The relationships between static and dynamic variables in the description of root growth. Consequences for field interpretation of rooting variability

Field root investigations are often limited by the static nature of classic al observations, resulting in the need to develop alternative methodologies that allow dynamic interpretation of root architecture variability on the basis of static measurements. The objectives of this work were (i) to evalu ate the use of selected morphological indicators, namely root apical diamet er (Da) and the length of the apical unbranched zone (LAUZ), in predicting primary and lateral root growth patterns in banana trees, (ii) to propose a field methodology for the assessment of root dynamics based on static meas urements. Banana trees (Musa acuminata cv `Grande Naine') were grown in 5 r hizotrons as well as in field conditions, respectively on pouzzolane and Mo llic Andosols. In rhizotrons, root growth analysis was carried out by repor ting root elongation, Da and LAUZ, three times a week. In field conditions, 4 series of excavations were made at three-week intervals. Apart from root growth rate, measurements were the same as those in the rhizotrons. LAUZ was confirmed as a stable and good predictor of root growth rate for t he different types of roots. In the rhizotrons, the root growth of lateral roots was found to be well correlated to the product of Da and the growth r ate of the bearing root. Evaluation in field conditions from static observa tions attested consistent relationships between measured and predicted root length for lateral roots (slopes close to 1:1). The apical diameter can be considered as a good indicator of root growth potential, while actual late ral root growth depends on the bearing root elongation rate. Morphological static indicators calibrated from growth dynamics in rhizotrons are of majo r interest in explaining growth variability in field conditions. Especially the `growth rate-LAUZ' relationship can be considered a useful tool in int erpreting field patterns of growing roots in relation to various soil condi tions.