Water stress affects how sugarcane plants absorb light for photosynthesis. By studying sugarcane with a special device, researchers found that water stress changes how chlorophyll in the plants reacts to light. This means that the plants' ability to convert light into energy is reduced, leading to lower photosynthetic activity and carbon assimilation. In simpler terms, when sugarcane is stressed by lack of water, its ability to use sunlight for energy is impaired.