Recognition of Superior Photosynthetic Efficiency in the Field Using the CO(2)-Depletion Technique

The relationship between CO(2) exchange rate (CER) and growth of crops in the field was investigated in Connecticut Broadleaf tobacco (Nicotiana tabacum) using the CO(2)-depletion technique. A particular objective was to determine if modest (i.e. <10%) varietal differences could be distinguished in mean CER. Statistical analysis of numerous CER values obtained over a wide range of irradiances during the course of the season indicated that differences of as little as 7% in the mean CER between varieties would be significant (n approximately 400). The usefulness of the CO(2)-depletion technique in detecting modest differences in photosynthetic efficiency has thus been demonstrated. These results are discussed in relation to the prospects for introducing and detecting genetic traits which would diminish photorespiration and increase CER and growth.