Last stand of the Saharan Cypress?

One of the guiding principles of the Millennium Seed Bank Partnerships is that there is no technical reason why a species should go extinct. I don’t know if it’s true, but I know preservation is not always easy. One critically endangered plant is the Saharan Cypress or Tarout (Cupressus dupreziana). However, it’s maybe a little less endangered following the publication of a paper by Jana Lábusová and colleagues reviewing propagation techniques. There isn’t really much information about C. dupreziana, so they use information from other plants with similar life cycles. So the result should help guide conservation of other, similar, plants.

C. dupreziana is found, if you look hard enough, in the Tassili n’Ajjer mountains in the Central Sahara. Scientists have found 8000 year old Cupressaceae pollen grains close to the current populations. “As no other Cupressaceae are recorded in the area, this pollen could likely be attributable to C. dupreziana and therefore the cypress may have thrived here during the African wet phase of the Holocene,” conclude Lábusová and colleagues.

C. dupreziana along with neighbours Saharan or Laperrine’s olive (Olea europea L. subsp. laperrini) and Saharan myrtle (Myrtus nivellei Batt & Trab) appear to be relict species, hanging on in an area of the Sahara that gets enough rainfall for them to survive. But their range is shrinking. This could be a big loss and understanding how they have adapted to the drying climate could be useful knowledge for the coming decades. 

In the wild, C. dupreziana is hanging on through cloning and apomixis, the production of seeds using only female material. Lábusová and colleagues describe additional techniques for propagation. Cuttings are an obvious example, but there is only so much you can safely cut off a plant. For this reason, the more useful, and longer section, is on micropropagation in vitro.

Micropropagation involves taking plant tissue and growing it in medium. As you’re dealing with a few cells, getting the medium and the conditions right is critical. This has been done for other cypresses. It has been a challenge, but protocols now exist for micropropagating some cypresses. Sadly not for C. dupreziana though.

Lábusová and colleagues describe their many attempts to get C. dupreziana to root. It might sound corny, but while the experiments didn’t produce roots, they were not failures. The team has found a lot of ways not to micropropagate Saharan Cypress. And documenting these attempts means other people don’t have to waste their time attempting the same techniques.

Despite these failures, the authors do note that there has been one successful attempt.  “There is the only paper reporting successful accomplishment of the entire process including rooting and ex vitro transfer (Hřib and Dobrý 1984). It is very likely that the authors accidentally applied one or more essential condition(s) critical for the rooting phase, but which was not regarded by them as important and therefore not mentioned in the resulting paper.”

The problem here is that when you’re dealing with such a small organism at the start of the process, even a tiny difference in initial conditions could be – comparatively speaking – large.

Lábusová and colleagues say that regardless of economic value, endangered plants are worth saving as they provide valuable genetic diversity, that may become critically important in the future. But in current times, thinking to the distant future might not be very persuasive. So they also include a couple of more immediate benefits. One is that C. dupreziana is long-lived plant. If you’re looking a plant for the Green Wall of Africa, to help combat desertification, the C. dupreziana is a strong candidate for plant – if you can propagate enough of them. The other reason is that the plant must be an expert in handling changing climates, and those are traits that we need to study now.

Lábusová and colleagues write: “Cupressus dupreziana exhibits an outstanding ability to survive highly unfavourable environmental conditions, i.e., extreme temperatures or water scarcity. This is proven not only by its survival under inhospitable desert conditions, but also by its longevity. Some individuals are thought to be several thousand years old, surely having experienced very different conditions during their lifetime, such as climatic conditions in the Sahara region, which changed remarkably during the upper Holocene. Therefore, it represents a valuable experimental model to study mechanisms of stress tolerance or resistance.”