Sap flow and trunk diameter fluctuations of young lemon trees under water stress and rewatering

Potted 2-year-old lemon trees (Citrus limon (L.) Burm. fil, cv. Verna) grafted on sour orange (C. aurantium L.) rootstock and growing under field conditions were subjected to water stress by withholding irrigation for 6 days. After that time, irrigation was restored and plant recovery was studied for 8 days. The results indicate that sap flow (SF) measurement by the heat-pulse technique is a suitable plant-based method for estimating the daily transpiration for young lemon plants. The most sensitive continuously recorded plant-based indicators of water stress and recovery were daily minimum trunk diameter (MNTD) and daily maximum trunk shrinkage (MDS) followed by SF. It was concluded that the water supplied to the trees from soil has a direct influence on daily MDS. Besides reflecting tree water status, SF and MNDT were clearly influenced by weather conditions, meaning that it is possible to develop reference or baseline relationships to interpret plant-based indicator measurements for irrigation scheduling.