Research On The Mechanism Of Heavy Metal Cadmium Pollution On Grassland Agricultural Crops

The subject of this paper is the cross hot research field of grass science and pollution ecology.Due to the biotoxicity and non-degradation,heavy metal Cd causes very serious contamination to the environment,affects the growth and quality of agricultural crops,had seriously restricted the sustainable development and the construction of ecological environment of polluted cultivated land and grassland agriculture around mining area.Given this background,seeking the pollution mechanism of Cd and researching the effective management countermeasures of polluted cultivated land and grassland planting has become a problem demanding prompt solution.Some grassland agricultural crops have gradually evolved a variety of adaptive mechanisms to cope with heavy metal stress,but the solidification of heavy metal uptake,heavy metal detoxification mechanism based on chelation,intracellular metal ion regionalization and cell automatic regulation need further research.Based on the scientific problems above,this thesis designed the experiment in the laboratory,revealed the tolerance evaluation of M.sativa and Z.mays to heavy metal Cd and the transport mechanism of heavy metal Cd in aboveground and underground parts of plants,combined plant physiological experiments,toxicology,food safety and geographic information system to research the classified management of contaminated soil.The main findings are as follows:（1）Heavy metal Cd was seriously polluted in the study area.Under the condition of the same sampling depth in the three streams,the farther away from the streams,the lower the concentration of heavy metal Cd in the soil.Under the condition that the sampling sites are the same distance from streams,the deeper the sampling layer,the lower the concentration of heavy metal Cd in soil.（2）M.sativa and Z.mays can accumulate heavy metal Cd to a certain extent,and maize have higher transport efficiency of heavy metal Cd than alfalfa.However,the translocation factors（TF）and bioconcentration factors（BCF）in the experimental are not enough to determine them as the hyperaccumulator for heavy metal Cd.（3）Under 25 mg kg^-1cadmium treatment,in M.sativa roots,cadmium accumulation was most frequently observed in the endodermis,pericycle,phloem,and xylem,and less in the cortex region,stele region is main cadmium transport pathway.In M.sativa stems,cadmium accumulation was most frequently observed in the primary xylem and cambium,and less in the primary phloem,the primary xylem is the main cadmium transport pathway.In M.sativa leaves,cadmium accumulation was most frequently observed in the palisade tissue and xylem of main vein,and less in the mesophyll cells adjacent to the lower epidermis,the main vein is the main cadmium transport pathway.（4）Under 25 mg kg^-1cadmium treatment,in Z.mays roots,cadmium accumulation was most frequently observed in the endodermis,pericycle and xylem,and less in the cortex region,the pericycle and xylem region are the main cadmium transport pathway.In Z.mays stems,cadmium accumulation was most frequently observed in the vascular bundle,including phloem,metaxylem,protoxylem and vascular sheath,the vascular bundle is the main cadmium transport pathway.In Z.mays leaves,cadmium accumulation was most frequently observed in the Xylem,vascular sheath,and endodermis cells of vein,the vein is the main cadmium transport pathway.（5）From the first growth period to the fourth growth period,the structural differentiation of root,stem and leaf of M.sativa and Z.mays became more and more obvious,such as xylem and phloem.However,the distribution of heavy metal Cd in plants has not changed.The effect of transpiration can cause the passive transport of heavy metal Cd in plants.（6）The study area was divided into different functional areas according to the safe utilization mode of contaminated cultivated land,the unsuitable planting area of M.sativa and Z.mays in the study area was 71.63%and 71.82%respectively,and the suitable planting area was less than 30%.The current cultivation methods and utilization of cultivated soil in the study area are unreasonable,which may cause great threat to food and feed safety,and affect livestock and human health.