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Plant Cell Environ. 2016 Feb;39(2):320-8. doi: 10.1111/pce.12612. Epub 2015 Nov 9.

Bark water uptake promotes localized hydraulic recovery in coastal redwood crown.

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Department of Plant Sciences, University of California Davis, One Shields Ave., Davis, CA, 95616, USA.
Graduate Group in Ecology, University of California Davis, One Shields Ave., Davis, CA, 95616, USA.
Department of Land, Air and Water Resources, One Shields Ave., Davis, CA, 95616, USA.
USDA-Agricultural Research Service, Davis, CA, 95616, USA.
Deparment of Viticulture and Enology, University of California, Davis, CA, 95616, USA.
School of Forestry & Environmental Studies, Yale University, 195 Prospect Street, New Haven, CT, 06511, USA.
USDA Forest Service, PSW Research Station, 1731 Research Park Dr., Davis, CA, 95618, USA.


Coastal redwood (Sequoia sempervirens), the world's tallest tree species, rehydrates leaves via foliar water uptake during fog/rain events. Here we examine if bark also permits water uptake in redwood branches, exploring potential flow mechanisms and biological significance. Using isotopic labelling and microCT imaging, we observed that water entered the xylem via bark and reduced tracheid embolization. Moreover, prolonged bark wetting (16 h) partially restored xylem hydraulic conductivity in isolated branch segments and whole branches. Partial hydraulic recovery coincided with an increase in branch water potential from about -5.5 ± 0.4 to -4.2 ± 0.3 MPa, suggesting localized recovery and possibly hydraulic isolation. As bark water uptake rate correlated with xylem osmotic potential (R(2)  = 0.88), we suspect a symplastic role in transferring water from bark to xylem. Using historical weather data from typical redwood habitat, we estimated that bark and leaves are wet more than 1000 h per year on average, with over 30 events being sufficiently long (>24 h) to allow for bark-assisted hydraulic recovery. The capacity to uptake biologically meaningful volumes of water via bark and leaves for localized hydraulic recovery throughout the crown during rain/fog events might be physiologically advantageous, allowing for relatively constant transpiration.


embolism; fog; foliar uptake; phellem; sequoia sempervirens

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