ENVIRONMENTAL
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  PHYTOREMEDIATION

  ETHYLENE STUDIES

  RESPIRATION AND
    CARBON USE EFFICIENCY

  SPECTRAL IMAGING

  SUPER-DWARF CROPS

  LETTUCE STUDIES

  DIGITAL CAMERA
    IMAGING

  LUNAR CROP
    PRODUCTION & FAILURE
    ANALYSIS

  WATER STRESS STUDIES

  PHOTOBIOLOGY /
    LIGHT STUDIES

  TURFGRASS RESEARCH

RESEARCH: LETTUCE STUDIES

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CLICK ON THE TITLES TO VIEW ABSTRACTS:

• Exploring the Limits of Crop Productivity:
  Beyond the Limits of Tipburn in Lettuce
  Jonathan Frantz, G. Ritchie, N. Cometti, J. Robinson, and B. Bugbee - 2004
  Jour. ASHS 129:331-338

ABSTRACT  The productivity of lettuce in a combination of high light, high temperature, and elevated CO₂ 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 μmol m^–2·s^–1 (57.6 mol m^–2 d^–1); 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, CO₂ was elevated to 1200 μmol m^–2 mol^–1, which increased the temperature optimum from 25 to 30 ^oC. 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 ^oC in high CO₂. The highest productivity was 19 g m^–2 d^–1 of dry biomass (380 g d^–1 fresh mass) averaged over the 23 days the plants received light. Without the limitation of tipburn, the combination of high PPF, high temperature, and elevated CO₂ resulted in a 4-fold increase in growth rate over productivity in conventional environments.

• Exploring the Limits of Crop Productivity:
  High Light Studies with Lettuce
  Jonathan Frantz and B. Bugbee - 2001

INTRODUCTION  There are many different leaf lettuce cultivars and they range in color from light green and yellow to deep green as a result of higher concentrations of chlorophyll in the leaves. We tested four cultivars in high light to explore the limits of lettuce productivity.

• Exploring the limits of crop productivity: quantum yield,
  radiation capture, and carbon use efficiency of lettuce
  in a high light, temperature, and CO₂ environment
  Jonathan Frantz, G. Ritchie, N. Cometti, J. Robinson and B. Bugbee

ABSTRACT There have been several analyses to determine the theoretical maximum yield of a crop community.  Many crops are grown in sub-optimal conditions and maximum growth rates are sacrificed in order to improve some other characteristic of crop production (e.g. timing for the market).  As a result, theoretical maximum yields have not been analyzed for several important crops and breeders have little information as to what, if anything, may be most limiting to productivity.  Most productivity studies are performed under ambient or field CO₂ concentrations.  Photorespiration is reduced substantially by elevating CO₂, even in warm temperatures, and electron transport becomes the rate limiting factor in CO₂ fixation.  As a consequence, crops photosynthetic rate can be much higher in elevated rather than in ambient CO₂.  Radiation capture is also a critical component of productivity models.  Leaf expansion rate is greatly influenced by temperature and along with leaf emergence rate, provide a plant the means to effectively capture light as it develops from seedlings.  The temperature optimum for leaf expansion differs for different crops.  Carbon use efficiency (CUE) is a measure of how well a plant incorporates newly fixed carbon into new biomass.  Little information exists for lettuce CUE in different environments.  We examined growth of lettuce canopies at five constant temperatures: 21, 25, 30, 32.5, & 35 ^oC with two replicate chambers at each temperature.  Our studies indicate that the temperature optimum for leaf expansion, light interception, and growth is 30 ^oC, which is much higher than used in previous studies. The growth rate increased by more than 3-fold from 21 to 25 ^oC and by 40% from 25 to 30 ^oC; but decreased by 20% from 30 to 32.5 ^oC. These results indicate that the temperature optimum for lettuce growth and appearance is 5 to 10 ^oC above that used in previous studies.  In a separate study, PPF levels were increased up to 1000 ΅mol m^-2 s^-1.  Lettuce productivity continued to increase with higher light.  These results indicate that lettuce can be pushed with high light, temperature, and CO₂ by improving radiation capture, QY, and CUE.

• We Thought We Knew How to Grow Lettuce:
  Exploring the Limits of Crop Productivity
  Jonathan Frantz, G. Ritchie, and B. Bugbee

ABSTRACT The temperature optimum for lettuce is thought to be 20 to 25 C. Warmer  temperatures are not used because they increase bitterness and tip burn.  Temperatures above 25 C are also thought to reduce growth rates. We examined growth of lettuce canopies at five constant temperatures: 21, 25, 30, 32.5, & 35 ^oC with two replicate chambers at each temperature.  Our studies indicate that the temperature optimum for leaf expansion, light interception, and growth is 30 ^oC, which is much higher than used in previous  studies. The growth rate increased by more than 3-fold from 21 to 25 ^oC and by 40% from 25 to 30 ^oC; but decreased by 20 % from 30 to 32.5 ^oC. Plants appeared chlorotic at 20 and 25 ^oC, but chlorophyll content increased with  increasing temperature, and was more than 30 times higher at 35 than at 21 ^oC. Tip burn was not observed at or below 30 ^oC. These results indicate that the temperature optimum for lettuce growth and appearance is 5 to 10 ^oC above that used in previous studies.  In a separate study, PPF levels were reduced by 20 to 80% in the middle of the life cycle to examine adaptation rates. Whole plant photosynthesis and respiration rates adapted to within 80% of the initial rate after a few days.  These results indicate that lettuce is surprisingly tolerant of the system failures that are associated with power loss in space flight conditions.