Current Theses

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.

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.

Polycyclic aromatic hydrocarbons (PAHs) occur ubiquitously in terrestrial and aquatic ecosystems all around the world and are a group of chemicals among the so called “persistent organic pollutants” (POPs). PAHs comprise several hundred chemically related compounds and some of them are known to have toxic, mutagenic, and carcinogenic effects on humans and other living organisms Although PAHs are considered to be very poorly soluble in water, there appears to be transport of molecules in soil that allow them to be distributed, clog pores, or accumulate at the soil plant interface. Especially for high molecular weight PAHs, colloidal and particulate transport is assumed to be an important process. Little is known about the exact transport processes in soil and whether plants can influence this transport by suction

Hypotheses

• H1: PAHs bind to soil particles and can thus be transported in the soil despite their low water solubility.
• H2: Plants influence the distribution of the particle bound PAHs in the soil through their water uptake at the roots, which leads to the accumulation of these particles in the rhizosphere.

Methods

To test the first hypothesis an experiment is to be carried out with undisturbed soil columns without plants. An irrigation head with needles will be used to supply water to the columns, which will also contain any tracers and particles. Three steps are planned: i nvisible tracer (e.g., chloride) chloride), p articles + PAH s, inv isible and visible tracer (brilliant blue) blue). For each step, the drainage at the bottom of the column will be collected and analysed, and at the end the distribution of the particle bound PAHs in the column will be investigated. To test the second hypothesis, undisturbed soil columns with maize plants are to be used. Again, particle bound PAHs will be supplied via the irrigation system; then drying and rewetting phases will follow. The drainage will be collected and analysed and the distribution of particle bo und PAHs around the root will be studied.