Effects Of Humic Acid On Havy Metal Forms And Antioxidant Enzymes Activities In Soil Contaminated By Lead And Cadmium

This subject to rape as the research object,through the different content of humic acid(humic acid,HA)on heavy metals lead(Lead,Pb)and cadmium(Cadmium,Cd)contaminated soil changes,and humic acid on the antioxidase activity of rape and its quality,the resistance of lead and cadmium pollution,discusses the effect of humic acid on lead and cadmium combined pollution remediation,and provide a theoretical basis for the study of soil heavy metal pollution control.The main findings are:1.The effect of humic acid on lead and cadmium form in lead and cadmium contaminated soilCompared with the blank group(CK: Pb 0 + Cd 0 + HA 0),the application of lead and cadmium significantly increased the exchangeable state,carbonate state,iron and manganese,organic and residual Pb and Cd in the soil.With the addition of HA 20,30,40,50 g · kg-1,the exchangeable state,cadmium and lead in the soil decreased gradually and significantly lower than that in the control group(T1: Pb 500 + Cd 60+ HA 0)decreased by 54.6%,43.0% and 38.7%,respectively.when the addition amount of HA was 50 g · kg-1,while the contents of Fe and Mn in the soil were increased and significantly increased 103.8%,73.8%,67.5%,84.2% and 240.5%,respectively,when the amount of HA was 50 g · kg-1.Therefore,the addition of HA to lead and cadmium contaminated soil can effectively reduce the mobility of heavy metals,thus reducing the biotoxicity of lead and cadmium in soil.When the amount of HA was 50 g · kg-1(T5: Pb 500 + Cd 60 + HA 50),the effect was the best.Compared with the blank group,the application of lead and cadmium significantly increased the soil available lead and cadmium.With the addition of HA 20,30,40,50 g · kg-1,the content of available lead and cadmium decreased gradually and significantly lower than that of the control group.When the humic acid was 50 g · kg-1 Respectively,decreased by 24.4% and 44.7%,indicating that the addition of humic acid significantly reduced the effectiveness of lead and cadmium in soil.2.Humic acid increases the biomass of rape in lead and cadmium contaminated soilLead and cadmium pollution reduced the aboveground and underground biomass of rapeseed,indicating that lead and cadmium pollution could significantly reduce the yield of rape.After adding 20,30,40,50 g · kg-1 humic acid,the biomass of rape increased significantly.Compared with the control group,the aboveground and underground increased by 33.2%,42.8%,51.2% and 59.6%,respectively,and 35.5%,46.1%,56.6% and 65.8% respectively.The results showed that the biomass of rape increased with the increase of humic acid.3.HA reduces the content of lead and cadmium in rape in lead and cadmium contaminated soilCompared with the blank group,increasing the content of lead and cadmium in the soil,significantly increased the content of heavy metals in rape.Compared with the control group,the contents of lead and cadmium in 20,30,40 and 50 g · kg-1 HA rape were decreased gradually.When the amount of humic acid was 50 g · kg-1,Lead decreased by 24.1% and 17.8%,respectively,and cadmium and underground cadmium decreased by 21.0% and 7.1%,respectively.Therefore,humic acid can reduce the absorption of Pb and Cd by rapeseed and its enrichment in rape,and effectively reduce the toxic effects of lead and cadmium pollution on rape in soil,and provide humic acid fertilizer for rapeseed Theoretical basis.4.Humic acid to lead and cadmium contaminated soil rape resistance increasedThe content of free proline in rapeseed was significantly higher than that in the control group,and the content of free proline was significantly lower than that of the control group.Compared with the control group,respectively,decreased by 20.3%,33.3%,38.9%,43.5%.Therefore,the application of humic acid is beneficial to reduce the free proline content in rape,that is,to improve the resistance of rape.The activities of Peroxidase(Peroxidase,POD),Superoxide Dismutase(Superoxide Dismutase,SOD)and Catalase(Catalase,CAT)in rape were decreased in lead and cadmium contaminated soils.The contents of POD,SOD and CAT in rape were increased by adding 20,30,40 and 50 g · kg-1 humic acid respectively.When the amount of humic acid was 50 g · kg-1,the contents of POD,SOD and CAT increased by 68.9%,104.7% and 47.2%,respectively.The results showed that humic acid could alleviate the inhibitory effect of lead and cadmium on the activities of three enzymes.In addition,the contents of malondialdehyde(Malondialdehyde,MDA)and superoxide anion radica(Superoxide Aion Radica,O2·-)in rape were significantly increased,indicating that lead and cadmium destroyed the stability of active oxygen scavenging system in rape,Oxidation intensifies,cytoplasmic membrane damage.With the addition of humic acid 20,30,40,50 g · kg-1,the content of MDA and O2·-were increased.When the amount of HA was 50 g · kg-1,it decreased by 45.2% and 49.4%,respectively,compared with the control.Indicating that humic acid significantly alleviated the Pb and Cd pollution on the lipid peroxidation of rapeseed.Lead and cadmium can also increase the content of nitrate in rapeseed,indicating that lead and cadmium promote the production of nitrate,and thus promote the production of nitrite nitrogen,reduce the quality of rape.The content of nitrate nitrogen was decreased by 15.1%,28.8%,41.0% and 46.5%,respectively,with the increase of humic acid additions of 20,30,40 and 50 g · kg-1.Therefore,humic acid can not only improve the quality of rapeseed nitrate,but also improve the activity of POD,SOD and CAT,decrease the content of MDA and O2·-,and promote the balance of antioxidant system and alleviate membrane lipid peroxidation.Therefore,humic acid on the cadmium stress under the physiological characteristics of rape have a certain mitigation effect,can enhance the resistance of lead and cadmium rapeseed resistance.