Effect Of Rice Rhizosphere Soil Heavy Metal Sapeciation And Activity Of The Enzyme

The mineral resource is very rich in Dabaoshan mine area Shaoguan City, Guangdong Province. However, the surrounding environment has been seriously polluted because of years of exploitation. The effects of root system of rice on the fractionation of cadmium, copper, lead and zinc were investigated using multiple lattice layer rhizobox system during the middle to later breeding stage of rice (tillering stage, booting stage, flowering stage and milk ripe stage). The soil samples were taken from the multimetal-contaminated paddy soils due to the irrigation of acid mine drainage houghout more than40years. And BCR sequential extraction procedure methods were used to evaluate the forms and mobilization of heavy metals in the rhizospheric soil. Use the fitting equation on studied the relationship between rice soil heavy metal pollution and soil catalase and acid phosphatase activities.studies by the following conclusions:(1) The results showed that copper, lead and zinc were dominated mainly by the forms of lower bioavailability and their mobility was not observed obviously from non-rhizospheric soil to the rhizospheric soil. Howerver, it was shown that there was a significant change in the forms of cadmium. The acetic acid extractable Cd in the root compartment (SO) was3times more than the other compartments.(2) The results also show that Cd content in different soil layer first increased and then decreased but it soon increased again with the extension of growth, the changes of Cu, Pb, Zn are not significantly.Furthermore, our results showed that the Cd concentration in SO compartment decreased significantly with the procedure of the rice growth which illustrated that Cd uptake in rice was still ongoing while the rapid accumulation of copper, lead and zinc was not observed obviously in the middle to later breeding stage.(3) In different periods of the rhizospere of rice growth,root,stem and leaf absorption of heavy metal content is different.The content ofCd, Zn,Cu,Pb in the different parts of the rice is:root>stalk>seed;The main parts absorbing Pb is root.(4) In different fertility of rice growth, except at tillering stage the catalase activity was low, the other three periods had not significantly change. The catalase activity of layer SO was about45%higher than that of layer S1in different soil layer, The catalase activity was going slowly up form the layer S1to S5, the adjacent two layers rised less than10%.(5) The changes of the acidic phosphatase activity was to reduce and rice again then after the first in the four fertility of rice growth. In different soil layer, the acidic phosphatase activity was lowest in the layer SO and then rised, the acidic phosphatase activity reduced form the layer S1to S3and then riced.(6) The acetic acid extractable Zn, Cu, Pb, Cd to the catalase activity had positive correlation, which played promoting and activating function and to the acidic phosphatase activity had negative correlation, which played inhibiting effect.(7) The reducible Pb to the catalase activity had positive correlation and the reducible Cd to that had negative correlation, and these two kinds of reducible metal to the acidic phosphatase activity had the opposite relationship. The reducible Zn and Cu to the two enzyme had different relationship in different fertility of rice growth. The oxidate Zn to the catalase activity had positive correlation.(8) The oxidate Pb to that had negative correlation, the oxidate Cu and Cd to the two enzyme had different relationship in different fertility of rice growth.The acidic phosphatase activity to the oxidate Zn and Cu had the negative correlation and to the oxidate Pb had positive correlation.(9) The residual Zn, Pb, Cd to the catalase activity had negative correlation, which played inhibiting function, and the residual Cu to the catalase activity had positive correlation, which played positive function. The residual Zn and Pb to the acidic phosphatase activity had positive correlation, which played positive function, and the residual Cu to the acidic phosphatase activity had negative correlation, which played inhibiting function. The residual Cd to the acidic phosphatase activity had different relationship in different fertility of rice growth.The experiment reveals the diversity of migration behavior of the four heavy metals Cd, Cu, Pb and Zinc in rhizosphere soil in the middle and late stage of the rice growth as well as the variation characteristics of scavenger enzymes and acid phosphatase. According to studying the relations between heavy metals and enzyme activity in the soil, the outcome shows that the virulence of acid extractable state is strongest and the influence on enzyme activity is largest. Based on what we mentioned above, we draw a conclusion that the influence on enzyme activity from heavy metals in soil is not only related to its varieties, but also to its forms.