ROOT COLD TOLERANCE OF BLACK SPRUCE SEEDLINGS - VIABILITY TESTS IN RELATION TO SURVIVAL AND REGROWTH

Root systems of 6-month-old, cold-hardened, container-grown black spru ce seedlings (Picea mariana (Mill.) B.S.P.) were exposed to 0, -5, -10 , -15, -20, or -22.5 degrees C. Freezing-induced damage to fine roots, coarse roots and the whole root system was assessed by various viabil ity tests including leakage of electrolytes, leakage of phenolic compo unds, water loss, root and shoot water potentials, and live root dry m ass. To assess the long-term effects of freezing-induced root damage, seedling survival and regrowth were measured. Leakage of both electrol ytes and phenolic compounds differed among fine roots, coarse roots, a nd whole root systems. In coarse roots and the whole root system, but not in fine roots, leakage of electrolytes, leakage of phenolic compou nds, water loss, and root and shoot water potentials were correlated w ith percentage of live root dry mass which, in rum, was highly correla ted with seedling survival and regrowth. Compared with live root dry m ass, electrolyte and phenolic leakage, water loss, and root and shoot water potentials were less well correlated with seedling survival and regrowth. Among the viability tests, electrolyte leakage of the whole root system correlated most closely with seedling survival and regrowt h. Under freezing conditions that destroyed less than 50% of each seed ling's root system, about 70% of the seedlings survived and subsequent growth was little affected, whereas under freezing conditions that de stroyed 70% of each seedling's root system, only about 30% of the seed lings survived and subsequent growth was reduced compared with that of undamaged plants.