Exploring the Limits of Crop Productivity: Beyond the Limits of Tipburn in Lettuce

Abstract

<jats:p>The productivity of lettuce in a combination of high light, high temperature, and elevated CO<jats:sub>2</jats:sub> 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 (<jats:italic>PPF</jats:italic>) to 1000 μmol·m<jats:sup>-2</jats:sup>·s<jats:sup>-1</jats:sup> (57.6 mol·m<jats:sup>-2</jats:sup>·d<jats:sup>-1</jats:sup>); two to three times higher than normally used for lettuce. Eliminating tipburn doubled edible yield at the highest <jats:italic>PPF</jats:italic> level. In addition to high <jats:italic>PPF</jats:italic>, CO<jats:sub>2</jats:sub> was elevated to 1200 μmol·m<jats:sup>-2</jats:sup>·mol<jats:sup>-1</jats:sup>, which increased the temperature optimum from 25 to 30 °C. 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 °C in high CO<jats:sub>2</jats:sub>. The highest productivity was 19 g·m<jats:sup>-2</jats:sup>·d<jats:sup>-1</jats:sup> of dry biomass (380 g·d<jats:sup>-1</jats:sup> fresh mass) averaged over the 23 days the plants received light. Without the limitation of tipburn, the combination of high <jats:italic>PPF</jats:italic>, high temperature, and elevated CO<jats:sub>2</jats:sub> resulted in a 4-fold increase in growth rate over productivity in conventional environments.</jats:p>

Non-destructive Phenotyping of Lettuce Plants in Early Stages of Development with Optical Sensors

“…These changes in the chlorophyll content are at odds with our observations that show overall increases in RCC with growing temperature ( Figures 7, 8 , and 13 ). Similar to our results, almost a 10-fold increase in chlorophyll content has been observed in plants of cultivar Grand Rapids when the average temperature was raised from 23 to 33°C (at 600 μmol m -2 s -1 ; Frantz et al, 2004). These large differences between studies may be caused by numerous factors, including accessions used in the studies, other environmental conditions interacting with temperature (photoperiod, PPFD, humidity, etc.…”

The effects of container geometry on water and heat regimes in soilless culture: lettuce as a case study

“…Increased root temperature above 25 °C was found to influence the translocation of ions from root to shoot (Kafkafi 2008). The occurrence of tip burn is often associated with high air temperatures (Misaghi and Grogan 1978;Frantz et al 2004). Our assumption is that plants in 30-cm-high container experienced root heat stress, which resulted in higher tip burn damage.…”

Tipburn in salt-affected lettuce (Lactuca sativa L.) plants results from local oxidative stress

“…Combined tipburn incidence and severity (tipburn index, TI) was evaluated according to Frantz et al (2004) as TI: {[(S · 5) + (M · 3) + (L · 1)] · 100}/P · 5, where S = number of plants with severe tipburn; M is the number of plants with medium tipburn; L is the number of plants with light tipburn and P is the total number of plants. The proportion of leaf area affected by tipburn was estimated in digital photographs by measuring necrotic areas and total leaf area with the image processing software ImageJ (http://rsbweb.nih.gov/ij).…”