DROUGHT SUSCEPTIBILITY AND XYLEM DYSFUNCTION IN SEEDLINGS OF 4 EUROPEAN OAK SPECIES

Seedlings of oak (Quercus robur, Q petraea, Q cerris and Q pubescens) were subjected to drought in pots to compare drought susceptibility in these contrasting species. Hydraulic dysfunction of the xylem vessels in petioles of seedlings was determined as the amount of air embolism that occurred under varying water potential (Psi). Curves relating vu lnerability to xylem embolism with Psi revealed that Q robur was more vulnerable than the other species examined. A loss of about 40% in pet iole conductivity occurred at a xylem water potential of about -3.0 MP a in Q robur, -3.9 MPa in Q petraea, -3.7 MPa in Q pubescens and less than -4 MPa in Q cerris. Detection of cavitation events by acoustic em ission (AE) failed to distinguish between species and AE did not incre ase until Psi was less than -3 MPa.