|摘要: ||本研究將平地造林樹種栽種於彰化縣政府所列管的鎘汙染農地，以評估與測試平地造林樹種植生萃取鎘之潛能。試驗樹種包括苦楝、烏桕、台灣櫸、黃連木、無患子、大葉桃花心木、台灣欒樹、杜英、台灣烏心石、羅漢松等10種。苗木栽植於試驗地12個月後，依生長情況分為三級，以了解同一樹種中不同生長情況的苗木對鎘累積之濃度或累積量是否會有差異，並檢測植物組織氮、磷養分狀態、鎘濃度及土壤pH值、鎘濃度，並以生物濃度係數 (bioconcentration factor, BCF)、轉移係數 (translocation factor, TF) 及植物體鎘累積量，篩選適合植生萃取鎘之樹種，此外，亦評估土壤鎘濃度減少之趨勢。|
栽植於試驗地之植物並無氮、磷養分缺乏的情況。以苗木生長級數而言，植物根部所累積鎘濃度與其生長級數並無一定趨勢存在，而某些樹種莖及葉部鎘濃度則有隨生長級數之增加而有提高之趨勢，另外一些樹種則隨生長級數之增加而有下降之趨勢，且植物對鎘的累積位置因樹種而異。試驗樹種中，以生長級數3級苦楝地上部所累積的鎘量為最高，約1,891.45 g ha-1 y-1，而BCF及 TF 值大於1之樹種僅有杜英，若考量鎘累積量、BCF 及 TF等為篩選條件，則是以苦楝、台灣櫸、烏桕、台灣欒樹及杜英較適合做為植生萃取之樹種。在土壤的部分，上層土 (0~15 cm)、下層土 (15~30 cm) 及根圈土壤pH值較試驗前土壤有上升之現象，各層土壤鎘濃度高低因樹種而有所差異，試驗前後，土壤鎘濃度並無顯著之差異，但土壤鎘濃度與土壤pH值呈負相關。
In this study, we planted 10 tree species in cadmium-contaminated farmland to assess the potential of their phytoextraction. The experimental field is supervised by the Changhua County government, and the planted species included Melia azedarach, Sapium sebiferum, Zelkova serrata, Pistacia chinensis, Sapindus mukorossii, Swietenia macrophylla, Koelreuteria formosana, Elaeocarpus decipiens, Michelia compressa var. formosana and Podocarpus macrophyllus. The seedlings were divided into three grades according to growing conditions to find out whether there were differences in accumulated concentraction or amount at the same grade and the same tree species. Twelve months after planting the seedlings in the experimental field, we examined the nitrogen, phosphorus and cadmium concentrations in the plant tissues, and the soil pH and its cadmium level. We next chose the tree species which were most suitable for phytoextraction and evaluated their capacities to reduce the cadmium concentration in the soil by measuring bioconcentration factor (BCF), translocation factor (TF) and the amount of cadmium in plant tissues.
The plants grown in the experimental field did not lack of nitrogen and phosphorous nutrients. The results indicated no significant correlations between cadmium concentrations in roots and seedling growth grades. However, the cadmium concentrations in stems and leaves increased as growth grades increased for some tree species, but decreased as growth grades increased for others. The locations of the accumulated cadmium varied from species to species. The third growth grade Melia azedarach accumulated approximately 1,891.45 g ha-1 y-1 of cadmium in their shoots, the highest amount of accumulation among all the planted species. Both the BCF and TF of the Elaeocarpus decipiens were greater than one. Taking the amounts of accumulated cadmium and the BCF and TF consideration, Melia azedarach, Zelkova serrata, Sapium sebiferum, Koelreuteria formosana and Elaeocarpus decipiens were most suitable for phytoextraction. In terms of the soil, soil pH was higher after the experiment than before in the topsoil (0~15 cm), subsoil (15~30cm) and rhizosphere, and the cadmium concentration in each soil layer differed from species to species. Although there were no significant differences in soil cadmium before and after the experiment, there was a negative correlation between soil cadmium concentration and soil pH.