The Effect of Oxygen Deprivation on Inorganic Nitrogen Uptake in an Antarctic Macrolichen

Snow meltwater containing 36 ng ml −1 NO 3 − −N (raised here to between 95–101 ng ml −1 NO 3 − −N) and 112 ng ml −1 NH 4 + −N was sprayed onto illuminated Usnea sphacelata at 2°C in a 2−1 capacity transparent perspex chamber force-ventilated with either air or O 2 − (and CO 2 − ) free N 2 . The NO 3 -concentration in meltwater recirculated through a layer of U. sphacelata fell to c. 8 ng ml −1 after 1.25 h. Although the pattern of decline was broadly comparable in both air and N 2 , the initial rate of decline was lower in N 2 . When undepleted meltwater was continuously sprayed onto the lichen and the effluent collected for analysis, the lichen was found to retain 55% of the wet deposited NO 3 − in air but only 27% under N 2 . Up to 90%) of NH 4 + supplied in a continuous spray of meltwater was retained by the lichen but this was affected little by O 2 and CO 2 deprivation.