Use of short-day treatment in the production of Norway spruce mini-plug seedlings under plant factory conditions

ABSTRACT

Mini-plug transplant seedlings of Norway spruce have been cultivated in closed growth systems, so-called plant factories, for few years. The aim of the experiment was to define a short-day treatment (SD) that harden seedlings to sustain 3 months of cold storage, but does not have adverse effects on growth, morphology, and vitality. The seedlings were subjected to one of the following treatments: (1) 12 h photoperiod + 3 weeks duration; (2) 8 h photoperiod + 3 wk duration; (3) 12 h photoperiod + 5 wk duration; and (4) 8 h photoperiod + 5 wk SD. All the SD treatments yielded healthy seedlings that grew well after the cold storage. The frost hardiness of the seedlings improved when the photoperiod was reduced from 12 to 8 h, and when the SD duration was increased from 3 weeks to 5 weeks, but reducing the photoperiod from 12 h to 8 h caused growth reductions. The root and shoot regrowth after cold storage was highest in seedlings that had received 12 h photoperiod and 5 wk duration. However, 12 h photoperiod and 3 wk duration may be an adequate practice for nurseries that treat multiple crops in their SD facilities.

KEYWORDS:

• Cold storage
• freezing tolerance
• mini-plug
• nursery production
• Picea abies
• long-night treatment
• transplanting

Acknowledgements

We would like to thank Dr. Risto Rikala for his valuable comments on the manuscript, and Mervi Ahonpää, Auli Lehtinen and Hanna Ruhanen for their skillful assistance with the laboratory analyses. We are also grateful to Dr. Juha Lappi for his valuable statistics advice.

Disclosure statement

No potential conflict of interest was reported by the author(s).