Estimating uptake and internal transport dynamics of irrigation water in apple trees using deuterium-enriched water

With future climatic scenarios foreseeing increased crop water demands and reduced irrigation water avail-ability, a deeper knowledge on the dynamics of water uptake and translocation inside plants is needed. Little is known about the time interval existing between the irrigation water supply and the presence of irrigation water inside trees, and whether the dripper localization can affect water uptake and translocation dynamics. Another research gap concerns the redistribution of irrigation water in the canopy following irrigation localized to one side of the tree.A field and a pot experiment were designed to gain more insight into this context. In the field experiment, we tested the effect of different drip irrigation layouts on the extent and velocity of water uptake by apple trees. Trees were irrigated using deuterium-enriched water using one, two, or four drippers per tree. Samples were collected from different heights in the canopy at regular intervals following the irrigation event. In the pot experiment, the soil was saturated with labelled water and samples were collected at different time intervals and heights along the tree stem. Labelled water was detected in the lowest stem section of potted trees after 1 h from irrigation. In field-grown trees, labelled water appeared in the shoots after 4 h and 6 h in the bottom and top part of the canopy, respectively. By increasing the number of drippers per tree, the fraction of irrigation water in the shoots increased accordingly. However, uptake and transport velocity were unaffected by the number of drip-pers, averaging 0.60-0.65 m h-1. In trees that were irrigated from one side only, irrigation water could be found on the opposite side in the top part of the canopy. Our results suggest that the localization and amount of irrigation water can significantly influence root water uptake in apple trees.