title: Spatial distribution of xylem embolisms in the stems of Pinus thunbergii at the threshold of fatal drought stress.
abstract: Although previous studies have suggested that branch dieback and whole-plant death due to drought stress occur at 50-88% loss of stem hydraulic conductivity (P50and P88, respectively), the dynamics of catastrophic failure in the water-conducting pathways in whole plants subjected to drought remain poorly understood. We examined the dynamics of drought stress tolerance in 3-year-old Japanese black pine (Pinus thunbergii Parl.). We nondestructively monitored (i) the spatial distribution of drought-induced embolisms in the stem at greater than P50and (ii) recovery from embolisms following rehydration. Stem water distributions were visualized by cryo-scanning electron microscopy. The percentages of both embolized area and loss of hydraulic conductivity showed similar patterns of increase, although the water loss in xylem increased markedly at -5.0 MPa or less. One seedling that had reached 72% loss of the water-conducting area survived and the xylem water potential recovered to -0.3 MPa. We concluded that Japanese black pines may need to maintain water-filled tracheids within earlywood of the current-year xylem under natural conditions to avoid disconnection of water movement between the stem and the tops of branches. It is necessary to determine the spatial distribution of embolisms around the point of the lethal threshold to gain an improved understanding of plant survival under conditions of drought.
authors.affiliation: Department of Natural Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8563, Japan toshiumebayashi@gmail.com.|Present address: Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Umebayashi
authors.affiliation: Department of Natural Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8563, Japan.
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Morita
authors.affiliation: Ashoro Research Forest, Kyushu University, Ashoro 089-3705, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Utsumi
authors.affiliation: The University of Tokyo Tanashi Forest, The University of Tokyo, Nishitokyo 188-0002, Japan.
authors.forename: Dai
authors.initials: D
authors.lastname: Kusumoto
authors.affiliation: Ashoro Research Forest, Kyushu University, Ashoro 089-3705, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Yasuda
authors.affiliation: MRTechnology Inc., Tsukuba 305-8573, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Haishi
authors.affiliation: Department of Natural Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8563, Japan.|Present address: Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Fukuda
mesh_terms: D055864:Droughts; D028223:Pinus / Q000378:metabolism*; D013312:Stress, Physiological; D014867:Water / Q000378:metabolism; D052584:Xylem / Q000378:metabolism*
chemical_list: D014867:Water
keywords: CMRI; cryo-SEM; tracheid