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

Abstract

ABSTRACTMini-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.