Assessment of root freezing damage of two-year-old white spruce, black spruce and jack pine seedlings

Whole root systems of 2-yr-old containerized white spruce [Picea glauca (Mo ench) Voss], black spruce [Picea mariana (Mill.) B.S.P.] and jack pine (Pin us banksiana Lamb.) seedlings, with intact root plugs, were exposed to vari ous Frost temperatures, which a preliminary test indicated would induce app roximately 0 (control), 20, 40, 60, 80 and nearly 100% frost damage. Damage to root systems was evaluated using: (1) two measures of electrolyte leaka ge (relative conductivity and total tissue leakage after autoclaving); (2) water loss after pressurization; (3) chlorophyll fluorescence (F-v/F-m, max imal PSII photochemical efficiency) measured 4, 21 and 30 days after the be ginning of seedling regrowth and (4) live root dry mass measured 21 days af ter the artificial frost and 60 days after the beginning of regrowth. Seedl ing survival and growth after the artificial frost were evaluated using liv e root dry mass measured after 60 days of regrowth and new shoot length, st em diameter, and root and shoot dry mass. Live root dry mass, dead tissue l eakage, jack pine root water loss and fluorescence measurements were all si gnificantly correlated with one or more of the growth variables and the num ber of significant correlations varied with species. Dead tissue leakage me asurements appear to be the most promising method for evaluating root damag e to 2-yr-old well-developed root systems of these species.