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 Tr uelove Lowland, Devon Island, Canada was investigated, using an in viv o assay of maximum potential nitrate reductase (NR) activity and appli cations of N-15. Plant species were selected on the basis of being cha racteristic of nutrient-poor and nutrient-rich habitats. In all specie s leaves were the dominant site of NR activity. Root NR activity was n egligible in all species except Saxifraga cernua. NO3- availability pe r se did not appear to limit NR activity of the species typically foun d on nutrient-poor sites (Dryas integrifolia, Saxifraga oppositifolia, and Salix arctica), or in Cerastium alpinum, as leaf NR activities re mained low, even after NO3- addition. (NO3-)-N-15 uptake was limited i n D. integrifolia and Salix arctica. However, the lack of field induct ion of NR activity in C. alpinum and Saxifraga oppositifolia was not d ue 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 li mited 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 op positifolia) do have the potential to utilize NO3- as a nitrogen sourc e under field conditions, with the highest potential to utilize NO3- o ccurring in three of the species typically found on fertile habitats.