Study On Species Composition And Population Distribution Pattern Of Tetraena Mongolica Desert In Western Ordos

Tetraena mongolica is a strong xerophytic succulent leaf shrub belonging to Tetraena Maxim.,Zygophyllaceae.It is a national secondary protected plant.Due to the easy abortion of T.mongolica seeds,human disturbance and habitat fragmentation,the population is constantly decreasing.In this study,the community characteristics and diversity,interspecific association and population distribution pattern of T.mongolica in western Ordos were analyzed,which provided basic data for further discussion on the structure and function of T.mongolica community,and also provided a basis for scientific protection of T.mongolica resources.The mainresults are as follows:(1)Through the investigation of 11 plots,44 species of plants were obtained,belonging to 18 families and 37 genera.Gramineae,Leguminosae,Compositae,Chenopodiaceae and Zygophyiiaceae were dominant,accounting for 61.36%of the total species.The main life forms are Shrubs,Subshrubs and Perennial herbs.Perennial herbs are the most(40.91%),but shrubs and Subshrubs(20.45%and 18.18%respectively)constitute the basic layer of T.mongolica desert;There are15 floristic geographical elements,mainly Gobi species(20.45%),Gobi-Mongolian species(20.45%),and Central Asia-Eastern Asia species(13.64%);The water ecological types were mainly xerophytes(86.36%)of which typical xerophytes accounted for the largest proportion(45.45%),followed by super(strong)xerophytes(34.09%),especially xerophyte shrubs and subshrubs.(2)There are 4 sub-formations and 10 associations in the investigated Tetraena mongolica desert.The 4 sub-formations are Tetraena mongolica-Shrubs-Herbs desert,Tetraena mongolica-Shrubs-Subshrubs-Herbs desert,Tetraena mongolica-Subshrubs-Herbs desert,Tetraena mongolica-Herbs desert.The results ofαdiversity analysis showed that the species richness(R)of Tetraena mongolica+Reaumuria soongarica-Peganum nigellastrum desert(T7)was the highest,and the Pielou index J value and Shannon-Wiener index H′value of Tetraena mongolica+Oxytropis aciphylla-Cleistogenes songorica+Stipa glareosa desert(T11)were the highest.On the whole,the diversity of Tetraena mongolica+Oxytropis aciphylla-Cleistogenes songorica+Stipa glareosa desert(T11),Tetraena mongolica+Ajania achilleoides-Allium polyrhizum desert(T10),Tetraena mongolica+Reaumuria soongarica-Peganum nigellastrum desert(T7)ranked the top three.Due to the low richness of Tetraena mongolica-Artemisia scoparia desert(T6)、Tetraena mongolica-Peganum nigellastrum desert(T9),the role of dominant species is prominent(Simpson dominance index D value is the largest),the uniformity is much,and the overall diversity level is the lowest.The diversity index of herbaceous plants in each association is mostly higher than that of shrubs and subshrubs,reflecting that herbaceous plants play a greater role in the diversity of the community.Theβdiversity of different communities is mainly related to habitat differences.(3)The species in the study area were screened and 27 main species were obtained.The correlation between species was analyzed byχ~2test,Pearson correlation test and Spearman rank correlation test.The results showed that the interspecific relationship of each species in the T.mongolica community in the Western Ordos area was mainly negative correlation.The positive and negative correlation ratios were 0.89、0.35and 0.74,respectively,but the positive correlation species pairs with significant(P<0.05)were significantly higher than the negative correlation species pairs.The significant rates ofχ~2test and Spearman were higher,which were 20.62%and 20.23%respectively,and there was a great consistency between significant species pairs.Pearson correlation test was significantly lower,which was 11.97%.For T.mongolica,the constructive species of the community,different methods showed a significant negative correlation with Bassia dasyphylla(P<0.05,the results of two correlation tests),and a significant positive correlation with Helianthemum ordosicum,Salsola passerina and Reaumuria trigyna(P<0.05,only one method showed).In general,the correlation with other plants is not strong.(4)Utilizing size structure instead of age structure,the T.mongolica individuals were divided into three classes of size(class 1,d≤40 cm;class 2,40 cm<d≤80 cm;class 3,d>80 cm.where denotes the cube root of the product of plant height and crown diameter).Based on the point pattern analysis method,the population structure characteristics,spatial distribution pattern of each size class and the correlation between size classes were studied.The results showed that:In both the core area or the northern edge of the distribution area,the individuals of T.mongolica were mainly concentrated in the class 2.Moreover,the age structure was stable,which reflected the stability of the plot environment;The distribution patterns of population and the class 2 and 3 were mainly randomly distributed.The class 1(young individuals)at medium and small scales followed an aggregated distribution,showing that their survival rate was improved through mutual dependence;The correlations between different classes were complex,The class 1 and class 2 plants had a significant positive correlation at medium and small scales in the two plots of the core area and 4.8 to 8 m in the plot of the northern marginal area,showing the dependence of young plants on a dult plants.However,the class 3 plants had significant negative correlations with the other 2 classes at medium and small scales,which showed the inhibitory effect of senior individuals on other classes.