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Harvard Forest Data Archive

HF268

Diurnal Patterns of Cavitation in Red Maple, Paper Birch and White Ash at Harvard Forest 2011-2012

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Data

Overview

  • Lead: James Wheeler, Brett Huggett, Alena Tofte, Fulton Rockwell, N. Michele Holbrook
  • Investigators:
  • Contact: N. Michele Holbrook
  • Start date: 2011
  • End date: 2012
  • Status: completed
  • Location: Harvard Forest
  • Latitude: +42.53 to +42.55
  • Longitude: -72.20 to -72.17
  • Elevation: 280 to 420 meter
  • Taxa: Acer rubrum (red maple), Betula papyrifera (paper birch), Fraxinus americana (white ash)
  • Release date: 2016
  • Revisions:
  • EML file: knb-lter-hfr.268.2
  • DOI: digital object identifier
  • Related links:
  • Study type: short-term measurement
  • Research topic: physiological ecology, population dynamics and species interactions
  • LTER core area: primary production
  • Keywords: hydraulic conductance, maple, oak, plant physiology, trees, water balance, wood
  • Abstract:

    Previous work at Harvard Forest has suggested that woody plants cavitate and re-dissolve embolisms in xylem on a daily basis. Here we investigated the common assumption that severing stems and petioles under water preserves the hydraulic continuity in the xylem conduits opened by the cut when the xylem is under tension. In red maple and white ash, higher PLC in the afternoon occurred when the measurement segment was excised under water at native xylem tensions, but not when xylem tensions were relaxed prior to sample excision. Bench drying vulnerability curves in which measurement samples were excised at native versus relaxed tensions showed a dramatic effect of cutting under tension in red maple, a moderate effect in sugar maple, and no effect in paper birch. These results suggest that sampling methods can generate PLC patterns indicative of repair under tension by inducing a degree of embolism that is itself a function of xylem tensions at the moment of sample excision.

  • Methods:

    Plant material

    Plant material included forest grown trees at Harvard Forest (HF), Petersham, MA. Red maple (Acer rubrum L.), paper birch (Betula papyrifera Marsh.), and white ash (Fraxinus americana L.) were studied. The maples were mature canopy trees, approximately 30 meters tall, while the birch and ash were in a 20-meter-tall mixed stand. All HF material was harvested using a 22-m-tall canopy lift, which allowed access to the upper crowns of the trees.

    In all cases, current year extension growth from the uppermost branches exposed to full sun was sampled. We limited the measured material to current year growth to avoid embolism that originated from conditions prior to the growing season (i.e. no freeze-thaw embolism) and to facilitate the cleanest cuts possible, thus reducing the possibility that damage to the xylem during harvest would affect our results. In addition, vessels from previous years may more vulnerable to cavitation compared to current year conduits (Melcher, Zwieniecki, and Holbrook 2003), a complication we wished to avoid.

    Hydraulic measurements

    Samples for flow measurement 4-14 cm in length (one to two internodes long) were cut from sample branches under tap water. The basal and apical ends were decorticated and the ends shaved with a fresh razor blade, wrapped in parafilm (to ensure a good seal) and fitted into silicone tubing to attach to the hydraulic apparatus. For stems containing more than one node the petioles were removed under water and the scars sealed with cyanoacrylate glue (Krazyglue all purpose, Elmer’s Products Inc.).

    Hydraulic conductance measurements were made by measuring the flow driven by a gravity head onto a balance (Sartorius CPA224S at HF, CPA225D at CC) on which the mass change was recorded every second (Sperry, Donnelly and Tyree 1988). To account for stem uptake from the balance, three flow measurements were made; initial and final measurements with no pressure across the segment, and a pressurized flow measurement with a gravity head of 25-40 cm. The mean flow of the initial and final measurements was then deducted from the value of the pressurized flow measurement (Torres-Ruiz, Sperry, and Fernández 2012). This compensation only made a difference in cases where the stems were narrow and dry (most notably in several of the centrifuge measurements at high tension), when the stems were well hydrated, the magnitude of these initial and final measurements was less than 5% of the measurement made with pressure.

    The measurement solution was ultra-filtered de-ionized water (Barnstead RO Reverse Osmosis System, series 1266, model D12661. Maximum conductance for each stem segment was determined by measurement after flushing for 30 minutes at 0.14 MPa, with a filtered 20 mM KCl solution. Percent loss of conductivity (PLC) was calculated as the difference between the flushed (kf) and initial conductivities (ki) normalized by the flushed value and expressed as a percentage (Sperry et al. 1988).

    Water potential measurements

    Leaf water potential was measured using a pressure chamber (PMS model 1000). To avoid inducing embolism in the measurement segments, the material used to measure water potential (small branches for red maple and paper birch, individual leaves for white ash) was collected from an adjacent limb concurrently with the branches collected for hydraulic measurements. Water potential samples were sealed in plastic bags immediately after removal from the tree and allowed to equilibrate for approximately one hour, except (where noted) when the samples were sealed in foil-covered bags several hours prior to sampling. For both maple species, pressure chamber measurements were made on leafy side branches (less than 1 cm in length) from which the bark had been removed. This was done because maple petioles frequently produce a foamy exudate when pressurized that makes it difficult to obtain an accurate balancing pressure. In birch, individual leaves were removed with a razor blade and placed in the pressure chamber. For ash a few millimeters were re-trimmed with a razor blade from the base of the petiole before placing the leaf in the pressure chamber.

    Diurnal PLC sampling

    During the 2011 summer growing season, branches of HF trees were collected in the afternoon (between 1 PM and 3 PM) and again the following morning (between 5:30 AM and 6:30 AM). Two individuals of paper birch, four of red maple, and six of white ash were sampled. All branches were collected in clear weather (full sun for the afternoon measurements, prior to direct illumination for the morning measurements) over three to five consecutive days. A split funnel was wrapped around the branch to be sampled, sealed using duct tape, and filled with water. The branch was then cut under water using razor clippers (1 megaCut S, Wolfcraft), which minimized crushing of the xylem, and the cut end immediately transferred to a bucket of water. The leafy end of the branch was covered with a large plastic bag and the branch, with its cut end remaining in water, was transferred to the laboratory. It took thirty to sixty minutes to transfer the samples to the laboratory. Based on subsequent measurements, xylem tension in the branches would have relaxed substantially before the measurements section was excised.

    In maple and birch the initial cut was roughly 0.5 m from the region within the current year’s extension growth that would subsequently be used for measuring PLC. When expressed in terms of vessel lengths, the distance between the initial cut and the measurement segment was at least four maximum vessel lengths for maple and at least two maximum vessel lengths for birch. In ash, the maximum branch diameter that could be severed within the water-filled funnel, coupled with much longer maximum vessel lengths (ca 1 m), resulted in collected branches in which the distance between the cut end and the measurement section was typically less than one maximum vessel length.

    In 2012 diurnal measurements of PLC in red maple were repeated in order to directly compare the effect on PLC of cutting xylem conduits under tension. In this experiment, two branches were collected from each of four trees twice a day, in the morning (5 AM to 6 AM) and the afternoon (1 PM to 3 PM), repeated over four days. One of the branches was collected by the method described above, while the other was collected by cutting the branch in air, a minimum of three maximum vessel lengths (0.4 m) from the intended measurement segment. Immediately after the latter branch was cut from the tree, the apical end of the branch was bent into a rectangular container (20 x 30 x 15 cm) and the measurement segment excised under water, where it remained during the thirty to sixty minutes necessary to begin hydraulic measurements on both sets of samples. For this study, sampling of leaf water potential was modified to provide estimates of stem potential. Short leafy shoots of red maple were sealed in aluminum foil covered plastic bags three to seven hours in advance of collecting the samples for measurement of PLC, one shoot per sample segment.

    Here we use “native tension” to refer to measurements made on sample segments excised from stems under tension, either due to naturally occurring tension in the plant at midday or imposed by bench drying. “Relaxed tension” refers to samples in which xylem tensions were reduced (by providing water and suppressing transpiration) prior to excision.

    PLC of crown-irrigated white ash

    Because we were unable to harvest white ash branches that were of sufficient length to avoid the possibility of severing xylem conduits that extended into the portion of the branch used to measure PLC, we conducted an experiment at HF in which branches cut from the tree under water during the afternoon (native tensions) were compared with branches cut under water following a 30 minute period during which water was supplied to the crown through a cut side branch (relaxed tension). Two adjacent branches (0.6 to 1.1 m in length) per tree from nine separate trees were harvested under water from the main axis near the apex of a tree during the afternoon. After the first branch was cut (native tension), the upper two meters of the crown was covered with a reflective bag to suppress transpiration and water was provided through the cut branch stub with water filled tubing that was attached to the cut end while it remained under water. After 30 minutes a second branch located within the bagged crown was cut under water (relaxed tension). Samples for leaf water potential were collected at the time that each branch was sampled. To ensure that the leaves sampled for these measurements did not introduce embolism into the measurement segments they were removed at least 1.5 meters from the sample segments. This experiment was conducted at the end of the 2011 summer season (late August).

  • 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:

    Wheeler J, Huggett B, Tofte A, Rockwell F, Holbrook N. 2016. Diurnal Patterns of Cavitation in Red Maple, Paper Birch and White Ash at Harvard Forest 2011-2012. Harvard Forest Data Archive: HF268.

Detailed Metadata

hf268-01: hydraulic conductance

  1. species: species
    • ACRU: Acer rubrum
    • BEPA: Betula papyrifera
    • FRAM: Fraxinus americana
  2. treat: treatment
    • AM: branches harvested in the AM
    • PM: branches harvested in the PM
    • CTRL: branches harvested under native tension
    • EXP: harvest after relaxing crown water potential
  3. knat: the hydraulic conductivity of the sample in kg/m/MPa/s (unit: number / missing value: NA)
  4. kmax: hydraulic conductivity of the same sample after flushing (unit: number / missing value: NA)
  5. plc: percent loss of conductivity, (1-Knat/Kmax)*100 (unit: dimensionless / missing value: NA)
  6. wp: water potential (unit: bar / missing value: NA)

hf268-02: red maple hydraulic conductance

  1. treat: treatment
    • AM_wet: branches harvested in the AM and sampled after relaxing xylem tensions
    • AM_dry: harvested in the morning and sampled under native tension
    • PM_wet: branches harvested in the PM and sampled after relaxing xylem tensions
    • PM_dry: harvested in the PM and sampled under native tension
  2. date: date of the experiment
  3. knat: hydraulic conductivity of the sample in kg/m/MPa/s (unit: number / missing value: NA)
  4. kmax: hydraulic conductivity of the same sample after flushing (unit: number / missing value: NA)
  5. plc: percent loss of conductivity, (1-Knat/Kmax)*100 (unit: dimensionless / missing value: NA)
  6. wp: water potential (unit: bar / missing value: NA)