THE ABILITY OF SEVERAL HIGH ARCTIC PLANT-SPECIES TO UTILIZE NITRATE-NITROGEN UNDER FIELD CONDITIONS

The ability to utilize NO3- 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 N-15. 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. NO3- 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 NO3- addition. (NO3-)-N-15 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 (NO3-)-N-15 labelled NO3- 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 NO3-. Additions of NO3- significantly increased leaf NR activity in these latter species, suggesting that potential NR activity was limited by the availability of NO3-. N-15 labelled NO3- was taken up by O. digyna. P. radicatum and Saxifraga cernua. Although two species (D. integrifolia and Salix arctica) showed little utilization of NO3-, 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 NO3- as a nitrogen source under field conditions, with the highest potential to utilize NO3- occurring in three of the species typically found on fertile habitats.