| Heavy metal cadmium(Cd)is an important environmental pollutant.It is widely present in the soil.It has strong mobility and biological toxicity and can be absorbed into the food chain through plants,posing a potential threat to human health.With the development of industry and agriculture and the rapid expansion of cities,soil Cd pollution in China is more serious.The effectiveness of Cd in soil depends on its presence in the soil,and the effects of soil conditions(such as pH,organic matter and clay content),acidic conditions can lead to increased soil Cd effectiveness.Soil Cd pollution repair mainly includes physical,chemical and biological repair methods,and microbial remediation technology has the characteristics of low cost and less pollution.This study attempted to study the effects of Cd bioavailability in soil and the absorption and enrichment of Cd in vegetables.The main conclusions of enrichment are as follows:(1)In this experiment,12 strains with elevated pH were isolated from the soil of acid Cd contaminated vegetable land in Xiangtan,Hunan Province.The strains were identified according to 16S rDNA sequence analysis,and their species were identified and named.The strain XT-4 was selected as the test strain according to the pH increasing ability,growth rate,pathogenicity of plants and plants,and the strain XT-4 was identified as Bacillus altitudinis.(2)By culturing the strain XT-4,it was found that the pH of the medium gradually increased with the growth of strain XT-4.The strain XT-4 was cultured for 21 hours in oligotrophic medium(PY medium)with initial pH of 5.0 and 5.5,under the without adding 10 mM MES(2-(N-morpholine)ethanesulfonic acid monohydrate,pH buffer)treatment conditions.The pH in the medium was increased by 2.67 and 1.88 units,respectively.The concentration of Cd in the medium supernatant containing the initial concentration of Cd 1.18 mg/L and 1.23 mg/L was decreased by 1.13 and 1.19 mg/L,respectively.Under the condition of adding 10 mM MES,the pH of the medium was increased by 0.63 and 0.48 units,respectively.The concentration of Cd in the medium supernatant containing the initial concentration of Cd 1.23 mg/L and 1.20 mg/L was decreased by 1.18 mg/L and 1.15 mg/L,respectively.(3)Potted experiment was carried out using Xiangtan acid soil(pH=5.1)with mild pollution(0.95 mg/kg)of Cd,planting Chinese cabbage,and adding strain XT-4(102 CFU/kg dw,104 CFU/kg dw,106 CFU/kg dw,108 CFU/kg dw)and bio-organic fertilizer containing strain XT-4(102 CFU/kg dw,104 CFU/kg dw,106 CFU/kg dw,108 CFU/kg dw)treatment.The results showed that the addition of strain XT-4 significantly increased the pH value of rhizosphere soil of Chinese cabbage,significantly decreased the extractable Cd content of CaCl2 and the bioavailable Cd content of shoots in rhizosphere soil,and there was a significant negative correlation between the rhizosphere soil pH and the extractable Cd content of CaCl2.The strain XT-4 has a function of increasing the pH of the acidic rhizosphere soil.The addition of bio-organic fertilizer containing strain XT-4 significantly increased the pH value of rhizosphere soil.When the concentration of inoculated strain XT-4 was low(102 CFU/kg dw,104 CFU/kg dw),rhizosphere soil The content of Cd extracted by CaCl2 and the content of Cd in the upper part of Chinese cabbage were significantly decreased.When the concentration of inoculated strain XT-4 was higher(106 CFU/kg dw,108 CFU/kg dw),the growth of Chinese cabbage was inhibited,and the effectiveness of cadmium was reduced.The effect is not significant.The results of this study indicated that the strain XT-4 isolated from the acid Cd-contaminated upland soil in Xiangtan,Hunan Province,could significantly increase the pH of the rhizosphere soil,reduce the bioavailability of heavy metal Cd in the soil,and reduce the aboveground part of the plant.Absorption and enrichment of heavy metal Cd promotes plant growth,and it is expected to be developed into microbial fertilizer for agricultural production. |
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