Macro and trace element contents in soils and plants of a serpentine ecosystem

• Main Authors: CHEN NIEN CHU, 陳念祖
• Other Authors: HSEU ZENG YEI
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/24443051669440788743

碩士 === 國立屏東科技大學 === 環境工程與科學系所 === 99 === Serpentinitic soils from ultramafic parent rocks are characterized by low availability of N, P, K, and Ca/Mg and extremely high contents of heavy metals like Cr, Co, and Ni. These metal levels in the serpentinitic soils can be much higher than the soil pollution control standards (SPCS) of Taiwan. Additionally, low contents of Si and Ca causes to poor growth of general plants. The heavy metals in the serpentinitic soils are not anthropogenic, but they have potential risk to ecosystem and human health. Therefore, this study selected an abandoned site of serpentine at Wang-Ron, Hualiean to collect 7 species of plant and the corresponding soils in the root zone. The plants include Crotalaria zanzibirica, Miscanthus floridulus, Leucaena leucocephala, Bidens pilosa, Dolichos lobatus Willd., Melilotus indicus and Conyza Canadensis. The purposes are to explore element contents in the soils and plants, to fractionate heavy metals by sequential extraction and single extraction, to understand the plant uptake of the elements and their compartmentation in different plant tissues, and evaluate the phyto-availability. The experimental results indicated that the Ca/Mg ratio was lower than 1.0 in most cases of soils and reflected the typical characteristics of serpentinitic soils. The concentrations of Cr and Ni ranged from 59 to 723 mg/kg and from 691 to 1220 mg/kg respectively, which greatly exceeded the SPCS. Regarding solid fractionation of Cr and Ni, the dominant phases of Cr and Ni are the residual forms which are fixed in the mineral framework. The DTPA- and HCl-extractable amounts of Ni was higher than that of Cr, which difference in trend betwee elements is the same to that by sequential extraction. Therefore, Cr is hard to be absorbed by the plants. The heavy metal contents in the studied plants were higher than those in the other plants. The concentrations of Mn, Cr, and Ni in the plant ranged from 10.4 to 69.4 mg/kg, from 6.08 to 36.9 mg/kg, and from 8.52 to 51.4 mg/kg. In addition, most Mn and Cr in the plant accumulated in the root, while Ni was in the leaves. This study elucidates that the plant may be potential accumulators of Ni, because the transfer factor (TF, leaf/root) of Ni is higher than 1.0, particullarly for Crotalaria zanzibirica with TF 2.27.