Azimuthal variability of stomatal conductance and photosynthesis of solitarily grown European ash tree

Different illumination of the leaves facing various azimuth sides results in spatial differences in stomatal conductance (g_s) and photosynthesis (P_N) within the crowns of mature trees.
We measured diurnal courses of g_s and P_N of semi-solitary European Ash (Fraxinus excelsior L. ‘Atlas’) in four azimuth directions in spring, summer, and autumn.
The g_s and P_N were the largest in the south-facing leaves.
The P_N per the unit of area in the east was larger than in the west due to the increase of vapor pressure deficit in the afternoon and consecutive decline in g_s. The g_s calculated from sap flow well matched the values from the leaf level measurements.
Sap flow measured on the stem could not capture the variability within the crown but it integrated the g_s of the whole tree.
Our research emphasizes the importance of choosing representative leaves for gas exchange measurements.
Sap flow may aid in the upscaling leaf-level photosynthesis to the whole tree and a canopy level.

XII International Workshop on Sap Flow

J. Urban, R.S. Majewski, M. Šenfeldr, J. Hájek, J. Weger, M. Barták

European ash, net photosynthesis, transpiration, semi-solitary tree, up-scaling of photosynthesis, leaf area distribution

https://doi.org/10.17660/ActaHortic.2025.1419.7