Effects Of Foliar Spray Of Zinc Fertilizer On Cadmium Uptake In A Pakchoi Cultivar With Low Cadmium Accumulation And Its Physiological-biochemical Mechanisms

A pot experiment was carried out to study the effects of soil application and foliar spray of Zn SO4 with different dosages on growth and concentrations of cadmium(Cd) and other trace elements of a low cadmium accumulating cultivar of B.chinensis. Results show that soil zinc(Zn) application significantly increased shoot biomass of the tested low cadmium accumulating cultivar, with a maximal increase of71.4% compared with the control. Soil and foliar Zn applications significantly decreased shoot Cd concentrations of the low cadmium accumulating cultivar, with a maximal reduction of 41.4%compared with the control. Although the difference between the Zn dosages of soil application and foliar spray were 8 to 10 folds, the reduction in shoot Cd concentration due to foliar Zn application was not significantly different from that due to soil Zn application. Soil Zn application increased the soil available Zn concentrations and had no effect on the soil available Cd concentrations. Soil and foliar Zn applications reduced significantly Cd net uptake via roots and Cd translocation factor of B.chinensis.The shoot Cd concentration was observed to significantly positively correlate with Cd net uptake via roots, and not significantly correlated with Cd translocation factor, which indicated that inhibition of Cd uptake by root resulted in decrease in shoot Cd concentration of B.chinensis under soil and foliar Zn treatments. In summary, foliar spray of Zn SO4 is suitable for safe production of the low cadmium accumulating cultivar of B.chinensis in Cd polluted soils.The resultsof experiment performed to identify the regulation effects of different kinds and concentrations of zinc(Zn) to the concentration of cadmium in low cadmium accumulating cultivar of B.chinensis showed that the application of Zn had no significant effect to the shoot biomass in the rapeseed. The spray of Zn effectively decreased the Cd content of the tested low cadmium accumulating cultivar. Compared to the control, the EDTA chelated Zn showed the best effect with a decline of 41.4%.Cd concentration of B. chinensis shoot spraying the EDTA chelated Zn and fulvic acid chelated Zn was line with national food safety standards. Correlation analysis showed that the concentrations of Cd in shoots of B. chinensis was significantly positively correlated with Cd net uptake via roots and was no significant correlation with Cd translocation factors. The concentrations of Fe in shoots of B. chinensis were above the normal range while Cu, Mn was in the nomal range. In summary, spraying EDTA chelated zinc and fulvic acid chelated zinc is better measure for low cadmium accumulating cultivar B.chinensis producted safety.The results of experiment carried out to study the physiological and biochemical mechanism of Zn foliar spraying application adjusting Cd contents of a low cadmium accumulating cultivar of B.chinensis showed that spraying EDTA chelated zinc, fulvic acid chelated zinc and Zn SO4 significantly reduced the cadmium content of shoot which EDTA chelated zinc best. Cadmium of the shoot of B.chinensis were mainly in the cytoplasm soluble fraction followed by cell walls and organelles. Spraying zinc fertilizer made the cell wall and cytoplasmic components cadmium content significantly reducing and partially processe organelle components cadmium content decreasing. EDTAchelated zinc and fulvic acid chelated zinc caused the proportion of cell wall components reduced and the proportion of cytoplasm and organelles component increasing. The mainly chemical forms of the shoot of B.chinensis were chloride extractable form followed by water extractable form, ethanol extractable form and acetic acid extractable form. Hydrochloric acid extractable form and residual form was lower.Chloride extractable form, acetic acid extractable form, hydrochloric acid extractable form cadmium concentrations of shoot were significantly reduced while ethanol extractable form cadmium concentrations significantly increasing. Various forms of distribution ratio change significantly. EDTA chelated zinc made the distribution ratio of ethanol, water extractable Cd increasing significantly and the distribution ratio of chloride extractable Cd reducing. Distribution ratio of acetic acid and hydrochloric acid extractable Cd were decreased under all treatments. In summary, spraying EDTA chelated zinc and fulvic acid chelated zinc can reduce the shoot cadmium content stably. Spraying zinc fertilizer reduced the cadmium contant of shoot significantly by reducing the cadmium contants of the cell wall, cytoplasmic, chloride extractable form, acetic acid extractable form and hydrochloric acid extractable form.