Abstract
Since biochar had been taken seriously, many studies are focused on whether biochar can increase the crop yield and biochar’s manufacture and process. However only few studies were about the removal of heavy metal in soil by biochar. The aim of this study is to investigate whether the biochar could absorb the heavy metal in soil and revive the plants. We divided the study into two parts using mung beans (Vigna radiate) as material. In the first part, the seed germination in Petri dish was examined; the second part was proceeded in soil to examine the growth of plants. In Petri dish test, we found that biochar absorb the copper ions from solution efficiently; plants grew better, exhibited higher fresh weight, dry weight, stem length and lower copper concentration. Biochemical measurement revealed that mung beans with biochar had higher soluble sugar and protein and lower malondialdehyde content. In the soil trials, we used red soil as material, tested five different soil copper concentrations, 0, 100, 200, 400, 1000 mg/kg according to the soil pollution control standards. For each soil concentration, four different biochar contents (0, 10, 20, 30%, v/v) were applied. After growing for a month, we measured fresh weight, dry weight, stem length, root length, copper concentration of plants, the content of soluble sugar and protein. In normal soil without copper, all the above data showed no significant difference; grown under 100 mg/kg, plants in 10% biochar content grew normally; at 200 mg/kg, 20% biochar is needed for proper growth; at 400 mg/kg, even 30% biochar content couldn’t restore plants back to normal, but with high biochar content, plants grew better; at 1000 mg/kg, plants could only survive with application of 20% and 30% biochar, but not in a good condition. In addition, copper ions reduced the chlorophyll content in mung beans, but biochar partially helped with the recovery. The values of Fv/Fm showed no difference among various groups, revealing that the site of action on photosynthesis is not located in PS II. At the molecular level, three genes related with ROS scavenging were chosen for the study: Cu/Zn SOD, CAT and APX. We found that at a lower copper concentration, three genes were upregulated, and downregulated when biochar was added; at a higher copper concentration, the more biochar we added, the better the plants grew and the higher the genes expressed.