Liesack W, Schnell S, Revsbech N P
Max-Planck-Institut für terrestrische Mikrobiologie, Marburg, Germany.
FEMS Microbiol Rev. 2000 Dec;24(5):625-45. doi: 10.1111/j.1574-6976.2000.tb00563.x.
Flooded rice paddies are one of the major biogenic sources of atmospheric methane. Apart from this contribution to the 'greenhouse' effect, rice paddy soil represents a suitable model system to study fundamental aspects of microbial ecology, such as diversity, structure, and dynamics of microbial communities as well as structure-function relationships between microbial groups. Flooded rice paddy soil can be considered as a system with three compartments (oxic surface soil, anoxic bulk soil, and rhizosphere) characterized by different physio-chemical conditions. After flooding, oxygen is rapidly depleted in the bulk soil. Anaerobic microorganisms, such as fermentative bacteria and methanogenic archaea, predominate within the microbial community, and thus methane is the final product of anaerobic degradation of organic matter. In the surface soil and the rhizosphere well-defined microscale chemical gradients can be measured. The oxygen profile seems to govern gradients of other electron acceptors (e.g., nitrate, iron(III), and sulfate) and reduced compounds (e.g., ammonium, iron(II), and sulfide). These gradients provide information about the activity and spatial distribution of functional groups of microorganisms. This review presents the current knowledge about the highly complex microbiology of flooded rice paddies. In Section 2 we describe the predominant microbial groups and their function with particular regard to bacterial populations utilizing polysaccharides and simple sugars, and to the methanogenic archaea. Section 3 describes the spatial and temporal development of microscale chemical gradients measured in experimentally defined model systems, including gradients of oxygen and dissolved and solid-phase iron(III) and iron(II). In Section 4, the results of measurements of microscale gradients of oxygen, pH, nitrate-nitrite, and methane in natural rice fields and natural rice soil cores taken to the laboratory will be presented. Finally, perspectives of future research are discussed (Section 5).
淹水稻田是大气甲烷的主要生物源之一。除了对“温室”效应有这种贡献外，稻田土壤还是研究微生物生态学基本方面的合适模型系统，例如微生物群落的多样性、结构和动态以及微生物群体之间的结构-功能关系。淹水稻田土壤可被视为一个具有三个区室（好氧表层土壤、厌氧主体土壤和根际）的系统，其特点是具有不同的理化条件。淹水后，主体土壤中的氧气迅速耗尽。厌氧微生物，如发酵细菌和产甲烷古菌，在微生物群落中占主导地位，因此甲烷是有机物厌氧降解的最终产物。在表层土壤和根际，可以测量到明确的微观化学梯度。氧剖面似乎控制着其他电子受体（如硝酸盐、铁（III）和硫酸盐）和还原化合物（如铵、铁（II）和硫化物）的梯度。这些梯度提供了有关微生物功能群活性和空间分布的信息。本综述介绍了目前关于淹水稻田高度复杂微生物学的知识。在第2节中，我们描述了主要的微生物群体及其功能，特别关注利用多糖和单糖的细菌种群以及产甲烷古菌。第3节描述了在实验确定的模型系统中测量的微观化学梯度的空间和时间发展，包括氧以及溶解态和固相铁（III）和铁（II）的梯度。在第4节中，将展示在天然稻田和带回实验室的天然水稻土芯中测量的氧、pH、硝酸盐-亚硝酸盐和甲烷微观梯度的结果。最后，讨论了未来研究的前景（第5节）。
