光照对水稻土中氧化铁还原的影响

EFFECT OF ILLUMINATION ON IRON OXIDE REDUCTION IN ANAEROBIC PADDY SOILS

选择不同地区的水稻土样品,采用泥浆厌氧恒温培育方法,在避光和光照条件下,测定了培养过程中土壤泥浆的Fe(Ⅱ)浓度及叶绿素a含量的变化。结果表明:光合微生物的产氧作用是影响水稻土中铁还原的主要原因,而光照对铁还原微生物没有直接影响;光合微生物仅在某些水稻土中大量繁殖,其叶绿素a含量随着光照时间延长由逐渐增加到趋于稳定。通过微生物镜检和光谱分析发现,由天津和四川水稻土中分离的光合微生物主要是念珠蓝细菌(Nostocsp.)和鱼腥蓝细菌(Anabaenasp.),其吸收光谱曲线均具有664 nm的叶绿素a吸收峰,表明其具有利用光合系统Ⅱ进行产氧光合作用的特征。在厌氧培养过程中Fe(Ⅱ)浓度与土壤中叶绿素a含量变化有着明显的负相关关系。

Soil samples collected in paddy fields in Tianjin （TJ） , Sichuan （SC） , Jiangxi （JX） and Hunan （HN） provinces of China. The experiment was designed to have four levels of illumination, i.e. entire dark （D）, light （L） and change from dark to light （D/L） and from light to dark （L/D） during anaerobic incubation of slurries prepared out of the paddy soil samples. Concentrations of Fe （ Ⅱ ） and chlorophyll a （ Chl a） were determined in the samples under incubation, to study effect of illumination on reduction of dissimilatory iron oxide. Results show that oxygen production of photosynthetic bacteria leads to oxidation of Fe（ Ⅱ ） in paddy slurry under anaerobic incubation. Light does not affect iron-reducing bacteria. Photosynthetic bacteria reproduce massively only in some paddy soils, and Chl a content increases first with illumination going on, and then levels off. Anabaena sp. and Nostoc sp. of Cyanobacteria were identified respectively in TJ and SC soils, and both of these Cyanobacteria had the same Chl a absorption peak at 664nm, which suggests that oxygen production by photosynthesis Ⅱ occurred. A significant negative correlation was observed between Fe （ Ⅱ ） and Chl a content in the two calcareous paddy soils under anaerobic incubation.