| Contents of heavy metals in vegetable garden are much higher than the rice field in different regions in China. Vegetable is one kind of the chief crops that vulnerable to heavy metal pollution, and the enrichment coefficient of heavy metal is much higher than other crops. Leafy vegetables have much higher ability of accumulating heavy metal than the fruit and root vegetables, and they are relatively more vulnerable to heavy metal pollution. Survey data have also showed that the contents of chromium, lead, cadmium,mercury and other heavy metals in vegetables of typical regions of the Pearl River Delta exceeded the national health standard seriously. Therefore, it is very important to seek effective agronomic measures to reduce the absorption and accumulation of heavy metals in vegetables. Now, research has made it clear that biochar can not only improve soil structure,increase soil carbon sequestration and improve soil productivity, but also improve soil pollution in situ. Our early test also found biochar can reduce heavy metal absorption of vegetables. So, in this paper, two Ipomoea aquatic Forsskal varieties with different ability of absorbing and accumulating chromium were used as vegetable materials. And sequentially the effect and the ecological and chemical mechanisms of reducing chromium accumulation of Ipomoea aquatic Forsskal under biochar with selenium were studied. On this basis, further study on the effect and the ecological and chemical mechanisms of reducing chromium pollution of Ipomoea aquatic Forsskal of the carbon source material in Ipomoea aquatic Forsskal-Leersia hexandra. The main results are as follows:1. The effect of using biochar with selenium to reduce chromium accumulation of Ipomoea aquatic Forsskal and their eco-chemical mechanisms.Biochar, Se and biochar + Se three kinds of treatment all can promote the growth oftwo kinds of Ipomoea aquatic Forsskal to some extent, and improve the quality of Ipomoea aquatic Forsskal. The treatment of Biochar and biochar + Se can also significantly promote the height, root length, increase biomass of Ipomoea aquatic Forsskal, and improve the content of soluble sugar and soluble protein in Ipomoea aquatic Forsskal.The chromium content of Ipomoea aquatic Forsskal was roots > stems > leaves, and chromium was mainly distributed in the cell wall and the cell sap. Three kinds of treatment of biochar, Se and biochar + Se all can reduce chromium concentration in the two Ipomoea aquatic Forsskal materials, and the treatment of biochar contributed most. And under the same treatment, the chromium content is higher in narrow-leaf(Thailand) than in narrow-leaf green-skin(Hong Kong).For all treatments, the contents of total chromium in soil showed no significant difference, but the contents of hexavalent chromium were lower than the control groups.And the hexavalent chromium content under biochar treatment was the lowest. The three kinds of treatment of biochar, Se and biochar + Se changed the mechanical composition of soil to some content, and significantly increased soil organic matter content. But there was little effect on soil p H value. And p H value is significantly higher than the control group only under the biochar treatment group. Se treatment had less impaction on available nitrogen, phosphorus and potassium. But biochar treatment can significantly improve the soil available nitrogen, phosphorus and potassium content.Biochar treatment significantly increased urease and invertase activity, but has no significant differences on catalase. All the other treatments have no significant differences with the control groups.Under biochar treatment, the number of three types of soil microbial(bacteria, fungi and actinomycetes) were significantly higher than the control. Se treatment has little effect on soil microbial quantity. Biochar + Se only significantly increased the number of actinomycetes, and has little effect on the number of soil bacteria and fungi.2. The effect of using different carbon source biomass to reduce chromium pollution of Ipomoea aquatic Forsskal in Ipomoea aquatic Forsskal-Leersia hexandra intercropping system.Seven kinds of treatments of biochar, biochar + Leersia hexandra, biochar + modifiedbagasse, modified bagasse, modified bagasse+ Leersia hexandra, Leersia hexandra, biochar+ modified bagasse+ Leersia hexandra promoted the growth of Ipomoea aquatic Forsskal,and increased the content of soluble protein and soluble sugar. And biochar + Leersia hexandra treatment was the most significant treatment.Under the seven kinds of treatments, the content of chromium in plants was lower than control groups. And the chromium content was the lowest under biochar + Leersia hexandra treatment. And the content of chromium in plant was roots > stems > leaves, mainly distributed in the cell wall and the cell sap.Under the condition of seven treatments, total chromium has no differences with control. The contents of hexavalent chromium declined under seven kinds of treatments.And the hexavalent chromium content declined the most under biochar +Leersia hexandra treatment. All treatments reduced sand content, and improved the content of clay, but allthe treatments did not reach significant levels with the control. Except Leersia hexandra treatment did not changed soil organic matter significantly, the soil organic matter content was significantly higher than the control under the other treatments. Soil p H value was changed slightly under the seven kinds of treatments. All the treatments had higher soil available nitrogen, phosphorus and potassium contents than the control. Only the content of soil available nitrogen, phosphorus and potassium under biochar + Leersia hexandra treatment was significantly higher than control.Apart from biochar + modified bagasse+ Leersia hexandra treatment which decreased soil invertase slightly, four kinds of enzyme activity of remaining treatment groups were higher than control.Under the condition of seven treatments, the soil microorganism quantity was all higher than control. Under biochar + Leersia hexandra treatment, the number of three kinds of soil microorganisms was the largest. |
PDF Full Text Request