We work in climate-controlled greenhouses at the UFZ research station Bad Lauchstädt under two scenarios: ambient temperature and CO2 vs. the International Panel on Climate Change (IPCC) RCP 8.5 climate scenario (+4°C and doubled atmospheric CO2 compared to ambient) at 10-hour day-night cycles, watered regularly to a 55% of the water holding capacity. The IPCC RCP 8.5 scenario was declared the worst-case scenario postulated for climate change by 2100 if we continue with "business as usual" and fail to implement significant climate policies.
The experiments are carried out using pots (2.5 kg soil capacity) and rhizoboxes (30 cm × 20 cm × 3.5 cm, 3 kg soil capacity), with 5 replicates per treatment. One off-shoot A. halleri clone is planted in each pot or rhizobox. We work with soils with different levels of heavy metals (Cd, Pb, Zn) to evaluate the interaction of metal contamination and climate change.
 

Metals are part of the earth’s crust and are found in all soils, but sometimes harmful metals can build up in large amounts, especially near polluted areas. This can affect plants, animals, and human health. Certain metals are essential for plant and animal health, like iron (Fe) and zinc (Zn). However, when some metals are present in large amounts, they can be toxic to plants, animals, and humans.
We measure metals in soils by collecting small soil samples and performing soil extractions with water or mild salts like 0.01 M CaCl2 to study the portion of metals that can be easily available for plants and soil biota. For this, we use inductively coupled plasma mass spectrometry (ICP-MS), which is an analytical technique that is used to measure elements at trace levels in biological fluids. In addition, we study the total concentration of metals in soils using small soil solid samples, and X-ray Fluorescence (XRF), which is an analytical technique that uses the interaction of X-rays with a material to determine its elemental composition. With this technique, it is also possible to map in 2D the metals in soils and study for example how the soil-plant interaction affects the metal distribution in the soils.
Finally, we also study other soil variables that are related to the availability of metals such as:
• Soil pH
• Organic matter in soil
• Soil texture
• Roots presence/absence
 

Arabidopsis halleri has a natural distribution in central and eastern Europe, and it can grow well in soils containing high concentrations of heavy metals. This plant has evolved mechanisms to tolerate and accumulate large amounts of heavy metals in its shoots and leaves, making it a good candidate for phytoremediation. Therefore, it has become a model plant as a metal hyperaccumulating species for Cd and Zn for scientific research and environmental applications.
Plants counter complex environmental stress conditions (abiotic and biotic) to minimize damage and ensure continued growth and reproduction. In this project, we study how the combination of two stressors, such as climate change and metal contamination, can affect phytoremediation efficiency. For this, we evaluate plant growth and metal accumulation in roots and shoots and relate them to the nutrient and metal availability and the soil microbial community composition.
 

The soil microbial community is essential for sustaining soil processes since it acts as the engine of the soil. It is comprised by organisms like bacteria, fungi, and other microbes that are actively involved in breaking down organic matter, recycling nutrients, and improving soil structure. They can also help plants to absorb water and nutrients, and degrade certain pollutants. Therefore, soil microbes keep soil healthy and productive, making them essential for growing food and supporting ecosystems.
We want to study how the microbial community structure is affected by the stress caused by heavy metals and the climate change pressure, and how the interaction of the microbial community with a metal hyperaccumulating plant can control nutrient cycling in phytoremediation. Therefore, we focus our study on the analysis of bacterial/archaeal communities from soil and rhizosphere using 16S rRNA gene and transcript amplicon sequencing.
 

Soil nutrients play a critical role in maintaining soil health and supporting healthy ecosystems since they provide the building blocks for plants and microorganisms to grow. Proper nutrient levels prevent soil degradation and ensure long-term productivity for crops. Although all organisms require a large variety of nutrients in different quantities, 3 major bricks sustain life: carbon (C), nitrogen (N), and phosphorus (P). Carbon in soils exists primarily in the form of soil organic matter (SOM), which is critical for maintaining soil structure, water retention, and microbial activity that releases essential nutrients for plant growth. Nitrogen is essential for the growth of plants and microorganisms, as it is a key component of proteins and enzymes. Nitrogen undergoes complex transformations in the soil, including mineralization and nitrification, making it available to plants in forms like ammonium and nitrate. Phosphorus is crucial for plants and microorganisms because it plays a key role in energy transfer, DNA synthesis, and root development. 

The cycling of these 3 nutrients is tightly coupled in soils. However, major disturbances can produce a decouple in their cycles and disrupt their balance. Therefore, in this project, we study how disturbances like metal contamination and climate change affect nutrient cycling. For this, we study the pools of organic and inorganic forms of C, N, and P in soils and hydrolytic enzyme activities that break down organic matter rich in C, N, and P. To study the inorganic forms of N and P we use colorimetric methods, and for the enzymes we use fluorescent dye-conjugated substrates, which do not fluoresce unless cleaved by respective enzymes. With the implementation of the zymography technique, we can map in 2D the distribution of enzyme activities in soils. Furthermore, we measure soil respiration and gross rates of N transformation processes like mineralization and nitrification using N isotope techniques. Finally, we link all these results to the composition of the microbial community and metal concentrations. 

For mapping metals in 2D, we were at the Stanford Synchrotron Radiation Lightsource (SSRL) in Stanford, California, USA. We used X-ray absorption spectroscopy imaging.

Zymography is a technique for the in situ 2-D visualization and localization of potential enzyme activities in soil by fluorescence (methylumbelliferone (MUF) or 7-amino-4-methylcoumarin (AMC)) based on substrate conversion. It has a spatial resolution of up to tens of micrometers. It is mainly applied for hydrolytic enzymes (break down labile organic compounds) in soils.