Second-year shoot development in black spruce Piceamariana (Mill.) B.S.P. container seedlings

Abstract

The relative contributions to 2nd-year shoot elongation by predetermined versus free growth were analyzed for black spruce (Piceamariana (Mill.) B.S.P.) seedlings. Seedlings from three hardening regimes, production run, short day, and extended greenhouse, were given various shoot-pruning treatments, from the terminal bud removed to the entire shoot removed except for a lateral shoot at the base. Pruned seedlings were compared with winter-damaged seedlings. Bud flushing was most rapid in short-day seedlings and in pruned seedlings regardless of hardening regime. The capacity for free growth in nonpruned seedlings varied little among seedlings of different hardening regimes, despite large initial differences in bud development between production-run, short-day, and extended greenhouse seedlings. Stem unit length and number of lateral buds per unit of stem length was greater in free growth compared with predetermined growth. Shoot pruning and winter damage had similar effects on shoot growth; the greater the degree of shoot removal, the greater the amount of free growth.