60-year,35-year,28-year and 6-year old Amorpha fruticosa growing on southern Mu Us Sandy Land were sampled using the total strain mining method.Aboveground morphological characteristics,soil moisture, root biomass,specific root length,root fraction,root volume,root surface area and root length density were studied to reveal the ecological adaptability of A.fruticosain a sandy habitat.Results indicated that with increasing soil depth,the root biomass,root volume and root surface area of A.fruticosaof all ages declined exponentially in the formY=ae-bx.Root extinction coefficient analysis showed that roots were concentrated close to the soil surface.Parameters of root distribution showed different degrees of correlation:Soil moisture was significantly correlated with above ground biomass,root biomass,and specific root length.Soil moisture was also positively related to root surface area.The root distribution parameters,moisture control factor and framework factor,were confirmed by principal component analysis.With increasing years,A.fruticosa did not show an aging phenomenon since its roots had the ability to self-thin and update constantly,adapting to the changes in the environment.

Sample spots were chosen from the southern edge of Mu Us Desert which locates in Jingbian county Yulin city,Shaanxi province.60-year-old,35-year-old,28-year-old and 6-year-old Amorpha fruticosa were selected to study the total nitrogen,ammonium nitrogen,nitrate nitrogen,organic carbon and change of pH in rhizosphere and bulk soil.Foundations of planting A.fruticosa in desert areas were established in this study.The results indicated that total nitrogen,ammonium nitrogen(except 28-year-old A.fruticosa),nitrate nitrogen and organic carbon cantents in rhizosphere soil were all higher than that in bulk soil,and organic carbon content in rhziosphere was significantly higher than that in bulk soil.Total nitrogen,ammonium nitrogen and nitrate nitrogen cantents of 35-year-old A.fruticosa in rhizosphere were 43.8%,30.3% and 230%,respectively,which were higher than that in bulk soil.Both in rhizosphere and bulk soil,organic carbon content increased while pH had an opposite trend with the age increasing.Correlation analysis indicated that total nitrogen in rhizosphere had a significant relationship with organic carbon,ammonium nitrogen and nitrate nitrogen contents,but no relationship was found in bulk soil.In a word,the nutrition of rhizosphere was higher than that in bulk soil,so soil nutrition can be improved effectively by planting A.fruticosa.

Taking Amorpha fruticosa with different cultivation ages in Southern Mu Us desert as objectives,a study was made on the physical composition and nutrient content of soil under A.fruticosa,and correlation between soil nutrients and dust particles were analyzed.The results showed that refined degree of soil under A.fruticosa increased gradually with the increasing of A.fruticosa cultivation ages.For example,the refined degree of surface soil(0-10 cm) was 1951>1976>1983>2005,and dust particles content of A.fruticosa planted in 1951 was 4.3%.pH values of vertical soil profile in A.fruticosa decreased from bottom,and pH value of surface soil(0-10 cm) was the lowest.pH values of the same soil layer reduced with the increasing of cultivation ages.All nutrients content(except of total K and NH4+-N) of soil(0-20 cm) increased in varying degrees.The content of organic carbon,total N,NO3——N,total P and rapid available P increased with the increasing of cultivation ages,while there was no apparent regularity in content of NH4+-N and total K.

Three native shrubs inhabiting in Maqu county, including Salix oritrepha, Amorpha fruticosa and Hippophae rhamnoides, were used as materials to investigate the differences of total P content, available P content and P fractions between rhizosphere and non-rhizosphere soils. It was found that there was a higher available P concentration in the rhizosphere soil comparing to that in the non-rhizosphere soils of A. fruticosa and S. oritrepha. The total P content in the rhizosphere soil was higher than that in the non rhizosphere soil of the three shrubs. The concentrations of total P and H20-P were lower in the non rhizo- sphere soil than that in the rhizosphere soil except H. rhamnoides. The contents of NaOH-Pi and NaOH- Po were higher in the rhizosphere soil than that in the non-rhizosphere soil of the three shrubs. The con- centration of HHCl Pi in the rhizosphere soil was lower than that in the non-rhizosphere soil except A. fruticosa. The concentration of HHCl-Po in the rhizosphere soil was higher than that in non-rhizosphere soil except S. oritrepha. Regression analysis indicated that there was a negative significant relationship be- tween available P concentration and pH in both soils of S. oritrepha and A. fruticosa, but no relationship was found between total P and available P concent in both of the rhizosphere and non-rhizosphere soils.

In the Maqu alpine sandy grassland,three cultivated shrubs were selected to study the various forms of nitrogen,the contents of organic carbon and pH changes in both rhizosphere and bulk soil.The results showed that organic carbon in the rhizosphere was higher by 71.5% than that of bulk soil.Total nitrogen in the rhizosphere was lower by 11.0%.The content of ammonium were higher than that of nitrogen in three shrubs soil.The rhizosphere soil showed more obvious enrichment effect on organic carbon.The differences of organic carbon,total nitrogen and ammonium between the rhizosphere and bulk soil showed significant linear relationships(P0.05).There was no correlation in soil organic carbon and nitrogen between the rhizosphere and bulk soil.