INTERACTION OF TEMPERATURE AND CO2 ENRICHMENT ON SOYBEAN - GROWTH AND DRY-MATTER PARTITIONING

Projected increases in atmospheric CO2 concentration will affect growth and productivity of many plant species under various environmental conditions. Since these increases in CO2 may also increase mean annual temperatures, it is important to determine how the soybean (Glycine max (L.) Merr.) will respond to changes in temperature regimes associated with atmospheric CO2 enrichment. Morphology and growth responses of the Ransom cultivar, which is adapted to a southern U.S.A. climate, to day/night temperature regimes of 18/12, 22/16, and 26/20.degree. C and atmospheric CO2 concentrations of 350, 675 and 1000 .mu.L L-1 were studied in controlled environment chambers. Plant responses were determined at 20, 40, 67 and 115 (late senescence to maturity) days after planting. Plant height and number of branches increased slightly with CO2 enrichment and more significantly with increasing temperature. Root to shoot ratio remained unchanged at different CO2 concentrations but decreased as temperature increased. Leaf weight ratio and specific leaf weight decreased with increasing temperature. Low temperature reduced dry weight of all plant parts, but the reduction was ameliorated by increasing atmospheric CO2 concentration. The results show that increasing the atmospheric CO2 level causes soybean to grow more vigorously at low temperatures. Although controlled environment experiments have their drawbacks in regard to natural field conditions, the present data indicate that soybean will have enhanced growth even at moderately cool temperatures in the future global CO2 concentrations.