3.2. Long-term greenhouse experiment

Two provenances of 2- to 4-year-old nursery-grown Scots pine and Norway spruce seedlings and a grafted clone of Scots pine were used. All the seedlings were from northern latitudes (65ºN–69ºN) (Fig. 1). The seedlings were planted in pots containing forest soil and sand (7:1). The plants were randomly distributed into the treatment categories, with six trees per provenance per dose treatment. Supplementary UV radiation was given in a greenhouse for seven days a week from 11 June to 30 September 1994 and from 1 February to 30 September 1995, using Philips Ultraviolet TL 100 W/01 lamps. The biologically effective UV-doses (UV-B,C_BE) were 0, 2.2–6.6 and 5.6–16.8 kJ m⁻² d⁻¹ (II).