Variables Affecting the CO(2) Compensation Point.

Some factors influencing dark respiration, photorespiration, and photosynthesis were examined for their effect on the CO(2) compensation point (70 mul/l) of detached soybean (Glycine max) leaf discs. A higher compensation point in young leaves decreased to the constant value after leaf expansion and maturation, but increased again during senescence. The compensation point was 40 to 50% higher in plants grown in the summer than in the winter. The compensation point and dark respiration increased with temperatures above 17 C. Below 17 C dark respiration continued to decrease, but the compensation point did not decrease further. Increasing light intensities did not affect the compensation point.The effect of selected chemicals on the compensation point were surveyed. Some buffer components did not greatly alter the compensation point but organic solvents lowered it. Potassium phosphate and pyrophosphate greatly increased it. Inhibitors of photosynthesis increased the compensation point. Hydroxypyridinemethanesulfonate and sodium bisulfite severely inhibited photosynthesis in soybean leaves, stimulated dark respiration, and increased the compensation point.