| Summary: | 碩士 === 國立臺灣大學 === 農業化學研究所 === 106 === Besides various mitigation methods suggested to reduce arsenic(As) bioavailability, decreasing inorganic arsenic accumulation in grain via organic matter addition into soil have been discussed in previous studies since organic As species were less toxic and may furthered leave rice plants through volatilization. However, previous studies also revealed that organic matter addition may mobilize soil-As resulting from promoted reductive dissolution of iron oxide. To evaluate feasibility of increasing organic As species by organic matter application, risk of increasing As availability should be considered at the same time. Our research aimed to investigate the effect of green manuring Black heart (Polygonum lapathifolium) into paddy soils on arsenic uptake by rice seedlings. Green manuring has received more attention recently owing to its low-cost and landscaping. Among of green manure plants, Black heart is a self-broadcasting wetland plant in paddy field and has been identified as the plant with potential on As remediation. In our research, three paddy soils in Taiwan, Guandu series (Gd), Chaikongtso series (Cl) and Chiwulan series (Ca) were used for pot experiments. There were two levels of As concentrations in each soil (i.e. high level(H): 74 -139 mg As kg-1 and low level(L): 21-38 mg As kg-1). In the results, As contents in black heart were mere comparing to that in rice plants, which implied that As releasing from black heart caused little influence on As availability of rice seedlings. Plowing black heart into soil brought slightly difference on pH and Eh measurements while As and iron(Fe) release were promoted based on porewater analysis. Competition of non-specific adsorption site between organic matter and As should also contribute to promoted As releasing after plowing black heart. Based on rice seedlings analysis, in soils that were with fine texture and less non-specifically adsorption-As such as GdL and CaL soil, plowing Black heart mobilized As without severe toxicity. In addition, increased organic-As proportion in plants was observed. In soils that were with coarse texture or more non-specifically adsorption-As such as GdH,ClL,ClH and CaH soil, plowing Black heart mobilized As and moreover, aggravated As toxicity in rice seedlings.
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