Researches On The Relationship Between Spatial Variation Of Soil And The Niche Of Artemisia Halodendron Population

This paper studied the different succession stages of Artemisia halodendron population in Kerqin sand.Our objective was to disclose the environmental limitation to plant and the plant adaptation to environment at species,synusia and water ecological groups scales by analyzing spatial distribution of soil moisture and nutrient content.It aims to explain the changes of community in composing structure and function caused by spatial variation of soil factor in the succession sequence of the population of sandy plant which leaded to the substitute of dominant species.The main conclusions are as follows:1.The spatial heterogeneity of soil characteristic in different types of sand indicated that:in fixed sand spatial heterogeneity of soil moisture on the 0-30cm is the pure block model caused by the random variation,that of soil moisture in semi-fixed and mobile sand shows the index model and has a strong spatial correlation,but the spatial related scale and Moran's I coefficient area of flow sand are larger than those of semi-fixed sand.In different types of sand,spatial distribution of soil organic carbon on 0-30cm is obviously different.The semivariogram analyses showed that the fitting models of mobile,semi-fixed and fixed sand are separately linear model,block model and spherical model.In mobile sand,the spatial heterogeneity of soil organic carbon has longer dependent distance at the study space-scale,and the range is 77.06m which is beyond spatial scope set in the sample area and far larger than the semi-fixed sand(16.55m).The fractal dimension shows that the semi-fixed sand(1.984)＞fixed sand(1.880)＞mobile sand(1.488).This result indicates that the spatial distribution of soil organic carbon in semi-fixed sand tended to uniform distribution and spatial heterogeneity of flow sand is stronger.In different types of sand,the spatial distribution of soil nitrogen on the 0-30cm can be better fitted to spherical model.In flow sand the range is the largest,the fractal dimension is the smallest and the positive relationship scope of Moran's I coefficient is also largest,respectively of 38.16m, 1.724 and 16m.That means the spatial heterogeneity of soil nitrogen in mobile sand is strong,and those of fixed and semi-fixed sand are weakened in turn.2.The study on the niche changes of A.halodendron population at different levels and scales(species,life forms,water ecology group) shows that:in shrub layer, niche breadth of A.halodendron populations is the biggest in the vanguard colonization(7.40) in flow sand.With the sand fixed,the niche breadth reduces to 2.97 and until being replaced by Artemisia frigida populations.The niche breadth of A.frigida is increase from 3.95 in semi-fixed sand to 5.88 in fixed sand in which A.frigida becomes a dominant species.Pioneer species of annual-biennial herbage synusia has been gradually replaced by grassland species of perennial herbage synusia.Due to human impact,in different succession stages the niche breadth of annual-biennial subordinate grass synusia is wider and the overlapping extent of niche between all types of sand population is higher,mostly between 0.4 and 0.7.The average value of niche overlap is that fixed sand(0.60)＞semi-fixed sand(0.50)＞flow sand(0.42).Niche overlaps of dominant species in fixed sand are all above 0.8.3.The results of dividing population are consistent between the methods of TWINSPAN classification and CCA(canonical correspondence analysis,CCA) ordination which revealed significant environmental gradient and divided communities into three groups:A.halodendron-annual plant colonization (pioneer community) in mobile sand,A.halodendron-herbage association in semi-fixed sand and A.frigid+A.scoparia+herbage association(steppe community) in fixed sand.By the further analysis using CCA,it shows that the first axis is negative to all environmental factors.The second axis are positively associated with soil nutrients,and negatively correlated with soil moisture.Soil moisture of 0-15cm plays a decisive role on the plants composing types and community distribution.The content of nitrogen in 15-30cm plays a restricted role.