施用矽酸鈉對種植於砷汙染土壤中水稻幼苗生長與吸收砷之影響

The effect of sodium silicate on growth and arsenic uptake of rice seedlings grown in As-contaminated soils

黃宣翰(Hsuan-Han Huang)

指導教授 ： 李達源

國立臺灣大學/生物資源暨農學院/農業化學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01739

摘要

前人研究指出提高土壤溶液中矽酸濃度可能降低水稻對砷之吸收。因此在砷污染之土壤中，施用矽酸或許可減少水稻對砷之吸收進而減輕砷的毒害。本研究目的在探討施用矽酸鈉對種植於砷汙染土壤中水稻幼苗的生長以及吸收砷之影響。本研究以四種台灣有效性矽含量低之代表性土壤:平鎮 (Pc)、台南 (Tn)、淇武蘭 (Ca) 和內埔系 (Np)、添加As (Ⅴ) 製備為200 mg As (Ⅴ) kg-1之砷汙染土；另取兩個不同砷濃度之關渡土壤為供試土壤。依據作物施肥手冊與文獻求得矽之推薦施用量為0.1753 g Si kg-1 (+all Si)，之後將試驗土壤分為四種不同矽酸鈉施用量之處理: (1) control (2) +1/4 Si (3) +1/2 Si (4) +all Si進行浸水孵育試驗與水稻幼苗盆栽試驗。土壤浸水孵育後測定土壤溶液中砷與矽濃度隨孵育時間之變化，結果顯示，隨著矽酸鈉施用量增加，台南、內埔、淇武蘭系土壤溶液中砷濃度也隨之上升，推測因矽酸根與砷酸根互相競爭土壤中鐵 (氫) 氧化物上相同的吸附位置所造成。然而，在平鎮與關渡土壤溶液中砷濃度並沒有因矽酸鈉的施用而有顯著差異，乃因這兩種土壤其吸附能力較強，施用矽酸鈉後，矽酸隨即被土壤中鐵 (氫) 氧化物吸附，而減少了與砷酸競爭的機率。台南、內埔、淇武蘭系不管是在未添加砷之土壤或是人工砷汙染土壤中，其土壤溶液中矽與砷濃度之間皆具有線性正相關。水稻幼苗盆栽試驗結果發現，種植於未添加砷之土壤與低濃度砷之關渡土壤中的水稻幼苗生質量並沒有因施用矽酸而有顯著差異，但其中內埔與淇武蘭系之水稻幼苗地上部砷含量，卻會隨著矽酸施用量增加而上升。種植於砷汙染土壤中的水稻幼苗毒害程度會隨著矽酸施用量增加而越嚴重。結果顯示，施用矽酸鈉皆會提高未受砷汙染之土壤與砷汙染之土壤溶液中砷濃度，但前者其增加的量尚未對水稻幼苗造成毒害，且土壤溶液中的矽酸濃度也不足以抑制水稻幼苗吸收砷。然而，在砷汙染土壤中，其提高的量超過水稻幼苗所能負荷之量，而使原本已經受砷毒害之水稻幼苗受害程度更嚴重。

關鍵字

土壤 ； 矽酸 ； 砷 ； 水稻 ； 吸附作用 ； 競爭

並列摘要

Increasing concentration of silicic acid in soil solutions may mitigate arsenic uptake by rice as reported by previous researchers. Therefore, in As-contaminated soils applying silicic acid may alleviate As toxicity of rice by decreasing As uptake. In this study, rice (Oryza sativa L.“Taichung 65”) was cultivated in As-contaminated soils for 38 days in Phytotron to evaluate the effect of application of silicic acid on growth and arsenic uptake of rice seedlings. Four low available Si contents of Taiwan soils were spiked with 200 mg As (V) kg-1 and two Guandu soils containing different levels of As were used in this study. The Si recommended application rate 0.1753 g Si kg-1 soil was used as the all Si treatment. The Si application levels (sodium silicate) included: (1) control (2) 1/4 Si (3) 1/2 Si (4) all Si. Concentrations of Fe, As, P and silicic acid in soil solutions under flooded incubation for 50 days and As concentrations in roots and shoots of rice seedlings were determined. The results indicate that the addition of sodium silicate significantly increased the concentrations of As in soil solutions of Tainan, Neipu and Chiwulan soils, presumably through a replacement of arsenite or arsenate adsorbed on Fe oxides/hydroxides by silicic acid. However, the phenomena were not observed in Pinchen and Guandu soils, because the adsorption capacity of Pinchen and Guandu soils were higher than those of other tested soils. When sodium silicate was applied to Pinchen and Guandu soils, silicic acid might be adsorbed on Fe oxides/hydroxides, thus the opportunity of competing with soil-adsorbed arsenic would be reduced. Moreover, there was a linear relationship between As and silicic acid concentrations in the soil solutions of non-added As (V) soils or As-contaminated soils of Tainan, Neipu and Chiwulan.

The results of pot experiments of rice seedlings show that the effect of silicic acid on biomass of rice seedlings was not significant in non-added As (V) soils and low level As concentration soil of Guandu. However, the As content in shoots increased with increasing rates of sodium silicate application in Neipu and Chiwulan soils. On the contrary, the growth of rice seedlings in As-contaminated soils was inhibited with increasing application rates of sodium silicate. The above results suggest that the addition of sodium silicate significantly increased As concentration in soil solutions of both non-added As (V) soils and As-contaminated soils. In non-added As (V) soils, the increase of silicic acid in soil solutions did not inhibit the growth and As uptake of rice seedlings. However, in As-contaminated soils, the amounts of As in soil solutions were greatly increased with increasing sodium silicate application, thus resulting in the increase of As toxicity of rice seedlings.

並列關鍵字

soil ； silicic acid ； arsenic ； paddy rice ； adsorption ； competition

參考文獻

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