Meta-metabolome ecology reveals that geochemistry and microbial functional potential are linked to organic matter development across seven rivers

Rivers receive substantial dissolved organic matter (DOM) input from the surrounding land which is transported to the ocean. As this DOM travels through watersheds, it undergoes biotic and abiotic transformations which impact biogeochemical cycles and release CO2 into the atmosphere. While recent research has increased our mechanistic knowledge of DOM development within watersheds, DOM development across broad spatial distances and within divergent biomes is under investigated. Here, we combined DOM characterization, geochemical analyses, and shotgun metagenomics to analyze samples from seven rivers ranging from the U.S. Pacific Northwest to Berlin, Germany. Initial analyses revealed that many DOM properties separated based upon river type (e.g., wastewater, headwater), though paired geochemical analyses indicated that geochemistry often explained some variation. Analyses rooted in meta-metabolome ecology indicated that, at the global scale, DOM was structured overwhelmingly by deterministic selection. When controlling for scale, however, analyses indicated that ecological assembly dynamics were again structure, in part, by river type. Finally, microbial analyses revealed that many riverine microbes from our systems shared core metabolic functional potential while differing in peripheral capabilities in spatially resolved patterns. Further analyses in the carbon degradation potentials of the recovered metagenomically assembled genomes indicated that the sample rivers had strong taxonomically conserved niche differentiation regarding carbon degradation and that the diversity in carbon degradation potential was significantly related to organic matter diversity. Together, these results help us uncover interconnections between the development of DOM, riverine geochemistry, and microbial functional potential. ### Competing Interest Statement The authors have declared no competing interest.