Effects Of Different Intercropping Distance On Remediation Of Farmland Soil Polluted By Cadmium And Arsenic By Pteris Vittata And Solanum Nigrum Intercropped With Maize

The exceeding status of heavy metal in cropland of China has been very serious.The cultivation of a single hyperaccumulator for the remediation of heavy metal polluted soil not only interrupts agricultural production,leading to the loss of economic benefits,but also results in low remediation efficiency due to many disadvantages such as its low biomass and long remediation cycle.As a traditional agronomic management method,intercropping can improve the efficient utilization of resources and increase the quality of co-planted crop species by using the principles of ecological niche and biodiversity.For the remediation of moderately or lightly metal polluted soil,intercropping system can be used to increase the concentrations of heavy metals in the hyperaccumulators by regulating the growth and development of hyperaccumulators and crops.Therefore,the utilization rate of land and economic benefits are increased based on the“Production while remediated”.The accumulation of heavy metals in hyperaccumulators are increased but the uptake of heavy metals in crops are decreased,so the yield and quality of crops are improved.Although there are many reports regarding the remediation of heavy metal polluted soil by intercropping of hyperaccumulators and crops,the drastic competition between hyperaccumulators and crops will happen if their root system are very near.However,the root interaction will be weakened if the root distance of the two plants are very far from each other.Therefore,how to determine the better distance between hyperaccumulators and crops will affect the effectiveness of intercropping remediaiton.In this paper,4 horizontal distances(0、5、10、15 cm)and 3 vertical distances(the same position,higher than 10 cm,and lower than 10 cm)between hyperaccumulator and maize were designed in a pot experiment.The growth status,metal uptake,physiological and biochemical responses of maize,Pteris vittata(PV)and Solanum nigrum(SN),as well as the soil p H,heavy metal total concentrations and their bioavailability after planting plants in each treatment were determined.The main results were shown as follows:(1)According to the growth status and dry weight of plants,the intercropping methods of T3(10 cm horizontal distance)and T5 in which maize root was 10 cm higher than SN were the best in maize-SN intercropping system,and W3(10cm horizontal distance)and W6 in which maize root was 10 cm lower than PV were the best in maize-PV intercropping system.There was no significant difference in the concentrations of heavy metals in the aboveground parts of maize intercropped with SN and PV.No significant difference in Cd concentration was shown in SN.It was found that the As concentration in root of maize at treatment W3 intercropped with Pteris vittata was the lowest,and no significant difference was found in other parts of maize.Combined with biomass under vertical intercropping condition,the Cd concentration of SN at treatment T5 in maize-SN intercropping system was the best.On the other hand,there was no significant change in arsenic concentration in other parts of two plants in maize-PV intercropping system,except the lowest shoot As concentration in maize at treatment W6.(2)According to the root activity of maize and hyperaccumulators,treatments T3 and W3 were the best.In the case of vertical intercropping,treatments T5,as well as W5 and W6 was the best.There was no difference in photosynthetic pigments between the two plants in maize-SN intercropping system,but treatment W3 showed the best in maize-PV intercropping system.There was no significant difference in photosynthetic pigments between W5 and W6 under vertical intercropping condition.Combined with antioxidant enzyme activities and MDA content,treatments T3 and W3 was the best under horizontal intercropping condition.Under vertical intercropping condition,treatment W6 was the best,and there was no significant difference in antioxidative enzymes between Solanum nigrum and maize.(3)The p H value in soil at treatment W3 was increased significantly under maize-PV intercropping system,but no significant difference was found in maize-SN intercropping system.Considering the p H value in rhizospheric soil of hyperaccumulators and maize comprehensively,we fond that treatments T5,T6 and W6 were the best.The total and bioavailable Cd and As in plants showed no significant change in horizontal intercropping treatments,but treatments T5 and W6 were the best in vertical intercropping treatments.To sum up,the 10 cm horizontal distance(T3)and 10 cm vertical distance in which the roots of maize were higher than SN in maize-SN intercropping system were the best.In the case of maize-PV intercropping system,the best horizontal distance between the two plants was shown in W3(10 cm)and the maize roots were 10 cm lower than PV(W6)in vertical distance.