The researchers studied how winter wheat plants grow better under sprinkler irrigation compared to surface irrigation. They measured the photosynthesis of the wheat leaves and found that under sprinkler irrigation, the plants had higher net photosynthesis rates and lower CO2 levels inside the leaves. The plants also had higher transpiration rates and stomatal conductance during midday, but lower at other times. The midday drop in photosynthesis was due to different factors under each irrigation method, with sprinkler irrigation improving the activity of mesophyll cells in the leaves. This change made the limiting factor for photosynthesis shift from nonstomatal to stomatal gradually.