| Summary: | 碩士 === 國立中興大學 === 土壤環境科學系 === 90 === Higher transpiration rate enhances Zn uptake by wheat. In soil environment, water soluble low molecular weight organic acids (LMWOAs) can complex with heavy metals to enhance the availability of heavy metals, or affect the mobility of heavy metals in soil solution and plants. Pb-precipitation forms on root surface via complexation and remains the same form in plant tissue. The experiment was conducted to investigate Pb uptake by roots and kinds and amounts of water soluble LMWOAs in rhizosphere with pot water spinach and leaf lettuce grown in in-situ Pb-contaminated soils controlled under high and low transpiration situations in two growth chambers. Five levels of Pb concentrations in soils were collected to test and then select three levels of Pb concentrations, which did not affect crop growth and its transpiration rate. The soils with selected three levels of Pb concentrations are naturally contaminated soils in situ. 0.1 M HCl and 0.05 M EDTA extractable Pb concentrations for the soils for planting water spinach were in the range of 224.7 - 393.8 and 203.8 — 413.6 mg kg-1, respectively. Those for planting leaf lettuce were 51.1 — 186.4 and 49.1 — 173.8 mg kg-1, respectively. The results showed that higher transpiration regime promoted better growth and higher total amount of Pb uptake of water spinach. However, transpiration regime did not affect the translocation of Pb from underground part to aboveground part. Higher transpiration regime did not affect growth and total amount of Pb uptake of leaf lettuce but did promote the translocation of Pb from underground part to aboveground part. Higher transpiration regime did not significantly promote total amount of Pb uptake by the two crops. This is probably because of the chemical properties and solid-state forms of Pb in in-situ contaminated soils, which limit the amounts of water soluble Pb2+ in soils. Transpiration regime did not significantly affect the species and amounts of water soluble LMWOAs in rhizosphere for planting water spinach and leaf lettuce. However, higher amount of available Pb in soil promoted the Pb uptake by the two crops. Correspondingly, higher amounts of water soluble LMWOAs were found in rhizosphere. This is mainly attributed to the relations between crop rhizosphere and physiological characteristics of microorganisms therein.
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