Master Thesis

Biophysical properties of root exudates and their impact on the shape of water in soil

Judith Schepers (09/2018-03/2019)

Support: Andrea Carminati, Mohsen Zare

Mucilage is a polymeric gel that is exuded at the root tips and that maintains the rhizosphere moist
during soil drying (Carminati et al. 2017). Despite mucilage has been recently subject of intensive
investigation, the knowledge of its physical properties and impact on soil hydraulic properties is still
unsatisfying.
Mucilage surface tension and viscosity are two key physical properties to understand the effect of

Mucilage is a polymeric gel that is exuded at the root tips and that maintains the rhizosphere moist
during soil drying (Carminati et al. 2017). Despite mucilage has been recently subject of intensive
investigation, the knowledge of its physical properties and impact on soil hydraulic properties is still
unsatisfying.

Mucilage surface tension and viscosity are two key physical properties to understand the effect of
mucilage on soil hydrology (Carminati et al. 2017). These properties are well summarized in the
Ohnesorge tension surface tension). is expected number As (Oh), the to decrease, soil which dries is viscosity and defined the as content to Oh= increase, (μ/√rσρ) of mucilage and (μ consequently isin viscosity, the soil ρ the solution is density, Ohnesorge increases, r is number radius, surface σ to  is increase, too (Carminati et al. 2017; Ohnesorge 1936). We hypothesized that the increase in the Ohnesorge number for high mucilage content is the key to explain the spatial configuration of the liquid phase in soils embedded with mucilage. In particular, we tested if the Ohnesorge number relates to the formation of 1-dimensional filaments and 2-dimensional surfaces spanning the pore space.

The experiments are conducted with gel from chia seed as and analogue of root mucilage and with
mucilage from maize seedlings, to see the differences between different types of mucilage (Benard
et al. 2018).

Benard, P., Zarebanadkouki, M., Hedwig, C., Holz, M., Ahmed, M. A., & Carminati, A. (2018). Pore-
Scale Distribution of Mucilage Affecting Water Repellency in the Rhizosphere. Vadose Zone Journal,
17(1), 0.
Carminati, A., Benard, P., Ahmed, M. A., & Zarebanadkouki, M. (2017). Liquid bridges at the root-soil
interface. Plant and Soil, 417(1–2), 1–15.
Ohnesorge, W. V. (1936). Die Bildung von Tropfen an Düsen und die Auflösung flüssiger Strahlen.
ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift Für Angewandte Mathematik
Und Mechanik, 16(6), 355–358.