Relation Between Cadimium And Rhizosphere Enzyme Activities And Passivation Of Water-soluble Organic Carbon On Cadimium

The heavy metal contamination to the soil which induces the threat to the health of human beings is paid much attention to in recent years. The key to solve this problem is the assessment and management of soil environment. We adopted the root-box simulated test and soil incubation-leaching test using rape and rice as research objects. The relation between total and available Cd and urease,alkaline phosphatase,catalase activities in rhizosphere and nonrhizosphere soil of different textures was studied. We also discussed the influence of water-soluble organic carbon (hereafter referred to as WSOC) on the distribution and form of Cd in soil. The result shows :In supported density range of Cd, with the increase of density of Cd, three kinds of enzyme activities demonstrated the trend of fading after strengthening. That is to say,when the density was low, Cd promoted enzyme activities while reduced them when the density was high. According to analysis result of dependence, the relation between Cd and rhizosphere and nonrhizosphere soil urease and alkaline phosphatase activities in different alluvisol textures reached the remarkable negative correlation level, but that between Cd and catalase activity didn't. In light-textured soil the dependence was better than that in the heavy-textured soil; In rhizosphere soil it was better than that innonrhizosphere soil. The correlation of available Cd and soil enzyme activities of different treatments was better than total Cd and enzyme.activities, and reached the extremely remarkable relevant level. The results established the foundation for the feasibility of combining urease,alkaline phosphatase activities in rhizosphere soil and available Cd together as the evaluation indexto appraise Cd contamination in soil.As to rice that grew under Cd coerce , WSOC promoted its growth, the effect of increasing the production of rice of Water-soluble products of pig manure was more obvious than that of the citric acid ; The citric acid promoted the absorption of Cd of rice while the water-soluble products of pig manure suppressed the absorption of heavy metal Cd of rice. Cd mostly concentrated in 0-10 cm soil layer. In the light-textured soil, the amount of Cd of soil layer under the 10cm with WSOC treatments was less than that with contrast water treatment ; In the heavy-textured soil, the majority of Cd was hold in the top layer of soil, but the amount of Cd under 10cm soil layer dealt with WSOC was relatively more than that with contrast water treatment; WSOC was playing an important role in Cd transforming in the soil. The percentage of available Cd in the soil dealt with citric acid was higher than that dealt with contrast water treatment, and that in the soil dealt with water-soluble products of pig manure was the lowest; In heavy-textured soil the percentage of available Cd was higher than that in the light-textured soil; In addition, the percentage of available Cd in the soil planting rice was higher than the soil not planting rice . These results as above will offer the theoretical and practical basis for reasonably selecting organic matter to protect and manage the heavy metal contamination in soil.