Effect of thawing duration and temperature on field performance of frozen-stored Norway spruce container seedlings

Abstract

Increasing use of frozen storage in nurseries at northern latitudes calls for thawing methods that are safe, economical and easy to apply on a large scale. The easiest and most economical method would be to thaw seedlings in the same boxes they were stored in. However, doing this safely requires more knowledge about how long and at what temperatures seedlings should or can be kept in the boxes without reducing field performance. In this study, 1-yr-old frozen-stored Norway spruce (Picea abies (L.) Karst.) container seedlings were thawed for 4, 8 or 16 days at 4 or 12 °C in cardboard boxes before planting on a reforestation site and on experimental field in mid-June. Some seedlings were also planted on these locations after thawing for only 7 hours at 12 °C in order to separate frozen root plugs. We found some evidence that planting seedlings after short thawing periods (7 hours at 12 °C and 4 days at 4 °C), under which conditions the root plugs remain completely or partly frozen, has a negative effect on field performance of Norway spruce seedlings. Thawing over a 4−8 day period in cardboard boxes at ca. 12 °C appears to ensure complete thawing of the root plugs and unaffected field performance, but is short enough to prevent the growth of mould.

Duration Limits on Field Storage in Closed Cardboard Boxes before Planting of Norway Spruce and Scots Pine Container Seedlings in Different Planting Seasons

“…Overall, the safe storage periods for the non-dormant seedlings are shorter than those for freezer-stored seedlings, with the latter being storable for up to two weeks after the root plugs have thawed under cool conditions [10]. However, the storage period for non-dormant seedlings in closed boxes is about the same (about a week) as that for freezer-stored and properly thawed seedlings under warm conditions [10].…”

“…The cardboard storage method was originally invented for dormant seedlings that can be stored in closed boxes in the freezer for several months without suffering a significant decrease in vigor [9]. Seedlings can be safely stored in closed boxes for up to two weeks after freezer storage in cool weather in spring, based on previous studies [10]. However, in practical forestry in Finland, freezer-stored seedlings are commonly kept in closed cardboard boxes for longer period than that [11].…”

An improved PVS2 cryopreservation technique for Ascocenda Wangsa Gold orchid using protocorm-like bodies

“…Thawing duration is thought to be one factor that could help avoid recrystallization and ensure the satisfactory recovery of vitrified material. Helenius et al (2004) reported that high thawing temperatures (>15 °C) would thaw frozen root plugs rapidly and could result in the depletion of carbohydrates. In our study, regrowth was obtained at 47% when the PLBs were thawed at 45 °C for 85 s after 4 weeks of recovery.…”

Damage caused by an exceptionally warm and dry early summer on newly planted Norway spruce container seedlings in Nordic boreal forests

“…In addition, during the summer months, the storage duration of seedlings in closed packaging cannot exceed 1-2 days (Luoranen et al 2019). This is the case even with freezer-stored seedlings if they are thawed, and air temperatures are high (Helenius et al 2004). Previously, Nilsson and Örlander (1995) and Luoranen et al (2005;2022a) also observed increased mortality in seedling material intended for spring plantings and planted late (July).…”