Nature Geoscience ( IF 18.3 ) Pub Date : 2022-06-30 , DOI: 10.1038/s41561-022-00968-5 Will A. Overholt, Susan Trumbore, Xiaomei Xu, Till L. V. Bornemann, Alexander J. Probst, Markus Krüger, Martina Herrmann, Bo Thamdrup, Laura A. Bristow, Martin Taubert, Valérie F. Schwab, Martin Hölzer, Manja Marz, Kirsten Küsel
The terrestrial subsurface contains nearly all of Earth’s freshwater reserves and harbours the majority of our planet’s total prokaryotic biomass. Although genetic surveys suggest these organisms rely on in situ carbon fixation, rather than the photosynthetically derived organic carbon transported from surface environments, direct measurements of carbon fixation in the subsurface are absent. Using an ultra-low level 14C-labelling technique, we estimate in situ carbon fixation rates in a carbonate aquifer. We find these rates are similar to those measured in oligotrophic marine surface waters and up to six-fold greater than those observed in the lower euphotic zone. Our empirical carbon fixation rates agree with nitrification rate data. Metagenomic analyses reveal abundant putative chemolithoautotrophic members of an uncharacterized order of Nitrospiria that may be behind the carbon fixation. On the basis of our determined carbon fixation rates, we conservatively extrapolate global primary production in carbonate groundwaters (10% of global reserves) to be 0.11 Pg carbon per year. These rates fall within the range found for oligotrophic marine surface waters, indicating a substantial contribution of in situ primary production to subsurface ecosystem processes. We further suggest that, just as phototrophs are for marine biogeochemical cycling, such subsurface carbon fixation is potentially foundational to subsurface trophic webs.
中文翻译:
地下水中的碳固定率与贫营养海洋系统中的碳固定率相似
陆地地下包含了地球上几乎所有的淡水储备,并拥有我们星球上大部分的原核生物量。尽管遗传调查表明这些生物依赖原位碳固定,而不是从地表环境中运输的光合作用衍生的有机碳,但缺乏对地下碳固定的直接测量。使用超低级别14碳标记技术,我们估计碳酸盐含水层中的原位碳固定率。我们发现这些比率与在贫营养海洋地表水中测得的比率相似,并且比在低透光区观察到的比率高出六倍。我们的经验碳固定率与硝化率数据一致。宏基因组分析揭示了可能是碳固定背后的未表征的 Nitrospiria 顺序的大量推定的化学自养成员。根据我们确定的碳固定率,我们保守地推断全球碳酸盐地下水的初级产量(占全球储量的 10%)为每年 0.11 Pg 碳。这些速率在贫营养海洋地表水的范围内,表明就地初级生产对地下生态系统过程的重大贡献。