Predicting spring frost sensitivity by bud development and temperature sum in Norway spruce seedlings

Abstract

Nurseries would benefit greatly if frost hardiness (FH) of seedlings could be predicted by some environmental variable or by bud development in spring. We investigated the FH of 1-year-old Norway spruce (Picea abies (L.) Karst.) seedlings of local origin. The seedlings were stored frozen until incubated in the growth chamber at six different temperature sums (TSs) (0, 55, 88, 142, 185 and 240 d.d., [5°C) from mid-February to mid-March. FH of the buds, stems and previous year needles was assessed on three occasions. When the TS was 88 d.d. or less, buds exhibited only microscopic signs of development, even when seedlings tolerated temperatures below -10°C. As TS increased, primordial needles and primordial stems of buds grew while FH weakened, especially in previous year needles. When the TS was at least 142 d.d., all plant parts were frost hardy to approximately -6°C. Monitoring TS and bud development can help predict FH of Norway spruce seedlings in spring. However, more studies with seedlings of different ages and from multiple locations are necessary to appreciate the generality of our results.

Reduced height of short day induced bud scale complex may partly explain early bud burst in Norway spruce seedlings

“…The scales in SD buds showed always cup-shape compared to conical shape in CTRL buds. Similar cup-shaped scales in the buds have been described earlier in Norway spruce (Templeton et al 1993 see Figure 3a; Luoranen et al 2010 see Figure 1a) and in coastal Douglas-fir exposed to SD treatments or moisture stress in long-day conditions (MacDonald and Owens 1993a,b). In our case, SD buds also had fewer scales, and they were shorter compared to scales in CTRL buds.…”

“…During bud development, the vascular tissue is differentiating and allows water to move to the elongating primordial shoots (the development phases from 1 to 3-4) (de Faÿ et al 2000;Luoranen et al 2010;Sutinen et al 2012). The development phases from 2 onwards are frost sensitive (Luoranen et al 2010). Thus, the SD seedlings with earlier bud burst are especially at risk to freezing.…”

“…The externally visible phenological stages of the buds were evaluated according to Luoranen et al (2010): Stage 0: no changes; Stage 1: slightly swollen; Stage 2: swollen, transparent bud scales; Stage 3: bud scales loosened; and Stage 4: bud burst and shoot elongated. The seedlings where all the buds had reached stage 4 were not sampled (microscopic analysis) further.…”

“…The seedlings where all the buds had reached stage 4 were not sampled (microscopic analysis) further. The phases of bud development towards bud burst inside the bud scales were determined from phase 0 to phase 4 as in Luoranen et al (2010): Phase 0: all needle primordia have rounded tips, and the apex is wholly visible; Phase 1: the tips of the needle primordia are pointed, beginning from the lowest part of the primordial shoot nearly up to the apex; Phase 2:, the needle primordia have elongated and are bending over the apex, and the elongation of the primordial shoot has started; Phase 3: the apex can no longer be seen due to the elongation of the primordial shoot and needles; Phase 4: needle primordia and shoot are elongating. , is 0 (no changes/all needle primordia have rounded tips and the apex is wholly visible) in both treatments.…”

“…SD treatment may also increase the number of buds that fail to burst (McClaren et al 1994;Luoranen et al 1994Luoranen et al , 2006Konttinen et al 2003;Luoranen and Rikala 2015). Reduced survival and growth of conifer seedlings caused by spring frost has been associated with a decreasing frost tolerance of the previous year's needles, together with visible bud development (Cannel and Smith 1984;Bigras et al 2004;Luoranen et al 2010) and recently also with the internal elongation of the primordial shoots in visible dormant buds (Luoranen et al 2010).…”