Study On The Community Characteristics And Geographic Distribution Of Stipa Gobica Steppe In China

Stipa gobica is a perennial xeromorphic fasciculate small herb,belonging to the genus of Stipa and Sect.Smirnovia,and its floristic geographical element is Middle Asia element.Stipa gobica steppe mainly distributs on the rocky slopes or rocky hills of desert steppe region,and can also be found in rocky hills or mountains of the typical steppe area eastwardly and some rocky slopes of the desert region westwardly.Due to the almost coincident distribution range and similar morphological characteristics between Stipa gobica and Stipa klemenzii and the complete reversal of community type dominated by the two species in Chinese and Mongolica major works(mainly as a result of scientific name upside down),the community description about two species is incompatible with the actual.Thus,the systematic deep study on the plant community characteristics and geographic distribution of Stipa gobica steppe in China is helpful to distinguish the community features between the Stipa gobica steppe and Stipa klemenzii steppe,revise the confusion of major vegetation works and expand the research field of steppe vegetation ecology,which can provide scientific basis for establishing natural regionalization scheme reasonably,and also play an important role in vegetation conservation of desert steppe and reasonable arrangements for grazing and livestock production.Based on the systematical understanding of the community characteristic and spatial distribution of Stipa gobica steppe and the detailed investigation of 116 plots in Stipa gobica steppe,we obtained the following conclusions:1.The constructive species Stipa gobica had similar distribution range with Stipa klemenzii,but its morphological characteristics was more similar to Stipa tianschanica and showed greater difference with Stipa klemenzii.Stipa gobica and related species Stipa tianschanica have obvious differences in the length of glumes,lemma,awn,awn needle and the feature of whether the ring of short hairs existing in the apex lemma.Additionally,for the geographical distribution Stipa gobica also had a relatively independent distribution center compare to Stipa tianschanica,so we can concluded that there were multiple independent and discontinuous variation of morphological characteristics between Stipa gobica and Stipa tianschanica,and the two species separately had their own abundance distribution center,being in line with the concept"Morphology-biology Species",so they were independent species in morphological characteristics and geographic distribution.2.According to the quadrat data,303 seed plants belonging to 40 families and 139 genera(including the subspecies,varieties and forms)were recorded in the Stipa gobica steppe of China,Among which there were 5 gymnosperm species belonging to 2 families and 2 genera,and 298 angiosperm species belonging to 38 families 137 genera and.The families having more than 10 species were Compositae,Gramineae,Leguminosae,Rosaceae,Liliaceae,Chenopodiaceae and Caryophyllaceae respectively.Hemicryptophyte,a total of 189 species is the dominant life form in Stipa gobica steppe,which accounted for 62.38%of the total species.As for the ecological type of water,xerophytes was the dominant plants,with a total of 127 species,accounting for 41.91%of all species.Middle Asia element(included the variants)areal-type(including 63 plant species)was the major floristic elements,containing 31.35%of the total species.The cover of 0.1%-1%was the dominant level in the cover class distribution of the species,including 64.1%of the total of the species;The constancy degree of I(0%-20%)was the dominant level in the constancy degree distribution of the species in Stipa gobica steppe,containing 94.87%of the all species.3.In accordance with the classification principle of community-appearance,Form.Stipa gobica was divided in to 8 Stipa gobica steppe association groups,and then,106 associations were divided from these 8 association groups based on community survey data.The distribution area and community characteristics of each associations were descripted and the relationship of ecological succession of the Stipa gobica communities was analyzed.4.The plant community diversity of Stipa gobica steppe varied regularly along the altitudinal and longitude gradient.With the rise of longitude,the overall level of ? diversity of the community increased in a straight line or in volatility.With the increase of the altitude,species richness increased firstly and then decreased and other diversity index showed a trend of increase.? diversity index showed a trend of rising volatility with the increased longitude.In the range of 108-109°E,Cody diversity index reached the peak while the Jaccard similarity coefficient reached the lowest.With the increase of altitude,? diversity index increased firstly and then decreased with the maximum value appearing at an altitude of about 1700 m.5.The soil microelement Cr and Cu were two major influcing factors to the distribution of Stipa gobica steppe community according to the comparative analysis of soil microelements and pH between Stipa gobica steppe and other zonal community-Stipa klemenzii steppe,Stipa breviflora steppe and Stipa krylovii steppe.The reasons were summarized as follows:First of all,the soil pH value in Stipa gobica steppe was significantly less than other steppes,and relative studies had shown that soil pH were negatively correlated with the content of Cr and Cu.Secondly,it was possible that Stipa gobica was of stronger selective absorption capacity of the two elements than other soil microelements,so Stipa gobica uptook these two elements from the stony rock weathering by roots,and with the death of the plant the two elements returned to soil again,which made the content of the two elements in Stipa gobica community being significantly higher than other steppe soil.Finally,the degree of stonification and wind erosion in Stipa gobica steppe were obviously higher than other zonal steppes,which made the speed of mineral weathering and decomposition being significantly faster than other steppe soil and thus lead to an increased content of soil microelements.This can be another reason why Stipa gobica steppe had higher soil microelement content than other zonal steppes,especially for Cr and Cu.