The metabolic mechanisms underlying zooplankton-derived dissolved organic matter’s chemical properties

Dissolved organic matter (DOM), the largest reservoir of organic material in the ocean, plays a crucial role in the global carbon cycle and the microbial loop. While existing studies have documented significant DOM release by zooplankton, the chemodiversity and bioavailability of this DOM, along with the physiological mechanisms influencing these characteristics in heterogeneous coastal water environments, remain inadequately explored. We conducted onboard zooplankton DOM release experiments in heterogeneous estuarine-coastal water systems, followed by molecular characterization of the DOM using Fourier-transform ion cyclotron resonance mass spectrometry. Additionally, we analysed zooplankton metabolic activities through meta-transcriptomics to elucidate the relationship between the chemical properties of the released DOM and the underlying physiological processes of zooplankton. Our findings reveal substantial variations in the molecular diversity of DOM released by zooplankton across heterogeneous environment, notably between estuarine and coastal communities. We found strong correlations between the chemical reactivity of the DOM and clusters of orthologous groups (COGs) genes associated with functions such as carbohydrate metabolism, nucleotide processing, energy production, and coenzyme metabolism. Importantly, the aromaticity index (AI) of the released DOM was closely linked to metabolism-related gene functions, indicating that zooplankton metabolic processes significantly influence DOM bioavailability. This study enhances our understanding of how the organism’s metabolic processes shape the molecular characteristics of DOM they release, highlighting its implications for carbon cycling in the environment.