Soybean cultivars with high photosynthetic efficiency were studied to see how they differ in their ability to convert sunlight into energy. The researchers found that these cultivars varied in their photosynthetic rate and dark respiration rate under specific conditions. They also observed differences in how much light each cultivar needed to start photosynthesis. The study showed that cultivars with high photosynthetic efficiency were less affected by too much sunlight compared to those with high yield. Additionally, the critical temperatures at which sunlight harms the plants were higher in the high photosynthetic efficiency cultivars.