Effects of water stress and rewatering on leaf water relations of lemon plants

Potted two-year-old lemon plants (Citrus limon (L.) Burm, fil.) cv. Fine, growing under field conditions were subjected to drought by withholding irrigation for 13 d. After that, plants were re-irrigated and the recovery was studied for 5 d. Control plants were daily irrigated maintaining the soil matric potential at about -30 kPa. Young leaves of control plants presented higher leaf conductance (g(l)) and lower midday leaf water potential (Psi(md)) than mature ones. Young leaves also showed higher leaf water potential at the turgor loss point (Psi(tlp)) than mature leaves. In both leaf types gl decreased with increased vapour pressure deficit of the atmosphere. From day 1 of the withholding water, predawn and midday leaf water potentials (Psi(pd) and Psi(md)) decreased, reaching in both cases minimum values of -5.5 MPa, with no significant differences between mature and young leaves. Water stress induced stomatal closure, leaf rolling and partial defoliation. No osmotic adjustment was found in response to water stress in either leaf type, but both were able to enhance the cell wall elasticity (elastic adjustment). After rewatering, leaf water potential recovered quickly (within 2 d) but g(l) did not.