Abstract:

To understand the dynamics of added nitrogen (N) in alpine meadow and the role of alpine plants and soil microorganisms in the retention of deposited N, the fate of 15N labeled nitrate and ammonium salts was determined in an alpine meadow for two months. Two weeks after 15N application, total recovery of 15N from NO3--15N was 73.5% while it was 78% from NH4+-15N. More 15N was recovered in plants than in soil organic matter or in microbial biomass, irrespective of forms of N added. After one month, 70.6% of added NO3--15N and 57.4% of NH4+-15N were recovered in soils and plants. 15N recovered in soil organic matter decreased greatly while that recovered in plants varied little, irrespective of the form N. Compared with the results of two weeks after 15N application, more NO3--15N than NH4+-15N was recovered in microbial biomass. Total recovery was 58.4% (six weeks) and 67% (eight weeks) from NO3--15N 15N, and 43.1% and 49% from NH4+-15N, respectively. Both plants and soil microorganism recovered more NO3--15N than NH4+-15N. But plants recovered more 15N than soil microorganisms. During the whole experiment plants retained more NO3--15N and 15N than soil microorganisms while 15N recovered in inorganic N pool did not exceed 1% due to lower amount of inorganic N. This indicates that plants play more important roles in the retention of deposited N although microbial biomass can be an important sink for deposited N in early days after N application. Key words: alpine meadow; soil microorganisms; retention of deposited N; percentage of 15N recovery; fate of NO3--15N and NH4+-15N

短期内¹⁵N 标记的铵盐和硝酸盐在青藏高原高寒草甸中的运移规律
徐兴良 欧阳华 裴志永 周才平
（中国科学院地理科学与资源研究所，北京100101）

摘要： 运用¹⁵N稳定性同位素示踪技术,对高寒草甸植物和土壤微生物固持沉降氮的能力及沉降氮在小嵩草(Kobresia pygaea)草甸中的运移规律进行了研究.施肥2周后,NO₃-¹⁵N和NH+₄-¹⁵N的总恢复率分别为73.5%和78%.无论是NO₃-¹⁵N,还是NH₄+-¹⁵N,植物所固持的¹⁵N总是比土壤有机质或者是土壤微生物固持的多.4周后,70.6%的NO₃-¹⁵N和57.4%的NH₄+-¹⁵N被固持在土壤和植物中.其中,土壤有机质所固持的15N均下降了很多,而植物所固持的15N却变化很小.同前面的结果相比,较多的NO₃-¹⁵N为土壤微生物所固持.在施肥6周和8周后,NO₃-^15N的总恢复率分别为58.4%和67%,而NH₄+-¹⁵N的总恢复率分别为43.1%和49%.植物和土壤微生物所固持的NO₃-¹⁵N比NH₄+-¹⁵N多.在整个实验期间,植物固持的NO₃-N较多,而且比土壤微生物固持了较多的¹⁵N.由于无机氮的含量一直很低,无机氮库所固持的¹⁵N一般不超过1%.上述结果意味着短期内植物在高寒草甸中对沉降氮的去向起着决定作用.

关键词： 高寒草甸；土壤微生物；¹⁵N恢复率；沉降氮的固持；NO ₃^- -N和NH₄+-N运移规律

通讯作者。Tel: 010-64889697; E-mail: ohua @ igsnrr.ac.cn 。