Bark water uptake promotes localized hydraulic recovery in coastal redwood crown

Authors: EARLES, J.MASON - University Of California; SPERLING, OR - University Of California; SILVA, LUCAS - University Of California; McElrone, Andrew; BRODERSEN, CRAIG - Yale University; NORTH, MALCOM - University Of California; ZWIENIECKI, MACIEJ - University Of California

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2015
Publication Date: 11/9/2015
Citation: Earles, J., Sperling, O., Silva, L., Mcelrone, A.J., Brodersen, C.R., North, M., Zwieniecki, M. 2015. Bark water uptake promotes localized hydraulic recovery in coastal redwood crown. Plant Cell and Environment. 39(2):320–328. doi: 10.1111/pce.12612.

Interpretive Summary: Significant water uptake through the bark of redwood stems was documented using a variety of hydraulic measurement and microCT (a type of CAT scan). The capacity to uptake a biologically-meaningful source of water via bark and leaves throughout the crown during rain/fog events would prepare redwood to use more soil water when transpiration resumes and better recover from water deficit once water becomes available.

Technical Abstract: 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, along with potential flow mechanisms and biological significance. Using isotopic labeling and microCT imaging, we found evidence that water entered the xylem via bark and reduced the number of embolized tracheids. Moreover, bark wetting restored hydraulic conductivity in isolated branch segments and, when neither bark nor leaves were kept dry, whole branches. We expected that water potential should be at or near 0 before hydraulic recovery could occur in whole branches. Instead, branch water potential only increased from about -5.5 ± 0.4 MPa to -4.2 ± 0.3 MPa concurrent to hydraulic recovery in whole branches, suggesting localized recovery and possibly hydraulic isolation. As xylem osmotic potential corresponded with long-term bark water uptake rate, 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 hours per year on average. Thus, the capacity to uptake a biologically-meaningful source of water via bark and leaves suggests localized hydraulic recovery throughout the crown during rain/fog events that would prepare redwood to use more soil water when transpiration resumes.