Advances in the Application of Ground-Penetrating Radar for Detection and Quantification of Plant Roots

Abstract:

Because of the crucial role that woody roots play in plant functions and Critical Zone processes, knowledge about the size, architecture, and biomass of woody roots is essential. The use of ground-penetrating radar (GPR), a non-invasive geophysical technique, to characterize woody roots dates back to 1999. Here, we summarize major advances in using GPR to detect and quantify woody roots achieved in the past decade. The accuracy of detecting and locating roots has been improved by coupling GPR with different antenna frequencies, repeating GPR surveys in different seasons, and adopting optimized survey line layouts and 3D GPR systems. New GPR signal indices have been established to promote the accuracy of measuring root biomass and root water content. Automatic identification of roots in GPR images has been developed, allowing applications for larger areas. A method of reconstructing root system architecture has been proposed and tested in sandy soils. A forward simulation protocol of root GPR signals has been developed to assess the impacts of limiting factors on root investigation by GPR. The geometry of the root’s reflection in GPR images has been used to derive GPR wave velocity and soil water content, which has been further enhanced to map 3D root-zone soil water content. Based on these advances in methodology, the GPR method has been extended to determine vertical root distribution, root activity, fine root biomass, root branching patterns, and preferential flow along roots. These new applications have strengthened our ability to study root competition, root-soil-water interaction, root penology, and the above- and below-ground relationship. We hope that this work can stimulate the continuous advancement of non-invasive detection and quantification of woody roots in the Critical Zone, such as the integration of multiple geophysical techniques.