Dynamic Changes in Enzyme Activity in Fluvo-aquic Soil under Application of Lanthanum

Dynamic changes in enzyme activity in fluvo-aq uic soil under application of lanthanum (La) was studied through simulation expe riments.The activities of soil dehydrogenase,alkaline phosphatase, urease and su crase decreased with the time of incubation.La inhibited strongly the activity o f soil dehydrogenase,and to a significant level (P<0.05) with a maximum inh ibition ratio reaching up to 39% when its concentration was over 30 mg/kg.La als o showed an inhibitory effect on the activity of soil alkaline phosphatase and a maximum inhibition ratio of 15%.But its effect on soil urease was not as signif icant.It stimulated the activity of soil sucrase to a varying degree,with the ma ximum stimulation ratio being 15%.Consequently,the soil activity of dehydrogenas e can be taken as a sensitive index for assessing environmental effect of rare e arth elements.