Elevational Patterns in Archaeal Diversity on Mt. Fuji

Little is known of how archaeal diversity and community ecology behaves along elevational gradients. We chose to study Mount Fuji of Japan as a geologically and topographically uniform mountain system, with a wide range of elevational zones. PCR-amplified soil DNA for the archaeal 16 S rRNA gene was pyrosequenced and taxonomically classified against EzTaxon-e archaeal database. At a bootstrap cut-off of 80%, most of the archaeal sequences were classified into phylum Thaumarchaeota (96%) and Euryarchaeota (3.9%), with no sequences classified into other phyla. Archaeal OTU richness and diversity on Fuji showed a pronounced ‘peak’ in the mid-elevations, around 1500 masl, within the boreal forest zone, compared to the temperate forest zone below and the alpine fell-field and desert zones above. Diversity decreased towards higher elevations followed by a subtle increase at the summit, mainly due to an increase in the relative abundance of the group I.1b of Thaumarchaeota. Archaeal diversity showed a strong positive correlation with soil NH4+, K and NO3−. Archaeal diversity does not parallel plant diversity, although it does roughly parallel bacterial diversity. Ecological hypotheses to explain the mid diversity bulge on Fuji include intermediate disturbance effects, and the result of mid elevations combining a mosaic of upper and lower slope environments. Our findings show clearly that archaeal soil communities are highly responsive to soil environmental gradients, in terms of both their diversity and community composition. Distinct communities of archaea specific to each elevational zone suggest that many archaea may be quite finely niche-adapted within the range of soil environments. A further interesting finding is the presence of a mesophilic component of archaea at high altitudes on a mountain that is not volcanically active. This emphasizes the importance of microclimate – in this case solar heating of the black volcanic ash surface – for the ecology of soil archaea.

目前学界对土壤古菌的多样性及其群落生态学沿海拔梯度的变化规律尚缺乏深入认知。我们选取日本富士山作为研究样区，该山体地质构造与地形地貌均一性良好，且覆盖了跨度极广的海拔梯度带。针对土壤DNA中古菌16S rRNA基因（archaeal 16S rRNA gene）进行聚合酶链式反应（Polymerase Chain Reaction, PCR）扩增，随后采用焦磷酸测序（Pyrosequencing）技术完成测序，并基于EzTaxon-e古菌数据库进行分类学注释。在自举法（Bootstrap）置信阈值为80%的筛选标准下，绝大多数古菌序列被归类至奇古菌门（Thaumarchaeota，占比96%）与广古菌门（Euryarchaeota，占比3.9%），未检测到其他门类的古菌序列。富士山土壤古菌的操作分类单元（Operational Taxonomic Unit, OTU）丰富度与多样性呈现显著的“中海拔峰值”特征：在海拔1500米（meters above sea level, masl）左右的寒温带针叶林带，其多样性显著高于下方的温带森林带，以及上方的高山碎石荒地带与荒漠带。随着海拔进一步升高，古菌多样性逐渐降低，但在山顶区域出现小幅回升，这一现象主要由奇古菌门I.1b类群的相对丰度提升所导致。古菌多样性与土壤铵态氮（NH4+）、钾离子（K+）及硝态氮（NO3−）含量呈显著正相关关系。古菌多样性并未与植物多样性呈现同步变化趋势，但大致与细菌多样性保持一致的变化格局。解释富士山古菌多样性中海拔峰值现象的生态学假说包括中度干扰效应，以及中海拔区域兼具上坡与下坡生境镶嵌组合的结果。本研究结果清晰表明，土壤古菌群落的多样性与群落组成均对土壤环境梯度具有强烈的响应特征。各海拔带特有的古菌群落结构表明，多数古菌可在土壤生境范围内实现精细的生态位适配。另一项值得关注的发现是，在这座非活火山的高海拔区域，仍检测到嗜中温古菌类群的存在，这凸显了微气候——即本研究中黑色火山灰表面的太阳辐射增温效应——对土壤古菌生态学的重要性。