HIGH-TEMPERATURE TOLERANCE OF HERITAGE RIVER BIRCH ROOTS DECREASED BYPOT-IN-POT PRODUCTION SYSTEMS

Membrane thermostability of Heritage river birch (Betula nigra L. Heri tage) was measured by electrolyte leakage from excised roots of plants grown in pot-in-pot (PIP) and conventional aboveground production sys tems (CPS), The predicted critical midpoint temperature (T-m) for a 30 -min exposure was 54.6 +/- 0.2 degrees C for PIP and 56.2 +/- 0.6 degr ees C for CPS plants. Plants grown PIP had a steeper slope through the predicted T-m, suggesting a decreased tolerance to high root-zone tem peratures in relation to plants grown aboveground. Since the root syst ems of Heritage river birch grown PIP are damaged at lower temperature s than plants grown aboveground, growers should prevent exposure of ro ot systems to high temperatures during postproduction handling of plan ts grown PIP.