Hardening and dehardening of shoots and roots of containerized black spruce and white spruce seedlings under short and long days

Abstract

Containerized black spruce (Piceamariana (Mill.) B.S.P.) and white spruce (Piceaglauca (Moench) Voss) seedlings that were 120 days old were acclimated under short-day (8-h photoperiod) and long-day (16-h photoperiod) conditions at 10 °C for 12 h and 5 °C for 12 h for 28 days. Afterwards, they were exposed to 3 °C (8-h photoperiod) for 21 days and to 0 °C (without light) for 28 days. Finally, seedlings were dehardened at 10 °C (14-h photoperiod) for 21 days. Hardening of needles, excised stem parts, and whole seedlings was increased by short-day treatment, whereas roots hardened only in response to lowering of temperature. Whole seedlings and needles exposed to the short-day treatment dehardened earlier, whereas roots dehardened only in response to temperature changes. Bud formation was not influenced by photoperiod treatment, but seedlings exposed to the short-day treatment had an earlier bud break. No significant difference was observed between photoperiod treatments for water, sugar, and mineral content of shoots and roots prior to or during dehardening.