Soybean cultivars with high photosynthetic efficiency have better photosynthesis rates than those with high yield, but the latter have stronger dark respiration rates. Both types of cultivars show photoinhibition at high light levels, but those with high photosynthetic efficiency are less affected. The diurnal variation of photosynthesis in these cultivars follows a curve with two peaks, and the critical temperatures for photoinhibition are higher in high photosynthetic efficiency cultivars compared to high yield ones.