Interpreting trunk diameter changes in young lemon trees under deficit irrigation

Measurements obtained by the continuous monitoring of sap flow and parameters derived from trunk diameter fluctuations were compared with discrete measurements of conventional plant water status indicators in potted young lemon trees (Citrus limon (l.) Burm. fil, cv. Verna) grafted on sour orange (C. aurantium L.) rootstock submitted to high frequency deficit irrigation. The first detectable response to the deficit irrigation was a marked increase in maximum daily trunk diameter shrinkage (MDS) followed by a decrease in sap flow (SF), predawn leaf water potential and leaf conductance values. Daily maximum (MXTD) and minimum (MNTD) trunk diameters were directly influenced by the plant water supply from the soil. When the water stress increased in severity and the trunk growth rate increased, the MDS values in treated plants decreased to reach values similar to those of control plants. Thus, during the first days of deficit irrigation, when trunk growth was very low, MDS and SF served as the best plant water status indicators. Further, when water stress was more pronounced and trunk growth was greater, MNTD, MXTD and SF were the most reliable indicators.This research was supported by CICYT (AGL2000-9387-C05-02 and AGL2003-9387-C05-02) and PETRI (PTR1995-0693-OP-02-01) grants to the authors. M.F. Ortuño was a recipient of a Program I3P research fellowship from CSIC.Peer reviewe