CO₂enrichment of soybeans. Effects of leaf/pod ratio

The effect of varying leaf number on response of soybean ( Glycine max (L.) Merr. cv. Fiskeby V) to CO 2 enrichment was studied. Plants were trimmed at pod set to 15 pods and 1 or 3 leaves (15:1 and 5:1 pod/leaf ratio) and placed in 350 or 1000 μl/l CO 2 growth chambers. Photosynthetic rates and dry weights were measured 6 times in all plants at each CO 2 concentration over a period of 39 days. Measured at treatment CO 2 concentration, photosynthetic rates deelined rapidly in enriched plants, but remained higher than those of non‐enriched plants. When all plants were measured at the same CO 2 concentration, for most sampling dates, neither growth, CO 2 concentration or pod/leaf ratio significantly affected rates of photosynthesis per unit area of comparable leaves. CO 2 enrichment significantly increased total weights and pod weights in 15:1 but not 5:1 pod/leaf ratio plants. Plants with a 5:1 pod/leaf ratio had significantly higher total and pod weights than 15:1 ratio plants. Both the photosynthesis and dry weight data suggest that plants in the 5:1 ratio enriched treatment were sink‐limited, but plants in all other treatments were source limited.