Frost hardiness, carbohydrates and bud morphology ofPicea abiesseedlings after different lengths of freezer storage

Abstract

In Nordic conditions, conifer seedlings are frozen stored up to eight months. However, there is only little information on the extended freezer storage (more than six months) on frost hardiness (FH) and carbohydrate concentrations in the shoots of Norway spruce seedlings. FH of two-year-old Norway spruce [Picea abies (L.) Karst.] container seedlings were placed in storage on 23 October and kept in storage for 172, 193, 228 or 256 days. Bud structure and carbohydrate concentrations of the needles were analysed. DT₅₀ (temperature causing 50% increase in proportion of needles, stem and buds after freezing exposure) of the measured parts of the seedlings decreased, and changes in DT₅₀ of buds and stems were small between the 172nd and the 193rd day of freezer storage. The concentration of starch increased and the concentration of soluble sugars decreased during the first 172 days of freezer storage. Longer duration of freezer storage, however, did not cause any further changes. The first phase of bud development (pointed lower needle primordial) was already seen in the autumn. The bud development did not change during freezer storage but both the length of the primordial shoot and that of the whole bud increased from October through mid-July. This study suggests that Norway spruce seedlings can be frozen-stored safely for longer periods (eight to nine months) than they are generally stored for currently (six to seven months).