The ability of several high arctic plant species to utilize nitrate nitrogen under field conditions.

The ability to utilize NO inf3sup- in seven high arctic plant species from Truelove Lowland, Devon Island, Canada was investigated, using an in vivo assay of maximum potential nitrate reductase (NR) activity and applications of 15N. Plant species were selected on the basis of being characteristic of nutrient-poor and nutrient-rich habitats. In all species leaves were the dominant site of NR activity. Root NR activity was negligible in all species except Saxifraga cernua. NO inf3sup- availability per se did not appear to limit NR activity of the species typically found on nutrient-poor sites (Dryas integrifolia, Saxifraga oppositifolia, and Salix arctica), or in Cerastium alpinum, as leaf NR activities remained low, even after NO inf3sup- addition. 15NO inf3sup- uptake was limited in D. integrifolia and Salix arctica. However, the lack of field induction of NR activity in C. alpinum and Saxifraga oppositifolia was not due to restricted nitrate uptake, as 15NO inf3sup- labelled NO inf3sup- entered the roots and shoots of both species. Leaf NR activity rates were low in three of the species typical of nutrient-rich habitats (O. digyna, P. radicatum and Saxifraga cernua), sampled from a site containing low soil NO inf3sup- . Additions of NO inf3sup- significantly increased leaf NR activity in these latter species, suggesting that potential NR activity was limited by the availability of NO inf3sup- . 15N labelled NO inf3sup- was taken up by O. digyna. P. radicatum and Saxifraga cernua. Although two species (D. integrifolia and Salix arctica) showed little utilization of NO inf3sup- , we concluded that five of the seven selected high arctic plant species (C. alpinum, O. digyna, P. radicatum, Saxifraga cernua and Saxifraga oppositifolia) do have the potential to utilize NO inf3sup- as a nitrogen source under field conditions, with the highest potential to utilize NO inf3sup- occurring in three of the species typically found on fertile habitats.