Shewanella putrefaciens CN32对粘土附着态铵氮释放的影响

Effects of Shewanella putrefaciens CN32 on the release of clay-sorbed NH4+

摘要:

[目的] 研究产胞外分泌物微生物Shewanella putrefaciens CN32对土壤中常见粘土矿物附着态NH₄⁺的释放效果及影响机制。[方法] 以吸附NH₄⁺的蒙脱石、蛭石、伊蒙混层矿物和黑云母为对象，通过监测S.putrefaciens CN32作用下不同粘土释放的NH₄⁺含量及过程，以及监测微生物量及释放的胞外聚合物（Extracellular Polymeric Substances，EPS）的含量变化，研究S.putrefaciens CN32作用下不同粘土矿物类型附着态NH₄⁺释放的差异性。[结果] 粘土矿物附着态NH₄⁺含量从高到低依次为蒙脱石 > 蛭石 > 伊蒙混层矿物 > 黑云母（黑云母NH₄⁺吸附量极低，会在非生物作用下几乎完全释放），CN32作用下粘土附着态NH₄⁺相对释放量依次为蒙脱石 > 伊蒙混层矿物 > 蛭石；然而，尽管CN32有效促进了粘土附着态NH₄⁺释放，但释放的NH₄⁺并未在溶液中大量累积，而是多被微生物同化吸收转化为生物有机氮（EPS为主）并吸附在粘土表面，且粘土对EPS的吸附能力表现为蒙脱石 > 伊蒙混层矿物 > 蛭石 > 黑云母；由于粘土吸附NH₄⁺及EPS都与矿物中的羟基（结构水或层间水）关系密切，推测EPS对矿物羟基的竞争吸附可能是CN32促进NH₄⁺释放的重要原因之一。[结论] 以上结果表明，产EPS微生物S.putrefaciens CN32能够促进各类粘土矿物的附着态NH₄⁺释放，但释放的NH₄⁺可以通过微生物作用转化为有机氮，从而在减少NH₄⁺流失的同时增加土壤氮肥的生物可利用性，因此微生物在降低土壤氮肥流失、转化土壤氮肥污染过程中可能起到了重要作用，也揭示了深入系统地分析不同类型土壤（粘土类型不同）中粘土附着态NH₄⁺在不同功能微生物作用下的迁移转化过程，是精准评估土壤氮肥施用效率及流失风险的前提之一。

Abstract:

[Objective] This study was conducted to explore the effect and mechanism of Shewanella putrefaciens CN32, a typical bacterium secretes extracellular polymeric substances (EPS), on the release of clay-sorbed NH₄⁺ in soils. [Methods] The common clay minerals in soil, including smectite, vermiculite, smectite-illite mixlayer mineral and biotite were used for NH₄⁺ sorption and then was inoculated by S. putrefaciens CN32. The contents of clay-sorbed N, dissolved NH₄⁺, the microbial biomass and EPS were monitored to understand the variation of NH₄⁺ release from different types of the clay minerals. [Results] The content of clay-sorbed NH₄⁺ was dependent on clay types, with high to low in smectite > vermiculite > smectite-illite mixlayer mineral (in biotite was too low). With the activity of S. putrefaciens CN32, the percentage of released NH₄⁺ was highest in smectite, followed by in smectite-illite mixlayer mineral and lowest in vermiculite. Although CN32 effectively promoted the release of clay-sorbed NH₄⁺, the released NH₄⁺ did not accumulate in the solution but assimilated by the bacterial cells, which was transformed into bio-organic nitrogen (mainly EPS) and attached on the clay surface. The adsorption of EPS was highest on smectite, followed by smectite-illite mixlayer mineral and vermiculite. FTIR analysis revealed that the adsorption of both NH₄⁺ and EPS on clays were closely associated with the hydroxyl groups in minerals (structural or interlayer water), thus, it is speculated that the competitive adsorption on mineral hydroxyl may be one of the important reasons for stimulated release of NH₄⁺ by CN32. [Conclusion] The results of the present study demonstrated that the EPS-producing S. putrefaciens CN32 can promote the release of clay-sorbed NH₄⁺ from all kinds of clay minerals. The released NH₄⁺ does not necessary to be leached from the soil profile but instead to be transformed into organic nitrogen and increases the bioavailability of nitrogen fertilizer. Therefore, microorganisms may play an important role in reducing nitrogen loss and easing ammonia pollution from soils. It is important to systematically understand the microbial effects on the migration and transformation of clay-sorbed NH₄⁺ in different types of soils (with different assemble of clay minerals), which serves for the precise prediction of the efficiency and loss risk of nitrogen fertilizers in soils.