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AOBPreview published online on September 12, 2007
Annals of Botany, doi:10.1093/aob/mcm198
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© The Author 2007. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Conservative Decrease in Water Potential in Existing Leaves during New Leaf Expansion in Temperate and Tropical Evergreen Quercus Species

Takami Saito1,3,*, B. Paul Naiola2 and Ichiro Terashima3

1 Department of Biology, Graduate School of Science, Osaka University, 1-1 Machikeneyama-cho, Toyonaka, Osaka 560-0043, Japan
2 Treub Laboratory, Botany Division, Indonesian Institute of Science (LIPI), Bogor, Indonesia
3 Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

* For correspondence. E-mail takami{at}biol.s.u-tokyo.ac.jp

Received: 16 March 2007    Returned for revision: 31 May 2007    Accepted: 5 July 2007   

Background and Aims: This study aimed at clarifying how the water potential gradient ({Delta}{Psi}) 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. serrata, in Osaka, and two tropical evergreen species, Q. gemelliflora and Q. subsericea, in Bogor.

Key Results: (1) In Osaka, the midday leaf water potential ({Psi}midday) was slightly higher in OLD (–0·5 MPa) than in CEX leaves (–0·6 MPa), whereas {Psi}tlp was significantly lower in OLD (–2·9 MPa) than in CEX leaves (–1·0 MPa). In Bogor, {Psi}midday was also higher in OLD leaves (–1·0 MPa) despite the low {Psi}tlp (–1·9 MPa), although stomatal conductance was not always low in OLD leaves. In the branch bearing CEX and OLD leaves, most of the hydraulic resistance (86 %) exists in the current-year branch, leading to differences in water supply between CEX and OLD leaves. The removal of buds just before breaking did not affect the high {Psi}midday in OLD leaves after 1 month. {Psi}midday in OLD leaves thus appears to be independent of that in CEX leaves.

Conclusions: The moderate decrease in {Psi}midday in OLD leaves would contribute to maintenance of {Delta}{Psi} in the shoots during leaf expansion.

Key words: Cohesion–tension theory, hydraulic resistance, leaf expansion, leaf water potential, pressure–volume curve, Quercus, turgor maintenance, water potential gradient


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