A novel rhizotron platform to evaluate root plastic responses to soil water heterogeneity

It is commonly thought that plastic responses of root hydraulics and morphology to water availability have evolved to help plants face the heterogeneous soil water availability under unpredictable climatic conditions. However, quantifying these responses is an experimental challenge, as water uptake is continuously affecting root environment. The objective of this study is to investigate the structural and functional plasticity of roots under soil water heterogeneity from the plant down to the organ scales. We developed a novel rhizotron platform comprising 15 independent rhizotrons, each equipped with 9 hydraulically isolated compartments (three rows × three columns) and individual control units that allow for imposing constant spatial moisture patterns or differing water potentials in each compartment while monitoring local water consumption with minute time resolution and tracking root growth and development. A trial was made in which maize plants (cv. B104) grew in the rhizotron platform during four weeks at constant and homogeneous water potential, followed by a fifth week during which three water potentials were imposed. Morphological and hydraulic root responses to these different levels of water availability have been observed using manual root annotation and continuous leaf psychrometer measurements. These results allowed us to compute the elongation of main and lateral roots and real-time changes of the transpiration and local water consumption. This platform will be instrumental to dissect the complex response of maize plants in heterogeneous and variable soil water environments.