| The pollution of heavy metal cadmium?Cd?is becoming more and more serious.Cd can be easily transferred from soil to plant leading food safety problems.Food chain is a key pathy way through that Cd in Environment affect human healty adversely.Vegetables is one of the main sources of dietary Cd in humans,while leafy vegetables are susceptiblely to Cd pollution than other vegetables,so the safe production of leafy vegetables in Cd-contaminated vegetable fields has attracted high attention.In this study,Cd hyperaccumulator plant Tagetes patula L.and Brassica chinenesis L.were planted intercropped in order to screen the intercropping combination with better remediation effect on Cd-contaminated soil;on this basis,put forward regulation measures suitable for strengthening the remediation effect of intercropping;and the mechanism of plant rhizosphere intercropping affecting Cd uptake by the plants under intercropping treatments was elucidated through rhizobox experiment.This study can provide technical support for the safe utilization and pollution restoration of mildly Cd-contaminated vegetable fields in China.The main results of this study are as follows:?1?A pot experiment was conducted to reveal the effects of intercropping of low-cadmium?Cd?accumulating cultivar and Cd hyperaccumulator on safe utilization and phytoextraction of Cd-polluted soils.Two cultivars of Brassica chinensis L.,i.e.the low-Cd accumulating cultivar Huajun and the common cultivar Hanlv were intercropped with four cultivars of Tagetes patula L.,i.e.Dwarf Red,Dwarf Yellow,Tall Red,and Tall Yellow.We examined the biomass,photosynthetic characteristics,and Cd accumulation in the tested plants and available Cd content and dissolved organic carbon?DOC?content in soils.The results show that under the intercropping treatments,the biomass of B.chinensis decreased significantly and those of T.patula increased significantly compared with the monoculture treatments.When intercropped with T.patula,the net photosynthetic rate,stomatal conductance,and transpiration rate in the leaves of B.chinensis decreased significantly compared with the monoculture treatments.When Huajun was intercropped with Dwarf Red,the shoot Cd content of Huajun significantly decreased by 14.5%,and that of Dwarf Red increased significantly by 36.5%compared with the monoculture.Under the other intercropping treatments,the shoot Cd content of B.chinensis increased significantly or showed no significant change,and that of T.patula showed no significant change.Under the intercropping treatments,the total amount of Cd in the shoot of B.chinensis decreased significantly and that of T.patula increased significantly compared with the monoculture.There were no significant differences in the Cd extraction ratios between the intercropping treatments and the monoculture of T.patula.The shoot Cd content of B.chinensis was significantly correlated with soil available Cd content and DOC content?P<0.01 and 0.05,respectively?.In conclusion,the intercropping treatment of Huajun and Dwarf Red significantly reduced shoot Cd content in B.chinensis and increased that in T.patula,and it did not affect the Cd extraction ratio,which is suitable for the safe utilization and phytoextraction of Cd-polluted soils.?2?A Pot experiment was conducted to study the effects of mercapto-modified palygorskite,potassium sulfate and foliar spraying of manganese sulfate on plant growth,Cd accumulation and soil Cd speciation under monoculture and intercropping modes.The results showed that the application of mercapto-modified palygorskite significantly reduced the Cd content in shoot of pakchoi and Tagetes patula,the accumulation of Cd in pakchoi,the Cd extraction rate of plant,and the available Cd content in the soil,reduced the exchangeable Cd ratio of the soil,and increased the proportion of soil iron-manganese bound Cd.The application of 0.4 g·kg-1 of potassium sulfate significantly increased the accumulation of Cd in Tagetes patula and reduced the Cd content of the pakchoi in intercropping.The application of potassium sulfate increased the proportion of exchangeable Cd and reduced the proportion of residual Cd in the soil under monoculture patterns,reduced the exchangeable Cd ratio in the rhizosphere of pakchoi,and increased the residual Cd ratio of soil in intercropping partterns.Spraying 0.6 g·L-1 of manganese sulfate in monoculture significantly reduced the Cd content and Cd accumulation of shoot in pakchoi.From the perspective of reducing the Cd content in the shoot of pakchoi to ensure safe production without affecting the extraction and restoration of plant Cd,the effect of 0.4 g·kg-1 potassium sulfate treatment is the best in intercropping patterns.?3?The spatial distribution characteristics of root system,soil pH,available Cd and total Cd content of the two plants in monoculture and intercropping modes were studied by rhizobox experiments.The results showed that the root system of Tagetes patula was more developed than that of Brassica chinenesis.Planting Brassica chinenesis increased soil pH and decreased soil total Cd and available Cd contents in the near-root region;while planting Tagetes patula decreased soil pH and increased soil total Cd and available Cd contents in the near-root region.Under intercropping treatments,the effect of Tagetes patula on reducing soil pH and increasing the available Cd content in the near root region was dominant;the available Cd content in the near root soil of Tagetes patula was lower than that in the monoculture treatments,while the available Cd content in the near root soil of Brassicachinenesis was higher than that in the monoculture treatments,which is the important reasons for the change of Cd content in the shoots of the two plants under intercropping treatments. |
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