Radially transmitted changes in hydraulic and osmotic pressures help
explain reversible and irreversible patterns of tree stem expansion
- Sebastian Pfautsch,
- John Drake,
- Mike Aspinwall,
- Victor Resco de Dios,
- Craig Barton,
- Patrick Meir,
- Mark Tjoelker,
- David Tissue,
- Maurizio Mencuccini
John Drake
SUNY College of Environmental Science and Forestry
Author ProfileVictor Resco de Dios
Southwest University of Science and Technology
Author ProfileAbstract
It is easy to measure annual growth of a tree stem. It is hard to
measure its daily growth. The reason for this difficulty is the
microscopic scale and the need to separate processes that simultaneously
result in reversible and irreversible stem expansion. Here we present a
model that separates reversible from irreversible cell expansion. Our
model is novel, because it explains reversible expansion as consequence
of longitudinally and, importantly, radially transmitted changes of
hydraulic and osmotic pressures in xylem and bark. To capture and
quantify these changes, we manipulated daily stem growth by applying a
phloem girdle to stems of 9-m tall trees. The model was informed by
measurements of radial movement in stem tissues and sap flow before and
after and positions below and above the girdle. Additional measurements
of whole-crown fluxes of H2O and CO2, leaf water potentials,
non-structural carbohydrates and respiration were used to document the
physiological impacts of girdling. This work sheds new light on the role
of radial transport processes underpinning daily growth of tree stems.
The model helps explain diel patterns of stem growth in trees.