The Research Of Dominant Species To Absorb Soil Nitrogen In Alpine Meadow

This research is conducted at the alpine meadow ecosystem on Qinghai-Tibet Plateau. By theoretical knowwledge in plant nutrition ecology , we want to determine the uptake kinetics of NH₄⁺,NO₃^-,a variety of amino acids by alpine dominant spieces in rivalless circumstance and to examine extent of niche separation in N source uptake of diffeerent plant species in alpine communties.Through above research ,we may improve our understandings of the nutrition characteristics of alpine plant species,N cycle of and alpine meadowecosystem and provide scientific basis tor sustainable development of alpine meadow ecosystem on Qinghai-Tibet plateau.(1)There are some advantage respective free amino acid in Alpine Kobresia humilis meadow,K. tibetica meadow,and degenerative Kobresia humilis meadow soil.They are phenylalanine, aspartic acid,leucine, arginine, proline,glutamic acid and qlycocoll. They accounted 70-90 percent in total free amino acid.The trend is not remarkable with the type of meadow and the change of time. Throughout the growing season the average concentration of total free amino acid N is 6.90mg N/kg in dry soil in K. tibetica meadow.The highest value happens about in June 30th between 5.47 to 8.29mg/kg.In Kobresia humilis meadow the average concentration is 7.44N/kg in dry soil. It changes between 4.50 to 10.82 mg/kg in degenerative Kobresia humilis meadow soil total amino nitrogen is not significant with season change, the average density is 5.04 mg/kg.(2)Helictotrichon,Festuca sinensis,E. nutan and Elymus has different performances to management in different forms and concentration nitrogen(inorganic and organic nitroge ) Helictotrichon,s rootstalk proportion performance is not very obvious to different nitrogen treatment. Different concentrations , E. nutans ,s rootstalk proportion is significant in nitrate,ammonium nitrate and benzedrine .Their rootstalk proportion significantly reduced.with nitrogen accumulation. Elymus has no significant performance in glycine of different concentrations but in other kinds of inorganic nitrogen, organic nitrogen it has significant performance.Its rootstalk proportion is depressed with increased concentration.But Festuca sinensis rootstalk proportion showed obvious differences in defferent concentration ammonium and ammonium nitrate Its rootstalk proportion significantly reduced.with nitrogen accumulation.E. nutans nitrogen concentration increases with nitrogen accumulation in all kinds of nitrogen forms treatment .But Helictotrichon ,s nitrogen accumulation is not consistent in all kinds of nitrogen forms treatment.But it can explain the two plants can absorb organic nitrogen in sterile training conditions (3)We injece 5NH₄Cl,K¹⁵NO₃,¹⁵N-Glycine and ¹⁵N-Asp in alpine Kobresia humilis meadow and K. tibetica meadow the results showed: except Leguminosae plants is symbiotic nitrogen fixation, we found that Kobresia tibetica, Blysmus sinocompressus, Carex atro-fusca, Gentiana straminea can uptake nitrogen by special way, maybe they belong to non-leguminous nitrogen-fixing plants. To our knowledge, this is the first documentation that there are many plant species uptake nitrogen by special way in alpine meadow; As far as plant uptake of organic N was concerned, Kobresia humilis, Ranunculus brotherusii, Poa pratensis, Carex duriuscala, Poa crymophila can effective uptake organic nitrogen. 25-35% of plant nitrogen comes from soil glycine. These data showed many plant species in alpine meadow may effective utilize dissolve organic nitrogen such as amino acids, and there are diversity ways of uptake nitrogen of different species in alpine meadow.