Effects Of Biochar On Plant Growth And Uptake Of Heavy Metal Cadmium

With the rapid development of urbanization, industry and agriculture, heavy-metalcontamination in soil, water and atmosphere has been steadily increasing. In China, somecultivation areas of crops, vegetables and medicinal plants are suffering from a terrible threat ofheavy-metal contamination. Particularly, Cd contamination, which causes excessive Cd inagricultural products and is very harmful to human health, is becoming one of the most seriousissues. Due to the close relationship between edible and medicinal plants and human’s life andhealth, it’s of great scientific value and practical significance to investigate the safe production andcontamination remediation of vegetables and medicinal plants in heavy-metal contaminatedenvironment. Biochar has excellent characteristics, especially its great advantages on soilamelioration and contamination remediation. The previous studies have shown that application ofbiochar has significant influence on the morphological and migration behavior of heavy metals insoil and reducing the phytotoxicity. However, it remains unclear on how much it can reducepollution, how to apply biochar, and its potential in agricultural production.To evaluate the effects of adding biochar to Cd-contaminated soil on growth of vegetables,medicinal plants and alleviation of heavy-metal pollution, as well as the optimum amount ofbiochar adding to soil, the root vegetable Raphanus sativus L., leafy vegetable Brassica chinensis L.,multifunctional aquatic plant Nelumbo nucifera ’Taikong Lian36’, and the terrestrial medicinal herbSalvia miltiorrhiza Bunge were respectively tested by adding5biochar-soil weight ratios of biocharin different size into artificially Cadmium-polluted soil. The main results are as follows:(1) Adding biochar into soil could significantly increase the growth of four species of plants (P<0.05), among which leaves growth, plant height and fresh weight in biochar treatments were allsignificantly better than the control, which means that biochar could reduce the harm caused by Cd.According to the root-shoot ratio, adding biochar could improve root biomass of R. sativus and leafbiomass of B. chinensis more obviously. The biomass of underground part and rhizome of N.nucifera ’Taikong Lian36’ was significantly increased, indicating that biochar can promote the yieldof major edible parts of tested plants. Plant growth was significantly influenced by particle size ofbiochar, but no regularity was found between it and the proportion of biochar added in soil.(2) The physiological stress was easily made by artificial Cd contamination but was notsignificantly mitigated by adding different proportions of biochar, especially for N. nucifera and S.miltiorrhiza. It is possibly due to that concentration of Cd applied in soil was not sufficient to hurtthe two species seriously, or both species are tolerant to Cd at low concentrations. With thecomplexity of the physiological indicators, no clear relationship is observed between theproportions and particle sizes of biochar and the physiological stress on these four tested plants.(3) Adding biochar could reduce Cd content in the underground parts of R. sativus andaboveground parts of B. chinensis by81.21%and83.04%, respectively. The Cd in rhizomes,petioles and leaves of N. nucifera ’Taikong Lian36’ were reduced by68.51%,81.41%,54.66%,respectively and the Cd in the roots and leaves of S. miltiorrhiza Bunge reduced by43.63%,52.81%,respectively. Also, biochar reduced Cd bioconcentration factor of the four plants. Besides N.nucifera ’Taikong Lian36’, biochar had a significant impact on inhibiting the transportation of Cdfrom the underground part to the aboveground part of other3species, therefore reduced the contentof Cd in edible part of plant.(4) In the contaminated soil with4mg/kg Cd, the optimum amount of biochar was10%for two vegetables, while in the soil with3mg/kg Cd, the optimum amount of biochar was20%for twoedible and medicinal plants. These optimum proportions not only promoted plant growth anddevelopment, alleviated physiological stress caused by heavy metals, but also significantly reducedthe content of Cd in plants, making it meet the food safety standards. Therefore, biochar is provedto be an effective soil mixture for the safe production of green vegetables and medicinal plants andfor restoration of heavy-metal pollution.