Seeds cleverly screwed into the ground

Video: Carnegie Mellon University

Oak wood shavings provide torque: Researchers have developed a sophisticated drilling equipment for seeds that literally screws the seeds into the ground. They technically implemented and optimized the natural patent of a plant. In this way, the bionic seed carriers can also effectively transport large seeds into the subsoil in unfavorable soil conditions and thus ensure better chances of germination. Most notably, the concept could be used in aerial seeding to help trees sprout again on degraded land, the scientists say.

After deforestation, fires, erosion and droughts, the soil quality is poor in some regions of the world, so that plants can hardly gain a foothold. The ecosystems are getting more and more into a downward spiral and even deserts are spreading. In order to counteract this problem, attempts are being made in many places to promote the resettlement of plants in a targeted manner. Aerial application of seeds is best suited to cover large and otherwise inaccessible areas. However, the effectiveness of these measures is often limited. Because on the partially hardened and exposed surfaces, seedlings have difficulty penetrating the soil, they are exposed to the weather and animals can eat them.

Natural role model

A group of plants has already developed a clever concept against precisely these adversities: the seeds of the Erodium family are equipped with their own planting tools. It is a corkscrew-shaped structure when dry with a laterally protruding extension. The highlight: when this structure gets wet, it begins to unwind. The protruding extension supports the construction on the ground and so the seed, which is pointing diagonally downwards, is set in rotation at the lower end. When the corkscrew element subsequently dries, it twists back in, causing torque again. So it can drill the seed into the ground.

A team of Chinese and US researchers has now devoted itself to the task of technically reproducing the drilling system of the rowan family and making it usable for the seeds of other plants and for other applications. As they report, after tests with various materials for the replica of the drilling system, oak wood chips emerged as the most suitable. The researchers explain that the material is readily available, biodegradable and is ideal for providing the rotating mechanism. In order to create the dynamic elements, thin strips of wood are treated with certain liquids, then twisted up while still wet and finally dried fixed in this form. Analogous to the version of the heron’s beak, the element also has a protruding extension. The shavings processed in this way actually showed the same behavior as their natural models: they unwind when they are wet and unwind again when they dry.

Automatic planting tool

With these elements, the scientists have produced bionic seed carriers in various sizes and versions. At the lower end of the corkscrew structure, the respective seed is attached with a pointed casing. In the event of moisture or subsequent drying, this structure is then rotated by the system with a drilling effect. The researchers report that it was shown that the effectiveness of the natural system can be increased: If the twisted wood chip is equipped with two additional extension elements, the construction can anchor and align itself better, which clearly benefits the drilling effect. Through tests, the researchers were able to show that their three-armed E-Seeds can also penetrate smooth soil structures well compared to the simple version. In this way, depths are reached that lead to a significantly increased germination success, the investigations showed.

The researchers emphasize that the system can be adapted to various requirements: For example, larger tree seeds can also be “planted automatically”. There is therefore considerable potential for use in afforestation in problem regions. In concrete terms, drones could drop the e-seeds there and ensure growth on degraded soils. In addition, it would also be possible to introduce measuring probes or certain beneficial soil organisms, such as mycorrhizal fungi, into problem soils, say the researchers.

The researchers are now working on optimizing the system and other possible applications. An important point is to develop manufacturing processes that make widespread use practicable and profitable. “Capabilities of manufacturing through digital design and manufacturing methods are critical to our long-term goals,” says co-author Guanyun Wang of Carnegie Mellon University in Pittsburgh.

Source: Carnegie Mellon University, journal article, Nature, doi: 10.1038/s41586-022-05656-3

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