Interspecific competition negates CO₂ benefits for most plant species

Elevated CO₂ (eCO₂) frequently stimulates plant growth and is widely assumed to enhance productivity in multispecies communities^1,2, yet species responses to eCO₂ vary widely with biotic and abiotic context^1,3,4. Whether eCO₂ relaxes competition or amplifies existing competitive hierarchies, shaping how growth benefits are distributed among species, remains poorly resolved. Here we synthesize data from 19 CO₂ enrichment experiments (glasshouse, chamber and field studies), encompassing 97 plant species from grass-dominated ecosystems to quantify how competitive context alters species- and mixture-level responses. Although most species respond positively to eCO₂ without neighbours, over half show neutral or negative responses in mixtures. Despite this, dominant species often drive modest increases in total mixture biomass under eCO₂. Trait analyses indicate that acquisitive strategies, rather than intrinsic CO₂ sensitivity alone, predict success under competition. Together, our results indicate that under competition, eCO₂ redistributes growth benefits unevenly among species, favouring dominant species while many subdominants experience neutral or negative responses.