Subsurface investigation and interaction by self-burying
Background and motivation
A thick layer of dust covers the surface of the terrestrial planets of the Solar Systems,
of moons, and some asteroids, hiding the ground underneath and its mysteries. This
regolith has been formed over billions of years by the impact of large and small
meteoroids breaking down surface rocks. On Moon, nearly the entire surface is
covered with regolith, bedrock being exposed only on very steep-sided crater walls
and the occasional lava channel, and also on Mars, regolith covers vast expanses of
surface. When in December 2007, the rover Spirit's dead wheel scraped off the upper
layer of the Martian soil, it uncovered a patch of ground that thrilled scientists,
showing evidence of a past environment that would have been perfect for microbial
1.1 The seed
Erodium cicutarium L. plants are characterized by explosive dispersal, in the sense
that seeds are discharged by the rupture of the fruit, produced by the elastic
contraction of its tissues. The distance reached by seeds is usually quite short
compared with the distance reached by other means (Bullock and Primack, 1977;
Willson, 1993). For this reason, this explosive dispersal is coupled with the additional
strategy of the self-planting that increases the chances of success (Westoby and Rice,
1981; Andersen, 1988; Stamp and Lucas, 1990). Each fruit consists of five seeds
joined together and forming a spine like structure. As the fruits dry, they increase their
tension, and stresses developed in the structure cause them to separate abruptly and fly the spinning seeds up to half-a-meter away (Stamp 1989).
Each seed is equipped with a special dispersal unit (botanically called “awn”) that
give the seed the ability of self-burial. This is possible thanks to movements achieved
by changes of external humidity (Stamp 1984). The long awn has two preferred
shapes: the dry awn is helical while the wet one is linear. Once on the ground the
humidity changes cause the awns to unwind straight when wet, and rewind back to
their helical shape when dry. The resulting motor action, combined with hairs on the
seed and along the length of the awn, moves the seed across the surface, eventually
lodging it into crevice and causing it to bury itself into the ground.
Fig. 1: The seeds of Erodium cicutarium. Photo courtesy of Steve Hurst @ USDA-NRCS PLANTS Database
2. Study Objective
The objective of this study is to evaluate the performance of self-planting seeds (in particular of the Erodium cicutarium) as subsurface penetrators for different soil textures, understanding the role of the launch phase as well as of the above mentioned four main structures. The final goal is to lay the bases for the biomimetic transfer of the self-burial strategy for applications to space exploration needs.
3. Proposed Methodology
Two main research themes form the study.
3. Is the initial launch mechanism and resultant landing important for the selfburial performance?
The results shall then serve for the second part of the study, which will be performed
concurrently and mainly by the ACT, based on the results of the experimental part.
The following questions will be addressed:
The experimental part will be performed mainly by the proposing research team /
University. It aims at getting a deeper insight into the strategies of the model seed. In
order to do so, the seed will be confronted with different experimental situations
where they have to dig themselves. By changing soil texture and seed accessory
structures, the properties of the strategy in question will be assessed.
The second part will be mainly done by the ACT in close collaboration with the university, and will consist of:
- Analysis of the results and quantification of the self-burial behaviour;
- Selection of the key parameters that contribute to the performance in view of the modelling;
- Study of the mechanical properties of the seed and its structures;
- Quantification of the contribution of the mass of the seed and consequently of gravity to the strategy;
- Evaluation of how the efficiency changes depending on the depth of penetration.
In this phase some additional experiments might become necessary and universities will be asked to perform them in order to give a description of the strategy as complete as possible.
This study is mainly addressed to research laboratories in the fields of plant biology, botany or ecology.
4. ACT Contributions
The project will be conducted in close scientific collaboration with ACT-researchers who will work together with the university in the evaluation of the performance and definition of the key parameters. ACT-researchers will also provide expertise in the characterization of the physical processes, in the modelling and in space related issues. Based on the outcome of the study, the team will also evaluate and propose material and structures that could be used to successfully mimic the self-burying strategy of the seed in order to conclude the biomimetic process of the study.
 Abraham, Y., Tamburu, C., Klein, E., Dunlop, J. W. C., Fratzl, P., Raviv, U., and Elbaum R. (2011). Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn. J. R. Soc. Interface published online August 24, 2011, doi:10.1098/rsif.2011.0395
 Evangelista, D., Hotton, S. and Dumais, J. (2011). The mechanics of explosive dispersal and self-burial in the seeds of the filaree, Erodium cicutarium (Geraniaceae). J. Exp. Biol. 214, 521-529.
 Stamp, N. E. (1984). Self-burial behaviour of Erodium cicutarium seeds. J. Ecol. 72, 611-620.
 Stamp, N. E. (1989). Efficacy of explosive versus hygroscopic seed dispersal by an annual grassland species. Am. J. Bot. 76, 555-561.
 Stamp, N. E. (1989). Seed dispersal of four sympatric grassland annual species of Erodium. J. Ecol. 77, 1005-1020.
 Stamp, N. E. and Lucas, J. R. (1983). Ecological correlates of explosive seed dispersal. Oecologia 59, 272-278.