Second and third growth period responses of Picea abies families to first growth period photoperiodic, light intensity and temperature treatments.

Abstract

Seedlings of Picea abies (L.) Karst. full-sib families of contrasting origin were cultivated in a phytotron under different photoperiodic, light-intensity and temperature treatments during their first growth period. The effects of the treatments on juvenile growth traits – whether enhanced or delayed maturation was induced – were observed during the two subsequent growth periods. The following hypotheses were tested: (A) Enhanced maturation can be induced after treatments in the first growth period from sowing with (i) a long period of continuous light during active growth (24 weeks vs. 8 weeks); (ii) a shorter night during bud maturation (12 h vs. 16 h); a high temperature (25 °C vs. 20 °C) during (iii) active growth, growth cessation and bud maturation; and during (iv) the latter part of growth cessation and bud maturation only. (B) Delayed maturation can be induced after (i) a low light intensity during growth cessation and bud maturation (114 µmol m–2 s–1 vs. 340 µmol m–2 s–1); a low temperature (15 °C vs. 20 °C) during (ii) active growth, growth cessation and bud maturation; and during (iii) the latter part of growth cessation and bud maturation only. The most dramatic treatment effect was 24 weeks of continuous light during active growth. All traits showed a significantly more mature performance in the second growth period compared with the control. The effect for all but one trait was carried over to the third growth period. This is in accordance with the hypothesis that the activity of the apical shoot meristems controls the maturation process. For the other treatments there was only weak or no support for the hypothesis of inducing enhanced or delayed maturation. Strong family effects were observed for all traits. Differential responses of the various latitudinal families were observed, suggesting that family effects must be considered to predict and interpret correctly how plants will respond to environmental effects.