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Harvard Forest Symposium Abstract 2013

  • Title: Investigating xylem embolism formation, refilling and water storage in tree trunks using frequency domain reflectometry
  • Primary Author: Guang-You Hao (Arnold Arboretum of Harvard University)
  • Additional Authors: Guillermo Goldstein (University of Miami); Noel Michele Holbrook (Harvard Forest); James Wheeler (Harvard University)
  • Abstract:

    Trunks of large trees play an important role in whole-plant water balance but technical difficulties have limited most hydraulic research to small stems, leaves and roots. To investigate the dynamics of water-related processes in tree trunks, such as winter embolism refilling, xylem hydraulic vulnerability, and water storage, volumetric water content (VWC) in the main stem was monitored continuously using frequency domain moisture sensors in adult Betula papyrifera trees from early spring through the beginning of winter in 2012 at Harvard Forest. An air injection technique was developed to estimate hydraulic vulnerability of the trunk xylem. Trunk VWC increased in early spring and again in autumn concurrent with root pressure during both seasons. Diurnal fluctuations and a gradual decrease in trunk VWC through the growing season were observed, which, in combination with VWC increase after significant rainfall events and depletion during periods of high water demand, indicate the importance of stem water storage in both short-and long-term water balance. Comparisons between the trunk air injection results and conventional branch hydraulic vulnerability curves showed no evidence of “vulnerability segmentation” between the main stem and small branches in B. papyrifera. Measurements of VWC following air injection, together with evidences from air injection and xylem dye perfusion, indicate that embolized vessels can be refilled by active root pressure but not in the absence of root pressure. The precise, continuous and non-destructive measurement of wood water content using frequency domain sensors provides an ideal way to probe many hydraulic processes in large tree trunks that are otherwise difficult to investigate.

  • Research Category: Physiological Ecology, Population Dynamics, and Species Interactions