4.7 Article

Carbon Limitation Leads to Thermodynamic Regulation of Aerobic Metabolism

Journal

ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS
Volume 7, Issue 7, Pages 517-524

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.estlett.0c00258

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Funding

  1. U.S. Department of Energy (DOE), Office of Biological and Environmental Research (BER), as part of Subsurface Biogeochemical Research Program's Scientific Focus Area (SFA) at the Pacific Northwest National Laboratory (PNNL)
  2. DOE [DE-AC06-76RLO 1830]

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Organic matter (OM) metabolism in freshwater ecosystems is a critical source of uncertainty in global biogeochemical cycles, yet the processes regulating aerobic respiration in aquatic environments remain poorly understood. Aerobic respiration is typically predicted through kinetic controls such as organic carbon and oxygen concentrations, while assuming thermodynamic regulation has no influence. The role of OM thermodynamics has been mainly explored under anaerobic conditions; however, recent observations have suggested that thermodynamic properties of OM may influence aerobic respiration rates. Here, we explicitly test OM thermodynamics as a key regulator of aerobic respiration. We pair controlled microcosm experiments with ultrahigh-resolution OM characterization to show that aerobic respiration increases with OM thermodynamic favorability under carbon limitation. We also demonstrate a shift in the regulation of aerobic respiration from OM thermodynamics to nitrogen content when carbon is in excess, highlighting a central role for OM thermodynamics particularly in carbon-limited ecosystems. This illuminates a structural gap in aquatic biogeochemical models by demonstrating that both kinetic and thermodynamic constraints can modulate aerobic respiration. Our work therefore proposes a new conceptual model in which thermodynamic and nutrient limitations dually control aerobic respiration.

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