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

Saito, Takami, Naiola, B. Paul, Terashima, Ichiro
Annals of botany 2007 v.100 no.6 pp. 1229-1238
Quercus glauca, branches, buds, leaf water potential, leaves, shoots, stomatal conductance, trees, turgor, Indonesia, Japan
BACKGROUND AND AIMS: This study aimed at clarifying how the water potential gradient (ΔΨ) is maintained in the shoots of evergreen trees with expanding leaves, whose leaf water potentials at the turgor loss point (Ψtlp) 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 (Ψmidday) was slightly higher in OLD (-0·5 MPa) than in CEX leaves (-0·6 MPa), whereas Ψtlp was significantly lower in OLD (-2·9 MPa) than in CEX leaves (-1·0 MPa). In Bogor, Ψmidday was also higher in OLD leaves (-1·0 MPa) despite the low Ψtlp (-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 Ψmidday in OLD leaves after 1 month. Ψmidday in OLD leaves thus appears to be independent of that in CEX leaves. CONCLUSIONS: The moderate decrease in Ψmidday in OLD leaves would contribute to maintenance of ΔΨ in the shoots during leaf expansion.