Graducate School of Science and Technology, Shizuoka University, 836 Ohya, Suruga-ku, Shiuoka 422-8529, Japan.
Microbes Environ. 2008;23(4):337-45. doi: 10.1264/jsme2.me08541.
Denitrification activity and bacterial community constituents were investigated in both well-drained and poorly drained soils of a temperate forest in central Japan by (15)N tracer experiments and a cloning-sequencing approach. Denitrification activity was much higher in wet soil than in dry soil, based on (15)N(15)N ((30)N(2)) and (15)N(15)NO ((46)N(2)O) production. Labeled nitrate ((15)NO(3)(-)) was immediately reduced to (30)N(2) in wet soil, whereas it was only reduced to (46)N(2)O in dry soil. Thus, the wet soil at the lower end of the catchment is a functional site for the scavenging for NO(3)(-) and N(2)O. Nitrite reductase gene (nirK and nirS) fragments from these soils were PCR amplified, cloned, and sequenced. Both nirK and nirS fragments were detected in the wet soil, whereas only nirK fragments were detected in the dry soil. All the nirK and nirS clones showed less than 90% similarity to known clones. Numerous operational taxonomic units for nirK and nirS were found in the wet soil. Considerable diversification within the largest clade on the nirK phylogenetic tree, which contained no known sequence, was observed in wet soil. Thus, a wet soil environment can provide both the habitat and conditions for the expression of denitrification activity.
采用（15）N 示踪实验和克隆测序方法，研究了日本中部温带森林中排水良好和排水不良土壤中的反硝化活性和细菌群落组成。基于（15）N（15）N（（30）N（2））和（15）N（15）NO（（46）N（2）O）的产生，湿土中的反硝化活性明显高于干土。在湿土中，标记的硝酸盐（（15）NO（3）（-））立即被还原为（30）N（2），而在干土中仅被还原为（46）N（2）O。因此，集水区下游的湿土是（30）N（2）和 N（2）O 的功能位点。从这些土壤中扩增、克隆和测序了亚硝酸盐还原酶基因（nirK 和 nirS）片段。在湿土中检测到 nirK 和 nirS 片段，而在干土中仅检测到 nirK 片段。所有的 nirK 和 nirS 克隆与已知的克隆相似性均小于 90%。在湿土中发现了大量的 nirK 和 nirS 操作分类单元。在湿土中，nirK 系统发育树上最大的分支内观察到相当大的多样性，其中没有已知的序列。因此，湿土环境既能为反硝化活性的表达提供栖息地，又能提供条件。
