The single and joint toxic effects of hydrophobic organic compounds 1,4-dichlorobenzene(1,4-DCB) and heavy metal Cd on the activities of urease and dehydrogenase in the millimeter rhizosphere were investigated through rhizobox culture experiments. The interactions modes between 1,4-DCB and Cd were further analyzed and assessed based on the mathematical models. The results showed that the occurrence of 1,4-DCB inhibited dehydrogenase activities, but enhanced urease activities in the millimeter rhizosphere of soybean, compared with the control. Single stress of lower concentrations of 1,4-DCB reduced the activities of dehydrogenase and urease in the millimeter rhizosphere of wheat, while higher levels of 1,4-DCB promoted the activities of dehydrogenase and urease in the near-millimeter rhizosphere of wheat. The single stress of lower concentrations of Cd promoted the activities of dehydrogenase while the stress of higher concentrations of Cd inhibited the activities of dehydrogenase in the millimeter rhizosphere of soybean. The activities of urease in the millimeter rhizosphere of soybean increased with the increasing concentration of Cd. The single treatments of Cd inhibited the activities of dehydrogenase and urease in the millimeter rhizosphere of wheat, compared with the control. The changes of the activities of dehydrogenase and urease in the millimeter rhizosphere with distances were complicated under the pollution of 1,4-DCB and Cd. Generally, the stress of 1,4-DCB and Cd resulted in the increases of urease activities in near-rhizosphere (1 mm) of soybean and the decreases of dehydrogenase activities in root compartment and near-rhizosphere (1 and 2 mm) of wheat. The interactive modes of 1,4-DCB and Cd on enzymes activities in the millimeter rhizosphere depended on their concentration combinations, crop species, distances of millimeter rhizosphere and enzyme types.
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