Bigger genomes provide environment-dependent growth benefits in grasses

Increasing genome size (GS) is associated with slower rates of DNA replication and greater cellular nitrogen and phosphorus demands. Nevertheless, plant species vary enormously in GS. Using data on grass species’ climatic niches and growth rates under different environmental conditions, we tested for growth costs or benefits associated with GS. We found that evolutionary history, photosynthetic pathway and life-history all influence the distribution of grass species’ GS. GS was constrained in annual and C4 species, the latter allowing for small cells necessary for C4 leaf anatomy. We found that larger GS were advantageous under high nitrogen availability and, for perennial species, low growth-season temperature. Increased GS benefits are likely due to associated larger cell sizes, allowing rapid biomass production where soil fertility meets nitrogen demands or when growth occurs via temperature-independent cell expansion. Our findings reveal that GS is a globally important predictor of grass performance dependent on environmental conditions.