Abstract
Groundwater ecosystems sustain drinking water supplies and play key roles for global biogeochemical cycles. Their functions are largely conveyed by microorganisms; so to understand and predict their response to global change, functional insights into groundwater microbiomes are essential. By combining metabolic labeling and omics methods to mechanistically trace microbial functions, we aim to reveal the role of non-phototrophic primary production in groundwater and its global significance.