Effects of temperature on the light quality effects on bud set

Fig. 21 Picture illustrating the variation in growth in seedlings of Subalpine fir exposed to FR (7 W

m-2) as day extension from light emitting diodes, all at a temperature of 18°C after 6 weeks in treatment in the third experiment.

3.4.1 Effects of temperature on the light quality effects on bud set

In experiment 2, 19% of the FR-22°C-treated seedlings had already developed buds at experiment start. After 3 days of treatment all of these buds had flushed again.

However, after 27 days a total of 94% of the FR-exposed plants had terminal buds, but several of these thereafter showed bud burst and after 51 days 63% of the plants had buds (fig. 22). The same tendency is shown at 18°C, which after 27 days 94% of the seedlings had developed buds. Many of these flushed again, and after 51 days 31% of the FR-18°C-treated seedlings had developed terminal buds (fig. 22).

6% of the B-18°C-treated seedlings had developed buds at experiment start.

They did not burst under the B treatment, and after 51 days a total of 81% had developed terminal buds. There was a trend of higher percent bud appearance in B-22°C-treated seedlings, which after 51 days had 94% of the seedlings with buds (fig.

22).

After 51 days in treatment, 100% of the 18°C-treated and 94% of the R-22°C-treated had developed buds. 94% SD-treated seedlings had developed buds after 51 days (fig.22).

Fig. 22 Percentage buds in seedlings of Subalpine exposed to day extension with different light quality treatments from light emitting diodes, i.e. blue (B), far-red (FR) and red (R) (7 W m-²) as compared to short days (SD) without day-extension, all at a temperature of 18 or 22°C in the second growth experiment. Results are mean of 16 plants in each treatment.

In the second experiment almost all SD, B and R-treated seedlings seem to have fully developed, brown buds after 51 days in both 18 and 22°C-treatments, whereas many FR-treated seedlings seem to grow (average stage of 0.75) (fig. 23). An average higher then 0 indicates that not all seedlings had fully developed buds after 51 days.

Further analysis showed a temperature effect on bud development in seedlings exposed to R light (p≤0.05), i.e. R light with elevated temperature delayed bud

0  

Fig. 23 Stages of bud set in seedlings of Subalpine fir exposed to day extension with a light quality from light emitting diodes, i.e. blue (B), far-red (FR) and red (R) (7 W m-²) as compared to short days (SD) without day extension, at a temperature of 18 or 22°C in the second growth experiment. 1 = growth, 0.5 = green bud, 0 = brown bud. Results are mean ± SE of 14-16 plants in each treatment.  

0   0,5   1  

0   3   6   9   12   15   18   21   24   27   30   33   36   39   42   45   48   51  

Stages  

Time  (days)   SD  (18°C)  

B  (18°C)   FR  (18°C)   R  (18°C)  

0   0,5   1  

0   3   6   9   12   15   18   21   24   27   30   33   36   39   42   45   48   51  

Stages  

Time  (days)   SD  (22°C)  

B  (22°C)   FR  (22°C)   R  (22°C)  

Tab. 10 Results from cumulative link model in R run to investigate the effects of temperature (T; 18 and 22°C) on the light qualities, i.e. blue (b), far-red (FR) and red (R) (7 W m-²) as day extension on bud set in seedlings of Subalpine fir compared to short days (SD) as the dummy variable in the second experiment. Positive estimated coefficient indicates an increase probability for bud set, while negative estimated coefficient indicates a delay in bud set  

Treatment Coefficient SE Z

Significance levels: * P<0.05, ** P<0.01, *** P<0,001

In experiment 3, many seedlings had already developed buds at experiment start, which explains the disorderly pattern in the beginning (fig. 24). After 39 days 100%

of the seedlings exposed to B and SD-treatment at 18°C had developed buds and this was unchanged after 57 days in treatment. 100% of the R-18°C treated seedlings had developed buds after 57 days, with a tendency of less bud development at 24°C in both SD, R and B treatment. At the end of the experiment, after 57 days, the FR-treatment seemed to have a higher degree of bud development in 24°C compared to 18°C, with 68% of the seedlings with buds at 18°C and 74% of seedlings with buds at 24°C (fig. 24).

Fig. 24 Percentage buds in seedlings of Subalpine exposed to day extension with different light quality treatments from light emitting diodes, i.e. blue (B), far-red (FR) and red (R) (7 W m-²) as compared to short days (SD) without day-extension, all at a temperature of 18 or 24°C in the third growth

experiment. Results are mean of 19 plants in each treatment.

Almost all SD, B and R-treated seedlings seem to have fully developed, brown buds after 57 days in both the 18 and 24°C-treatments, whereas many FR-treated seedlings still showed growth or delayed bud set (fig. 25). Further analysis showed a significant effect of temperature on bud development in seedlings exposed to B light as day extension, i.e. B light with elevated temperature delayed bud development (p≤0.001) (tab 11). On the other hand, B light alone accelerated bud development in these seedlings (p≤0.001) (tab.11). The analyses also show that FR and R light alone delay bud development (p≤0.05).

0   10   20   30   40   50   60   70   80   90   100  

0   3   6   9   12   15   18   21   24   27   30   33   36   39   42   45   48   51   54   57  

Percent  bud  set  (%)  

Time  (days)   SD  (24°C)  

B  (24°C)   FR  (24°C)   R  (24°C)  

Fig. 25 Stages of bud set in seedlings of Subalpine fir exposed to day extension with a light quality from light emitting diodes, i.e. blue (B), far-red (FR) and red (R) (7 W m-²) as compared to short days (SD) without day extension, at a temperature of 18 or 24°C in the third growth experiment. 1 = growth, 0.5 = green bud, 0 = brown bud. Results are mean ± SE of 19 plants in each treatment.  

0   0,5   1  

0   3   6   9   12   15   18   21   24   27   30   33   36   39   42   45   48   51   54   57  

Stages  

Time  (days)   SD  (18°C)  

B  (18°C)   FR  (18°C)   R  (18°C)  

0   0,5   1  

0   3   6   9   12   15   18   21   24   27   30   33   36   39   42   45   48   51   54   57  

Stages  

Time  (days)   SD  (24°C)  

B  (24°C)   FR  (24°C)   R  (24°C)  

Tab.  11  Results from cumulative link model in R run to investigate the effects of temperature (T; 18 and 24°C) on the light qualities, i.e. blue (b), far-red (FR) and red (R) (7 W m-²) as day extension on bud set in seedlings of Subalpine fir compared to short days (SD) as the dummy variable in the third experiment. Positive estimated coefficient indicates an increase probability for bud set, while negative estimated coefficient indicates a delay in bud set  

Treatment Coefficient SE Z

Significance levels: * P<0.05, ** P<0.01, *** P<0,001