THE INTENSITY OF NIGHT-TIME WATER USE DIFFERS WITHIN A CROWN OF A FOREST-GROWN TILIA CORDATA TREE

Night-time/daytime water relations were studied in crown of a small-leaf linden tree.
Branch sap flow (F_b) varied strongly with crown positions, whereas the upper branch showed about 2.5 times higher values of F_b compared to the lower-crown branch.
Differences in F_b between canopy positions were observed also at night.
The analyses of covariance revealed that the most relevant (p<0.001) environmental variable affecting F_b is the atmospheric vapour pressure deficit (VPD). The relationship between F_b and VPD suggested that nocturnal sap flow is much more sensitive to changes in VPD in the upper crown position (p<0.001), while this relationship in the lower crown turned out to be insignificant at night.
The predawn leaf water potential (_pd) depended strongly (p<0.001) on soil water potential (_S), whereas _S turned out to be more important factor than VPD or canopy position to account for the variability in _pd. The significantly higher nocturnal sap flow in the upper branch resulted in higher night-time water use compared to the lower branch (15.7 and 8.2%, respectively; p<0.001) calculated over the entire study period.
The higher night-time F_b and lower predawn leaf water potential suggest that the upper canopy experiences greater water use than the lower canopy at night.

VII International Workshop on Sap Flow

P. Kupper, A. Sellin

canopy position, predawn leaf water potential, night-time/daytime branch sap flow, soil water potential, vapour pressure deficit

https://doi.org/10.17660/ActaHortic.2009.846.24