Maize is a staple crop in Northern Ghana, where climate change is increasing the frequency and severity of droughts. Understanding how elevated atmospheric CO₂ interacts with water limitation is critical for improving crop productivity and food security. This study evaluated the effects of drought and elevated CO₂ on maize photosynthesis, stomatal conductance, and yield under field conditions.

Maize plants were grown under ambient (≈410 ppm) and elevated CO₂ (≈600 ppm) conditions, with well-watered and drought-stressed treatments. Leaf-level gas exchange and biochemical assays were used to measure photosynthetic rate, Rubisco activity, and stomatal conductance. Canopy-level carbon fluxes were monitored using portable flux chambers.

Results showed that drought reduced net photosynthesis by 42% (from 22.5 ± 1.2 to 13.0 ± 0.8 μmol CO₂ m⁻² s⁻¹) and stomatal conductance by 55% (from 0.35 ± 0.02 to 0.16 ± 0.01 mol H₂O m⁻² s⁻¹) under ambient CO₂. Elevated CO₂ partially mitigated these effects, increasing net photosynthesis by 28% under drought conditions and reducing stomatal closure by 15%. Canopy-level measurements indicated that total aboveground biomass decreased by 38% under drought at ambient CO₂, but only 22% under elevated CO₂.

These findings indicate that elevated CO₂ can partially offset drought-induced declines in maize productivity, but significant reductions still occur under severe water limitation. Breeding and management strategies that enhance drought tolerance while optimizing CO₂ responsiveness could improve maize yield stability in Ghana’s increasingly variable climate.