Characteristics And Spatial Variations Of Microelements Contents Of Soil In Planted And Natural Pure Forests In Arid Region From Shaanxi To Inner Mongolia

As a result of single-species composition, and after a long-term growth or continuous planting, soil properties of artificial or natural pure forests will emerge the phenomenon of degradation or polarization, which seriously affected the stability and sustainable development of forests. The auther studied the widely disputed, mature grown pure forests in arid region from Shaanxi to Inner Mongolia (including subhumid loess hilly region of northern Shaanxi—Huangling region, semiarid loess hilly region of northern Shaanxi—Yan'an region, semiarid windy-and-dusty region of northern Shaanxi—Jingbian region and semiarid hilly region of Inner Mongolia—Wuchuan region). We've studied the characters of the total and the available contents and the spatial variability disciplines of the soil major microelements such as Cu, Zn, Fe, Mn, Ni, Cd, F in soil of different pure forests and mixed forests. And we get polarization index of these soil microelement, which provided theories to run the local forests, to transformate, and to prevent soil from degradation and polatization.The main conclusions of the study were as follows:1. The contents of Cu, Fe, Ni, Cd of soil in most pure forests in Shaanxi to Inner Mongolia region beyond the national average concent level. Larix gmelini land in Huangling region was rich in Cu, Ni, Cd; Ulmus pumila land in Wuchuan region was rich in Fe, etc. However, the contents of Zn, Mn, F of soil were far below average content level. grassland (CK) in Jingbian region,was serious lack of Zn and total Mn of soil; Pinus armandii land in Huangling region was lack of available Mn of soil; and Populus simonii land in Yan'an region, was serious lack of F of soil.2. The contents of a majority of microelements, liked avilable Zn in Huangling region, and the 4 microelements of soil in Wuchuan region, have the phenomenon of“surface-accumulating”. But, the content of available Cu of soil accumulates in the lower layer in the majority of lands in Yan'an region, etc.3. Pinus armandii×Quercus liaotungensis mixed forest land in Huangling region significantly multiply the available Fe content compared to pure forests, however, Pinus tabulaeformis×Larix principis-rupprechtii mixed forest land in Wuchuan region significantly pull down the available Cu and Fe contents compared to pure forests. 4. The contents of a majority of microelements except Fe were serious polarized. The positive polarizations of total Cu contents in Robinia pseudoacacia and Ulmus pumila lands in Yan'an region were serious. Meanwhile, the negative polarization of total Cu contents in Populus simonii land in Jingbian region was serious, that was going pull down the Cu contents. The polarizations of total Zn, total Fe, available Fe, total Mn, total F contents in Amorpha fruiticosa land in Jingbian region were positive directed, which was good for soil microelements collection. The contents of available Zn and available Mn in Hippophae rhamnoides land in Jingbian region was serious positive direction polarized, which was also good for available Zn and available Mn collection. The contents of available Zn content in Picea asperata land in Wuchuan region and that of available Mn content in Pinus armandii land in Huangling region were serious negative polarized, which was pulling down more contents of available Zn, Mn. The contents of total Ni and total Cd in Larix gmelini land in Huangling region had a large positive derected polarization trend, which could raise the total Ni, Cd contents. While the contents of total Ni, Cd in Pinus tabulaeformis land in Yan'an region and in Picea asperata land in Wuchuan region had a negative derected polarization trend, and this could release the total Ni, Cd contents.