Table_2_Daylight-driven carbon exchange through a vertically structured microbial community.XLSX

Interactions between autotrophs and heterotrophs are central to carbon (C) exchange across trophic levels in essentially all ecosystems and metabolite exchange is a frequent mechanism for distributing C within spatially structured ecosystems. Yet, despite the importance of C exchange, the timescales at which fixed C is transferred in microbial communities is poorly understood. We employed a stable isotope tracer combined with spatially resolved isotope analysis to quantify photoautotrophic uptake of bicarbonate and track subsequent exchanges across a vertical depth gradient in a stratified microbial mat over a light-driven diel cycle. We observed that C mobility, both across the vertical strata and between taxa, was highest during periods of active photoautotrophy. Parallel experiments with 13C-labeled organic substrates (acetate and glucose) showed comparably less exchange of C within the mat. Metabolite analysis showed rapid incorporation of 13C into molecules that can both comprise a portion of the extracellular polymeric substances in the system and serve to transport C between photoautotrophs and heterotrophs. Stable isotope proteomic analysis revealed rapid C exchange between cyanobacterial and associated heterotrophic community members during the day with decreased exchange at night. We observed strong diel control on the spatial exchange of freshly fixed C within tightly interacting mat communities suggesting a rapid redistribution, both spatially and taxonomically, primarily during daylight periods.自养生物（autotroph）与异养生物（heterotroph）之间的相互作用，是几乎所有生态系统中跨营养级碳（C）交换的核心环节；而代谢物交换则是空间结构化生态系统内碳分配的常见机制。然而，尽管碳交换至关重要，但学界对微生物群落中固定碳的转移时间尺度仍知之甚少。本研究采用稳定同位素示踪剂结合空间分辨同位素分析，定量测定了光合自养生物对碳酸氢盐的摄取，并在光驱动的昼夜周期内，追踪了分层微生物垫中沿垂直深度梯度的后续碳交换过程。研究观察到，无论是跨垂直层还是物种类群间的碳流动性，在活跃光合自养阶段均达到峰值。采用13C标记有机底物（乙酸盐与葡萄糖）的平行实验显示，微生物垫内的碳交换水平相对更低。代谢物分析显示，13C被快速掺入两类分子中：一类可构成系统内部分胞外聚合物（extracellular polymeric substances），另一类可介导光合自养生物与异养生物间的碳转运。稳定同位素蛋白质组分析显示，日间蓝细菌（cyanobacterium）与其共生异养群落成员间存在快速碳交换，夜间交换则有所减弱。本研究观察到，紧密互作的垫状群落内新固定碳的空间交换受到强烈的昼夜节律调控，表明碳主要在日间发生快速的空间与分类学层面的重新分配。