Effects Of Cadmium On Carbon And Nitrogen Metabolism In Maize And Study Of The Effect Of Soil Amendments

Cadmium (Cd) is a toxic environmental contaminant that has been classified as ahuman carcinogen, and the area of contaminated farmland continuously expands. Famousscientists from all over the word have payed their attention on the remediation of heavymetal contaminated land. This study aims at studying the effects of Cd fortified in the soil onmaize carbon and nitrogen metabolism at different stages. A pot experiment with five Cdconcentrations (0,1,4,8and16mg kg-1) in soil was conducted. The major results can beconcluded as follows:(1) High Cd doses treatment (8and16mg kg-1) significantly decreased theconcentrations of chlorophyll in leaves and nitrogen in stems, and increased the solublesugar content in leaves and stems at the stages before flowing stage, that is to say, the carbonmetabolism was inhibited by the application of cadmium. Furthermore, the effects wereenhanced with the increase of Cd dose and exposure time.(2) High Cd dose (8and16mg kg-1) treatment could inhibit, or even reverse thetransfer of soluble sugar and nitrogen from stems to seeds, which probably resulted in thedecrease of yield and starch accumulation in the seeds. Results of this experiment could bevalidated by the observe of the decrease of the key enzyme activity related this.(3) The threshold value research suggested that maize is capable of absorbing Cd easilyfrom the soil. When the Cd concentration was1mg kg-1, the seeds cannot be used as food;when the Cd concentration in soil was higher than8mg kg-1, the straws cannot be used asthe feed.After getting the information on the effect of cadmium on carbon and nitrogenmetabolism, further study of remediation of heavy metal contaminated soil was carried out.In order to select the suitable amendments for the remediation of heavy metal polluted soilin northern part of China, a pot experiment was conducted in2011-2012. The effects ofKH2PO4, Na2SiO3, manure, turf and their combination application on cadmium uptake bywheat and maize in different degrees of polluting situations (1mg kg-1,30mg kg-1) weretested by a pot experiment. The main results were as follows:(4)The application of different amendments could significantly increase the yield ofwheat and maize, and remarkably decreased cadmium content both in crop seeds and soilwhich is available to plant. High dose treatment of KH2PO4+manure worked the best amongall these amendments treatment, yield increased in wheat and maize was149%and109%,respectively, Soil available cadmium concentration and cadmium concentration in wheat andmaize seeds was decreased by62.63%,60.92%and75.00%、74.09%, respectively.(5)The combination application of KH2PO4and manure could significantly cause adecrease in soil pH, especially in the severely polluted situation. This can be attributed to thedissociation of H2PO4-and the combination of Cd2+and PO43-, lead to the chemicalequilibrium move to the right side, and thus cause a mobility increase of PO43-, this is helpful to the improve the effect of amendment.(6)In most of the amendments treated treatments, cadmium concentration in maize seedsin the light contaminated soil (1mg kg-1) were lower than that allowed in national hygienicstandard for food. While, when it comes to the heavily contaminated soil (30mg kg-1), all ofthe cadmium concentration in maize seeds exceeded that allowed in the national hygienicstandard for food, though showed a significant decrease when compared with the control. Inpractical, we should consider both the degrees of contamination and the crop cultivaries toget better effeck of controlling the cadmium content in food and soil. What’s more, resultswe got from this experiment could be a reference to the practice of remediation of heavymetal contaminated soil in northern part of China.