Homeostatic regulation of elemental stoichiometry by Lemna gibba L. G3 when nutrient interact with toxic metals.

We investigated responses of Lemna gibba L. to exposure to UO(2)(2+) and AsO(4)(3-) under variable PO(4)(3-) concentration. Total plant phosphorus (P(tot)) in L. gibba and accumulation of dissolved organic carbon (DOC) in the media were quantified and tested for correlation with plant yield and initial concentrations of PO(4)(3-), UO(2)(2+) and AsO(4)(3-). The accumulation of DOC in medium was high under low PO(4)(3-) supply and increased loading of either UO(2)(2+) or AsO(4)(3-). The P(tot) was low in high initial concentration of UO(2)(2+) and AsO(4)(3-) as well under acute low PO(4)(3-) supply. The DOC accumulation correlated negatively to the P(tot). This reveals interaction between PO(4)(3-) and UO(2)(2+) or AsO(4)(3-) in the medium interferes with the uptake process of PO(4) (3-). Hence, the DOC accumulation is exudation of low molecular weight organic substance by L. gibba in response to the reduced P(tot): biomass ratio (carbon in the yield) due to delimited acquisition of phosphorus from the medium. It is a homeostatic regulation of the stoichiometry, which is disturbed during the interaction between PO(4)(3-) and UO(2)(2+) or AsO(4)(3-). Further investigations are necessary to relate these interactions to traditional resource stoichiometry elements of C, N, and P.