Effects Of Different Active Red Soil Particles On Adsorption, Desorption Acvitities Of Acid Phosphatase

The red soil which was collected from Xianning, Hubei Province was divided into four kinds of clay fractions: <0.2μm de-organic clay fraction (IRS), <0.2μm organic clay fraction (ORS), 0.2-2μm de-organic clay fraction (IRL) and 0.2-2μm organic clay fraction (ORL). Effects of organic matter and particle size of the soil colloids on adsorption, desorption, activities, thermal stability and pH stability of acid phosphatase were studied. The influences of goethite and kaolinite on the adsorption characteristics of acid phosphatase were also investigated. These studies have important significances in scientific field and practice for probe into interaction mechanism of the relate compositions in the adsorption of enzymes and for clarification the factors affecting soil enzyme activity, as well as for improving soil fertility and environmental quality. The main results were outlined as following:1, The content of organic matter for tested soil colloids ranged from 0.71 to 3.22 g kg"1, among which the ORS colloid was the greatest and the IRL colloid was the lest. The specific surface area (SSA) was from 140.4 to 201.1 m² g^-1 for the four clay fractions, and the SSA of goethite and kaolinite was 153.8m² g(-1) and 35.7m² g^-1 respectively. The concentration of the free iron for the four tested soil colloids was increased from 55.3 to 81.7 g kg"1 with the decrease of the particle size.2,The adsorption isotherm of acid phosphatase on the examined soil colloids and minerals fitted to the Langmuir equation well (r>0.96). The maximum adsorption of acid phosphatase adsorbed by the four tested soil colloids was follow the sequence goethite > ORS colloid > IRS colloid > ORL colloid > IRL colloid > kaolinite. There were correlations between the amount of enzyme adsorbed and the content of organic matter and free iron of the soil colloids. The difference capabilities of the soil colloids to adsorb enzyme might be mainly attributed to the discrepancy in the Langmuir parameter K for the adsorption of enzyme by the soil colloids which were affected by the specific surfacearea and the concentration of organic matter and free iron of the examined soil colloids.3? Large discrepancies were observed between the percentage of acid phosphatase desorbed with pH5.5, 0.1 mol L^-1 acetate buffer, phosphate buffer and pH5.5, 2 mol L^-1 NaCl solution from the soil colloid-enzyme composites. And the percentage of the enzyme desorbed was in the order of phosphate buffer > phosphate buffer > NaCl solution. As to the same desorption agent, the desorption ratio of the soil colloid-enzyme composites was affected by the content of organic matter and the particle size of the clay fractions, and follow the sequence ORL colloid > IRL colloid > ORS colloid >IRS colloid. The result of the test proved that the acid phosphatase molecues were immobilized on the surface of the soil colloids via ligand exchange and ion exchange.4? The specific activities of acid phosphatase immobilized on different soil colloids system ranged from 39.1% to 72.2%, and the residual activities of soil colloids-enzyme complex was in the order of ORL colloid < IRL colloid < ORS colloid < IRS colloid. The inhibitory capabilities of the 0.2-2祄 clay fractions was stronger than the <0.2祄 clay fractions. And with the same particle size, the higher concentration of organic matter of the soil colloids had the lower specific activities. The discrepancies between the residual activities of the soil colloids-enzyme composites might be owing to the inhibition of the organic matter and the Fe oxyhydroxides in the soil colloids to the acid phosphatase.5?Within the tested pH range (pH4.0-7.0), the optimal pH of the acid phosphatase adsorbed by the four examined soil colloids was the same as that of free acid phosphatase (pH5.5). The changing trend of the pH-activity curve of the soil colloid-enzyme complex and free enzyme were similar. By reason of the influence of the organic matter and Fe oxyhydroxides in the soil colloids on the pH value of the microenvironment of the soil colloid...