Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Parsons Laboratory 48, 15 Vassar Street, Cambridge, Massachusetts 02139, USA.
Ecology. 2012 Jul;93(7):1659-73. doi: 10.1890/11-1204.1.
Oxygen minimum zones (OMZs) are natural physical features of the world's oceans. They create steep physiochemical gradients in the water column, which most notably include a dramatic draw down in oxygen concentrations over small vertical distances (<100 m). Microbial communities within OMZs play central roles in ocean and global biogeochemical cycles, yet we still lack a fundamental understanding of how microbial biodiversity is distributed across OMZs. Here, we used metagenomic sequencing to investigate microbial diversity across a vertical gradient in the water column during three seasons in the Eastern Tropical South Pacific (ETSP) OMZ. Based on analysis of small subunit ribosomal RNA (SSU rRNA) gene fragments, we found that both taxonomic and phylogenetic diversity declined steeply along the transition from oxygen-rich surface water to the permanent OMZ. We observed similar declines in the diversity of protein-coding gene categories, suggesting a decrease in functional (trait) diversity with depth. Metrics of functional and trait dispersion indicated that microbial communities are phylogenetically and functionally more overdispersed in oxic waters, but clustered within the OMZ. These dispersion patterns suggest that community assembly drivers (e.g., competition, environmental filtering) vary strikingly across the oxygen gradient. To understand the generality of our findings, we compared OMZ results to two marine depth gradients in subtropical oligotrophic sites and found that the oligotrophic sites did not display similar patterns, likely reflecting unique features found in the OMZ. Finally, we discuss how our results may relate to niche theory, diversity-energy relationships and stress gradients.
氧气最小区（OMZs）是世界海洋的自然物理特征。它们在水柱中形成陡峭的物理化学梯度，其中最显著的是氧气浓度在小垂直距离（<100 米）内急剧下降。OMZs 内的微生物群落在海洋和全球生物地球化学循环中发挥着核心作用，但我们仍然缺乏对微生物生物多样性如何在 OMZs 中分布的基本了解。在这里，我们使用宏基因组测序来研究东热带南太平洋（ETSP）OMZ 三个季节期间水柱垂直梯度上的微生物多样性。基于小亚基核糖体 RNA（SSU rRNA）基因片段的分析，我们发现从富氧地表水到永久性 OMZ 的过渡过程中，分类和系统发育多样性都急剧下降。我们观察到蛋白质编码基因类别的多样性也有类似的下降，这表明随着深度的增加，功能（特征）多样性下降。功能和特征离散度的度量表明，微生物群落在含氧水中在系统发育和功能上更加分散，但在 OMZ 内聚集。这些离散模式表明，群落组装驱动因素（例如竞争、环境过滤）在氧气梯度上差异显著。为了了解我们发现的普遍性，我们将 OMZ 结果与两个亚热带贫营养站点的海洋深度梯度进行了比较，发现贫营养站点没有显示出类似的模式，这可能反映了 OMZ 中存在的独特特征。最后，我们讨论了我们的结果如何与生态位理论、多样性-能量关系和应激梯度相关。
