(Table S2) Relative abundance of archaeal 16S rRNA genes in sediment cores

Deep drilling into the marine sea floor has uncovered a vast sedimentary ecosystem of microbial cells (Parkes et al., 1994, doi:10.1038/371410a0; D'Hondt et al., 2004, doi:10.1126/science.1101155). Extrapolation of direct counts of stained microbial cells to the total volume of habitable marine subsurface sediments suggests that between 56 Pg (Parkes et al., 1994, doi:10.1038/371410a0) and 303 Pg (Whitman et al., 1998) of cellular carbon could be stored in this largely unexplored habitat. From recent studies using various culture-independent techniques, no clear picture has yet emerged as to whether Archaea or Bacteria are more abundant in this extensive ecosystem (Schippers et al., doi:10.1038/nature03302; Inagaki et al., doi:10.1073/pnas.0511033103 ; Mauclaire et al., doi:10.1111/j.1472-4677.2004.00035.x; Biddle et al., doi:10.1073/pnas.0600035103). Here we show that in subsurface sediments buried deeper than 1 m in a wide range of oceanographic settings at least 87% of intact polar membrane lipids, biomarkers for the presence of live cells (Biddle et al., doi:10.1073/pnas.0600035103; Sturt et al., 2004, doi:10.1002/rcm.1378), are attributable to archaeal membranes, suggesting that Archaea constitute a major fraction of the biomass. Results obtained from modified quantitative polymerase chain reaction and slot-blot hybridization protocols support the lipid-based evidence and indicate that these techniques have previously underestimated archaeal biomass. The lipid concentrations are proportional to those of total organic carbon. On the basis of this relationship, we derived an independent estimate of amounts of cellular carbon in the global marine subsurface biosphere. Our estimate of 90 Pg of cellular carbon is consistent, within an order of magnitude, with previous estimates, and underscores the importance of marine subsurface habitats for global biomass budgets.

对深海海底开展的深层钻探，揭示了一个广袤的微生物沉积生态系统（Parkes 等，1994，doi:10.1038/371410a0；D'Hondt 等，2004，doi:10.1126/science.1101155）。将染色微生物细胞的直接计数结果外推至可居住海洋次表层沉积物的总体积，可估算出这一迄今未被充分探索的生境中，可储存的细胞碳总量介于 56 Pg（Parkes 等，1994，doi:10.1038/371410a0）至 303 Pg（Whitman 等，1998）之间。近年来，诸多采用免培养技术的研究尚未明确古菌（Archaea）与细菌（Bacteria）在这一广袤生态系统中的丰度孰高孰低（Schippers 等，doi:10.1038/nature03302；Inagaki 等，doi:10.1073/pnas.0511033103；Mauclaire 等，doi:10.1111/j.1472-4677.2004.00035.x；Biddle 等，doi:10.1073/pnas.0600035103）。
本研究证实，在多样海洋环境下埋藏深度超过1米的次表层沉积物中，至少87%的完整极性膜脂（intact polar membrane lipids）——活细胞存在的生物标志物（biomarkers）——源自古菌细胞膜，这表明古菌在该生态系统的生物量中占据主要份额。采用经改良的定量聚合酶链式反应（quantitative polymerase chain reaction）与狭线印迹杂交（slot-blot hybridization）方案得到的结果，佐证了基于脂类的研究结论，并表明此前的相关技术曾低估了古菌的生物量。脂类浓度与总有机碳浓度呈正相关关系。基于这一关联，我们独立估算了全球海洋次表层生物圈的细胞碳总量。本次得到的90 Pg细胞碳估算值，与此前的估算值在一个数量级范围内保持一致，这也凸显了海洋次表层生境对全球生物量收支的重要意义。