Nicole Rudolph, Hanna G. Esser, Andrea Carminati, Ahmad B. Moradi, Andre Hilger, Nikolay Kardjilov, Stefan Nagl, Sascha Eric Oswald

• The rooted zone of a soil, more precisely the rhizosphere, is a very dynamic system. Some of the key processes are water uptake and root respiration. We have developed a novel method for measuring the real-time distribution of water and oxygen concentration in the rhizosphere as a biogeochemical interface in soil. This enables understanding where and when roots are active in respect to root respiration and water uptake and how the soil responds to it. We used glass containers (15 x 15 x 1 cm), which were filled with a quartz sand mixture. Sensor foils for fluorescence dye imaging of O-2 were installed on the inner side of the containers. A lupine plant was grown in each container for 2 weeks under controlled conditions. Then we took time series of fluorescence images for time-lapsed visualization of oxygen depletion caused by root respiration. Changing water content was mapped in parallel by non-invasive neutron radiography, which yields water content distributions in high spatial resolution. Also it can detect the root system of theThe rooted zone of a soil, more precisely the rhizosphere, is a very dynamic system. Some of the key processes are water uptake and root respiration. We have developed a novel method for measuring the real-time distribution of water and oxygen concentration in the rhizosphere as a biogeochemical interface in soil. This enables understanding where and when roots are active in respect to root respiration and water uptake and how the soil responds to it. We used glass containers (15 x 15 x 1 cm), which were filled with a quartz sand mixture. Sensor foils for fluorescence dye imaging of O-2 were installed on the inner side of the containers. A lupine plant was grown in each container for 2 weeks under controlled conditions. Then we took time series of fluorescence images for time-lapsed visualization of oxygen depletion caused by root respiration. Changing water content was mapped in parallel by non-invasive neutron radiography, which yields water content distributions in high spatial resolution. Also it can detect the root system of the lupine plants. By this combined imaging of the samples, a range of water contents and different oxygen concentration levels, both induced by root activities, could be assessed. We monitored the dynamics of these vital parameters induced by roots during a period of several hours. We observed that for high water saturation, the oxygen concentration decreased in parts of the container. The accompanying neutron radiographies gave us the information that these locations are spatially correlated to roots. Therefore, it can be concluded that the observed oxygen deficits close to the roots result from root respiration and show up while re-aeration from atmosphere by gas phase transport is restricted by the high water saturation. Our coupled imaging setup was able to monitor the spatial distribution and temporal dynamics of oxygen and water content in a night and day cycle. This reflects complex plant activities such as photosynthesis, transpiration, and metabolic activities impacting the root-soil interface. Our experimental setup provides the possibility to non-invasively visualize these parameters with high resolution. The particular oxygen imaging method as well as the combination with simultaneously mapping the water content by neutron radiography is a novelty.…