Application of geophysical tools for tree root studies in forest ecosystems in complex soils

Abstract

<p><strong>Abstract.</strong> While semiarid forests frequently colonize rocky substrates, knowledge is scarce on how roots garner resources in these extreme habitats. The Sierra San Miguelito Volcanic Complex in Central Mexico exhibits shallow soils and impermeable rhyolitic-rock outcrops, which impede water movement and root placement beyond the soil matrix. However, rock fractures, exfoliations, and soil pockets potentially permit downward percolation and root growth. With ground penetrating radar (GPR) and electrical resistivity tomography (ERT), two geophysical methods advocated by Jayawickreme et al. (2014) to advance root ecology, we studied root and water distribution in shallow-rocky-soils and rock fractures in a semiarid forest. We calibrated geophysical images with in-situ root measurements, and then extrapolated root distribution over larger areas. With GPR, we identified fine and coarse pine and oak roots with 6 to 75 mm diameters at differential depths in soil and fractures; besides, trees anchored their trunks with coarse roots underneath rock outcroppings. With ETR, we tracked monthly changes in humidity at the soil/bedrock interface, which clearly explained spatial root distribution of both tree species. Geophysical methods have enormous potential in elucidating root ecology. More interdisciplinary research could advance our understanding in belowground ecological niche functions and their role in forest ecohydrology and productivity.</p>

Sensing the electrical properties of roots: A review

“…Electrical resistivity tomography has also been used in orchards to study soil moisture dynamics and irrigation patterns near cash crops such as fruit trees (Lazzari et al., 2008; Loperte et al., 2006). These studies found an increasing resistivity in the root zone due to drying through root water uptake processes, but some root zones show lower resistivity than the background as shown in Figure 5 (Lazzari et al., 2008; Petersen & Al Hagrey, 2009; Rodríguez‐Robles, Arredondo, Huber‐Sannwald, Ramos‐Leal, & Yépez, 2017; Werban, Attia al Hagrey, & Rabbel, 2008). The low resistivity of fine roots and high resistivity of tree roots reported in the studies discussed above is an indication that roots are a contributing factor, although masked by other factors, as discussed above.…”