Conservative decrease in water potential in existing leaves during new leaf expansion in temperate and tropical evergreen Quercus species.

Background And Aims: This study aimed at clarifying how the water potential gradient (deltapsi) is maintained in the shoots of evergreen trees with expanding leaves, whose leaf water potentials at the turgor loss point (psi(tlp)) are generally high.

Materials: The water relations were examined in current-year expanding (CEX) and 1-year-old (OLD) leaves on the same shoots in temperate (Osaka, Japan) and tropical (Bogor, Indonesia) areas. A temperate evergreen species, Quercus glauca growing in both sites, was compared with a temperate deciduous species, Q.