Response Of CNP Stoichiometric Characteristics Of Different Plants To Nitrogen And Phosphorus Addition In Hulunber Grassland

Human activities accelerate the conversion of atmospheric N into the biosphere.Grassland ecosystem is mainly limited by N and is gradually limited by other elements,such as P or N,P.Therefore,this paper relied on the field N and P addition platform at the Ecosystem Research Station of the Erguna Forest and Grassland Transition Zone of the Shenyang Institute of Applied Ecology,Chinese Academy of Sciences.The site was continuously treated for N and P for three years(2014~2016).In order to simulate the impact of changes in N and P on grassland ecosystems.In this study,two dominant species of grassland,Leymus chinensis,Thermopusis lanceolata,and two typical bottom species,Cymbaria dahurica.and Potentilla acaulis.were selected as objects of study.By controlling P addition gradient,this study revealed the succession of Hulunber grassland ecosystems and the effects of these successions on different functional species.The main findings of this study are:(1)N addition significantly increased the content of soil ammonium and nitrate,significantly reduced soil available P content;P addition had no significant effect on soil ammonium and nitrate,significantly increased soil available P content.(2)P enrichment had no significant effect on the biomass and root-shoot ratio of four plants,but N enrichment promoted the increase of aboveground biomass of Leymus chinensis and Cymbaria dahurica,and significantly decreased the root-shoot ratio,but there was no significant difference in biomass between the upper and lower layers because of the height of growth.(3)The study area was mainly limited by N.As the available N content in the soil increased,the limiting factors of the plants in the study area were gradually limited by N to P conversion,and N limitation would increase after P addition.The restrictive elements of the four plants were as follows: Thermopsis lanceolata was neither restricted by N nor by P,and Leymus chinensis,Cymbaria dahurica,and Potentilla acaulis.were mainly limited by N and P.(4)The nutrient contents of C,N,and P in plant leaves were all greater than the plant roots,which reflected the differences of plant organ functions.(5)The C content in roots and leaves of the four plants did not respond to the addition of N and P;N addition significantly increased the N content in the roots,leaf N content of Leymus chinensis,Cymbaria dahurica,and the leaf P content of Potentilla acaulis;P additionsignificantly increased the P content in the roots,leaf P content of Leymus chinensis,and the leaf P content of Cymbaria dahurica,this reflects the differences of nutrient use and distribution strategies of different species.