Transfer Mechanism, Uptake Kinetic Process, and Bioavailability of P, Cu, Cd, Pb, and Zn in Macrophyte Rhizosphere Using Diffusive Gradients in Thin Films.

The transfer-uptake-bioavailability of phosphorus (P), Cu, Cd, Zn, and Pb in rhizosphere of Zizania latifolia (ZL) and Myriophyllum verticiilaturn (MV) cultivated in rhizoboxes in Lake Erhai (China) is evaluated by DGT (diffusive gradients in thin films) technique. DGT induced fluxes in sediments (DIFS) model reveals that resupply ability (r), liable pool size in sediment solid (kd), kinetic parameter (k-1), or response time (Tc) control the diffusion-resupply characters of P and Cu (standing for four metals) in rhizosphere interface. The linear fitting curves of element content in ZL or MV roots (Croot) against DGT (CDGT), porewater (C0), or sediment concentration demonstrate that Croot for five elements can be predicted by CDGT more effectively than the other methods. (I) DOC (dissolved organic carbon) in porewater controlled by OM (organic matter) in solid plus pH for Cu and Cd or (II) DOP/DTP ratio in porewater (between dissolved organic P and dissolved total P) for P controlled by Fe-bound P and OM in solid, can affect phytoavailability in rhizosphere. They lead to (I) the larger slope (s) and the linear regression coefficient (R2) in the first part than those for the complete fitting curve (ZL or MV root against CDGT(Cu) or C0(Cu) and MV root against CDGT(Cd)) or (II) the outliers above or below the fitting curve (ZL root (P) against C0(P) or CDGT(P)) and the larger R2 without outliers. DGT-rhizobox-DIFS should be a reliable tool to research phytoremediation mechanism of macrophytes.