喀斯特小流域石灰土硫形态和硫酸盐还原菌分布特征

Forms of Sulfur and Distribution of Sulfate-Reducing Bacteria in Limestone Soil of Small Karst Catchment

用土壤硫形态连续提取和微生物学方法分析了石灰土中总硫、SO_4^(2-)、总还原态硫(TRIS)、有机硫含量以及硫酸盐还原菌(SRB)类群和数量,目的是阐明西南酸沉降地区土壤中硫化物积累和SRB的分布特征。有机硫是主要的硫形态,SO_4^(2-)是主要的无机硫形态。石灰土中检出脱硫叶菌属和脱硫弧菌属-脱硫微菌属类群。石灰土剖面中SRB数量与TRIS含量增大的深度对应SO_4^(2-)-S含量降低的深度,指示石灰土中存在SO_4^(2-)异化还原反应。石灰土较高pH值和较低的黏粒含量不利于SO_4^(2-)吸附,生物滞留后剩余SO_4^(2-)主要通过淋溶迁移出石灰土剖面。有机硫是石灰土中大气酸沉降输入SO_4^(2-)的主要硫滞留方式,在硫沉降输入通量显著降低后,石灰土中有机硫矿化在较长时期内可能导致大量SO_4^(2-)输入流域水体,与SO_4^(2-)淋溶输出有关的流域土壤和水体物理化学组成变化应予以关注。

Samples of limestone soil collected from a small karst catchment affected by acid deposition in Southwest China were collected for analysis of total sulfur （TS）,organic S,SO4^2-S,total reduced inorganic sulfur （ TRIS）,and groups of sulfate-reducing bacteria （SRB） and their populations with the soil sulfur sequential extraction method and microbiological methods in an attempt to determine forms of sulfur and to characterize SRB distribution in the soil. It w,as found that organic sulfur was the major for^m of sulfur,while SO42 was that of inorganic sulfur in the limestone soil. Bacteria of Desulfobulbus genus and Desulfovibrio-Desulfomicrobium group were detected in the limestone soil. The depth of the soil layer where SRB began to increase in population and TRIS in content corresponded well to that where SO4^2--S began to decrease in content, which indicates that dissimilatory SO4^2- reduction occurs in the limestone soil. The high pH and low clay content of the soil are adverse to SO42 adsorption; therefore the remaining SO42 after biological S retention is easily leached out of the lime-stone soil. SO4^2- entering the soil with atmospheric deposition is retained mostly in the form of organic sulfur, of which mineralization releases large volumes of SO4^2- into rivers and groundwater for a long period of time after annual sulfur depo-sition rate dropped by a large margin, thus affecting physic-chemical properties of the soils and chemical composition of the surrounding waterbodies. Therefore, more attention should be paid to such environmental responses in future.