ROOT FREEZING TOLERANCE AND VITALITY OF NORWAY SPRUCE AND SCOTS PINE-SEEDLINGS - INFLUENCE OF STORAGE DURATION, STORAGE-TEMPERATURE, AND PRESTORAGE ROOT FREEZING

This study investigated the effect of different cold storage condition s on (i) root freezing tolerance of Norway spruce (Picea abies (L.) Ka rst.) and Scots pine (Pinus sylvestris L.) and (ii) the vitality of se edlings that suffered freezing injury to roots prior to storage. Conta iner-grown seedlings, 1 year old, were stored from the end of October to April in three environments with different root temperatures: outdo or storage (-0.5 to 11.0 degrees C), cool storage (0.7 to 3.7 degrees C), or frozen storage (-5.0 to -3.8 degrees C). Root freezing toleranc e was determined prior to storage in October and during storage in Jan uary and March. Maximum root freezing tolerance for both species occur red in January, when over 50% of spruce and pine seedlings survived 2 h exposure to -25 and -20 degrees C, respectively. At this time, roots of frozen-stored spruce were significantly more freezing tolerant tha n outdoor-stored seedlings, whereas storage environment had no signifi cant effect on pine. Freezing tolerance in roots of both species decre ased from January to March in all test environments but to a lesser ex tent at the subzero temperatures in the frozen storage. Root freezing to -10, -15, or -20 degrees C in late October before storage resulted in reduced poststorage survival of seedlings in April. Pine was more a dversely affected (0-13% survival) than spruce (0-85% survival). Freez ing of roots prior to storage caused the lowest survival with frozen s torage.