Pre-cultivation of Scots pine and Norway spruce transplant seedlings under four different light spectra did not affect their field performance

Forest nurseries use different greenhouse light sources including new light technologies to produce conifer seedlings without knowing their real impact on subsequent field performance. The aim of the experiment was to investigate whether different growth light spectra during pre-cultivation of Scots pine and Norway spruce seedlings under controlled conditions affect growth and morphology of seedlings, and whether the possible differences between the treatments will be maintained after outplanting to a field site. The seedlings were pre-cultivated for 5.5-6.5 weeks in a darkened greenhouse under four light spectra consisting of different proportions of blue (B, 400-500 nm), red (R, 600-700 nm), and far-red (FR, 700-800 nm), with high-pressure sodium lamps (HPS) serving as controls. The light treatments (250 lmol m(-2) s(-1) photosynthetically active radiation) were provided using light-emitting diodes, and the treatments included the following: (1) 25 % B + 70 % R + 5 % FR; (2) 25 % B + 75 % R; (3) 55 % B + 45 % R; and (4) HPS: 6 % B + 44 % green (500-600 nm) + 41 % R + 9 % FR (control). Growth and morphology were studied at the time of transplanting in spring, and again, at the time of outplanting the seedlings in the field site in autumn. Growth, survival and phenology of the seedlings were followed in the field for 1 year. Growth and morphology of the seedlings were modified by the different growth light spectra during pre-cultivation, but by the time of outplanting, these differences between the treatments had disappeared. In conclusion: Growth and morphology of seedlings can be modified by adjusting the spectral composition of growth light during pre-cultivation, but the modifications may not be long-lasting.