Extreme abiotics drive sediment biocomplexity along pH gradients in a shallow submarine volcanic vent

Volcanic emissions in shallow vents influence the biogeochemistry of the sedimentary compartment, creating marked abiotic gradients. We assessed the spatial dynamics of the sediment compartment, as for the composition and origin of organic matter and associated prokaryotic community, in a volcanic shallow CO₂ vent (Vulcano Island, Italy). Based on elemental (carbon, nitrogen content and their ratio) and isotopic composition (δ¹³C, δ¹⁵N and δ³⁴S), the contribution of vent-derived organic matter (microbial mats) to sedimentary organic matter was high close to the vent, while the marine-derived end-members (seagrasses) contributed highly at increasing distance. Chemoautotrophic Campylobacterota and hyperthermophilic Achaea prevailed close to the vent, whilst phototrophic and chemoheterotrophic members dominated at increasing distance. Abiotic gradients generated by the volcanic CO₂ vent drive relevant changes in the composition, origin and nutritional quality of sedimentary organic matter, and influence the structure and complexity of associated prokaryotic communities, with expected relevant impact on the entire food-web.