Dynamic oxygen mapping in the root zone by fluorescence dye imaging combined with neutron radiography

Abstract

Purpose 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. Materials and methodsWe used glass containers (15×15× 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 timelapsed 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. Results and discussion 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. Conclusions 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 rootsoil 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.

Two decades of chemical imaging of solutes in sediments and soils – a review

“…However, the optical insulation layer makes the sensor non-transparent and decreases the sensor response time (see Section 4.2.3). Due to these inconveniences, only a few studies have used the pure intensity based approach to date [127,163,164].…”

“…stronger when roots of bean and maize grew alone compared to growing in close vicinity to each other. Another study combined O 2 optode imaging with the determination of the water distribution in soil by neutron radiography [164] which enabled to directly link O 2 dynamics to root respiration, plant transpiration, and soil water distribution. Strömberg [227] investigated the NH 4 + turnover around roots of tomato (Solanum lycopersicum), (Fig.…”

Root distributions in a laboratory box evaluated using two different techniques (gravimetric and image processing) and their impact on root water uptake simulated with HYDRUS

“…Our box thickness was the same as in the study by Moradi et al (2010). Thinner boxes were used for example by Whiting et al (2000) 2 cm, Rudolph et al (2012) 0.5 cm, and Youssef and Chino (1988) 1 mm. However, such a narrow space for root growth strongly affects the root architecture.…”

“…thickness, transparency etc. ), roots can be either directly photographed or the neutron, x-ray computed tomography, NMR, 2D light transition imaging technique can be applied (de Dorlodot et al, 2007;Doussan et al, 2006;Garrigues et al, 2006;Moradi et al, 2009Moradi et al, , 2010Moradi et al, , 2013Moran et al, 2000;Oswald et al, 2008;Rudolph et al, 2012Rudolph et al, , 2013Rudolph-Mohr et al, 2014;Stingaciu et al, 2013). These techniques were mostly applied to analyze root development in the early stage of plant and roots growth.…”

Recent developments in neutron imaging with applications for porous media research

“…This makes neutrons an isotope-sensitive probe. Neutron imaging (both radiography and tomography) can quantify very small amounts of fluid, even when the pore space itself cannot be resolved, as demonstrated in several porous media studies (Schaap et al, 2008;Carminati et al, 2007;Robinson et al, 2008;Rudolph et al, 2012;Zarebanadkouki et al, 2014;Zhang et al, 2010;Lal et al, 2014). It is particularly relevant for investigations of water displacement in bulk samples where the detailed structure of the pore space is known, is unchanging, or is of lesser importance in understanding the fluid processes.…”