Determination of safe times at which to transfer seedlings to freezer storage is problematic in forest tree nurseries. The present study aimed to determine the relationship between pre-storage frost hardiness (FH) of different plant parts, dry matter content (DMC), chilling hours (the sum of hours when temperature was between −5 °C and +5 °C), and post-storage vitality, and the impact of short-day (SD) treatment on these relationships. One and a half year old control seedlings and SD-treated seedlings of Norway spruce were transferred to freezer storage (−3 °C) on five occasions during autumn. On each occasion, the FH of buds, needles, stem, and roots, as well as DMC, were determined, and chilling hours were calculated. The vitality of the freezer-stored seedlings was determined through their root growth capacity in the subsequent spring, and through the field performance of the seedlings (shoot growth and seedling damage) at the end of the following two growing seasons. Seedlings were considered to be storable when the FH of the needles was at least −25 °C, and the FH of the roots was about −10 °C in both treatments. Early storage reduced the vitality of the seedlings. SD treatment did not advance the storability of the seedlings, although it alleviated some of the negative effects of early storage by improving the FH of needles and stem, but not that of the roots. The DMC value, indicating storability, was higher for SD-treated seedlings than for control seedlings. When data from five experiments conducted in Suonenjoki were combined, it was found that the relationship between accumulation of chilling hours and needle FH was dependent on nursery treatment and assessment year, which reduces the reliability of using chilling hours in predicting the storability of Norway spruce seedlings. The predicted climate change may complicate the fall acclimation of seedlings. New, user-friendly methods for determining storability of seedlings are urgently needed.

中文翻译：

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短期处理对挪威云杉容器苗在冰柜中的可保存性的评估

在林木苗圃中，确定将幼苗转移到冷冻库的安全时间是有问题的。本研究旨在确定不同植物部位的储藏前霜冻硬度（FH），干物质含量（DMC），冷藏时间（温度在−5°C和+5°C之间的小时总和）之间的关系。 ，存储后的生命力以及短期（SD）处理对这些关系的影响。挪威云杉的一年半的对照幼苗和经SD处理的幼苗在秋季分五次转移至冷冻室（−3°C）。在每种情况下，都要确定芽，针，茎和根以及DMC的FH，并计算冷藏时间。冷藏的幼苗的活力取决于随后春季的根系生长能力，在接下来的两个生长季结束时，通过幼苗的田间表现（生长和幼苗受损）。在两种处理中，当针的FH至少为-25°C，而根的FH约为-10°C时，则认为幼苗可以储存。早期储存降低了幼苗的活力。SD处理虽然提高了针叶和茎的FH而不是根部的FH，减轻了早期贮藏的一些负面影响，但并未提高幼苗的耐贮性。SD处理的幼苗的DMC值表明了可存储性，高于对照幼苗。结合在Suonenjoki进行的5个实验的数据，发现冷藏时间的累积与针叶FH的关系取决于苗圃的处理和评估年份，这降低了使用冷藏时间预测挪威云杉幼苗的耐贮性的可靠性。预计的气候变化可能会使幼苗的秋天适应变得复杂。迫切需要一种新的，用户友好的方法来确定幼苗的耐贮性。