Scaling laws link conserved gene-abundance distributions to adaptive expression in diatom communities worldwide

Marine microbes sustain Earth's major biogeochemical cycles, yet how they maintain stable ecosystem functions across diverse environments remains unclear. We analyzed metagenomic and metatranscriptomic data from diatom communities sampled during the Tara Oceans global expedition. While gene abundance distributions remain statistically similar across sample, gene expression varies systematically across geographical locations, a global pattern we show reflects predictable scaling laws. Global distributions, scaling relationships, and variability among sampling stations are captured by a stochastic model linking gene abundance dynamics to gene expression. While colder waters are associated with higher transcriptional activity and warmer regions show more selective gene usage, we find that transcript abundance increases nonlinearly with transcript richness. This general scaling is captured by our model and suggests that diatom communities balance high expression of core genes with specific functional diversity. These scaling relationships hold consistently across ocean basins, with temperature, used as an effective large-scale environmental descriptor whose signature cannot be fully disentangled from spatial structure, sufficing to predict transcriptional patterns from genetic composition. Our findings reveal how the stability of gene-abundance structure in diatom ecosystems coexists with transcriptional variability, enabling flexible functional responses.