Cadmium Dynamics in the Rhizosphere and Cd Uptake of Different Plant Species Evaluated by A Mechanistic Model

Abstract

Maize, sunflower, flax, and spinach differed in the accumulation of Cd when grown on a Cd contaminated soil. This was mainly due to the different Cd net influx, In , that varied among species by a factor of up to 30. The objective of this study was to find possible reasons for the different Cd In by using a mechanistic model. After 14 days of Cd uptake the model calculated only a small Cd depletion at the root surface, e.g. from 0.22 μmol L−1down to 0.19 μmol L−1for maize and from 0.48 μmol L−1down to 0.35 μmol L−1for spinach. Even so the model always overestimated the Cd In , for spinach by a factor of 1.5 and for maize by a factor of 10. Only simulating a decrease of CLi or the root absorbing power, α, by 40% to 90% gave an agreement of calculated and measured In . This may be interpreted as that about 40% in the case of spinach and 90% in the case of maize of the Cd in soil solution were not accessible for plant uptake. The high sensitivity to α also shows that not the Cd transport to the root but α was limiting the step for Cd uptake.