Cutting xylem under tension or supersaturated with gas can generate PLC and the appearance of rapid recovery from embolism

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 percent loss of conductivity (PLC) in the afternoon occurred when the meas...

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Bibliographic Details
Published in:Plant, cell and environment cell and environment, 2013-11, Vol.36 (11), p.1938-1949
Main Authors: WHEELER, JAMES K., HUGGETT, BRETT A., TOFTE, ALENA N., ROCKWELL, FULTON E., HOLBROOK, N. MICHELE
Format: Article
Language:English
Subjects:
Acer - physiology
Air
air injection
bench drying
Betula - physiology
Biological and medical sciences
Circadian Rhythm - physiology
diurnal recovery
Fundamental and applied biological sciences. Psychology
Gases - metabolism
Pressure
refilling
Trees - physiology
Water
Xylem - physiology
xylem cavitation
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Summary: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 percent loss of conductivity (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. We also found that air injection of cut branches (red and sugar maple) at pressures of 0.1 and 1.0 MPa resulted in PLC greater than predicted from vulnerability curves for samples cut 2 min after depressurization, with PLC returning to expected levels for samples cut after 75 min. 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 or supersaturation of dissolved gases (air injection) at the moment of sample excision. Implications for assessing vulnerability to cavitation and levels of embolism under field conditions are discussed. The assumption that cutting samples under water preserves the state of embolism in the xylem is shown to be incorrect. Cutting stems under water while tension exists in the xylem can induce embolism, and the degree of induced embolism increases with xylem tension. Excising samples when the xylem fluid is supersaturated with gas, as for in‐situ air‐injection, can also result in embolism formed at the moment of excision. Both of these artifacts can generate the appearance of rapid recovery from embolism, driving diurnal patterns in PLC or apparent repair after air injection as the saturation state relaxes with time. This work calls into question the view that cavitation under typical transpiration‐induced levels of xylem tension, and subsequent diurnal repair, is an adaptive hydraulic strategy common to many plants. Commentary: Cutting‐edge research or cutting‐edge artifact? An overdue control experiment complicates the xylem refilling story
ISSN:0140-7791
1365-3040
DOI:10.1111/pce.12139