Effects Of Long-term Nitrogen Addition On The Diversity Of Medicinal Plants And Ethnic Plants In Inner Mongolia Typical Steppe

Since the industrial revolution,nitrogen deposition caused by human activities has been widespread in the world,threatening a large number of terrestrial and aquatic ecosystems.Atmospheric nitrogen deposition has been proved to be able to increase ecosystem productivity,reduce biodiversity,change the cycling of nutrients of terrestrial ecosystems,and prompt changes in the structure and function of ecosystems.China is also one of the hot regions of nitrogen deposition.The grassland in the North accounts for about 78% of the grassland area in China,which is the major component of the grassland area in China.At the ecosystem level,the impacts of nitrogen deposition on biodiversity are mainly concentrated on species richness,soil acidification,cytotoxicity of cationic,changing physiological response,and interaction between above ground and underground part and other correlated mechanisms.However,studies on which resident species will be extinct,especially on their use for human beings,which have not been fully explored.The diversity of herbaceous medicinal herbal plants and ethnic plants is the basis of providing functions and services for ecosystem.However,there is still a lack of clear understanding of the response of medicinal plants and ethnic plants to nitrogen deposition.In order to solve this problem,based on 3200 km transect of northern grassland and Xilinhot long-term positioning monitoring platform,and using the experimental platform of the control of nitrogen addition of Inner Mongolia Grassland Ecosystem Research Station of Chinese Academy of Sciences,a 10-year period of nitrogen addition(0,1,2,3,5,10,15,20,50 g N-m-2 yr-1)and 4-year period of cease of nitrogen addition were carried out in typical temperate steppe of Inner Mongolia.In the experiment,the effects of nitrogen addition and cease nitrogen addition on medicinal and ethnic plants were explored by using the method of logistic regression analysis and other statistical methods.The following conclusions are drawn from the study:(1)There are abundant plant species in the northern grassland.There are 118 species of medicinal plants belonging to 76 genera and 30 families in the 3200 kilometer transect.In the composition structure of families,plant species are mainly concentrated in the two families of Leguminosae and Compositae,while only the minority and single plant are found in the most families.There were totally 4 types of flora characteristics of elements and 11 types of geographic elements in the transect,which generally show nature of the temperate zone.There were 96 Temperate Distribution-types,accounting for 58% of the total species in the transect.There were 51 species of medicinal plants belonging to 36 genera and 22 families in Xilinhot,which can be divided into 4 main groups according to phylogenetic analysis.The first main group included 18 species of 7 families,including Rosaceae,Moraceae and Leguminosae;the second main group included 23 species of 11 families,including Labiatae,Scrophulariaceae and Compositae;the third main group included only two species of Ranunculaceae;the last group included 8 species of 3 families,Including Iridaceae,liliaceae,Gramineae.There were 53 species of medicinal plants belonging to 44 genera and 22 families in Xilinhot nitrogen deposition platform.(2)The continuous addition of nitrogen resulted in the decrease of species diversity.Different species responded differently to nitrogen addition.Even when the concentration of nitrogen addition was very low,the species diversity would still be reduced by nitrogen addition.Comparing with non-medicinal plants,medicinal plants and ethnic plants were not sensitive to nitrogen addition,and the threshold concentration of nitrogen addition was 10 g N m-2 yr-1.Medicinal plants and ethnic plants have higher ability to resist the cumulative effect of nitrogen addition and there was a lag period of 1 year compared with non-medicinal plants.Nitrogen addition had different effects on different functional groups of medicinal plants and ethnic plants,but both of them showed a downward trend.The threshold nitrogen concentration for extinction of perennial rhizomatous grasses and biennial rhizomatous grasses was 10-15 g N m-2 yr-1,while that of perennial grasses decreased significantly only at 50 g N m-2 yr-1.The protection and application of the diversity of forbs of medicinal plants and ethnic plants should be emphasized.(3)After nitrogen addition stopped,plant species diversity was still affected by nitrogen addition and there was no significant change in the processing time of continuous nitrogen addition.After four years of recovery on nitrogen deposition,the species richness of both medicinal and ethnic plants and non-medicinal plants remained unchanged.However,it increased only when the nitrogen concentration was 50 g N m-2 yr-1.The results of 4 year cease of nitrogen addition experiment showed that the restoration of the species diversity of weeds community was a long process and whether it could be restored or not to the original state of diversity was still unclear.In real environments,nitrogen deposition does not stop immediately,but it is a very slow process of changes.Therefore,whether species diversity affected by nitrogen deposition can be restored to the level without nitrogen addition needs long-term and sustained observation in order to assess the impact of future reduction of nitrogen deposition on ecosystem productivity.