Predictable functional biogeography of marine microbial heterotrophs

Microbial heterotrophs (‘picoheterotrophs’) drive global carbon cycling, but how to quantitatively organize their functional complexity remains unclear. Here, we generate a global -scale, mechanistic understanding of marine picoheterotrophic functional biogeography with a novel model -data synthesis. We build picoheterotrophic diversity into a trait -based marine ecosystem model along two axes: substrate lability and optimization for growth rate (copiotrophy) vs. substrate affinity (oligotrophy). Using genetic sequences along an Alaska -to -Antarctica Pacific Ocean transect, we compile 21 picoheterotrophic guilds and estimate their degree of copiotrophy. Data and model agreement suggests that gradients in predation and substrate lability predominantly set biogeographical patterns, and identifies ‘slow copiotrophs’ subsisting at depth. Results demonstrate the predictability of the marine microbiome and connect ecological dynamics with carbon storage, crucial for projecting changes in a warming ocean.