Nutrient availability and the effect of increasing UV-B radiation on secondary plant compounds in Scots pine

Growth and pigment composition of plants can be affected by both UV-radiation and availability of nutrients. Therefore, the UV-induction in a plant as a protective response against UV-B radiation may depend on the UV-B dose encountered and the nutritional state of a plant. To test this, young Scots pine (Pinus sylvestris) seedlings were grown under two nutrient levels (relative nutrient addition fates, RAR, of 4 and 6%) and exposed to six different daily doses of UV-radiation (UV-A and UV-B) for one growing season. Both the growth and the accumulation of photosynthetic pigments were positively affected by the availability of nutrients, while the accumulation of condensed tannins and its precursor, (+)-catechin decreased significantly under higher nutrient level, which may imply some trade-off between primary and secondary metabolites. However, nutrient level did not markedly affect the total accumulation of flavonols. Since there was no decrease in the growth of the seedlings and the content of photosynthetic pigments in needles under increased UV-B levels, the seedlings had apparently good protection against UV-B radiation. Protection was probably dependent on the UV-induction of flavonoid compounds in needles, which differed between the two nutrient levels used. Under moderate nutrient availability (RAR 4%), the accumulation of flavonols and also chlorophylls was highest at the ambient or near to ambient levels of UV-radiation, the levels that pines are generally adapted in natural conditions. As the availability of nutrients and thereby, the resources in seedlings increased (RAR 6%), the UV-B levels higher than ambient increased specifically the accumulation of diacylated flavonols when dose responses were detected. Furthermore, the enhancement of UV-A radiation caused an accumulation of the dihydroflavonols, ampelopsin and taxifolin, under high nutrient availability. Since the flavonoid responses were very compound-specific, and in some cases were also dose-dependent and different between the two nutrient levels used, it can be suggested that the induction of secondary compounds in the flavonoid pathway is multi-step regulated by both environmental factors, UV-radiation and nutrients. Already the present variation in the ambient range of UV-B radiation at northern latitudes can influence the chemical composition of Scots pine seedlings and enhancement in nutrients may increase their responsiveness, particularly to high UV-intensities. (C) 2002 Elsevier Science B.V. All rights reserved.