Community Characteristics And Geographic Distribution Of Leymus Chinensis Steppe In China

Leymus chinensis is a perennial rhizome grass,belonging to the family of Gramineae,and its floristic geographical element is Daurli-Mongolian species.It is widely distributed in meadow grassland,typical grassland,and desert grassland in China,and has complex ecological and geographical conditions.Many literatures define it as a broad-spectrum xerophyte.However,the classification status of the Leymus chinensis community in vegetation has been controversial and has not been uniformly defined so far.Affected by hydrothermal factors,geographical distribution of Leymus chinensis community has obvious zonal characteristics.Thus,the systematic study on the plant community characteristics and geographic distribution of Leymus chinensis community in China is helpful to understand the nature of Leymus chinensis community.Also this could provide scientific basis for establishing natural regionalization scheme reasonably,and then have important practical guidance for China's vegetation conservation and reasonable arrangements for grazing and livestock production.Based on the systematical understanding of the community characteristic and spatial distribution of Leymus chinensis steppe and the detailed investigation of 136 plots in Leymus chinensis steppe,we obtained the following conclusions:1.The species composition of the Leymus chinensis steppe in China is rich,with a total of 325 vascular plants recorded,belonging to 43 families and 178 genera;247 species are dicotyledons,belonging to 38 families and 134 genera;78 species of monocots,belonging to 5 families and 44 genera.The major families with more than 30 species were Compositae,Gramineae,and Leguminosae,followed by Rosaceae and Chenopodiaceae(between 15 and 30 species).In addition,there are also8-15 species in Ranunculaceae,Labiatae,Liliaceae,Caryophyllaceae,Cyperaceae,Cruciferae and Scrophulariaceae.The genera with a large number of species are Artemisia(19 species),Potentilla(16 species),Astragalus(8 species),Allium(7 species),Iris(7 species),and Cleistogenes(6 species).The plants Life form that make up the Leymus chinensis community are very rich,with 243 species are perennial herbs,64 species are annual herbs,9 species are shrubs and 7 species are sub-shrubs.Although the proportion of some lifeforms is not large,their presence has greatly enriched the life form spectrum of the plant communities of Leymus chinensis.In terms of the Plant water ecotypes in the Leymus chinensis grassland plant,0.62% were strong xerophyte,24.62% were xerophyte,18.64% were mesial xerophyte,40% of mesophytes,10.7% were drought mesophyte,2.15% were wet mesophytes,and hygrophyte were 3.38%.In general,43.88% of all xerophyte and mesophytes accounted for 52.92%.It shows that the basic nature of the Leymus chinensis community is close to that of a typical grassland,and it also has meadow-forming communities and salinization community types.The geographical composition of the Leymus chinensis grassland consists of 140 species,which account for 43.08% of the ancient Arctic composition.The East Asian composition ranks the second place,with 60 species accounting for 18.46%.The Pan-Arctic composition ranks the third,with 45 species,accounting for 13.85%.The Central Asian component also occupies a considerable proportion,with 22 species,accounting for 6.77%.2.In accordance with the classification principle of community-appearance,Leymus chinensis was divided in to 7 Leymus chinensis steppe association groups and 113 associations based on community survey data.The distribution area and community characteristics of each associations were systematically described.3.With the increase of longitude,altitude and rainfall,the overall ?diversity showed a trend of rising first and then decreasing.In the range of longitude of about 115-118°,altitude of about 1000 m,and annual average rainfall of 350-400 mm,the ? diversity index reaches a highest value.With the increase of temperature,the ? diversity of Leymus chinensis steppes showed a decreasing trend overall.The correlation analysis showed that the ? diversity of Leymus chinensis community had the greatest correlation with temperature.The ? diversity showed a fluctuating upward trend with the increase of longitude.At 121-125° east longitude,the species replacement rate was the largest.The ? diversity of Leymus chinensis community increased with altitude.The species replacement rate first decreased to a steady state and then increased.At altitudes of 130-430 m and 1630-2030 m,the species replacement rate is the highest and the community is most unstable.4.In general,the soil water content of the Leymus chinensis community was significantly higher than that of the Stipa community in the same area.In the Songnen Plain,there was a significant difference in soil pore water conductance between the single dominant species of Leymus chinensis community and bare land,Suaeda corniculata and Chloris virgata communities.The order of conductivity is Chloris virgata community > Suaeda corniculata community > bare land > Leymus chinensis community.5.In the linear regression relationship between functional traits of Leymus chinensis and temperature and rainfall,plant height,stem length below the lowest leaf,stem mass,stem mass/leaf mass,stem length,height of leaf layer showed a significant positive correlation.The aboveground biomass was only significantly positively correlated with rainfall,and leaf width was significantly negatively correlated with temperature and rainfall.The specific leaf area was only significantly negatively correlated with rainfall,and there was no significant correlation with other traits.There was a clear synergistic relationship between the various traits of Leymus chinensis.The ratio of leaf length to width showed a significant positive correlation with temperature and rainfall,and increased with rainfall and temperature.In the Leymus chinensis community with large disturbance of herd pressure,the ratio of leaf length to width the second and third leaves of Leymus chinensis were all less than 30,and the ratio of leaf length to width of the grazing relative to the cutting grass leaves were relatively small.The multivariate linear regression model of individual plant weight and stem morphological index model of Leymus chinensis was: AB(g)= 0.001 × PH(mm)+0.336 × SD(mm)-0.389(R2=0.85,F=69.81,P<0.001).Moreover,it has been verified that the model has high precision and could be applied to various kinds of Leymus chinensis plants.