Abstract:

The fate of ¹⁵N-labeled ammonium and nitrate was determined in a Kobresia pygaea C. B. Clarke meadow after 11-13 months following ¹⁵N additions in order to understand the role of alpine meadows in retention of deposited nitrogen (N). It was shown that the fate of NO₃^--¹⁵N or NH₄⁺-¹⁵N was distinctly different. In 11-13 months after ¹⁵N additions, total ¹⁵N recovery of NO₃^--¹⁵N was 92.83%, 92.64% and 79.96% while ¹⁵N recovery of NH₄⁺-¹⁵N was 49.6%, 63.33% and 66.22%. Their different fates were obviously shown on partitioning of ¹⁵N among different components in alpine meadows. After 11-13 months following ¹⁵N additions, more NO₃^--¹⁵N was recovered in plants than in soil organic matter or in soil microorganisms. ¹⁵N retained in soil organic matter was also high and increased with time. ¹⁵N immobilized in soil microorganisms was close to that retained in soil organic matter within 11-12 months while it decreased significantly after 13 months. When NH₄⁺-¹⁵N was added, more ¹⁵N was retained in soil organic matter than in plants or in soil microorganisms. ¹⁵N taken up by plants was constant while that immobilized in soil microorganisms altered greatly. Eleven to thirteen months after ¹⁵N additions, plants and soil microorganisms took up more NO₃^--¹⁵N than NH₄⁺-¹⁵N while soil organic matter recovered more NH₄⁺-¹⁵N than NO₃^--¹⁵N. It indicates that alpine meadows play different roles in retention of deposited NO₃^- and NH₄⁺ after a long time.

Key words: NO3^--¹⁵N, NH4⁺-¹⁵N, Kobresia pygaea meadow, soil organic matter, soil microorganisms, alpine plants