A Study On The Characteristics Of Inorganic Phosphorus Fractions In The Rhizosphere Of Super-xerophytic Shrubs

The concentrations of total phosphorus (P) in soil are always not too low, however, the low availability of P makes it as the main restrict resource to plant. Although the P concentrations in the soils of the Alashan Desert was extremely low, some xerophytic grew well, what indicated that P ultilizing effeictive of those xerophytic was great. We investigated the concentations of total P, available P, inorganic P fractions in bulk soil and rhizosphere and the relationships between available P and all fractions, and between PO4 and other soluble ions. The results showed that:(1) there were consistently higher total phosphorus and available phosphorus concentrations in rhizosphere than non-rhizosphere soils of Zygophyllum xanthoxylum,Ceratoides holmgern,Atraphaxis bracteate,Tetraena Mongolica, whereas Reaumuria Soongorica showed a higher total phosphorus concentration in rhizosper than non-rhizospere soils but a lower available phosphorus concentration in rhizophere than non-rhizosphere soils. Regression analyses indicated that there was a significant correlation between the total phosphorus and available phosphorus concentrations in non-rhizosphere soil but no significant relationship was found between the total phosphorus and available phosphorus concentrations in rhizosphere soils.(2) The primary fraction in the soils of the Alashan desert was Ca-P, especially the Ca10-P, which dominate more than half of all fractions. Nevertheless, the concentrations of Ca2-P that was available for plant were low. The availibility of those fractions were vary between each other. The most available fraction was Ca2-P, after which were Al-P, Fe-P and Ca8-P. The availibility of O-P and Ca1-P were lowwest but the concentration of which in the rhizosphere of Tetraena Mongolica were lowwer than that in bulk soil.(3) In the bulk soil, there was a significant relationship between available P and O-P as well as Ca-P, and between PO₄^3-and Ca²⁺, NO₃^- and SO₄^2-. However, there was a significant relationship between available P and O-P, Al-P and Fe-P in rhizosphere. Furthermore, the available P and Ca²⁺ had non-significant relation but avaialbe P also had significant positive relationship with NO₃^- and SO₄^2- and PO₄^3- had negetive relationships with Na⁺, K⁺ and Cl^-.(4) The soil pH were decrease in rhizosphere of all four shrubs. The results of Geochem simulation showed that the effect of soil pH on P availibility was efficient in the rhizosphere of Z. xanthoxylum,,A. bracteate and T. mongolica, but the effect was low in the rhizosphere of C. holmgern.All the results indicated that the availibility of P in rhizosphere was significantly changed and the effect of rhizosphere for P was distinct. All inorganic fractions were available for xerophytic, including Ca10-P and O-P, which were commonly treatred as extremely low available fractions. At the same time, the results showed that the supply of P in rhizosphere strongly affected other ions and soil pH changes were primarily contributed to rhizosphere effect.