VIABILITY TESTS FOR ESTIMATING ROOT COLD TOLERANCE OF BLACK SPRUCE SEEDLINGS

After freezing tests, various methods for evaluating root damage were compared and correlated to the regrowth of 16-week-old containerized black spruce seedlings (Picea mariana (Mill.) B.S.P.) hardened in growth chambers. During the hardening regime, three experiments were performed. The first experiment evaluated the influence on the test results of washing the roots before or after a freezing test and compared the frost sensitivity of fine roots (<0.3 mm), larger roots (>0.3 mm), and whole root systems. The second experiment tested the effect of pressures of 0.05, 0.10, and 0.15 MPa on water loss. Experiment 3 compared four viability tests: electrolyte leakage, ninhydrin reactive compounds leakage, phenolic leakage, and water loss. Results were as follows: (i) washing the roots before or after the freezing test did not affect the results of the ninhydrin reactive compounds test; (ii) fine roots (<0.3 mm) were more sensitive to freezing damage than larger roots (>0.3 mm); (iii) sampling of fine roots (<0.3 mm), larger roots (>0.3 mm), or whole root systems gave different results for the ninhydrin reactive compounds test; (iv) tests of electrolyte leakage, phenolic leakage, and ninhydrin reactive compounds leakage had the ability to indicate tissue damage; (v) high values of these variables were associated with poor seedling regrowth; (vi) root water potential also indicates tissue damage but is less correlated to regrowth than electrolyte leakage, phenolic leakage, and ninhydrin reactive compound leakage; and (vii) the water-loss test seems less reliable than the others.