Abstract: The present paper deals with the characteristics of iron oxide transformation in rice rhizosphere and its ecological significance in two paddy soils and two red soils after growing rice (Oryza sativa L.) in rhizobox experiment.It was shown that the contents of Feo, Fed and Fee and the ratio of Feo/Fed were lower in rice rhizosphere grown in paddy soils, and the same was true for Fee content in red soils.However, the amounts of Fed and Feo and the ratio of Feo/Fed were higher in rice rhizosphere cultivated in red soils. The Mssbauer spectroscopic results indicated that Q.S. increased, while Hi decreased in rhizosphere soils as compared to nonrhizosphere soils.Meanwhile,the Fe(Ⅱ) was more in rice rhizosphere grown in paddy soils, and there existed a new iron oxide mineral,i.e.maghemite in the rhizosphere in one of red soils.These findings suggested that iron oxide in rhizosphere microecosystem were activated as the results of the rice root's physiological activity and exudation, microorganism's action on the root surface and in the rhizosphere. In addition, the results of DTA-TGrevealed that the water retention capacity was higher in rhizosphere mieroecosYstem because of much more amorphous iron oxides and organic matter etc. in it. Rhizosphere effect of iron oxide transformation would affect: 1) adsorption and desorption of heavy metals and other pollutants; 2) bioavailability of soil iron oxides: 3) absorption of other nutrients such as Pand Mn by crops: 4) matter flow and the effective use of water and nutrients in the rhizosphere microecosystem; and finally the ciop growth and quality of agricultural products.

Key words: Differential thermal analysis, Iron oxide transformation, M?ssbauer spectroscopy, Rhizosphere effect, Rhizosphere microecosystem