CHLOROPHYLL A FLUORESCENCE AND PRESEASON SEEDLING DIMENSIONS AS INDICATORS OF WOOD FORMATION RATES IN WHITE SPRUCE (PICEA-GLAUCA)

Variable chlorophyll a fluorescence and dimensions of white spruce (Picea glauca (Moench) Voss) seedlings were measured, and their effectiveness as noninvasive indicators of current-season wood formation rates (cambial activity) in white spruce were compared. Average fluorescence was over 300 s and was correlated with cambial activity (r2 = 0.773). Fluorescence amplitudes at M2 (maximum level) and T (terminal steady level) of the induction curve were also correlated with cambial activity (r2 = 0.542 and 0.684, respectively). Relationships between these fluorescence parameters and cambial activities were reduced in wounded seedlings and absent in geotropically stressed seedlings. Neither preseason cross-sectional stem areas nor preseason seedling heights were strongly correlated with cambial activities of untreated seedlings; however, a weak relationship between current-season leader lengths and cambial activities (r2 = 0.420) was indicated.