Deserts can be challenging environments to live in, doubly so when you are a parasitic plant that has to latch onto the roots of a specific host plant to live. Cynomorium songaricum is an endangered holoparasitic plant living in the deserts of northwest China, and it parasitises nitre bushes. Nitre bushes are known for their edible, slightly salty fruits, but C. songaricum is also prized for its culinary and medicinal value. In China, the fruits of this holoparasitic plant are known as "锁阳" and are used in traditional Chinese medicine.
 |
| Top left: A Cynomorium songaricum plant, Top right: Ants on the stem of a C. songaricum plant, Bottom left: Beetles feeding on the stem of a C. songaricum plant, Bottom right: C. songaricum seeds collected from the nest of Messor desertora ants. Photos from Fig. 1 and 4 of the paper. |
Despite its important cultural value, as is often the case with parasitic plants, very little is known about its ecology or how it propagates. Cynomorium songaricum is a root parasite, which means its dust-like seeds have to either come in contact with or at least be very close to its host's roots in order to germinate. And the roots of its host are located about three metres underground beneath the dry desert sand - so how do C. songaricum's tiny seeds reach all the way down there?
To find out, scientists from Inner Mongolia University conducted a series of studies in the eastern part of the Tengger Desert and the Badain Jaran Desert in Inner Mongolia. Over multiple days, these scientists observed the C. songaricum plants on rotating shifts during daytime and throughout the night, and when it got too cold at night to observe the holoparasites in person, remote cameras were used to keep an eye on the activities around the plants. They also collected samples from some of those plants, which were used for feeding experiments involving C. songaricum seeds and various insects.
Like many other holoparasitic plants, C. songaricum has stinky flowers that attract flies to serve as pollinators. But when it comes to its seeds, it offers up something sweeter, which makes them attractive to hungry desert insects. And the main customers for what C. songaricum's offerings seems to be beetles and ants. The beetles eat the pulpy material around the seeds and then poop the seeds out after a day or two, which are then buried by wind. That way of reaching the host plant is a bit hit-or-miss since there's no guarantee that the seeds would be buried anywhere near the host plant's roots. But beetles are messy eaters, and in the process, they also drop some of the seeds onto the desert sand.
That's when C. songaricum solicits help from another common desert insect. Each seed has a little fleshy tag on it called an elaisome, and it turns out this little tag attracts the attention of desert ants, which considers the elaisome to be a tasty snack. So as with all things the ants find tasty, they haul the seeds back to the larder of their nest, which works out exactly in C. sonagrisum's favour. Because it just so happens that those ants often make their homes around nitre bushes, and these nests can extend up to three metres underground - placing them right on the same level as the nitre bush's roots. So by taking the C. songaricum seeds back to the nest, the ants also inadvertently plant them in the strike zone of the host plant's roots
So that's how a parasitic plant is able to disperse its seeds across a wide, sandy desert - with the help of some little friends. To most observers, a desert may seem empty and barren. But if you take a closer look, you will find that it can be a place which is full of life and connections.
Reference:
