Daily courses of water potential (Ψ) of pedunculate oak (Quercus robur) and
sessile oak (Q. petraea) saplings were investigated under different weather
conditions (with a focus on hot summer days) and the availability of soil water.
Water potential measurements were taken on two consecutive hot sunny days
(July 16 and 17), first after a dry period (dry soil) and the next day after rewatering (soil saturated with water the evening before). On both days species
did not differ in pre-dawn water potential (Ψpd). In dry soil Ψ decreased below
-2.5 MPa for Q. petraea, while daily minimum Ψ were between -2 and -2.5
MPa in Q. robur. We could not, however, prove the significant differences
between the daily minima of Ψ of two species. The opposite pattern was
observed in wet soil where Q. robur exhibited lower midday water potentials,
which was confirmed with additional measurements during a heat wave in midAugust (August 13). The results are discussed with respect to literature data on
wood anatomy, ecophysiology and ecology of both species.
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