GERMINATION AND SEEDLING DEVELOPMENT OF SOYBEANS IN A CARBON DIOXIDE‐DEFICIENT ATMOSPHERE

Abstract

During the initial phase of germination and seedling development of soybeans, most of the increase in dry weight in the embryo axis occurred in the hypocotyl. The epicotyl did not undergo a rapid increase in size and dry weight until the 4th to 5th day of growth. From day 1 to 11 dry weights of the hypocotyls in the “CO2‐normal” and “CO2‐Iimiting” (less than 50 ppm [0.005%] atmospheric CO2) treatments were similar. By day 13 the CO2‐normal hypocotyls had continued their rapid increase in dry weight while the dry weight of the hypocotyls grown under CO2‐limiting conditions had decreased. The parallel decrease in dry weight of the cotyledons that occurred for both CO2 treatments (days 1 to 13) suggested that CO2 content of the atmosphere is not a controlling factor in the digestion or hydrolysis of food reserves in the cotyledon during germination and seedling development. This is supported by the failure of the CO2 treatments to produce significantly different patterns in utilization of lipids, total carbohydrates, or proteins in the cotyledons. The seedlings grown under either the limiting or normal CO2 atmospheres utilized their cotyledonary carbohydrates and lipids before the proteins. Sufficient food reserves are present in the soybean cotyledon storage cells for seedling development until about day 9. Net CO2 uptake by soybeans in a CO2‐normal environment first occurred between days 9 to 11.