and restoration.
How did you become interested in seeds?
My fascination with seeds started when I came across a book called Australian Seeds (Sweedman & Merritt, 2006). I must have been 20 or 21, between second and third year university. I read that cover to cover and became fascinated with seeds and then the notion of seed banking and seed conservation.
You work at the Australian PlantBank. What is it?
PlantBank is a $20 million state of the art germplasm research and conservation facility. At its heart is the ex situ conservation seedbank that holds over 13,000 seed collections representing about 20–25% of Australia’s flora. We have about 5,000 Australian species in the seedbank, with around half of New South Wales’ endemic seedbearing flora and 72% of New South Wales’ threatened flora.
Alongside the seedbank are germination and research facilities. Scientists like me use these and the collection to undertake seed biological research to better understand how we can store, maintain and grow our native flora. There’s also the tissue culture collection and cryostorage facilities for what we call ‘exceptional’ or recalcitrant species. These are the species whose seeds don’t tolerate orthodox conditions to slow their ageing, which we do by drying the seeds to a small percentage of their moisture content before placing them in storage at −20 °C. Usually these seeds have a lot of internal oils and lipids that tend to break down at −20 °C, destroying their viability. There are also species like many of the Myrtle Rust affected plants that just aren’t producing viable seeds. Putting them into tissue culture or growing them from cuttings and incorporating them into the living collection is the main way we can conserve these species in the absence of seed material.
What’s the process once the seeds are brought into the PlantBank?
We remove all the non seed material collected with the seeds and check seed quality. This involves looking at the fill rate (1) of seeds because plants produce different proportions of empty seeds, or the seeds may have been damaged by predators. We want to limit the amount of non viable material in the collection where possible. We then do a viability test. The best way to determine the viability of a collection is by germinating the seeds. We then dry the collection down under controlled environmental conditions at 15 °C and 15% relative humidity to about 5% of its original moisture content. This limits the moisture in the seeds and the amount of ice crystals that can form when frozen (2).
We then store the seeds at −20 °C, which slows the ageing rate of the seeds considerably. For some species viability can be maintained in storage for years, others, decades, or for some of our harder seeded species like the acacias, it can be up to 100 years.
Although the ageing process is significantly delayed, it still occurs, with seeds losing viability over time, albeit more slowly. This means that as well as understanding their initial viability when they go into storage, we must continue to monitor the viability to see how they’re progressing over time. We need to know whether they’ve dropped below a viability level that would trigger a re collection or a propagation event to get more seed material if that population or that species doesn’t exist in the wild at that time or at some time in the future.
Seed banking is the most cost-effective way of maintaining collections ex situ.
We will store collections or seek collections of species even if they have 10 or 50 seeds, because that’s still critical genetic material. Where we can’t collect seeds, we have to look at other collection methods. This is typically through vegetative cutting or propagation and that’s where our horticulturalists in the nursery get involved. These plants may also get incorporated into the tissue culture or cryostorage collection. They may also be incorporated into the living collection across our three botanic garden sites.
Which species do you focus on?
A key focus for us is on the species listed in the New South Wales Biodiversity Conservation (BC) Act 2016. We work with New South Wales Department of Climate Change, Energy, Environment and Water to prioritise species within that list based on several considerations, such as their listing status. It makes sense to target those that are Critically Endangered and Endangered because they’re obviously on the fast path to decline and extinction.
We also focus on species for which we don’t have representative collections in the seed bank or in the living collection here at the gardens, as well as species that have complex seed dormancy and seed germination requirements. It’s one thing to make collections of threatened species and put them in the bank but if we don’t understand how to propagate them and grow them into plants, what’s the point of holding them in a repository?
Do you treat the threatened species differently to other species?
We’re starting to treat them a little bit differently in how we prioritise the collecting strategy: what we collect and how we collect it out in the field. Threatened species tend to have lower genetic diversity. This is inherent in many of these species because they’re in small populations, often very isolated and fragmented, and this is part of the reason why they are threatened in the first place. Often there’s a short term or even an immediate need to translocate these species, or build resilience into declining populations by adding new genetic diversity to them.
We are now employing a strategy where we collect seeds of threatened species by maternal line, keeping the seed collected from maternal plants separate (van der Merwe et al., 2023). Traditionally, we would bulk all the collections in what we term a composite collection, but now we are looking to retain the genetic integrity of these collections. This is so that when genetic data on these species become available, we can relate it back to our collections and look at those genotypes and understand where the diversity lies within those maternal lines. We can also better identify if we have, by accident, picked clones or hybrids. If we have a composite collection, it is difficult to separate and identify the diversity within it. In cases where specific genetic diversity is needed, these collections have a greater risk of failing to meet that requirement. That’s really the main difference that we’re employing between threatened species and common species at the moment. We are using this strategy as a test case to see whether it’s a viable strategy for all species. We can always bulk the seeds later for whatever purpose. Once they are bulked in the field, however, you can never really tease them apart.
We have a genetics team within the Botanic Gardens of Sydney (BGoS), the Research Centre for Ecological Resilience (RCER), that checks the genetics. They have refined and published workflows for genomics sequencing and studies on plant species in which they address several key conservation and taxonomic questions (Rossetto et al., 2021). This relies on the collection of leaf material from plants that are the target species, but in a lot of cases there may be additional sampling from closely related taxa; for example, if there’s an issue with taxonomic integrity of those species, such as if you’ve got a lot of subspecies or perhaps a species that’s split by one or two morphological characteristics.
We collect leaf samples of the maternal plants as well as seeds. We then have the linked genetic data to those seed maternal lines. The beautiful thing about sampling leaf material is once it’s freeze dried, it can stay in storage for (almost!) eternity. This means we can collect material for which there might not be funding for genetic sampling immediately, but it’s still there for when funding becomes available. That helps our collection strategy and planning in two ways. First, if the genetic studies have been performed, we can better target our collecting strategy for specific populations or genotypes where we know the diversity is present. Secondly, we can employ best practice to sample leaf material geographically representatively across populations. Then, when funding becomes available, we have that data linked so we can go back and look at our collections and see how well we guesstimated the genetic diversity. Did we capture it sufficiently or are there additional populations or pockets of diversity that we need to go back and supplement our collections with?
The beautiful thing about sampling leaf material is once it’s freeze-dried, it can stay in storage for (almost!) eternity.
How close are you to holding insurance populations for your current threatened species list?
We have just over 72% of plants classified as under threat by the New South Wales BC Act 2016 secured by at least one seed collection in the seedbank, but that doesn’t include any additional species that may be represented in our living collections.
If species are stored by at least one collection, it doesn’t necessarily mean that they’re representatively sampled or secured, but there is at least some level of genetic security as an insurance for those species. We’d really like to be able to confidently say that we have 72% of all those species representatively sampled across their known genetic diversity and distribution. It’s a new way of thinking about collections, rather than just going out and making collections systematically. We want to know, for example, how to propagate them, how to germinate them and what relaxes their seed dormancy, so we have all the information and as much material available as possible.
Are you looking to prevent other plants from joining the threatened species list or are you focusing only on the current ones on the list?
Our seedbanking program is statewide. It includes all New South Wales species, and we have an ongoing collection program. A lot of our external funding and external projects are threatened species related because that’s where a lot of the focus is but Threatened Ecological Communities (TEC) are also starting to receive more funding, which is great to see. The focus over the last probably 10 to 15 years has, however, been on threatened species as the major target for us (for example, see Cuneo et al., 2018).
What is the value of all botanic gardens working collaboratively on threatened species?
I think botanic gardens are stewards of conservation. The best place to conserve any species is in its natural habitat, but where that’s just not possible, that’s where botanic gardens play a vital role, not just ensuring against extinction, but also understanding more about the ecological requirements of those plants – what they need to be able to survive and to reproduce so that they persist in the environment, and indeed into changing environments in the future.
Through collaborations we can ensure a broader collection of genetic material that is secured across multiple sites, helping to mitigate the risk of losing plant diversity. It also supports the exchange of research findings, data and best practices for managing ex situ collections of threatened species. Joint initiatives among botanic gardens can lead to stronger outreach and education programs, raising public awareness about the importance of conserving threatened species.
What do you need facility-wise to be part of threatened species protection?
It varies on a species by species basis. There are species with orthodox seeds that can be stored using typical conditions. We have a walk in freezer that’s set to −20 °C, but you can store seeds when they’re dried down in the fridge or you can put them into a standard home freezer to preserve their viability over time.
Where it becomes more difficult is where we have these ‘exceptional’ species that don’t really conform to standard international procedures. We recently published a collaborative paper that discusses the various types of exceptional species and the knowledge gaps associated with them (Martyn Yenson et al., 2024). That’s where it becomes difficult for organisations with fewer resources to be able to conserve those species due to these knowledge gaps. This is where major botanic gardens like the BGoS can focus because we have the appropriate facilities and capacity.
It’s critical that we share this information with other organisations so that they can better understand whether they have the capacity or the facilities to be able to also include that particular species as part of their day to day operations or, for example, whether they need to seek more funding to get further facilities.
What advice would you have for some of those smaller regional gardens if they wanted to get involved in conserving their local flora?
Being part of collaborative networks and groups like BGANZ is great to get information on what’s out there and to engage with other botanic gardens. From BGoS’s perspective, too, we’d love to know what regional botanic gardens have in their living collections and what capacity they have for additional species as well.
In our Wollemi Pine work, we’ve developed the idea of metacollections. These are small groups of plants that represent a significant percentage of a species’ diversity. We’ve propagated a ‘metacollection pack’ for the Wollemi Pine that we sent out to different botanic gardens across the world to lower the risk of genetic loss in this species. There are certainly other candidates for such metacollections where it would be of significant benefit, for example, the Myrtle Rust affected species. I think projects like this really help to showcase or increase the value of regional botanic gardens, demonstrating that they’re stewards of species that are in decline.
What is one of the highlights you’ve experienced working with threatened species?
The most recent one was what we called securing a ‘holy grail’ type species (Emery, 2024). It’s an Endangered aquatic plant called Aponogeton queenslandicus and is only known in New South Wales from a single, temporary swamp habitat northwest of Bourke. We’ve attempted to go out there and collect it multiple times when the conditions seem right, but we just haven’t been able to find it. We were told in March this year that there were hundreds of plants flowering and starting to produce seed. That was an exciting piece of news, so we dropped everything and organised a whirlwind trip out to Bourke. We secured seeds and exhumed some plants to bring back to place in water tanks in the nursery with the hope of being able to collect further seed. We also wanted to potentially incorporate these into the living collection here at the BGoS.
This collecting trip was critical because the site is in a temporary water body. By the time the team got out there, a lot of it was just mud and a lot of the plants were starting to die back to their tuberous roots. It was really a massive win for us — being able to secure this species and start to understand more about its germination and dormancy requirements. Then we can relate this information back to conditions on the ground and get a better understanding of whether the intensity or the duration of the boom–bust environment with droughts and floods might impact the species’ persistence in that environment into the future.
I’m happy to say that the exhumed plants in the water tanks survived and grew. Now that it’s cooler they’ve died back and hopefully will persist via tubers. We will maintain them through to spring and summer to see whether they reshoot under warmer temperatures, but in the meantime, we’re processing the seed and germination testing the seed collections.
We collected seeds using maternal line sampling and leaf samples for genetic testing. The capacity of our collecting program to do this type of work all over the state is important, as some parts of New South Wales may not see another human for a long time. It’s important that when we’re there, we’re not just thinking about collecting the seed of our target species. We think about whether there is value in collecting leaf samples or in collecting as much environmental information about that area as possible because it may be useful for that species or another species’ ongoing conservation management. We really try to take the time to be able to collect as much material and as much information as we can.
What is your favourite part of the job?
I don’t know whether there is a favourite! I enjoy the whole process of being able to understand what we have in the collection, identify where the gaps are and then work towards plugging those gaps. Making those collections out in the field is really satisfying — to put seed into a bag is always exhilarating. But it’s just as exhilarating to bring that collection back, put it into the germination incubators and understand its temperature and moisture requirements, or find out if it requires post fire triggers. Does it need smoke water or heat shock to relax dormancy and enable that seed or that species to germinate? It’s also fantastic to be able to communicate the findings with others, whether it’s in a scientific paper, a conference presentation, a presentation to the public — or in this magazine!
Further reading
Cuneo, P, Emery, N, Errington, G et al. (2018). Assisted run(a)way: translocation planning to secure the Bankstown Hibbertia. Australasian Plant Conservation, 27(1):23–25. http://dx.doi.org/10.5962/p.373747
Emery, N (2024). The holy grail: scientists collect seeds from rare aquatic plant. Botanic Gardens of Sydney website. https://www.botanicgardens.org.au/discover and learn/watch listen read/holy grail scientists collect seeds rare aquatic plant#
Martyn Yenson, A, Sommerville, K, Guja, L et al. (2024). Ex situ germplasm collections of exceptional species are a vital part of the conservation of Australia’s national plant treasures. Plants People Planet, 6:44–66. https://doi.org/10.1002/ppp3.10421
Rossetto, M, Yap, J Y, Lemmon, J et al. (2021). A conservation genomics workflow to guide practical management actions. Global Ecology and Conservation, 26, e01492. https://doi.org/10.1016/j.gecco.2021.e01492
Sweedman, L, and Merritt, D (2006). Australian seeds: a guide to their collection, identification and biology. CSIRO Publishing. DOI:10.1071/9780643094079 van der Merwe, M, Bragg, J, Dimon, R et al. (2023). Maintaining separate maternal lines increases the value and applications of seed collections. Australian Journal of Botany, 71(7), 406–419. https://doi.org/10.1071/BT22136
A measure of the proportion of visually undamaged seeds that have all the tissues essential for germination, i.e. an intact endosperm and embryo. This is usually performed by X ray or a cut test.
The formation of ice crystals in living cells may lead to the bursting of the cell or an increase in the concentration of minerals to a toxic level. Both are usually fatal.
Brigalow Acacia harpophylla (either dominant in the tree layer or co dominant with other species) is a TEC found in NSW and QLD. Nationally, Brigalow has declined to about 10% of its former area.
