WA-Organic Isotope Geochemistry Centre, The Institute for Geoscience Research, School of Earth and Planetary Sciences, Curtin University, Perth, WA, Australia.
School of Biological Sciences, University of Western Australia, Crawley, Western Australia, Australia.
PLoS One. 2020 Aug 28;15(8):e0237730. doi: 10.1371/journal.pone.0237730. eCollection 2020.
Freshwater ecosystems play a key role in shaping the global carbon cycle and maintaining the ecological balance that sustains biodiversity worldwide. Surficial water bodies are often interconnected with groundwater, forming a physical continuum, and their interaction has been reported as a crucial driver for organic matter (OM) inputs in groundwater systems. However, despite the growing concerns related to increasing anthropogenic pressure and effects of global change to groundwater environments, our understanding of the dynamics regulating subterranean carbon flows is still sparse. We traced carbon composition and transformations in an arid zone calcrete aquifer using a novel multidisciplinary approach that combined isotopic analyses of dissolved organic carbon (DOC) and inorganic carbon (DIC) (δ13CDOC, δ13CDIC, 14CDOC and 14CDIC) with fluorescence spectroscopy (Chromophoric Dissolved OM (CDOM) characterisation) and metabarcoding analyses (taxonomic and functional genomics on bacterial 16S rRNA). To compare dynamics linked to potential aquifer recharge processes, water samples were collected from two boreholes under contrasting rainfall: low rainfall ((LR), dry season) and high rainfall ((HR), wet season). Our isotopic results indicate limited changes and dominance of modern terrestrial carbon in the upper part (northeast) of the bore field, but correlation between HR and increased old and 13C-enriched DOC in the lower area (southwest). CDOM results show a shift from terrestrially to microbially derived compounds after rainfall in the same lower field bore, which was also sampled for microbial genetics. Functional genomic results showed increased genes coding for degradative pathways-dominated by those related to aromatic compound metabolisms-during HR. Our results indicate that rainfall leads to different responses in different parts of the bore field, with an increase in old carbon sources and microbial processing in the lower part of the field. We hypothesise that this may be due to increasing salinity, either due to mobilisation of Cl- from the soil, or infiltration from the downstream salt lake during HR. This study is the first to use a multi-technique assessment using stable and radioactive isotopes together with functional genomics to probe the principal organic biogeochemical pathways regulating an arid zone calcrete system. Further investigations involving extensive sampling from diverse groundwater ecosystems will allow better understanding of the microbiological pathways sustaining the ecological functioning of subterranean biota.
淡水生态系统在塑造全球碳循环和维持全球生物多样性的生态平衡方面发挥着关键作用。地表水与地下水通常相互连通，形成一个物理连续体，它们的相互作用被报道为地下水系统中有机物质（OM）输入的关键驱动因素。然而，尽管人们越来越关注不断增加的人为压力和全球变化对地下水环境的影响，但我们对调节地下碳流动的动力学的理解仍然很匮乏。我们使用一种新的多学科方法来追踪干旱区钙结含水层中的碳组成和转化，该方法结合了溶解有机碳（DOC）和无机碳（DIC）的同位素分析（δ13CDOC、δ13CDIC、14CDOC 和 14CDIC）与荧光光谱学（发色溶解有机物质（CDOM）特征）和代谢组学分析（细菌 16S rRNA 的分类和功能基因组学）。为了比较与潜在含水层补给过程相关的动态，我们从两个具有不同降雨量的钻孔中采集水样：低降雨量（（LR），旱季）和高降雨量（（HR），雨季）。我们的同位素结果表明，在钻孔场的上部（东北），现代陆地碳的变化有限且占主导地位，但在下部（西南），HR 与增加的古老和 13C 富集的 DOC 之间存在相关性。CDOM 结果表明，在同一下部钻孔中，雨后从陆地向微生物衍生化合物发生转变，该钻孔也进行了微生物遗传学采样。功能基因组学结果表明，HR 期间，与芳香族化合物代谢相关的降解途径相关的基因编码增加。我们的结果表明，降雨会导致钻孔场不同部位的不同反应，下部场的古老碳源和微生物处理增加。我们假设这可能是由于 HR 期间 Cl-从土壤中迁移或从下游盐湖中渗透导致盐分增加。本研究首次使用稳定和放射性同位素与功能基因组学相结合的多技术评估方法来探测调节干旱区钙结系统的主要有机生物地球化学途径。进一步涉及从不同地下水生态系统广泛采样的研究将有助于更好地了解维持地下生物群生态功能的微生物途径。
