Autumn Colouration of First Year Pinus sylvestris Seedlings during Frost Hardening

Autumn colouration, dry matter content and frost hardiness of Pinus sylvestris seedlings were monitored during their first autumn. Seedlings of southern (62 degrees N, 24 degrees E) and northern (67 degrees N, 26 degrees E) Finland origin were grown under two fertilization regimes in Suonenjoki (63 degrees N, 27 degrees E). Northern seedlings turned purple earlier than southern ones, and low fertilized earlier than normal fertilized. Northern seedlings also hardened earlier than southern ones, while fertilization had no effect on hardening. Neither purple autumn colour nor dry matter content was clearly related to frost hardiness of seedlings when treatment means were compared. Comparison of seedlings within treatments suggested, however, that purple seedlings had higher dry matter content than green seedlings at the beginning of hardening period but the relationship between colouring and frost hardiness was not clear.