15N abundance in the Dry Valley area, south Victoria Land, Antarctica: Eco-physiological implications of microorganisms

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Stable nitrogen isotope ratio in nitrogen-bearing substances from the Dry Valley area, south Victoria Land, was reported. The lowest δ^<15>N value of around -50‰ was found for the epibenthic algae collected from nitrate-rich saline ponds in the Labyrinth. In Lake Vanda, nitrate in its maximum layer (57-59m) was significantly rich in ^<15>N (10.3-13.4‰) as compared with the sedimentary organic nitrogen (-4.6‰). The variation of δ^<15>N seemed to probably result from nitrogen isotope fractionation associated with nitrate assimilation by algae. In the east lobe of Lake Bonney, the δ^<15>N value in nitrate increased with depth from 4.9 to 31.2‰. Dissolved N_2 gas in the west lobe exhibited the highest δ^<15>N value (1.5-2.5‰) among those observed in anoxic layers of various aquatic systems. The latter results from denitrification of nitrate with high δ^<15>N value at temperatures lower than 0℃.
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