title: Altitudinal changes in leaf hydraulic conductance across five Rhododendron species in eastern Nepal.
abstract: This study investigated altitudinal changes in leaf-lamina hydraulic conductance (KL) and leaf morphological traits related to KLusing five Rhododendron species growing at different altitudes (2500-4500 m above sea level) in Jaljale Himal region in eastern Nepal. Sun leaves were collected from the highest and the lowest altitude populations of each species, and KLwas measured with a high pressure flow meter method. Leaf-lamina hydraulic conductance ranged from 7.7 to 19.3 mmol m-2s-1MPa-1and was significantly positively correlated with altitude. The systematic increase with altitude was also found in KL, leaf nitrogen content and stomatal pore index. These relationships suggest that plants from higher-altitude habitats had a large CO2supply to the intercellular space in a leaf and high CO2assimilation capacity, which enables efficient photosynthesis at high altitude. The variation in KLwas associated with the variation in several leaf morphological traits. High KLwas found in leaves with small leaf area and round shape, both of which result in shorter major veins. These results suggest that the short major veins were important for efficient water transport in unlobed leaves of Rhododendron species. The extent of lignification in bundle sheaths and bundle sheath extension was associated with KLLignified compound primary walls inhibit water conduction along apoplastic routes. All species analyzed had heterobaric leaves, in which bundle sheath extensions developed from minor veins, but strongly lignified compound primary walls were found in Rhododendron species with low KLIt is still unclear why cell walls in bundle sheath at minor veins were markedly lignified in Rhododendron species growing at lower altitude. The lignified cell wall provides a high pathogenic resistance to infection and increases the mechanical strength of cell wall. The data imply that lignified bundle sheath may provide a trade-off between leaf hydraulic efficiency and leaf mechanical toughness or longevity.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan taneda@bs.s.u-tokyo.ac.jp.
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Taneda
authors.affiliation: Department of Plant Resources, National Herbarium and Plant Laboratories, Godawari, Lalitpur 44709, Nepal.
authors.forename: Dhan Raj
authors.initials: DR
authors.lastname: Kandel
authors.affiliation: Center for Ecological Research, Kyoto University, 2-509-3 Hirano, Ohtsu, Shiga 520-2113, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ishida
authors.affiliation: The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ikeda
mesh_terms: D000531:Altitude; D017753:Ecosystem; D009390:Nepal; D018515:Plant Leaves / Q000378:metabolism; D029793:Rhododendron / Q000378:metabolism*; D013045:Species Specificity; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water
keywords: alpine plant; leaf anatomy; leaf carbon isotope discrimination; leaf shape; lignification; water relations