title: Physiological and morphological acclimation to height in cupressoid leaves of 100-year-old Chamaecyparis obtusa.
abstract: Cupressoid (scale-like) leaves are morphologically and functionally intermediate between stems and leaves. While past studies on height acclimation of cupressoid leaves have focused on acclimation to the vertical light gradient, the relationship between morphology and hydraulic function remains unexplored. Here, we compared physiological and morphological characteristics between treetop and lower-crown leaves of 100-year-old Chamaecyparis obtusa Endl. trees (~27 m tall) to investigate whether height-acclimation compensates for hydraulic constraints. We found that physiological acclimation of leaves was determined by light, which drove the vertical gradient of evaporative demand, while leaf morphology and anatomy were determined by height. Compared with lower-crown leaves, treetop leaves were physiologically acclimated to water stress. Leaf hydraulic conductance was not affected by height, and this contributed to higher photosynthetic rates of treetop leaves. Treetop leaves had higher leaf area density and greater leaf mass per area, which increase light interception but could also decrease hydraulic efficiency. We inferred that transfusion tissue flanking the leaf vein, which was more developed in the treetop leaves, contributes to water-stress acclimation and maintenance of leaf hydraulic conductance by facilitating osmotic adjustment of leaf water potential and efficient water transport from xylem to mesophyll. Our findings may represent anatomical adaptation that compensates for hydraulic constraints on physiological function with increasing height.
authors.affiliation: Department of Plant Science, Graduate School of Agricultural Science, Kobe University, Kobe 657-8501, Japan.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Shiraki
authors.affiliation: Department of Plant Science, Graduate School of Agricultural Science, Kobe University, Kobe 657-8501, Japan.|Field Science Education and Research Center, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Wakana
authors.initials: W
authors.lastname: Azuma
authors.affiliation: Department of Plant Science, Graduate School of Agricultural Science, Kobe University, Kobe 657-8501, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Kuroda
authors.affiliation: Department of Plant Science, Graduate School of Agricultural Science, Kobe University, Kobe 657-8501, Japan.
authors.forename: H Roaki
authors.initials: HR
authors.lastname: Ishii
mesh_terms: D000064:Acclimatization; D000531:Altitude; D029780:Chamaecyparis / Q000254:growth & development / Q000502:physiology*; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology*; D014197:Trees / Q000502:physiology
keywords: hydraulic conductance; hydraulic limitation; light acclimation; transfusion tissue; water stress