Finished Theses

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.

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.

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.

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.  

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.