Effect of Foliar and Soil Application of Sodium Silicate on Arsenic Accumulation in Rice Seedlings Grown in As-Contaminated Paddy Soils

• Main Authors: Chia-Chen Huang, 黃佳貞
• Other Authors: 李達源
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/63948818809221029167

碩士 === 國立臺灣大學 === 農業化學研究所 === 103 === Intake of arsenic (As) from rice consumption poses a threat to food safety and human health globally. Silicon (Si) and As(III) share the pathway of uptake and translocation in rice. Si application into hydroponic culture solutions can decrease As uptake and toxicity to rice plant shown in previous studies. However, Si application into soils, both enhancing and inhibition effects on As bioavailability could occur because of increasing As release into soil solutions resulted from competitive sorption, and decreasing As uptake caused by competing pathways into rice plants. Since the adverse effects may come with the competition adsorption onto soils between As and Si, foliar application of Si fertilizer might be an alternative and more efficient way to enhance rice growth and to reduce As accumulation and toxicity than soil applications. Therefore, this study evaluated the effect of foliar and soil application of Si on rice seedlings grown in As contaminated soils and investigated the influence of various application rates of Si on arsenic accumulation in rice seedlings. Pot experiments of rice seedling growth in the greenhouse were conducted with four soils, including two geogenic As-elevated Guandu soils [GdL and GdH with low (17 mg kg-1) and high (128 mg kg-1) levels of As, respectively] and two Chiwulan soils [CaL and CaH with As-unspiked and spiked (80 mg As(V) kg-1), respectively]. In the Si treatments, sodium silicate was added into soils at the application rates of 0, 1, and 3 times (S0x, S1x, S3x) of Si fertilizer recommendation rate (0.175 g Si kg -1 soil) for soil application, and was sprayed on rice at the application rates of 50 mL of 0, 0.1%, and 0.3% Si (F0x, F1x, F3x) solutions per pot for foliar application. The applications were performed at the 15 and 30 days after rice transplanting respectively. After 50 days of growth, the rice seedlings were harvested. The concentrations of Si, As and As species in soil solutions and As concentrations in roots and shoots of rice seedlings were determined. The results show that the Si concentrations in the soil solution were increased significantly by soil application of Si. Due to the lower capacity of Si retention in Ca soils, the concentrations of Si in Ca soil solutions were one order of magnitude higher than those in Gd soils. The concentrations of As in soil solutions were increased significantly treated by S3x in CaL, CaH, and GdH. For high As contaminated/spiked soils with soil application of Si, the biomass of rice plants and shoot-As concentration decreased with the Si application rates, whereas the shoot-Si concentrations were increased. Although soil application of Si led to higher As concentrations in soil solutions, it decreased shoot-As concentrations compared with the control, resulting from the increase of Si/As molar ratio in soil solutions and thus causing competition between Si and As for plant uptake. The decrease of As uptake by rice seedlings may result from As phytotoxicity of rice plants grown in high-As soils. However, foliar application of Si had no significant effect on pH, Eh, Si and As concentrations in soil solution, plant biomass and shoot-Si and shoot-As concentrations of rice seedlings. It suggested that the foliar application of Si in this study were not available for plant uptake.