Max-Planck-Institute for Terrestrial Microbiology, Karl-von-Frisch-Str.10, 35043, Marburg, Germany.
Environ Microbiol. 2013 Sep;15(9):2588-602. doi: 10.1111/1462-2920.12161. Epub 2013 Jun 13.
Irrigated rice fields in Uruguay are temporarily established on soils used as cattle pastures. Typically, 4 years of cattle pasture are alternated with 2 years of irrigated rice cultivation. Thus, oxic upland conditions are rotated with seasonally anoxic wetland conditions. Only the latter conditions are suitable for the production of CH4 from anaerobic degradation of organic matter. We studied soil from a permanent pasture as well as soils from different years of the pasture-rice rotation hypothesizing that activity and structure of the bacterial and archaeal communities involved in production of CH4 change systematically with the duration of either oxic or anoxic conditions. Soil samples were taken from drained fields, air-dried and used for the experiments. Indeed, methanogenic archaeal gene copy numbers (16S rRNA, mcrA) were lower in soil from the permanent pasture than from the pasture-rice alternation fields, but within the latter, there was no significant difference. Methane production started to accumulate after 16 days and 7 days of anoxic incubation in soil from the permanent pasture and the pasture-rice alternation fields respectively. Then, CH4 production rates were slightly higher in the soils used for pasture than for rice production. Analysis of δ(13) C in CH4, CO2 and acetate in the presence and absence of methyl fluoride, an inhibitor of aceticlastic methanogenesis, indicated that CH4 was mainly (58-75%) produced from acetate, except in the permanent pasture soil (42%). Terminal restriction fragment length polymorphism (T-RFLP) of archaeal 16S rRNA genes showed no difference among the soils from the pasture-rice alternation fields with Methanocellaceae and Methanosarcinaceae as the main groups of methanogens, but in the permanent pasture soil, Methanocellaceae were relatively less abundant. T-RFLP analysis of bacterial 16S rRNA genes allowed the distinction of permanent pasture and fields from the pasture-rice rotation, but nevertheless with a high similarity. Pyrosequencing of bacterial 16S rRNA genes generally revealed Firmicutes as the dominant bacterial phylum, followed by Proteobacteria, Acidobacteria and Actinobacteria. We conclude that a stable methanogenic microbial community established once pastures have been turned into management by pasture-rice alternation despite the fact that 2 years of wetland conditions were followed by 4 years of upland conditions that were not suitable for CH4 production.
乌拉圭的灌溉稻田暂时建立在用作牧场的土壤上。通常，牛牧场的 4 年与 2 年的灌溉水稻种植交替进行。因此，好氧旱地条件与季节性缺氧湿地条件轮换。只有后者条件适合有机物质的厌氧降解产生 CH4。我们研究了永久性牧场的土壤以及牧场-水稻轮作不同年份的土壤，假设参与 CH4 产生的细菌和古菌群落的活性和结构会随着好氧或缺氧条件的持续时间而系统地变化。从排水田地中采集土壤样本，风干后用于实验。实际上，与牧场-水稻轮作田地相比，永久性牧场土壤中的产甲烷古菌基因拷贝数（16S rRNA、mcrA）较低，但在后者中，没有显著差异。在永久性牧场和牧场-水稻轮作田地的土壤中，分别经过 16 天和 7 天的缺氧培养后，甲烷生成开始积累。然后，在用于牧场的土壤中，CH4 产生速率略高于用于水稻生产的土壤。在存在和不存在抑制乙酸营养型产甲烷作用的甲基氟化物的情况下，对 CH4、CO2 和乙酸中的 δ(13) C 的分析表明，除了在永久性牧场土壤中（42%），CH4 主要（58-75%）来自乙酸。古菌 16S rRNA 基因的末端限制性片段长度多态性（T-RFLP）分析表明，在以甲烷鬃毛菌科和甲烷八叠球菌科为主要产甲烷菌的牧场-水稻轮作田地的土壤中没有差异，但在永久性牧场土壤中，甲烷鬃毛菌科相对较少。细菌 16S rRNA 基因的 T-RFLP 分析允许区分永久性牧场和牧场-水稻轮作的田地，但仍然具有很高的相似性。细菌 16S rRNA 基因的焦磷酸测序通常显示厚壁菌门为优势细菌门，其次是变形菌门、酸杆菌门和放线菌门。我们的结论是，一旦牧场转变为牧场-水稻轮作管理，稳定的产甲烷微生物群落就会建立起来，尽管随后是 4 年的旱地条件，不适合 CH4 生产。
