Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2003
Publication Date: 5/1/2004
Citation: Frantz, J., Ritchie, G., Cometti, G., Robinson, J., Bugbee, B. 2004. Exploring the limits of crop productivity: beyond the limits of tipburn in lettuce. Journal of the American Society for Horticultural Science. 129(3):331-338. Interpretive Summary: Fast growth of lettuce results in a calcium disorder called tipburn, which greatly reduces quality and marketability. We eliminated tipburn by blowing air directly onto the meristem, which allowed us to increase the photosynthetic photon flux (PPF) to 1000 micromoles per square meter per second (57.6 moles per square meter per day); two to three times higher than normally used for lettuce. Eliminating tipburn doubled edible yield at the highest PPF level. Increasing the carbon dioxide also increased productivity by about 30%, but had the additional effect of shifting the temperature optimum for growth from 25 degrees Celsius to 30 degrees Celsius. Increasing growing temperature increased the rate at which leaves expanded and emerged further increasing lettuce yields. This work demonstrates the effect of optimizing the plant growth environment for both total mass gain and maintaining high plant quality. It also mechanistically provides a way for plant breeders to study the factors that most limit lettuce productivity, which are tipburn, slow leaf expansion, and relatively low temperature optimum.
Technical Abstract: The productivity of lettuce in a combination of high light, warm temperature, and elevated carbon dioxide has not been commonly studied because rapid growth usually causes a calcium deficiency in meristems called tipburn, which greatly reduces quality and marketability. We eliminated tipburn by blowing air directly onto the meristem, which allowed us to increase the photosynthetic photon flux (PPF) to 1000 micromoles per square meter per second)57.6 moles per squaare meter per day); two to three times higher than normally used for lettuce. Eliminating tipburn doubled edible yield at the highest PPF level. In addition to high PPF, carbon dioxide was elevatef to 1200 micromoles per moles, which increased the temperature optimum from 25 to 30 degrees Celsius. The higher temperature increased leaf expansion rate, which improved radiation capture and more than doubled yield. Photosynthetic efficiency, measured as canopy quantum yield in a whole-plant gas exchange system, steadily increased up to the highest temperature of 32 degrees Celsius in high carbon dioxide. The highest productivity was 19 grams of dry biomass per square meter per day (380 grams fresh mass per square meter per day) averaged over the 23 days the plants received light. Without the limitation of tipburn, the combination of high PPF, high temperature, and elevated carbon dioxide, resulted in a 4 fold increase in growth rate over productivity in conventional environments.