Effect of different nitrogenous nutrients on the cadmium hyperaccumulation efficiency of Rorippa globosa (Turcz.) Thell.

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Abstract
This experiment was used to explore whether the 11 nitrogenous nutrients affect the hyperaccumulation of Rorippa globosa (Turcz.) Thell. to Cd. Pot culture experiments using soil spiked with Cd as CdCl2·2.5H2O and 11 nitrogen-containing chemicals were conducted to determine the efficiency of the accumulation of Cd by R. globosa. Application of all 11 nitrogenous nutrients significantly (p < 0.05) enhanced Cd accumulation by R. globosa (Turcz.) Thell. Two major modes of Cd accumulation were observed: (i) through increase of biomass yield without reduction of Cd uptake and (ii) through increase of Cd uptake efficiency in parallel with increase of biomass yield. Bicarbonate > phosphate > chloride compounds of NH4 enhanced the biomass yield to the greatest extent, while oxalate > nitrate > chloride > and bicarbonate caused a significant increase of Cd uptake by R. globosa. Competition between N and Cd translocation caused either significant reduction of Cd translocation factor or decrease of biomass yield. Of studied nutrients, ammonium bicarbonate NH4HCO3 and ammonium chloride NH4Cl exerted the best joint effect of these two processes on the efficiency of R. globosa as a Cd hyperaccumulator. Application of these chemicals caused increase of Cd concentrations in roots of R. globosa by 35.1 and 41.1 %, and in shoots by 13.9 and 56.4 %, while biomasses of roots increased by 5.8- and 3.8-fold and in shoots by 7.4-fold, and 6.4-fold, respectively, compared to the control. As a result, accumulated load (μg pot−1) of Cd in roots increased by 8.2- and 5.8-fold and in shoots by 8.6- and 10.6-fold in both pots. Consequently, chemicals (NH4HCO3 and NH4Cl) that enhanced both Cd enrichment and biomass yield had the greatest effect on the bioaccumulation capacity of R. globosa.

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