Estimating root elongation rates from morphological measurements of the root tip

To measure the elongation rate of individual roots in soil remains a challenge. A novel method for estimating elongation rates of excavated roots is presented. Morphological markers are identified along the tip of excavated roots, and their distance relative to the apex is measured. These markers correspond to developmental stages which follow known temporal patterns. Hence, their distance relative to the apex reflects root elongation during the period corresponding to their development. The method was tested on maize roots grown in a range of conditions and substrates. It was found that distances from markers to apices were proportional, with some variability, to elongation rates. Remarkably, the linear relationships between these distances were neither affected by substrate, nor by growing conditions. Using several markers allows covering time periods ranging from 0.3 day to 3 days as well as cross validation of estimates. Provided further testing, under a wider range of environmental conditions, is conducted, the concepts presented in this paper may serve to define a new measurement technique.