The Effect And Mechanism Of Crop Intercropping On Heavy Metal Absorption

Along with the development of the industry, a great deal of heavy metal was released into the environment, causing serious pollution to soils especially the farmland soil. Heavy metal can transport through the food chain, and finally accumulate in the human body, resulting in serious human health concerns. So the remediation of heavy metal contamination is imminent. Compared with the traditional physical or chemical remediation methods, the new method, phytoremediation with advantages of inexpensive, causing fewer disturbances to the soil, and not lead to secondary pollution, is known as the best method for remediation of soil heavy metal contamination. Due to the hyperaccumulators which are often used in the phytoremediation are always of small biomass and grow slowly, the remediation efficiency is not ideal. Thus, it is urgent to develop new methods of enhancing the efficiency of remediation of contaminated soil, or decrease heavy metal extraction by crops for safe food production in contaminated soil.1. In this study, four plant species with significantly different Cd absorption ability were chosen (relatively Cd high-accumulator: greengrocery and tomato; relatively Cd low-accumulator:cabbage and maize) to intercropping in the soil of Cd contamination. The results indicated as follow:1) Compared with monoculture, intercropping of greengrocery and cabbage increased the Cd extraction by greengrocry (increased from 6.55 mg kg-1 to 9.29 mg kg-1 in shoot and from 4.45 mg kg-1 to 7.65 mg kg-1 in root), and decreased the Cd extraction by cabbage (decreased from 3.70 mg kg-1 to 0.54 mg kg-1 in shoot and from 3.32 mg kg-1 to 1.99 mg kg-1 in root), when cultured in soil with 2.62 mg kg-1 Cd. Compared with monoculture, intercropping and restricted intercropping of tomato and maize increased the Cd extraction by tomato (increased from 13.52 mg kg-1 to 24.94 mg kg-1 and 27.30 mg kg-1 in leaves). Thus, the remediation efficiency of Cd contamination was advanced while output from contaminated soil is safe to eat through intercropping. 2) Compared with non-planted soil, after culture of greengrocery and cabbage, soil pH decreased a little, activities of acid phosphatase increased and activities of urease decreased. The most decrease of soil pH and the least decrease of urease activities were determined in monoculture of greengrocery. After culture of tomato and maize, soil pH decreased, activities of acid phosphatase increased and activities of urease decreased. The most alteration of soil pH and acid phosphatase activities, and the least decrease of urease activities were determined in intercropping of tomato and maize. All the alteration influenced the Cd form in soil, eventually leading to the alteration of Cd absorption ability by plants. At the same time, intercropping increased the microorganism species abundance which are beneficial to heavy metal extraction, and decreased the microorganism species abundance which will block the heavy metal extraction in the rhizosphere soil of tomato, finally achieved the enhancing of Cd absorption capability by tomato. Therefore, intercropping influenced the heavy metal absorption ability through the alteration of soil pH, soil enzyme activity, and microorganism species abundance in the rhizosphere soil.2. In this study, greengrocery, cabbage, tomato, maize, and Japan Clover Herb which is reported as a heavy metal high accumulator, were cultured in monoculture and intercropping, in field which is contaminated by a variety of heavy metal (Cd,Pb,Cr,Cuå’ŒFe) in low concentrations. The study evaluated the heavy metal absorption status between different plant species, different heavy metals, and different planting patterns. The results showed that tomato absorbed a great amount of heavy metals (especially Cd). Furthermore, accumulation of heavy metals increased when tomato was intercropped with other plant species. Thus, tomato planted in intercropping is suitable for remediation of soil heavy metal contamination. Maize absorbed much Cr, Cu and Fe. The heavy metal concentrations were reduced when maize was intercropped with other plant species. Thus, maize planted in intercropping is suitable for producing safe products from heavy metal contaminated soil. The roots of Japan Clover Herb were easy to accumulate Cd and Pb. The heavy metal concentrations were reduced when Japan Clover Herb was intercropped with other plant species. Greengrocery and cabbage are neither suitable for repair the soil heavy metal contamination, nor for output of safe production from the heavy metal contaminated soil.This research provided clues for simultaneous efficient remediation of heavy metal contamination and output of safe production from contaminated soil.