Photosynthesis and Productivity of Soybean [Glycine max (L.) Merr.]

The peculiarities of leaf carbon dioxide gas exchange in soybean genotypes grown in field over a large area and contrasting in duration of vegetation, photosynthetic traits and productivity were studied. Varietal differences in the daily and ontogenetic changes in photosynthesis and photorespiration were identified. It was established that the period of the high activity of photosynthetic apparatus in high productive soybean genotypes lasts for a longer time. The photosynthetic rate and the rate of CO2 release in light due to photorespiration are higher in high productive genotypes. The magnitude of photorespiration in contrast soybean genotypes constitutes about 28-35% of photosynthetic rate. The ratio between true photosynthesis and photorespiration in genotypes with different productivity is constant enough during ontogenesis, indicating a direct positive correlation between true photosynthesis and photorespiration.