TIMING OF COLD TEMPERATURE EXPOSURE AFFECTS ROOT AND SHOOT FROST HARDINESS OF PICEA-MARIANA CONTAINER SEEDLINGS

Seventeen-week-old black spruce seedlings were hardened under short da ylengths and one of three short day length environments, which were ei ther warm (24/16-degrees-C, day/night) throughout a 10 week hardening period (WW), cool (10/5-degrees-C) throughout hardening (CC), or warm for three weeks followed by seven weeks of cool temperatures (WC). Gre atest root and shoot frost hardiness resulted from the exposure of see dlings to three weeks of warm followed by seven weeks of cool temperat ures. Seedlings receiving warm temperatures throughout hardening incre ased in root and shoot frost hardiness, but to a lesser extent than se edlings exposed to cool temperatures. The frost hardiness of woody roo ts was generally greater than that of fine roots, but the extent of th e difference in frost hardiness depended on the time since bud initiat ion and on the hardening treatment.