Water dynamics in the root-zone of plants using neutron imaging

Background/Question/Methods

Water flow from soil to roots is not well understood and presents challenges at the scales of single root and also root system. This is due to the complexity of the processes in the root-soil interface, dynamic character of the root-soil interactions, heterogeneity of soil, and technical difficulties accessing the roots without disturbing their functions. Traditional methods of measuring soil parameters such as point-like measurements and extraction of soil solution are for many purposes too invasive, tedious, expensive, and insufficient with respect to spatial and temporal resolution. There is a growing need for the direct, non-destructive and non-invasive measurements of processes in the root-zone. Neutron imaging is a unique tool to study water dynamics in soil, root developments, and root-soil interactions. This study discusses the application and evaluates the capabilities and limitations of neutron imaging technique for root-zone studies with particular emphasize on soil moisture and root developments in soil. A range of neutron radiography and tomography experiments have been carried out in recent years focusing on water distribution in soil and water uptake by roots. Selected examples of these studies at various scales of micrometers to decimeters will be presented.

Results/Conclusions

At the scale of single root, soil water was found to have a different dynamics in the rhizosphere than in the bulk soil. Rhizosphere held higher water content than the bulk soil during a drying period and rewetted more slowly after re-watering. At the scale of root system, roots developed different structures under different soil water regimes. Water uptake by plants stayed constant in samples with partial root-zone irrigation as long as part of the root-zone was irrigated well. However, the transpiration decreased over the next days as the soil water content in the wet part decreased. These applications demonstrate the dynamic character of root-soil interactions and important role of rhizosphere in water flow to roots and highlight the need for non-invasive measurement methods for monitoring water distribution in the root-zone with high spatial and temporal resolutions.