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Harvard Forest Data Archive


Xylem Embolism Formation, Refilling and Water Storage in Tree Trunks at Harvard Forest 2012

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  • Lead: N. Michele Holbrook, Guillermo Goldstein
  • Investigators: Guang-You Hao, James Wheeler
  • Contact: N. Michelle Holbrook
  • Start date: 2012
  • End date: 2012
  • Status: completed
  • Location: Prospect Hill Tract (Harvard Forest)
  • Latitude: +42.53
  • Longitude: -72.18
  • Elevation: 330 meter
  • Taxa: Betula papyrifera (paper birch)
  • Release date: 2016
  • Revisions:
  • EML file: knb-lter-hfr.269.2
  • DOI: digital object identifier
  • EDI: data package
  • DataONE: data package
  • Related links:
  • Study type: short-term measurement
  • Research topic: physiological ecology, population dynamics and species interactions
  • LTER core area: primary production
  • Keywords: hydraulic conductance, tree physiology, water balance
  • 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. 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.

  • Methods:

    Volumetric water content

    Moisture sensors based on frequency domain reflectometry (FDR) technology (Model GS3, Decagon Devices, Inc. Pullman, WA) were installed in the trunks of adult B. papyrifera trees at breast height. Three holes of 5.5 cm in depth spaced 2.54 cm apart were drilled radially into the trunk using an electric drill, with a drill bit of 3.26 mm in diameter. A customized drill guide with three holes of the same diameter was used to facilitate the drilling. After inserting the three prongs (5.5 cm in length, 3.26 mm in diameter and 2.54 cm apart) of the sensor into the drilled holes, the moisture sensors were gently hammered until the prongs were completely within the tree. The gaps between the sensor overmold and the tree were sealed with silicon caulk to prevent infiltration of water from precipitation. The whole sensor was insulated with foam and aluminum foil to avoid heating by direct sun light. In addition to VWC, trunk temperature was measured by the thermocouples embedded in the sensor overmold. Data were logged using EM50 data loggers (Decagon Devices, Inc. Pullman, WA) every 5 minutes for 24 hours a day. Three sensors were installed in three trees (numbered 1, 2 and 3) in early spring (March) of 2012 and measurements were made continuously until the end of the year. The FDR sensor calibration was conducted in the laboratory using wood of B. papyrifera and the results showed that the sensor VWC output based on the factory calibration matches well with VWC calculated by a gravitational method. The factory calibration was thus used in the present study.

    Root pressure

    Hydrostatic pressures in trunks of the same three trees were measured using electronic pressure transducers (PX26-015GV, Omega Engineering, Inc. Stamford, CT). Two holes of 1.59 mm in diameter and ca. 2 cm in depth were drilled near the base of a tree trunk and hypodermic needles of the same outer diameter with bent tips (to avoid clogging by wood debris) were inserted to the sapwood and glued in place with epoxy. The pressure transducers were connected to the hypodermic needles through a short piece of non-elastic water-filled tubing (Bev-A-Line IV, Cole Parmer Instrument Co., Chicago, IL). The output voltage of the pressure transducers was logged at 5-min intervals with a CR10X data logger (Campbell Scientific, Logan, UT, USA). Every two to three weeks, transducers were moved to fresh-drilled holes to avoid gradual clogging of xylem. Measurements of root pressure were made from March to June and from September to November 2012.

    The pressure transducers were calibrated in laboratory prior to and after the field measurements and no significant drift was found. Briefly, transducers were connected with a high-precision digital pressure gauge (Model DPG1000AD; Omega Engineering, Inc., Stamford, CT) and were connected to a high-pressure nitrogen tank through a regulator. The pressure applied to the transducer was increased in a stepwise manner from 0 to ca. 138 kPa with an interval of 1 psi (ca. 6.89 kPa) and the output data were recorded using a CR10X data logger. Linear regressions between voltage outputs and applied pressures were used to calculate the root pressures.

  • Use:

    This dataset is released to the public under Creative Commons license CC BY (Attribution). Please keep the designated contact person informed of any plans to use the dataset. Consultation or collaboration with the original investigators is strongly encouraged. Publications and data products that make use of the dataset must include proper acknowledgement.

  • Citation:

    Holbrook N, Goldstein G. 2016. Xylem Embolism Formation, Refilling and Water Storage in Tree Trunks at Harvard Forest 2012. Harvard Forest Data Archive: HF269.

Detailed Metadata

hf269-01: birch data

  1. datetime: date and time
  2. vwc1: tree 1 stem volumetric water content (unit: cubicMetersPerCubicMeters / missing value: NA)
  3. temp1: tree 1 stem temperature (unit: celsius / missing value: NA)
  4. ec1: tree 1 stem bulk electrical conductivity (unit: microsiemensPerCentimeter / missing value: NA)
  5. vwc2: tree 2 stem volumetric water content (unit: cubicMetersPerCubicMeters / missing value: NA)
  6. temp2: tree 2 stem temperatures (unit: celsius / missing value: NA)
  7. ec2: tree 2 stem bulk electrical conductivity (unit: microsiemensPerCentimeter / missing value: NA)
  8. vwc3: tree 3 stem volumetric water content (unit: cubicMetersPerCubicMeters / missing value: NA)
  9. temp3: tree 3 stem temperatures (unit: celsius / missing value: NA)
  10. ec3: tree 3 stem bulk electrical conductivity (unit: microsiemensPerCentimeter / missing value: NA)
  11. p.temp: data logger panel temperature (for pressure sensors) (unit: celsius / missing value: NA)
  12. p1: tree 1 stem pressure (replicate 1) (unit: megapascal / missing value: NA)
  13. p2: tree 1 stem pressure (replicate 2) (unit: megapascal / missing value: NA)
  14. p3: tree 3 stem pressure (replicate 1) (unit: megapascal / missing value: NA)
  15. p4: tree 2 stem pressure (replicate 1) (unit: megapascal / missing value: NA)
  16. p5: tree 2 stem pressure (replicate 2) (unit: megapascal / missing value: NA)
  17. p6: tree 3 stem pressure (replicate 2) (unit: megapascal / missing value: NA)