A Laboratory Comparison of Two Minirhizotrons for Measuring Fine Root Turnover: The CID Bio-Science, Inc. CI-600 and RhizoSystems, LLC AMR-A Minirhizotrons

The NEON design for measuring ecological change includes minirhizotrons for quantifying fine root biomass production and turnover. A manual minirhizotron (i.e. the CID Bio-science CI-600) and a fully automated minirhizotron (i.e. RhizoSystems, LLC AMR-A) were tested and compared across a number of parameters to inform the NEON design for belowground, fine root turnover measurements. Measured parameters were quantified using optical test targets and analyzed for the sharpness of images (resolution), ability of the camera to return to a specified location (repeatability) and to accurately capture a range of colors (color accuracy).  Other factors related to minirhizotron functionality, such as power requirements, time required for imaging and ease of calibration were also considered during testing.  Additionally, the AMR-A was tested to determine if heat generated by the instrument will have a significant effect on soil temperature, and therefore possibly on root growth.  To analyze for heat output to the soil profile, the AMR-A was placed in a uniform soil environment, and soil temperatures were recorded at three depths and two distances from the minirhizotron, in rest mode and while actively imaging. The CI-600 does not generate significant heat and was therefore not tested for effect on soil temperature. Image analysis with the Interactive Data Language (IDL) revealed significantly greater resolution and repeatability with the AMR versus the CI-600. There were no significant differences in color accuracy.  With regards to overall instrument functionality, AMR-A performance met or exceeded that of the CI-600 in nearly all categories.