Dehardening and second-year growth of white spruce provenances in response to duration of long-night treatments

Abstract

Long-night treatments (16 h) of 0 (control), 4, 8, 12, and 16 days duration were applied, in August 1994, to four provenances of 10-week-old white spruce (Picea glauca (Moench) Voss) seedlings. This was to determine the shortest duration that would produce seedlings having acceptable morphological and physiological characteristics for reforestation. The effects of these treatments and of the latitude of origin of seedlings on the course of dehardening and second-year growth were studied. Terminal bud burst, shoot and root dry mass accumulation, and frost tolerance were followed during the spring, and terminal shoot growth was measured until August. Seedlings exposed to 0 (control) or 4 long nights exhibited significant amounts of damage in the spring. This damage had occurred the previous fall or winter. Seedlings receiving 4 to 16 days of long-night treatments did not differ in timing of bud burst the following spring, while the most northern provenance flushed first (May 18) and the most southern flushed last, 4 days later. Seedlings subjected to 8, 12, and 16 long nights exhibited similar amounts of terminal shoot growth, dry matter accumulation, and frost tolerance. Frost tolerance of the 8-, 12-, and 16-d treatments during dehardening was unaffected by the latitude of origin of seedlings. Our results suggest that under the experimental conditions used, an 8-d long-night treatment applied in the fall would produce seedlings with the same morphological and physiological characteristics in the spring as a 12- or 16-d treatment. Resume : Des semis de quatre provenances diOpinette blanche (Picea glauca (Moench) Voss) ont OtO soumis, durant le mois diaost 1994, ‡ des traitements de nuits longues (16 h) pour des durOes de 0 (tOmoin), 4, 8, 12 et 16 jours afin de dOterminer la plus courte durOe produisant des semis pour le reboisement ayant des caractOristiques morphologiques et physiologiques acceptables. Les effets des traitements et de la latitude diorigine sur le dOsendurcissement et la croissance de deuxime annOe ont OtO OtudiOs. Le dObourrement des bourgeons terminaux, liaccumulation de matire sche des parties aOriennes et racinaires et la tolOrance au gel des semis ont OtO suivis au printemps et la croissance de la pousse de deuxime annOe a OtO mesurOe jusquiau mois diaost. Les semis tOmoins et ceux exposOs au traitement de 4 nuits longues ont dOmontrO des niveaux importants de dommages au printemps, ceux-ci ayant eu lieu liautomne ou lihiver prOcOdent. Le dObourrement des semis ayant reAu 4 ‡ 16 nuits longues siest effectuO de faAon synchrone et la provenance la plus au nord a dObourrO en premier (le 18 mai) et celle la plus au sud en dernier, 4 jours plus tard. Les semis exposOs ‡ 8, 12 et 16 nuits longues ont montrO une croissance terminale, une accumulation de matire sche et des niveaux de tolOrance au gel similaires. Pendant le dOsendurcissement, la latitude diorigine nia pas affectO la tolOrance au gel des semis ayant subi des traitements de 8, 12 et 16 jours. Nos rOsultats suggrent que, sous les conditions expOrimentales utilisOes, un traitement de 8 nuits longues appliquO ‡ liautomne produirait des semis ayant les mŒmes caractOristiques morphologiques et physiologiques au printemps quiun traitement de 12 ou 16 nuits longues.