Tree root imaging by electrical resistivity tomography: geophysical tools to improve understanding of deep root structure and rhizospheric processes

Tree roots influences potential biosphere-atmosphere interactions and regulates diverse biogeochemical cycles. Trees among many complex functions help in extracting soil-water at low water potentials, ensure nutrient uptake to support tree health, and provide overall stability. Hence, it becomes important to understand the complex root structure and patterns to strengthen our predictions for various rhizosphere processes which play important role in ecological studies but due to lack of appropriate instrumentation support have been lacking. In the present study we have aimed at imaging the tree root biomass using 2D Electrical Resistivity Tomography (ERT) and the field measurements were carried out in the campus of the National Environmental Engineering Research Institute in Nagpur, India that has lush green 43 ha. of urban forest in the heart of Nagpur city. High-resolution resistivity tomogram with Dipole-Dipole, Schlumberger and Wenner configurations having 24 electrodes spaced 2 m apart were used to detect the spatial variability of roots. Root biomass distribution for two important tree species in the avenue plantations (Peltophorum pterocarpum (06) and Delonix regia (01) having average stem radius of 640 cm as measured by Electrical Resistivity Tomography. Results showed that Wenner array was found to be effective however, the Schlumberger and Dipole-Dipole arrays was unable to provide clear signature for root patterns and delineate root boundaries.