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Faculty for Biology, Chemistry, and Earth Sciences

Soil Physics

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Finished Theses



Bachelor's Theses
Lara Kersting (2024) The impact of root exudates on the soil hydraulic properties of soil and root water uptake

Securing food availability foran  increasing global population is a major challenge.Water shortage and degradation are already limiting crop yields, and this problem will further intensify due to the expansion of agricultural areas into less fertile locations and the impact of climate change itself. The rhizosphere, the interface between roots and soil, represents a unique environment enriched with a diversity of substances like mucilage exudated from plant roots. Mucilage is a gel-like substance released from the tips of the roots and provides several benefits.

 

  • We hypothesized that root exudates alter the pore space of the soil, thereby improving the soil hydraulic properties, increase available water in the rhizosphere and/or prolonging the contact of the roots with the soil matrix.

To assess the potential of mulicalge on reducing water stress, two different soils (loam and sand) are being tested for their drying properties with varying concentrations of mucilage. For this purpose, the study makes use of HYPROP and WP4C instruments. Maize mucilage is introduced into the soil at various concentrations.



Supervisor: Asegidew Akale, Mutez Ali Ahmed, Efstathios Diamantopoulos
Anna Dürringer (2024) The effect of Arbuskular Mikoriza Fungi (AMF) on root water uptake and on soil hydraulic properties

The growing world population and increasing demand for food present significant challenges, especially in the context of climate change. As freshwater resources become increasingly scarce, particularly in already arid regions, and with agriculture responsible for approximately 70% of global freshwater consumption, there is a growing need to find sustainable solutions for agriculture and food production. One approach is to investigate the interactions of soil-dwelling microorganisms with plants and their roots. The symbiosis between plants and mycorrhizal fungi affects around 90% of land plants, with the association with arbuscular mycorrhizal fungi (AMF) being particularly relevant for crop plants. AMF not only enhances plant nutrient uptake but also improve the water status, especially in dry soils, leading to plants in symbiosis exhibiting lower negative leaf water potentials and prolonged water uptake compared to plants without fungal partners. Based on this background knowledge, two hypotheses were formulated:

 

  • H1: The presence of arbuscular mycorrhizal fungi (AMF) influences the water uptake of plant roots, leading to increased water uptake by the roots and consequently positively affecting the leaf water potential of the plants. (Anna Dürringer)
  • H2: The symbiosis between plants and AMF alters soil hydraulic properties, improving water retention and hydraulic conductivity in the soil, resulting in increased water availability for the plants. (Ilvy Steinlein)

To test these hypotheses, an experiment was conducted with Sorghum plants under controlled laboratory conditions, where representative Sorghum plants of the same variety were divided into two groups. One group was planted in sterilized soil without AMF spores, while the other group was planted in sterilized soil with AMF spores. This setup ensured comparable growth conditions for plants with and without AMF symbiosis in a climate chamber. The experiment involved a dry-down phase during which leaf water potentials and leaf areas were measured. After the experiment, root colonization rates by AMF were evaluated using potassium hydroxide (KOH) and subsequent root staining with an ink-vinegar solution. Additionally, soil hydraulic properties were examined for both soil treatments using Hyprop and WP4C measurements to identify potential changes in soil hydraulic parameters.



Supervisor: Anna Sauer, Mutez Ali Ahmed, Efstathios Diamantopoulos
Ilvy Steinlein (2024) The effect of Arbuskular Mikoriza Fungi (AMF) on root water uptake and on soil hydraulic properties

The growing world population and increasing demand for food present significant challenges, especially in the context of climate change. As freshwater resources become increasingly scarce, particularly in already arid regions, and with agriculture responsible for approximately 70% of global freshwater consumption, there is a growing need to find sustainable solutions for agriculture and food production. One approach is to investigate the interactions of soil-dwelling microorganisms with plants and their roots. The symbiosis between plants and mycorrhizal fungi affects around 90% of land plants, with the association with arbuscular mycorrhizal fungi (AMF) being particularly relevant for crop plants. AMF not only enhances plant nutrient uptake but also improve the water status, especially in dry soils, leading to plants in symbiosis exhibiting lower negative leaf water potentials and prolonged water uptake compared to plants without fungal partners. Based on this background knowledge, two hypotheses were formulated:

 

  • H1: The presence of arbuscular mycorrhizal fungi (AMF) influences the water uptake of plant roots, leading to increased water uptake by the roots and consequently positively affecting the leaf water potential of the plants. (Anna Dürringer)
  • H2: The symbiosis between plants and AMF alters soil hydraulic properties, improving water retention and hydraulic conductivity in the soil, resulting in increased water availability for the plants. (Ilvy Steinlein)

To test these hypotheses, an experiment was conducted with Sorghum plants under controlled laboratory conditions, where representative Sorghum plants of the same variety were divided into two groups. One group was planted in sterilized soil without AMF spores, while the other group was planted in sterilized soil with AMF spores. This setup ensured comparable growth conditions for plants with and without AMF symbiosis in a climate chamber. The experiment involved a dry-down phase during which leaf water potentials and leaf areas were measured. After the experiment, root colonization rates by AMF were evaluated using potassium hydroxide (KOH) and subsequent root staining with an ink-vinegar solution. Additionally, soil hydraulic properties were examined for both soil treatments using Hyprop and WP4C measurements to identify potential changes in soil hydraulic parameters.



Supervisor: Anna Sauer, Mutez Ali Ahmed, Efstathios Diamantopoulos
Lara Ketterer (2024) The effect of fluorinated ski wax on the wetting properties of sandy and loamy soils

Ski sports like cross-country skiing, downhill skiing, and biathlon are popular winter sports. Applied ski waxes reduce the friction between snow and ski and therefore increase the ski gliding. Parts of the ski waxes can enter the soil due to snow melting.

 

  • We hypothesize that ski wax increases the soil-water contact angle and consequently the water repellency of soils.

To test this hypothesis the contact angle is measured directly with the sessile drop measurement and indirectly by the Washburn method with the DCAT 11 advice. Two PFAs containing wax products (powder and liquid) are applied to sandy soil in various concentrations. The concentrations are based on their PFAs content and the PFAs concentrations measured directly in Nordic Skiing areas.  



Supervisor: Frederic Leuther, Efstathios Diamantopoulos
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


Master's Theses
Hai Anh Nguyen (2024) Simultaneous quantification of water states, fluxes and bVOCS emissions in agriculture soils

Volatile organic compounds (VOCs) produced by living organisms via biological processes, which are known as biogenic volatile organic compounds (BVOCs), are an important group of chemicals that has significant influences on atmospheric chemistry, climate system, as well as the bioactivities of plants and animals. Whereas plant-emitted BVOCs have been widely studied for the past decades, the understanding of soil related BVOCs remains inadequate.  A variety of abiotic and biotic processes taking place beneath the ground makes soil both a sink and a source for BVOCs.

Hypotheses

  • BVOCs emission and/or uptake are highly affected by the percent of organic matter in the soil and the water content.
  • The dynamics of BVOCs exchange are subject to memory effects, following the hysteretic water content vs matric potential relationship.

Methods

To test the two hypotheses, we conduct transient water drying and wetting experiments, and we quantify simultaneously BVOC sources and sinks, as well as soil water states and fluxes.



Supervisor: Frederic Leuther, Anke Nölscher, Efstathios Diamantopoulos
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
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