The Effect Of Intercropping Of Tagetes Patula L. And Crops On Remediation Of Cadmium Polluted Soils

Soil metal pollution becomes much more serious,as the rapid development of industry and agriculture.Cadmium pollutants in farmland affected not only the crops yield and quality,but also the health of the people through the bioaccumulation of the food chain.With cultivated area decreasing and continuous farming in polluted land,intercropping crops with hyperaccumulator could not only remedy contaminated soils but also increase quality of crops.It has become a new research derection of farmland soil remediation.The study was first conducted to select the optimal Tagetes patula culticar through determining Cd accumulation and Cd fraction in the rhizosphere soil of seven Tagetes patula cultivars(Little Hero Orange,Durango Yellow,Janie Yellow Bright,LuciferYellow,Hero Flame,Hongyun Red,Konghuang Yellow).The selected cultivar was then intercropped with four crops(maize,tomato,water spinach and soybean).We exploredthe effect of interspecific interaction on the absorption of heavy metals in Little Hero and four crops,in order to find the mechanism of Cd bioavailability influenced by rhizosphere of the intercropping system.The results showed:(1)T.patula cultivars showed strong tolerance and accumulation to Cd.The biomass of seven cultivars were higher than control when treated with Cd10.Little Hero showed the strongest Cd tolerance and the biomass did not decrease at Cd50.Cd concetration in the shoot of Little Hero and Kong Huang were 33.36 mg kg-1 and 30.52 mg kg-1,respectively,higher than other cultivars.For most cultivars,Cd treatments significantly affected rhizosphere pH values,but had a slight effect on dissolved organic carbon(DOC).Among seven cultivars,Little Hero Orange showed the greatest pH decrease,highest shoot Cd accumulation and Cd percentage in the exchangeable fraction,suggested that pH might be related to Cd bioavailability and their uptake by T.patula.pH were negatively correlated with Cd accumulation and Cd percentages in the exchangeable fraction in the rhizosphere soil of Little Hero Orange,Durango Yellow,and Konghuang Yellow.No significant correlation was observed between DOC,Cd accumulation and Cd percentage in the exchangeable fraction in the rhizosphere soil,except for Konghuang Yellow,suggesting pH might be the more important factor influencing the Cd accumulation of T.patula.(2)Cd concentration in Little Hero was higher than the four crops at CdO,Cd0.6 and Cd 1.2.Cd concentration in shoot was 13.026 mg kg-1 in the monocultured T.patula at Cd1.2.The absorbed Cd by corn was mainly accumulated in roots and least in seeds.The uptake of Cd in corn seeds was 0.09 mg kg-1 in the intercropping treatment,lower than that in monoculture,conforming to the standards for food safety.It is suggested that intercropping of T.patula and corn could be used to decrease Cd concentration of corn seeds.The absorbed Cd by tomato was mainly accumulated in roots.The uptake of Cd in fruits of tomato exceeded the standards for food safety in both the intercropping and single tomato planting at Cd0.6 and Cdl.2.Compared with monocropping,Cd absorption in tomato increased when it was intercropped.On the contrary,Cd concentration in the shoot of T.patula was decreased a little.The absorbed Cd by soybean was mainly accumulated in roots.The uptake of Cd in edible part of soybean exceeded the standards for food safety in both the intercropping and monocropping at Cd0.6 and Cd1.2.Intercropped with T.patula,Cd accumulation in seeds of soybean was decreased.Conversely,Cd concentration in T.patula was increased.For water spinach,the Cd concentration in shoots of the second harvest were significantly higher than that of the first harvest.The Cd concentration in shoots of the two harvests were both higher than the standards for food safety.The accumulation of Cd in both water spinach and T.patula reduced when water spinach was intercropped at Cd1.2.(3)Intercropper with T.patula,the DTPA extractable Cd concentration in the rhizosphere of corn,tomato,soybean and water spinach were significantly increased at Cd1.2.Intercropped with T.patula,the pH values in the rhizosphere of the four crops were mostly decreased insignificantly.The DOC concentrations in the rhizosphere of T.patula,corn,tomato and water spinach were significantly increased when intercropped with T.patula.DOC plays the more important role for Cd accumulation in intercropping system,compared with pH.This study established a foundation for the improvementof the safety of produce and the remediation of slightly Cd-polluted farmland soil.It has double significance of environment and health.