Quantifying the impact of soil compaction on root system architecture in tomato (Solanum lycopersicum) by X-ray micro-computed tomography

We sought to explore the interactions between roots and soil without disturbance and in four dimensions (i.e. 3-D plus time) using X-ray micro-computed tomography. The roots of tomato Solanum lycopersicum oAilsa Craig' plants were visualized in undisturbed soil columns for 10 consecutive days to measure the effect of soil compaction on selected root traits including elongation rate. Treatments included bulk density (12 vs. 16 g cm(3)) and soil type (loamy sand vs. clay loam). Plants grown at the higher soil bulk density exploited smaller soil volumes (P 005) and exhibited reductions in root surface area (P 0001), total root volume (P 0001) and total root length (P 005), but had a greater mean root diameter (P 005) than at low soil bulk density. Swelling of the root tip area was observed in compacted soil (P 005) and the tortuosity of the root path was also greater (P 001). Root elongation rates varied greatly during the 10-d observation period (P 0001), increasing to a maximum at day 2 before decreasing to a minimum at day 4. The emergence of lateral roots occurred later in plants grown in compacted soil (P 001). Novel rooting characteristics (convex hull volume, centroid and maximum width), measured by image analysis, were successfully employed to discriminate treatment effects. The root systems of plants grown in compacted soil had smaller convex hull volumes (P 005), a higher centre of mass (P 005) and a smaller maximum width than roots grown in uncompacted soil. Soil compaction adversely affects root system architecture, influencing resource capture by limiting the volume of soil explored. Lateral roots formed later in plants grown in compacted soil and total root length and surface area were reduced. Root diameter was increased and swelling of the root tip occurred in compacted soil.