The effects of acclimation to sunlight on the xylem vulnerability to embolism in Fagus sylvatica L.

We assessed the effects of irradiance received during growth on the vulnera bility of Fagus sylvatica L. xylem vessels to water-stress-induced embolism . The measurements were conducted on (1) potted saplings acclimated for 2 y ears under 100% and 12% incident global radiation and (2) branches collecte d from sun-exposed and shaded sides of adult trees. Both experiments yielde d similar results. Light-acclimated shoots were less vulnerable to embolism . Xylem water potential levels producing 50% loss of hydraulic conductivity were lower in sun-exposed branches and seedlings than in shade-grown ones (- 3.0 versus -2.3 MPa on average). The differences in vulnerability were n ot correlated with differences in xylem hydraulic conductivity nor vessel d iameter. Resistance to cavitation was correlated with transpiration rates, midday xylem and leaf water potentials in adult trees. We concluded that vu lnerability to cavitation in Fagus sylvatica may acclimate to contrasting a mbient light conditions.