| Cadmium(Cd)is a highly biologically active heavy metal element that is highly toxic and widely distributed in terrestrial ecosystems.In recent years,various improper human activities have caused a large amount of cadmium to be released into the environment,and the cadmium pollution in farmland soil is particularly serious.Selenium(Se)is an essential micronutrient element for the normal physiological activities of organisms,and also a "natural antidote" against heavy metals.It can produce antagonistic action with heavy metal cadmium in plants,reduce the toxicity of cadmium to plants,and reduce the absorption and accumulation of cadmium by plants.As an important carrier of selenium cycling in nature,plants can be used as an important carrier for selenium cycling in nature.The selenium in the environment can be absorbed and converted into organic selenium with strong biological activity and low biological toxicity,so as to improve the daily intake level of selenium.As the main source of cadmium intake,vegetables also have the ability to enrich selenium.Since the type,concentration and application of selenium have great differences on different crops,it means that the application of selenium in agriculture needs a set of sound scientific basis as a guide.Nano selenium is a new type of nanomaterial,which has higher biological activity and lower biological toxicity than traditional selenium fertilizer.At present,there are few related studies on nano selenium to alleviate the toxicity of cadmium on crops.Therefore,this study took pak choi as the research object.Soil culture and pot experiment were used to explore the cadmium pollution levels of different degrees(0,1,2,5mg/kg).Effects of leaf application of different concentrations of bio-nano selenium(0,5,10,20,40mg/L)on growth,morphology,nutritional quality,antioxidant enzyme activity and selenium-cadmium accumulation of paki choi were investigated to explore the optimal amount of selenium application and the synergistic/antagonistic mechanism of selenium-cadmium for growth and resistance to cadmium poisoning of paki choi,in order to provide scientific theoretical basis for the safe production of crops in cadmium-contaminated soil.The main conclusions are as follows:(1)The growth and morphological characteristics of pak choi were significantly affected by the interaction of selenium and cadmium.Compared with the control treatment,different concentrations of cadmium had different effects on the growth of pak choi.Low level of cadmium(1mg/kg)stress was helpful to increase the plant height of pak choi,indicating that low concentration of cadmium could promote the growth of pak choi,while medium and high level of cadmium(2,5mg/kg)stress significantly inhibited the growth of pak choi.The root length,plant height and fresh weight of edible parts were significantly lower than that of control.In conclusion,proper concentration of bio-nano selenium can significantly alleviate the toxic effect of cadmium and promote the growth and development of pak choi,which showed that root length,plant height and fresh weight of edible part were increased to a certain extent compared with that of single cadmium treatment group.(2)The accumulation of selenium and cadmium in the shoot of pak choi was significantly affected by the interaction of selenium and cadmium.In the soil polluted by 1and 2 mg/kg cadmium,20mg/L selenium in leaves significantly reduced the content of cadmium in edible parts of pak choi by 31.59% and 29.17%,respectively,while under5mg/kg cadmium stress,the optimal selenium concentration of 10mg/L decreased by 23.82%.At the same time,selenium content of pak choi is also affected by cadmium stress level.Under 5 and 40mg/L selenium treatment,the increase of cadmium concentration will inhibit the absorption of selenium of pak choi,while under 10 and 20mg/L selenium treatment,the medium-low level cadmium stress will inhibit the absorption of selenium of pak choi,while high concentration of cadmium will promote the absorption of selenium of pak choi.(3)The selenium-cadmium interaction significantly affected the nitrate-nitrogen,the soluble sugar and the soluble protein contents of pak choi.Compared with the control treatment,with the increase of soil cadmium stress level,the nitrate nitrogen content of pak choi increased significantly by 27.83% to 112.95%,the soluble sugar content showed a trend of first decreasing and then increasing,while the soluble protein content showed a trend of first increasing,then decreasing and then increasing.Leaf application of bio-nano selenium significantly increased the soluble sugar content,decreased the nitrate nitrogen content,and improved the quality of pak choi.(4)The antioxidative capacity of pak choi was significantly affected by selenium and cadmium interaction.Compared with the control group,POD activity and MDA content of pak choi were positively correlated with cadmium stress concentration.Low level of cadmium induced increased CAT activity,while high concentration of cadmium induced severe damage and decreased CAT activity of pak choi.Leaf application of bio-nano selenium can alleviate the oxidative stress of pak choi and significantly reduce the malondialdehyde content of pak choi.Under low concentration of cadmium stress,the application of selenium can improve the activities of POD and CAT in leaves and help plants resist cadmium poisoning.Under high concentration of cadmium stress,the application of selenium can reduce the activity of POD and alleviate the respiratory outbreak of plants. |
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