Study of the trace metal ion influence on the turnover of soil organic matter in cultivated contaminated soils

The role of metals in the behaviour of soil organic matter (SOM) is not well documented. Therefore, we investigated the influence of metals (Pb, Zn, Cu and Cd) on the dynamic of SOM in contaminated soils where maize (C-4 plant) replaced C-3 cultures. Three pseudogley brown leached soil profiles under maize with a decreasing gradient in metals concentrations were sampled. On size fractions, stable carbon isotopic ratio (delta C-13), metals, organic carbon and nitrogen concentrations were measured in function of depth. The determined sequence for the amount of C-4 organic matter in the bulk fractions: M-3 (0.9) > M-2 (0.4) > M-1 (0.3) is in agreement with a significant influence of metals on the SOM turnover. New C-4 SOM, mainly present in the labile coarser fractions and less contaminated by metals than the stabilised C-3 SOM of the clay fraction, is more easily degraded by microorganisms. (c) 2005 Elsevier Ltd. All rights reserved.