The Norway spruce (Picea abies Karst.) is Europe’s most important conifer, both economically and ecologically. In Norway, it dominates regions such as Trøndelag, Eastern Norway, and Helgeland. With climate change leading to warmer and more variable autumn temperatures, understanding how these fluctuations affect the development of frost hardiness in seedlings is critical for successful forestry. This study investigated the autumn frost hardiness of first-year Norway spruce seedlings from four provenances: Undesløs seed orchard (latitude: 60.7° N, elevation: 140 m a.s.l.), L1 (63.3°- 65°N, 0-149 m), M4 (64°- 65°N, 350-449 m), and the long-distance transferred provenance Cv1 (59.1°-60.2°N, 0-149 m). Seedlings were grown under two controlled conditions: (i) a “typical autumn” with decreasing temperatures and (ii) an “atypical autumn” with fluctuating temperatures. In the “typical autumn” setting, day and night temperatures were programmed to decrease gradually over four weeks. In the “atypical autumn” setting, temperatures varied throughout the same period. Frost hardiness was assessed using a -25°C freeze test and quantified via shoot electrolyte leakage (SEL). An index of injury (SELdiff-25) value ≤ 4% indicated sufficient frost tolerance. Results showed that all seedlings from provenances Cv1, M4, and Undesløs developed sufficient frost tolerance. For provenance L1, 19 seedlings per treatment had SELdiff-25 values below 4, while one seedling in each treatment showed higher values (5.5 and 5.1, respectively). Negative SELdiff-25 values were observed in some seedlings across all provenances, particularly from Undesløs. The results demonstrate that first-year Norway spruce seedlings can successfully develop frost hardiness under both decreasing and fluctuating autumn temperature regimes. These findings highlight the potential for nursery practices to replicate natural climatic patterns, thereby enhancing seedling frost resilience. However, differences between controlled growth chamber conditions and natural nursery environments must be considered when applying these results to practical forestry. Overall, this study provides valuable insights into the variability in frost hardiness often observed in field trials involving young Norway spruce.
Ahuja et al. (Sun,) studied this question.