GROWTH AND ONTO-MORPHOGENESIS OF SOYBEAN (GLYCINE-MAX MERRIL) IN AN OPEN, NATURALLY CO2-ENRICHED ENVIRONMENT

Springs emitting carbon dioxide are frequent in Central Italy and prov ide a way of testing the response of plants to CO2 enrichment under na tural conditions. Results of a CO2 enrichment experiment on soybean at a CO2 spring (Solfatara) are presented. The experimental site is char acterized by significant anomalies in atmospheric CO2 concentration pr oduced by a large number of vents emitting almost pure CO2 (93%) plus small amounts of hydrogen sulphide, methane, nitrogen and oxygen. With in the gas vent area, plants were grown at three sub-areas whose mean CO2 concentrations during daytime were 350, 652 and 2370 mumol mol-1, respectively. Weekly harvests were made to measure biomass growth, lea f area and ontogenetic development. Biomass growth rate and seed yield were enhanced by elevated CO2. In particular, onto-morphogenetic deve lopment was affected by elevated CO2 with high levels of CO2 increasin g the total number of main stem leaf nodes and the area of the main st em trifoliolate leaves. Biochemical analysis of plant tissue suggested that there was no effect of the small amounts of H2S on the response to CO2 enrichment. Non-protein sulphydryl compounds did not accumulate in leaf tissues and the overall capacity of leaf extracts to oxidize exogenously added NADH was not decreased. The limitations and advantag es of experimenting with crop plants at elevated CO2 in the open and i n the proximity of carbon dioxide springs are discussed.