A Multi-Omics Approach to Understand the Molecular and Microbial Transformations Associated with Dissolved Organic Matter Turnover in Coastal Waters

Blue carbon habitats, or coastal ecosystems such as salt marshes and mangroves, sequester approximately 5.3 Pg of carbon (C) globally and can be a source of dissolved organic matter (DOM) to coastal waters. The priming effect (PE), or non-additive effects on organic matter (OM) degradation when in the presence of mixed substrates, may influence the turnover of DOM exported from blue carbon habitats. The PE has been well described as a mechanism of soil OM turnover, but mixed reports of positive (enhanced OM degradation), neutral, or negative (suppressed OM degradation) priming effects have been reported in aquatic systems, and the direction/magnitude of priming can vary depending on ecosystem type, experimental design, and the response variables measured. Here, we used a laboratory experiment to study the molecular and microbial transformations associated with DOM turnover and to evaluate the role that the PE may play in blue C remineralization. Incubations were established with four treatments: a seawater control (Control), a blue carbon leachate (Peat), a ¹³C-labeled algae leachate (Algae), and a peat and algae leachate treatment (Priming treatment). Changes in bulk geochemistry, CO₂ partial pressure, DOM composition, and microbial metatranscriptomes were monitored over the course of the incubation. The composition of DOM was characterized via liquid chromatography mass spectrometry and Fourier-transform ion cyclotron resonance mass spectrometry. On a bulk level, DOM was remineralized to CO₂ most rapidly in the Priming treatment. On a molecular level, features putatively identified as lignin phenols via LC-MS were more degraded in the Priming treatment. High resolution mass spectrometry data was compared with microbial transcriptomes to analyze the metabolic pathways associated with DOM turnover. Pairing multi-omic datasets will allow us to better evaluate the mechanisms of microbially driven blue C turnover in the coastal zone.