Relationship of Photosynthetic Rate to Growth and Fruiting of Cotton, Soybean, Sorghum, and Sunflower
- J. R. Mauney,
- K. E. Fry and
- G. Guinn
Cotton (Gossypium hirsutum L.), sorghum (Sorghum bicolor L.), soybean (Glycine max L.), and sunflower (Helianthus annuus L.) plants were exposed during daylight hours to an atmosphere enriched with CO2 to 630 ppm (v:v) (HiCO2) in a glasshouse. Temperature was trolled continuously to produce a daily maximum of 35 C and a minimum of 21 C. Days were cloudless and long, May to August, in Phoenix, Ariz. Average CO2 exchange rate (CER) increased 15% for cotton, 2% for sorghum, 41% for soybean, and 7% for sunflower compared to the CER of these species at 330 ppm CO2 (LoCO2). The increase in CER was not statistically significant for sorghum and sunflower. Measurements of relative growth rate and net assimilation rate showed the growth rate of all species increased during the juvenile stage (10d-30d) in the enriched atmosphere. and were not higher in the enriched atmosphere after the juvenile stage, but cotton and soybean plants maintained their larger size and greater absolute growth.
Final dry weights of cotton and soybean increased 110 and 380%, respectively, in HiCO2 compared to LoCO2. Lint yield of cotton was increased 180% by HiCO2 on a per-plant basis and 88% on a unit leaf area basis. Became of growth fimitations imposed by terminal flowers, the final size of sorghum and sunflower plants in HiCO2 was not significantly larger than in LoCO2 These results imply that selection for CER will not effectively increase yield of determinate species such as sunflower and sorghum, but may effectively increase yield of indeterminate species such as cotton and soybean, if a sensitive assay for CER can be found.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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