ARS | Publication request: PHOTOSYNTHESIS CARBOHRDRATE CONTENT AND EXPORT RATE IN SOYBEAN IN THE FIELD UNDER ELEVATED P CO2 (FACE)

Submitted to: Plant Physiology Supplement
Publication Type: Abstract
Publication Acceptance Date: August 7, 2002
Publication Date: N/A

Technical Abstract: Diurnal measurements of net photosynthetic CO2 uptake (A) and foliar carbohydrate contents were made at four stages during the development of the soybeans grown in the field at current (36Pa) and elevated (56 Pa) p CO2 using Free-Air CO2 Enrichment technology at the University of Illinois, soyFACE experiment. A carbohydrate export rate was calculated by mass balance from measurements of A, A being the total nonstructural carbohydrate content and respiration rate. Young soybeans showed the greatest total daily of A (A'). Leaves accumulated relatively high levels of carbohydrate during the photoperiod but export rates were high and all the carbon fixed was exported during the day. Soybeans grown in elevated p CO2 had higher photosynthetic rates but were able to export all the additional photosynthate. There was no evidence of reduced capacity to utilize the extra photosynthate produced at elevated p CO2. On an overcast day, toward the end of the season, there was no CO2 stimulation of A'. Despite the lowest A' observed in the study, there was a 4-fold increase in the amount carbohydrate accumulated during the photoperiod in the soybeans grown in elevated p CO2. Daytime export rates in the soybeans grown in elevated levels of p CO2 were lower than those grown in current p CO2. However, nighttime export of photosynthate in elevated p CO2 returned carbohydrate contents to their predawn levels. These results suggest that toward the end of the growth season soybeans grown using current agricultural practices may not be able to fully capitalize on a future high p CO2 environment.