[Spectral Evidence of In-Situ Regulatory Mechanisms on Chemical Speciation of Lead/Cadmium Affected by Dissolved Organic Matter Extracted from Rhizosphere Loess of Calendula Officinalis Seedling].

The various characteristics of DOM have great impact on the transformation process of contaminants in soil due to the generation of the feedback regulation in cycles of plant, Rhizosphere soil and environmental contaminants. Currently, more attention was paid on contaminants behaviors of adsorption, transformation, accumulation and detoxification than DOM derived from Rhizosphere soil. The chemical speciation of lead/cadmium and growth efficiency related variations were revealed in the growth process of Calendula officinalis seedlings, and the spectral characteristics of DOM in Rhizosphere loess were discussed with UV, FT-IR and 3D-EEMs spectra. The results showed: the dominant contents of lead/cadmium are in residual and exchangeable speciation, and the exchangeable contents increase greatly after the growth of Calendula officinalis seedlings. It causes negative effects on the height and emergency rate of Calendula officinalis seedlings with lead/cadmium, and the Calendula officinalis is able to positively improve loess characteristics. The root of Calendula officinalis appears to be longer, thinner and flexuous. The maximum absorption band of DOM in UV spectra locates in 200~240 nm, and the sharper and greater intensity of peaks can be detected under lead/cadmium stress. The absorption peaks in FT-IR spectra move from 3 444 and 1 637 to 3 440 and 1 645 cm-1, respectively, indicating the combination effects between metal ions and functional groups of—OH and CO. The dominant fluorescence peaks of DOM are found to be aroundλex/em=240/430, described as fulvic-acid like components, and metals in loess affect more on peaks intensity than locations. The characteristics of DOM in Rhizosphere loess of Calendula officinalis seedlings contain much micro-eco-environmental information, and the spectral approaches are efficient to reveal the relationship between DOM and chemical speciation of lead/cadmium.