Influences Of Combined Pollution Of Cadmium And Acetochlor On Physiological Property Of Maize Seedlings

Cadmium, as one of the bigger toxicity heavy metals, can be absorbed by the plants from the soil and it will affect the growth of plants and accumulate in their bodies, furthermore endanger human health through the food chain. Acetochlor is one of the biggest productions of herbicide in China, it is widely used in many kinds of plants for killing weeds such as soybean, corn, peanut, and cotton. In this thesis, with corn as an experimental subject, we study the effects of cadmium, the association of cadmium and acetochlor on the physiological characteristics of maize seedlings by the germination and the pot experiment. The main conclusions and results are presented in the following:1. The inhibitions to the germination of seeds are obvious by the single pollution of cadmium and the combined pollution of cadmium and acetochlor. For the first case of single pollution of cadmium, with the increase of concentration of cadmium, the germinating potentiality, germinating rate, sprout index and vigor index of seeds all presented a declined tendency. For the second case of combined pollution, it exhibits similar tendency with the former ones, but the inhibition effect is stronger than cadmium alone, and the degree of inhibition is proportional to the concentration of pollutions.2. The inhibition effects of cadmium and acetochlor on the growth of roots and bugs are obvious, and the roots and bugs have different sensitivities to the pollutions. Under the stress of single pollution of cadmium, by the low concentration of cadmium of 5～10 mg/L, the length of bugs has no significant difference with the control group; but the length of roots is greatly shorter than those of controls. Under the condition of combined pollution of cadmium and acetochlor, the inhibition becomes stronger. When the concentration of acethchlor in treatment is 50 mg/L, the length of bugs is less than 2 cm by the concentration of cadmium≥30 mg/L, and the length of roots is less than 2 cm by the concentration of cadmium≥5 mg/L, when the concentration of acethchlor in treatment is 100 mg/L, the length of bugs and roots is less than 2 cm by the lower concentration of cadmium, but it was less than 1 cm by the higher concentration of cadmium.3. The effects of cadmium and combined pollution with acetochlor on the growth of maize seedlings. The results of experiment show that, under the single pollution of cadmium, the height (the concentration of cadmium is 5～10 mg/kg) and biomass (the concentration of cadmium is 5 mg/kg) have no significant difference with the control group by low concentration of cadmium, but with the increase of concentration of cadmium, the plant height and biomass decrease apparently. Under the condition of combined pollution of cadmium and acetochlor, the height and biomass are greatly lower than those of control group by the low concentration of pollution, and the declining trends become more obvious with the increase of concentration of combined pollution.4. The contents of chlorophyll of maize seedlings decrease under the stress of cadmium and combined pollution with acetochlor. By the cadmium alone, the contents of chlorophyll a, b, a+b decrease with the increasing concentration of cadmium, and the phenomenon is evident than those of control group, while the value of chlorophyll a/b first increases and then decreases. Under the stress of combined pollution of cadmium and acetochlor, the changes of chlorophyll are similar with the treatment of cadmium alone, but the influence is more seriously and the degree is positively related to the concentration of cadmium and acetochlor.5. The effects of cadmium and acetochlor on the MDA content and relative electric conductivity of seedlings. By the treatment of cadmium alone, the MDA content has no obvious change in low concentration of cadmium, but when the concentration of cadmium >30 mg/kg, the MDA content increase drastically. Under the stress of combined pollution, the MDA content is greatly higher than those of controls in low cadmium concentration, and increase as the concentration of pollution increased. The relative electric conductivity demonstrates similar manners with the MDA but the amplitude of change is smaller than the MDA.6. The changes of antioxidant enzyme (SOD, CAT and POD) activities are different on cadmium and acetochlor stress. Under the stress of cadmium only, the activities of SOD, CAT reach the peak value when the concentration is 30 mg/kg, and then they decrease with the increasing of cadmium concentration, but the activity of POD increases and reaches the peak value at cadmium concentration of 100 mg/kg. Under the combined treatment of cadmium and acetochlor, the activities of SOD, CAT first increase and then decrease with the increasing concentration of cadmium, and the trends are more obvious when the concentration of acetochlor increasing, but the activity of POD is still increasing as the cadmium and acetochlor concentration increased. In this process, POD is greatly activated, and may be play a key role in these three antioxidant enzymes.In conclusion, both single pollution of cadmium and the combined pollution of cadmium and acetochlor are toxic to maize bugs and seedlings, and the toxic effect of combined pollution is more serious than single cadmium pollution. Therefore we can deduce that the toxicity of associated pollution of cadmium and acetochlor shows to be synergistic effect.