The Characteristics Of "Fertile Island" And Ecology Significance Of Populus Euphraticu In Xingjiang

The desertification does bad harm to environment, resource, the social economical development, the mass's living and subsistence, and it becomes an important factor of restricting the sustainable development in the large desertification area of China. Under the arid wilderness severe habitat, the Populus euphraticu is capable of living thousands of years, showing the arbor's powerful life-force and so it inevitably forms"fertile island".Using Geostatistics, this paper studied on characteristic of"fertile island"about the Populus euphraticu in Xinjiang. The results indicated that:Between the inner and outer canopy , the equal content of Populus euphraticu in the different growth stages shows different increasing rate among the soil characteristics: the contents of Ca and Mg show minus increasing rate, and the rates of large Populus euphraticu are respectively -57.69%,-51.06%, the middles are -45.07%,-32.94%,and the smalls are -34.39%,-58.12%; and the increasing rates of other soil characteristics( soil total salt, SO42-, Cl-, K++Na+, pH, soil total alkalinity, soil nutrient) are positive value. The rate's range of large Populus euphraticu is 13.51%～253.91%, among it, the maximum of soil total alkalinity is 253.91%, the minimum of pH is 13.51%; the range of middles is 5.36%～171.04%, and the maximum of soil total alkalinity is171.04%, the minimum of organic matter is 5.36%;the range of smalls is 1.47%～219.00%, and the maximum of available potassium is 253.91%, the minimum of soil total salt is 1.47%.Using the Duncan, the enrichment intensity of the soil characteristics of Populus euphraticu in the different growth stages is multi-compared, and the results indicate that: expect of soil total alkalinity, K++Na+ and available phosphorous, the other soil characteristics are remarkable difference. Besides, seeing the equal value of enrichment intensity, the enrichment ratio of soil total salt and SO42- presented that the large Populus euphraticu >the middle Populus euphraticu > the small Populus euphraticu, the enrichment ratio of Cl-, organic matter and soil total alkalinity presented that the large Populus euphraticu >the small Populus euphraticu > the middle Populus euphraticu, the enrichment ratio of available potassium presented that the small Populus euphraticu >the large Populus euphraticu > the middle Populus euphraticu. All of these show that the effect of"fertile island"of Populus euphraticu is related to the growth condition and ages of Populus euphraticu under the canopy.Using the semivariogram functions, the best estimate was made. The theoretic model of variation functions were Spherical model, Index model and Gaussian model. The C0 of available potassium was 1.1×106 , and C0 of other soil characteristics were less, which range was 0.002～125.00. The range of C0/(C+C0) of Ca, SO42-, soil total alkalinity, available nitrogen and available potassium was 25%～75%, which said the medium space relativity. And C0/(C+C0) of other soil characteristics were less than 25%, which said strong spacial relativity. The enrichment ranges of Ca2+, Mg2+, SO42-, K++Na+ and pH were 1.7~3.6m, which were inner the canopy of Populus euphraticu, and other's enrichment ranges were 6.1~11.1m, which were more than the radius of canopy of Populus euphraticu.At the research area, analyzing soil characteristics of section plane of Populus euphraticu, the results indicated: the distributing types of Ca2+, Mg2+, soil total alkalinity and available nitrogen were normal distributing after logarithm transform, but other soil characteristics needn't logarithm transform. Using the semivariogram functions, the best estimate was made. The theoretic model of variation functions were Spherical model, Index model,Linear model,and Gaussian model. The C0 of available potassium was 800, and the C0 of other soil characteristics were less, which range was 0.007～11.04. The C0 of Ca was min (0.007). The range of C0/(C+C0) was 16.5%～93.1%, among which, C0/(C+C0) of available potassium was 16.5%, C0/(C+C0) of SO42- was 93.1%, and the range of C0/(C+C0) of other soil characteristics was 25%～75%, which said soil characteristics had the medium space relativity. In the different soil depth, soil characteristics showed different diversity between the inner and outer canopy, and following the increasing of soil depth, the effect of"fertile island"had descending tide until to disappeared. From the Kriging interpolation map, we can see that the content distributing of soil characteristics formed an inverse taper in the soil section plane.