Root Water Uptake Dynamics of Cichorium intybus var. sativum Under Water-Limited Conditions

Chicory (Cichorium intybus L.) is a cash crop cultivated in Western Europe for inulin production. Due to actual and future climate changes, this plant could be exposed to severe water stress at the end of its growing period, leading to a decrease of its yield. The aim of this work was to investigate the chicory root water uptake dynamics and the plant ability to compensate a lack of water in the upper horizons. We performed a controlled experiment with 3 replicates under contrasted irrigation scenarios. We observed that, in case of drought, total root length decreased and root profiles developed deeper. We successfully used a one-dimensional Richards-based model with a stress function and a compensation mechanism (Hydrus 1-D) to inversely characterize the dynamics of the actual sink-term profiles under both irrigation scenarios. We could also use the model to assess the compensation thanks to a weighted stress index that is consistent between replicates. The extraction profiles evolved differently under water-deficit and controlled situations. The passive compensation mechanism allowed chicory roots under water-limited conditions to take water deeper in the soil, where they had only few lateral roots. We found that, in case of drought, compensation started before the plants had to reduce their transpiration rate. Because the soil kept drying out, compensation was not sufficient anymore,and the plants had to decrease their transpiration some days later. However, chicories maintained their metabolism and continued to transpire and to growth slowly. This allowed them to adapt thanks to an active compensation mechanism, by generating new lateral roots in wetter horizons. This study also showed that there was no unique Feddes stress parameter set able to describe plant behavior under contrasted irrigation conditions or even under different plant development stages.