One third of all threatened plant species might be unfit for seed banks

Seed banks are excellent ex-situ conservation projects that allows us to have long-term storage of plant seeds, in order to potentially use them if the plant goes extinct in the wild. These vaults are capable of storing several million seeds, and they have been a vital part of conservation efforts when it comes to plants, trees, and crops.

The purpose of a seed bank is to act as a fail-safe mechanism in case a plant species or local variety of a plant goes extinct in the wild, and if this happens we can simply turn to the vault and get seeds to put out in the wild again.

How the seed bank functions

The seed banks typically store seeds in a dried and frozen state with a temperature of around -20 °C, and the physical location of the banks tend to be in areas that have low humidity and a low temperature. One of the biggest fail-safe seed vaults for agricultural plants in the world is located in Norway, on the island Svalbard. This vault is designed in such as manner that it would keep the seeds dry and frozen even if the electricity were to be knocked offline.

About a year ago I wrote about how they had a small emergency when water leaked into the facility though, because they had not properly planned for climate change. The vault was built on a glacier to keep it cool, but this began to melt, and water ran down from the entrance. It has now been fixed, and luckily no seeds were damaged from the leak.

This is the entrance to the Svalbard Seed Vault, but most of the facility is located under ground. Photo by Frode Ramone, posted with the Creative Commons Attribution 2.0 Generic license.

The purpose of this vault is to store mostly agricultural seeds, and they aim to get local varieties of crops from all over the world, and give it back in case of a disaster that wipes them out. This might sound like a far-fetched scenario for most of us, but they have already returned seeds to Syria, allowing Syrian farmers that had been devastated by the war to grow crops adapted to the local climate and environment. So it might be useful in cases of wars, natural disasters, and other extreme problems that could potentially wipe out all of the crops in an entire region.

Other seed banks focus more on preserving biodiversity instead of just agricultural crops, and the reason here is the same; if the species or subspecies are to go extinct in the wild, we can return the seeds back into nature and give them a second chance. You might wonder why we don't just focus on preserving the species in the wild instead, and the answer is the same as always: it requires too much resources to protect so many plant species in the wild. It's much cheaper to store millions of seeds in one location instead, and it's considered a cost-effective conservation effort that is both cheap and easy to do.

Millennium Seed Bank in Kew Gardens is one of the seed vaults with the aim of conserving species instead of agricultural varieties, and they hope to have seeds from 25 % of the world's plant species by 2020. This seed bank already has several billion seeds, and they might just make the goal with some luck. However, a new research paper have pointed out that it might not be as easy as they had planned for.

The entrance to the Millennium Seed Bank. Photo by DAVID ILIFF. License: CC-BY-SA 3.0.

New research suggest that a lot fewer plants will actually fit into these ex-site conservation facilities

Seeds that are stored in seed banks obviously need to be capable of surviving both a drying process, as well as a freezing process, but it's not like all plant seeds are capable of this. The name used for the seeds who are unable to survive this is called recalcitrant seeds, and we have many popular plant species that belong to this group, including avocado, mango, cocoa tree, rubber tree, oaks, and sweet chestnuts. So if any these were to be wiped out in nature, we might not be able to get them back!

Oak leaves and acorns, one of the plants that we cannot keep in a seed bank. Photo by Wikipedia user MPF, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.

Previous estimations have put the number of recalcitrant plants at only 8 %, a rather small number. New research on the other hand used models to estimate it with better precision, and they found that species that are threatened tend to also be recalcitrant species, and as much as 35 % of plant species that are considered Vulnerable by the IUCN Red List won't be a good fit to ex-site conservation. Plant species that are considered Endangered by the IUCN Red List have 27 % recalcitrant species, with an average of 33 % across all threatened plant species.

One might begin to wonder if plants that produce recalcitrant seeds are less likely to survive the changing climate we see these days, and this new research certainly seem to indicate just that. It's important to keep in mind that threatened plants are not found randomly though, and we have a lot of threatened tropical moist forest trees that typically produce recalcitrant seeds.

The paper also argues that it will be next to impossible for the human race to save 75 % of all the species in the world with the current technique of using seed banks that dried and freezes the seeds, the goal we set ourself with the Global Strategy for Plant Conservation (GSPC) back in 1999.

Could cryopreservation be an alternative to regular seed banks?

A good alternative to regular seed banks with -20°C is to keep seeds in a much colder place by using liquid nitrogen to get the temperature down to -196°C. There are a few benefits to this method, including:

1. Recalcitrant seeds can be stored in this state, allowing us to preserve pretty much any seed in the entire world. I haven't heard of any plant seeds that are unable to be stored with the liquid nitrogen method.
2. The shelf life of the seeds is significantly longer when stored in liquid nitrogen compared to being stored in a cooled seed vault.

But if's not just benefits, there's also some disadvantages. Firstly, using cryopreservation as a tool to preserve plants requires a lot more effort than just collecting seeds and drying them. Instead lab technicians must remove the embryo from the seed before freezing it in the liquid nitrogen. As as you would expect, this process is also more expensive than just going out to the field and collecting seeds.

Despite having some big disadvantages, we might just have to look towards using more of the cryopreservation technique if we want to reach the goal of preserving 75 % of all the plant species in an ex-situ conservation location. It's still not impossible to reach the goal, but I find it to be very concerning that a lot of the plant species that are already threatened don't respond well to the conventional conservation strategies we have applied as a backup machanism for preserving their survival even in the case of an extinction in the wild.

Sources

• Wyse, S. V. et al. (2018). Seed banking not an option for many threatened plants. DOI: https://doi.org/10.1038/s41477-018-0298-3.
• "Millennium Seed Bank" from Kew Royal Botanical Garden.
• Engelmann, F. (2004). Plant cryopreservation: Progress and prospects.

Thanks for reading

I hope you enjoyed this post about the ex-situ seed bank facilities, and hopefully you learned something new from reading this. Let me know if you have any questions or comments to the post! Thanks for checking it out.