| In recent years, Cadmium (Cd) soil contamination has easily occurred in a large area of farmland due to the "three wastes" discharge by mining, electroplating, metallurgy and other industrial activities. Crops can absorb a certain amount of Cd from Cd contaminated soils, which changes components and elements of nutrients in fruits and vegetables, leading to the body get acute or chronic poisoning of Cd through food chain. Traditional project management methods take high cost and are often followed by destruction of soil structure and decrease of soil fertility; chemical method is easy to bring secondary pollution and unstable effect. In that case, methods of combinations of plant and microbial remediation have been studyed on Cd contaminated soil. In addition, reports on practical applications are less. Ryegrass (Lolium multiflorum L.) has strong accumulation capability to heavy metals Cd. Arbuscular mycorrhiza (AM) is a symbiont formed by plant root and arbuscular mycorrhizal fungi. AM can be found in various kinds of soil contaminated by heavy metal, and it may affect absorption, accumulation and transference of host plant to heavy metal. Tomato is a kind of popular solanaceous vegetables. Early studies have shown that tomato can accumulate large amount of Cd, affecting the food safety of tomato. In this research, Cd contaminated soil have been studied through pot experiments and application in field, aim to reveal that effects of Ryegrass and AM to tomato on Growth, physiological characteristics, Cd accumulation and chemical forms as well as the impact on soil microorganism, enzyme activity and Cd form. We have investigated heavy metal concentration in plants like Ryegrass responsed to soil inoculated with AM and whether it would reduce accumulation of heavy metal. We also investigated if AM addition would strengthen the role of Ryegrass on remediation of Cd contaminated soil. This research is for the purpose of providing theoretical foundation on Cd remediation. This experiment results are as follows:(1) The results of pot experiment showed that dry weights of fruit and plant, and contents of malondialdehyde (MDA) and antioxidant enzyme activities of leaf and root, and concentrations and accumulations of Cd significantly differed between two varieties of tomato. Dry weights of fruit, roots, stem, leaf and plant increased by single or compound remediation of ryegrass and AM, while MDA contents and antioxidant enzyme activities of leaf and root reduced.(2) The total extractable Cd, FE, FW,FNaCl,FHAC,FHCl and FR in fruit of two varieties of tomato reduced by 19.4%-52.4%,31.0%-75.2%,19.7%-59.1%, 3.11%-48.2%,20.0%-65.0%,40.7%-100% and 15.2%-50.0%, respectively. Cadmium accumulations in tomato were in order of leaf> stem> fruit> root. Cadmium concentrations in leaf, stem, root and fruit of both varieties decreased by single or compound remediation of ryegrass and AM, and Cd accumulations of stem and plant of two varieties also reduced. Cadmium accumulations in fruit of two varieties decreased by 42.9% and 43.7% in the compound remediation treatments, respectively. Tolerance and resistance of ’LUO BEI QI’ on Cd was more than ’De Fu mm-8’, and Cd concentrations and Cd accumulations in fruit and plant were in order of ’LUO BEI QI’ <’De Fu mm-8’ in the presence or absence of single or compound remediation of ryegrass and AM.(3) The results of pot experiment showed that ryegrass and AM single or compound reduced toxicity of Cd on tomato root tip cells. In the Cd-treated (control), two varieties of tomato root tip cells have become deformed, organelles, plasmolysis, and the cells distance became larger; in "Cd+ryegrass or AM" treatment, two varieties of tomato root tip cells had atrend to be normal, increased intracellular organelles, cell wall thickness, cell nucleus and vacuole are visible.(4) The results of pot experiment showed that AM increased total biomass of ryegrass in either aboveground or underground, the range of increase is 35.6% and 32.2%,11.3% and 13.6%,27.6% and 26.0%, respectively. AM reduced Cd in aboveground and underground of ryegrass, the range of reduce is 14.8% and 9.61%, 7.22% and 11.1% respectively. But AM increased Cd content and Cd accumulationin of ryegrass in either aboveground or underground, the range of increase is 15.7% and 19.7%,4.33% and 1.02%,10.3% and 12.2%, respectively.(5) The results of field trial showed that ryegrass or AM single or compound remediation reduced Cd concentrations in the fruit, leaves, stems and roots of tomato, the range of reduce is 6.92%-37.9% and 11.8%-40.9%,5.70%-38.6% and 12.2%-40.1%, 5.60%-34.7% and 4.61%-32.6%,9.82%-42.4% and 21.7%-41.4%. Cd content in the fruit were in order of ’De Fumm-8’>’LUO BEI QI’.(6) The results of field trial, ryegrass and AM single or compound remediation increased bacteria, fungi, actinomycetes of soil of two varieties of tomato, the range of increase is 59.9%-254% and 21.7%-169%,76.9%-231% and 205%-253%, 27.1%-72.9% and 27.9%-77.0%. Ryegrass and AM single or compound remediation increased urease, invertase, acid phosphatase, catalase activity of soil of two kinds of tomato.(7) The results of field trials, Cd content of soil in the order of RES-Cd> FeMn-Cd> CAB-Cd> EXC-Cd> OM-Cd. Ryegrass and AM single or compound remediation decreased EXC-Cd, CAB-Cd and FeMn-Cd in soil, CAB-Cd decreased are 16.9%-37.8% and 31.25%-34.4%; FeMn-Cd decreased are 20.6%-38.1% and 32.0%-38.6%. Ryegrass or AM decreased total Cd of the form of Cd in soil and Cd content in soil, the range of decreased are 8.6%-23.2% and 15.9%-27.5%,16.9%-22.7% and 25.4%-27.8%.(8) The results of field trial, AM increased total biomass of ryegrass in either aboveground or underground, the range of increase is 8.3%and 12.0%,18.4% and 15.3%,11.8% and 13.1%. AM significantly increased the Cd content and Cd accumulation in ryegrass, the range of increase of Cd concentrations is 18.0%and 63.5%,27.2% and 33.3%; the range of increase of Cd accumulation and total Cd is 26.1% and 87.5%,50.0% and 61.5%,36.6% and 75.9%. Ryegrass Cd content in the order of underground> aboveground, ryegrass Cd accumulation in the order of aboveground> underground. |
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