C4 plants like maize have a unique way of concentrating carbon dioxide (CO2) for photosynthesis. The researchers found that maize photosynthesis is affected by the amount of oxygen (O2) present, with a maximum rate at around 10% O2. High O2 levels above 10% can inhibit photosynthesis and reduce the efficiency of CO2 use. This inhibition is similar to what happens during photorespiration, a process that occurs when CO2 levels are low. Maize maintains high CO2 levels around the enzyme Rubisco in its leaf cells, which helps minimize photorespiration. Overall, the study shows that photorespiration does occur in maize, but it is not a major issue unless CO2 levels are severely limited.