Elevated air [CO2] improves photosynthetic performance and alters biomass accumulation and partitioning in drought-stressed coffee plants

•Elevated [CO2] improved carbon assimilation balance regardless of watering.•Elevated [CO2] decreased photorespiration rates and oxidative pressure under drought.•Improved growth under elevated [CO2] was more evident under drought than under full irrigation.•Elevated [CO2] led to more biomass partitioning towards roots with greater root length under drought.•Growth changes at elevated [CO2] were unrelated to altered hormonal pools, but rather with shifts on carbon fluxes.