Nitrate reductase activity in some subarctic species and UV influence in the foliage of Betula pendula Roth. Seedlings

Nitrate reductase ŽNR. activity was studied in the foliage of five subarctic species: mature trees of European white birch ŽBetula pubescens Erch. S.S.., Scots pine ŽPinus syl estris L.., Norway spruce ŽPicea abies L. Karst., Ericaceous shrub bilberry ŽVaccinium myrtillus L.., naturally growing in a forest, and seed-grown silver birch ŽBetula pendula Roth.. seedlings in an ultraviolet ŽUV. exclusion field experiment at the Pallas-Ounastunturi National Park in Finnish Lapland Ž68 N.. Mean NR activity ranged from 0 in bilberry to 1477 ŽS.D. 277.7. and 1910 ŽS.D. 785.4. nmol g 1 DW h 1 in mature trees of European white birch and silver birch seedlings, respectively. Significant differences due to UV exclosure treatments were determined for the NR activity of silver birch seedlings ŽF 3.62, P 0.025 . after three growing seasons Ž191 days. of UV exclusion. The ambient and control silver birch seedlings had or tended to have higher NR activity than those grown under UV exclusion. No relationship was found between the foliage NR activity and total nitrogen content, which ranged from 0.61 to 1.35% per seedling. The present study suggests large differences in NR activity between the species and the induction of NR activity in silver birch seedlings due to ambient UV radiation.