The study looked at how transpiration affects photosynthesis in crops like sweet potato, rice, soybean, and peanut. They found that in the late growth stage, restricting transpiration led to higher photosynthesis rates, suggesting a lack of water reaching the photosynthetic organs. High temperatures also decreased photosynthesis, likely due to water shortage and high stomatal resistance. The researchers calculated a water vapor transfer coefficient (D) that closely correlated with photosynthetic rates in most crops. This coefficient depends on stomatal resistance and external air resistance, showing the importance of water availability for efficient photosynthesis in plants.