Characteristics of Kobresia humilis Community Structure at Different Degraded Levels in Northern Qinghai

[ Objective] To reveal structure and function of alpine meadow ecosystem and thus to provide a scientific basis for development, utilization and scientific management of alpine meadow pasture as well as sustainable development of grassland agriculture. [ Method] Charactedstics of Kobresia humilis communities with primary vegetation （community I） and degraded vegetation （community II） were analyzed. [Result] Species richness, biodiversity index and biomass of the community I were respectively 42, 3. 531 and 3 553.1 g/m^2, which were respectively higher than those of the community II （37, 2.270 and 3 391.1 g/m^2）. Correlation analysis shows that community biomass was correlated positively with the dchness index （ P 〈 0.01 ）, and biodiversity index was correlated positively with the aboveground biomass and dchness index （ P 〈 0.01 ）. [ Conclusion] The Kobresia humilis community I has reasonable structure and large coverage of ground vegetation, which play an important role in maintenance of biodiversity and ecosystem function.

The uptake diversity of soil nitrogen nutrients by main plant species in Kobresia humilis alpine meadow on the Qinghai-Tibet Plateau

We studied the uptake of ammonium, nitrate, and a variety of amino acids by alpine plant species in the Kobresia humil alpine meadow ecosystem in situ. We examined the extent of niche separation in uptake of N source by different plant species in alpine communities, and investigated the contribution of symbiotically fixed N to the total N in alpine meadow. The results are （1） δ15N natural abundance values of 13 plant species lie between -2.680‰ and 5.169‰, and the scope is 7.849‰. （2） Le- guminous plants, such as Trigonella ruthenica, Gueldenstaedtia diversiffolia, and Oxytyopis ochrocephala, and non-legumi- nous plant Gentiana straminea uptake low amounts of 15N labeled ammonium, nitrate, glycine or aspartate in soil. （3） As far as the plant uptake of organic N is concerned, Kobresia humilis, Poa pratensis, and Gentiuna spathutifolta can effectively uptake organic nitrogen, and about 37%-40% of the nitrogen of these species comes from soil organic nitrogen sources （such as glycine and aspartate）. Stipa aliena can effectively uptake nitrate, and 60% of its nitrogen comes from soil nitrate. Potentilla anserina, Poa pratensis, and Thalictrum alpinum can effectively absorb ammonium in comparason to other plant species in the meadow, and about 25%-27% of the nitrogen in these plants comes from soil ammonium. （4） The contribution of leguminous fixed N to total N is 7.48%-9.26% in Kobresia humilis alpine meadow. （5） These data show many plant species of alpine meadow may effectively utilize dissolved organic nitrogen such as amino acids, and these plants have diverse ways to uptake soil nitrogen in alpine meadows. Based on the results we can partly explain why there are abundant biodiversities and how plants at alpine habitat utilize the limited soil N sources.