JXB Advance Access originally published online on June 27, 2005
Journal of Experimental Botany 2005 56(418):2267-2273; doi:10.1093/jxb/eri233
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RESEARCH PAPER |
How are leaves plumbed inside a branch? Differences in leaf-to-leaf hydraulic sectoriality among six temperate tree species
1Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
2Department of Biology, Tufts University, Medford, MA 02155, USA
3Harvard Forest, Petersham, MA 01366, USA
4The Arnold Arboretum of Harvard University, 125 Arborway, Jamaica Plain, MA 02130–3500, USA
5Department of Botany, University of Hawai'i at M
noa, 3190 Maile Way, Honolulu, Hawai'i, 96822, USA
* To whom correspondence should be addressed at Tufts University. Fax: +1 617 627 3805. E-mail: colin.orians{at}tufts.edu
The transport of water, sugar, and nutrients in trees is restricted to specific vascular pathways, and thus organs may be relatively isolated from one another (i.e. sectored). Strongly sectored leaf-to-leaf pathways have been shown for the transport of sugar and signal molecules within a shoot, but not previously for water transport. The hydraulic sectoriality of leaf-to-leaf pathways was determined for current year shoots of six temperate deciduous tree species (three ring-porous: Castanea dentata, Fraxinus americana, and Quercus rubra, and three diffuse-porous: Acer saccharum, Betula papyrifera, and Liriodendron tulipifera). Hydraulic sectoriality was determined using dye staining and a hydraulic method. In the dye method, leaf blades were removed and dye was forced into the most proximal petiole. For each petiole the vascular traces that were shared with the proximal petiole were counted. For other shoots, measurements were made of the leaf-area-specific hydraulic conductivity for the leaf-to-leaf pathways (kLL). In five out of the six species, patterns of sectoriality reflected phyllotaxy; both the sharing of vascular bundles between leaves and kLL were higher for orthostichous than non-orthostichous leaf pairs. For each species, leaf-to-leaf sectoriality was determined as the proportional differences between non-orthostichous versus orthostichous leaf pairs in their staining of shared vascular bundles and in their kLL; for the six species these two indices of sectoriality were strongly correlated (R2=0.94; P <0.002). Species varied 8-fold in their kLL-based sectoriality, and ring-porous species were more sectored than diffuse-porous species. Differential leaf-to-leaf sectoriality has implications for species-specific co-ordination of leaf gas exchange and water relations within a branch, especially during fluctuations in irradiance and water and nutrient availability.
Key words: Diffuse-porous, hydraulic conductance, orthostichy, phyllotaxy, ring-porous, sectoriality, temperate deciduous trees, vascular architecture
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