Effect Of Carbon Sources And Temperature On Iron Reduction In Calcareous Paddy Soil

Microbial Fe(Ⅲ) reduction is a form of anaerobic respiration, which widely exists in thenature of anaerobic environment. In this process, the Fe(Ⅲ) oxides as final electron acceptor,with organic matter or H2as electron donor, Fe(Ⅲ) was reduced to Fe(II) with microbegrowth and development. The quantity and species of microorganism, the morphology ofFe(Ⅲ) oxide, electron donor, electron acceptor, electron shuttle and other environmentalfactors can affect the microbial Fe(Ⅲ) reduction directly or indirectly. Soil texture as a factorof soil physical properties characterization, which can also affect the microbial Fe(Ⅲ)reduction through the adsorption of clay on nutrient and organic matter and the quantity andactivity of microorganism. Therefore, study the characteristics of microbial Fe(Ⅲ) reductionin different texture, might help better understanding the factor microbial Fe(Ⅲ) reductionprocess, which can not only deepen the understanding of the influencing factors for it,but alsoreveal the role of the clay in it.In order to study the relationship between soil texture and microbial Fe(Ⅲ) reduction, wechose three paddy soil samples from Ningxia. Adding exogenous carbon source and settingdifferent culture temperature were used in anaerobic mud culture, as well as, addingexogenous carbon source was used in anaerobic mixed culture. The main conclusions areshowed as follow:(1)With the temperature of30℃culture conditions in anaerobic mud culture, themaximum accumulation amount of Fe(II) and the maximum reaction rate of Fe(Ⅲ) wereincreased, meanwhile, the time to reach the maximum reaction rate of Fe(Ⅲ) was decreasedas adding pyruvate or lactate to three different soils. The addition of pyruvate or lactatepromoted the microbial reduction of Fe(Ⅲ). The addition of acetate made the maximumaccumulation amount of Fe(II) increased but delayed the start of microbial reduction of Fe(Ⅲ)in three different soils. The maximum accumulation amount of Fe(II) and the maximumreaction rate of Fe(Ⅲ) and the time to reach the maximum reaction rate of Fe(Ⅲ) were allincreased as adding glucose to NX1. The addition of glucose promoted the microbialreduction of Fe(Ⅲ) but also delayed the start of microbial reduction of Fe(Ⅲ) in NX1. Themaximum accumulation amount of Fe(II) and the maximum reaction rate of Fe(Ⅲ) were increased, meanwhile, the time to reach the maximum reaction rate of Fe(Ⅲ) was decreasedas adding glucose to NX2. The addition of glucose promoted the microbial reduction of Fe(Ⅲ)in NX2. The maximum accumulation amount of Fe(II) and the time to reach the maximumreaction rate of Fe(Ⅲ) were decreased, while, the maximum reaction rate of Fe(Ⅲ) wasincreased as adding glucose to NX3. The addition of glucose was not promot the microbialreduction of Fe(Ⅲ) in NX3.(2)Under the anaerobic mud culture condition, the maximum accumulation amount ofFe(II) and the maximum reaction rate of Fe(Ⅲ) were all increased as temperature rose, whilethe time to reach the maximum reaction rate of Fe(Ⅲ) was decreased as temperature rose inthree different soils with the temperature range of15℃～25℃. Temperature rising willpromote the microbial reduction of Fe(Ⅲ).(3) Soil texture can influence the time to reach the maximum reaction rate of Fe(Ⅲ). Theclay need longer time to reach the maximum reaction rate of Fe(Ⅲ) than the loam. The timeto reach the maximum reaction rate of Fe(Ⅲ) was longer as the soil texture was heavier.Owing to the presence of clay, the start of microbial reduction of Fe(Ⅲ) was delayed.(4) Under the anaerobic mixed culture condition, the microbial community from NX1can used lactate as the advantage of carbon source to reduce Fe(Ⅲ), which Fe(Ⅲ) reductionrate reached21.8%. The microbial community from NX1and NX2can used pyruvate as theadvantage of carbon source to reduce Fe(Ⅲ), which Fe(Ⅲ) reduction rate reached20.9%and25.7%.