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Faculty for Biology, Chemistry, and Earth Sciences

Soil Physics

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Finished Theses

Bachelor's Theses
Henri Michael Braunmiller (2020) Impact of soil drying on mucilage production and rheology

Mucilage is a polymeric gel containing polysaccharides and lipids. It is exuded by the root tips and holds large amounts of water. This keeps the rhizosphere moist, especially under dry conditions. With higher variability of rainfall and more extreme weather events (e.g. drought) caused by the human made climate change, this could be an important trait for our crops to maintain a constant yield even under unfavorable conditions.

The idea of my project is to show the effect of variety and water availability on the production of mucilage and its rheological parameters. Therefore I use two different maize varieties (B73 and Mo17) and two different water contents. The mucilage is being measured and compared for its amount, viscosity and surface tension value. In addition, we will observe the behavior of the mucilage in soil using a neutron radioscope. This allows us to measure it without intercepting the soil.

Supervisor: Mutez Ali Ahmed, Andrea Carminati
Jannik Christoph Heinrich Sauer (2020) Seasonal changes in soil water potential and soil water content in sandy and loamy field plots planted with maize

Determination of soil variables over a vegetation period of maize. Measurements were carried out in 4 field plots with two soil structures and two maize plant varieties. The soil structures contained loamy and sandy soil. The plant varieties contained a wild type maize and a mutant maize genotype without root hairs. The examination included not only an analysis of the data over the time of the vegetation cycle, but also a look at possible measurement errors and the accuracy of the sensors in the field.

Supervisor: Andrea Carminati, Mutez Ali Ahmed

Master's Theses
Anna Sauer (2020) Investigating drought traits in sorghum landraces - A lysimetric experiment in four soil textures

Water availability is a primary limitation to crop production and depends on water input and soil texture, among others. A huge variety of sorghum landraces promises unexplored traits to overcome water stress, like high transpiration efficiency or early maturity.

 To test these, four sorghum landraces and one elite line were grown in four soil textures in a lysimetric facility in ICRISAT, India. Nitrogen fertilization was either added by mineralized or organic sources. The soil was dried down to 30 % usable field capacity. Weekly measured transpiration and data of biomass, plant development, yield and more will be analyzed and may reveal traits to overcome drought stress.

Supervisor: Mutez Ali Ahmed, Andrea Carminati, Jana Kholova
Tina Köhler (2020) Emerging effects of root hairs and soil properties on soil-plant water relations under drought conditions

Limited water supply is one of the largest impediments to food production worldwide. Therefore, improving crop management of soil water depletion will be important to sustain the increasing food demand. The effect of belowground processes on transpiration and stomatal regulation remains controversial. Objective of this study was to understand the role of rhizosphere properties and processes, namely soil textural properties and root hairs, on transpiration, leaf water potential and stomata conductance with soil drying. We hypothesize that 1.) root hairs facilitate the water extraction from drying soils. This is expected to be reflected in the relation between transpiration rate and leaf water potential. Moreover, we expect 2.) different soil textures to affect root water uptake differently and therefore the relationship between leaf water potential and transpiration.

We compared maize (Zea mays L.) with (wild-type) and without (rth3-mutant) root hairs in three different soils (Alfisol, Vertisol and Sandy Soil) with different textural properties (loamy, clayey, sandy), respectively. Transpiration and leaf water potential were monitored, and stomata conductance calculated with decreasing soil water content and potential.

The hairless mutant declined transpiration at greater water contents or/ and exhibited lower transpiration rates in dry soils as compared to the wild-type. The relationship between leaf water potential and transpiration/ stomata conductance did not differ between genotypes, most likely because of prompt stomata closure. Moreover, plant transpiration responses to declining soil water content and – potential differed considerably between soils. Soil hydraulic characteristics and features like soil cracking in Vertisol as well as soil crust formation in Alfisol are believed to have influenced those relations. The relationship between transpiration and leaf water potential varied strongly between soils as well but stomata response to decreasing leaf water potential showed no direct sensitivity to soil texture. Therefore, we conclude that soil texture indirectly affected stomata by changing the soil-plant conductance.

In conclusion, this study provides experimental evidence of the strong link between stomata regulation and soil-root hydraulic properties. Further experiments will be needed for clarification and quantification.

Supervisor: Mutez Ali Ahmed, Andrea Carminati
Asegidew Akale (2020) Phenotypic differences of root exudates and their impact on drought tolerance across different varieties of maize.

Mucilage provides benefits for plant growth by maintaining the rhizosphere's water content during soil drying. The aerial root of maize (Zea mays L.) releases a significant amount mucilage to the rhizosphere. However, scarce information is available on quantitative and qualitative differences between the root exudation profile of the landrace and hybrid maize.

In this study, we find that mucilage production in the landrace is significantly different. The mucilage ability to store water potentially makes the landrace less vulnerable to drought. The variations of mucilage production in Maize cultivar would be significant for further analysis of crop adaptation to environmental stress.

Supervisor: Andrea Carminati, Mutez Ali Ahmed, Pascal Benard
Andreas Cramer (2020) Biogenic Si and its effect on soil hydraulic properties

The submitted thesis presents the effect of biogenic amorphous silica (BSi) on the retention and flow of water in the soil. It was hypothesized that the BSi due to its highly porous structure and high surface area could hold a large volume of water in the soil and therefore it could significantly contribute to retention and flow of water in the soil. The thesis tests its hypothesis in two directions: i) a synthetic pyrogenic amorphous silicic acid (ASi) was taken as an analog of BSi. The water holding capacity of pure ASi and soil mixed with different ASi contents were experimentally determined and a conceptual model was developed to describe the effect of ASi on water retention in soil, ii) in parallel, a set of different substrates and soils were selected and their water-holding capacities and Bsi contents were determined in order to relate the retention of water to the Bsi content.

Supervisor: Mohsen Zare, Jörg Schaller
Eva Bayreuther (2019) Displacement and behavior of microplastic particles in porous media at temporary water flow

Plastics have a high impact on our world, and it is estimated that about 6300 million tonnes of plastic waste werre produced until 2015 and 79% of it was released into the environment. In recent years, particles in the micro- and nanoscale have particularly moved into the focus of science, but how those particles impact our immensely important ecosystem, the soil, so far little is known.
The behaviour of the particles underground, or whether, for what reasons and at what rate they are distributed, whether they could get into the groundwater and whether they change the properties of the soil, is of particular interest.

The planned thesis hopes to answer some basic questions in an experimental way.
In order to better understand the basic behavior of microplastics in porous media with a temporary flow of water, experiments with particles of different material, shape and size will be conducted and modelled with an simplified soil model. Another focus is on whether and how repeated drying and rewetting cycles affect the mobility and accumulation behavior of the particles and whether microplastic causes changes in the contact angle between soil and water phase.

Supervisor: Andrea Carminati
Judith Schepers (2019) Biophysical properties of root exudates and their impact on the shape of water in soil

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
Mucilage surface tension and viscosity are two key physical properties to understand the effect of


Supervisor: Pascal Benard, Andrea Carminati, Mohsen Zare
(2019) Effects of soil heterogeneity on root water uptake under drying conditions and varying transpiration rates

Water flow in soils is heterogeneous at many scales. In a given representative elementary volume these heterogeneities can be described by an effective hydraulic conductivity. Standard root water uptake models commonly rely on this representative hydraulic conductivity and assume that the hydraulic conductivity of the soil cylinder around the roots is equal to that measured in soil samples representative of the bulk soil.



Supervisor: Andrea Carminati, Mohsen Zare
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