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  • 學位論文

提高繁星花萃取重金屬鎘栽培方式之探討

Studies on the Management of Enhancing Cadmium Phytoextration in Pentas lanceolata (Forsk.) Schum.

指導教授 : 張育森

摘要


本論文以繁星花[ Pentas lanceolata (Forsk.) Schum ‘Butterfly’](pentas)為材料,進行氮肥、pH值、螯合劑、修剪與葉施等試驗,探討能有效提高繁星花萃取鎘能力的栽培方式,目的在建立以繁星花進行鎘污染土壤修復時的肥培管理準則,以期早日達到恢復污染土壤的可利用性。 25 mg kg-1的鎘明顯抑制繁星花地上部及根的生長,此環境下,進行一週一次不同濃度(0、8、16、24或32 mM )的氮肥試驗,其中以24 mM的氮濃度處理,繁星花的地上部有最大的鎘累積量(16.4 μg),其地上部的鎘累積濃度為44.3 mg kg-1,乾重為0.32 g。 水耕養液以不同pH值(4、5、6或7)處理,養液pH值的高低與根鎘累積濃度和鎘累積量沒有明顯的相關性,但較低的pH值則有利繁星花將鎘運移到地上部貯存,故在pH 4的環境下,莖、葉都有最高的鎘累積濃度(977、94.0 mg kg-1)和累積量(529、76.2 μg)。 在土壤添加螯合劑(EDTA、citric acid)試驗中得知,添加2和5 mM EDTA有助於繁星花地上部吸收累積更多的鎘,但因EDTA具有嚴重的生物毒害作用,故必須提早採收。如欲進行長時間、連續的植物萃取方式來修復鎘污染土壤,採用2 mM citric acid (CA),不僅有提高地上部萃取鎘的功效,還有利植株在鎘逆境中生長,且CA在土壤中易被微生物分解,沒有過多殘留之虞。 輕剪及重剪處理的葉片鎘累積濃度各為9.59 mg kg-1和9.63 mg kg-1,均明顯大於沒有修剪處理的對照組(5.45 mg kg-1),其中重剪之後的營養生長較輕剪更為旺盛,故預測當重剪之後的生物量成長到與輕剪或不修剪處理相近時,地上部將會有更大的鎘累積量。將葉面處理KH2PO4、CO(NH2)2和GA3,在正常施肥管理情況下,均無助於提高繁星花萃取土壤中鎘的能力。 比較繁星花與雜草藿香薊和人莧對鎘的吸收累積能力,由盆栽試驗結果得知,地上部的鎘累積濃度及BCF值,大小依序為:人莧(79.5 mg kg-1) (7.4)>藿香薊(51.3 mg kg-1) (4.8)>繁星花(21.2 mg kg-1) (2.0),三者的BCF值均大於1,都屬鎘的高累積植物,但因前兩者地上部乾重遠小於繁星花,故地上部的鎘累積量反而是繁星花(99.7 μg)最多,藿香薊(68.4 μg)和人莧(42.3 μg)較少。繁星花為多年生宿根草本植物,根系發達,除有大的生物量外,還具有環境適應能力佳,易長側芽,耐修剪等特質,確實是進行植物萃取土壤中鎘的合適材料。

關鍵字

繁星花 植物萃取 氮肥濃度 pH 螯合劑 修剪 葉施 藿香薊 人莧

並列摘要


Plants of pentas [ Pentas lanceolata (Forsk.) Schum ‘Butterfly’ ] was used to investigate the enhancement of Cd phytoextraction. The experiments include the treatments of different nitrogen concentrations, pH values, chelators, pruning levels or foliar spraying applications. The aim of this study was to enhance Cd phytoextraction. The growth of pentas was suppressed in soil containing 25 mg kg-1 Cd. Under this condition, different nitrogen concentrations (0, 8, 16, 24 or 32 mM) were applied once a week. The 24 mM treatment resulted in the maximum of Cd total content, 16.4 μg that the dry weight was 0.32 g and the Cd concentration was 44.3 mg kg-1 in plants. In the hydroponic experiment with different pH values (4, 5, 6 or 7), roots absorbed Cd easily in all pH values, but the amount of Cd translocated from roots to shoots was hightly dependent on lower pH value. When solution pH value was 4, the maximum concentration (977, 94.0 mg kg-1), and total content (529, 76.2 μg) of Cd were measured in stems and leaves. In the applying chelators experiment, an addition of EDTA significantly increased the concentration of Cd in the shoot. However, EDTA was toxic to plants, so plants under the application of EDTA must harvest earlier. The 2 mM citric acid was recommended for Cd phytoextration, due to enhancement of Cd in the shoot and good growth for pentas. Citric acid is cheap and could be biodegraded rapidly by microbes in soil, so it could be used as soil amendment. Cd concentration increased in leaves of pentas either by light pruning or heavy pruning treatments, which resulted in Cd concentration of 9.59 mg kg-1 and 9.63 mg kg-1 respectively, both higher than control (5.45 mg kg-1) significantly. Because plants could grow vigorously by heavy pruning, so more Cd was accumulated in the shoot in heavy pruning treatment than that in light or none pruning treatments. Under normal fertilization (applying 200 ppm N from Peter’s 20-10-20 once a week), foliar spraying of KH2PO4, CO(NH2)2 or GA3 could not increase Cd extraction in pentas. Pentas, weeds Ageratum conyzoides and Acalypha australis were compared with the capability of Cd extraction. The result showed all these three plants were potential for phytoremediation of Cd-contaminated soil, because their BCF in shoots were higher than 1. Cd accumulated concentraction and BCF in shoot were Acalypha australis (79.5 mg kg-1, 7.4)>Ageratum conyzoides (51.3 mg kg-1, 4.8)>pentas (21.2 mg kg-1, 2.0), but the ranking of total content was in reverse order that pentas (99.7 μg)>Ageratum conyzoides (68.4 μg)>Acalypha australis (42.3 μg). The reason mainly was that the biomass of pentas is larger than the others. In conclusion, pentas is a perennial plant having plenty fibrous root system, adapting to the stress conditions and developing lateral shoot easily, so it is very suitable for phytoextration of Cd-contaminated soil.

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