2018 ASHS Annual Conference
Effects of Temperature and Potassium on Lettuce Biomass, Quality, and Phytonutrient Concentrations in a Controlled Environment
Effects of Temperature and Potassium on Lettuce Biomass, Quality, and Phytonutrient Concentrations in a Controlled Environment
Thursday, August 2, 2018
International Ballroom East/Center (Washington Hilton)
Lettuce is an economically important crop that generates sizeable income for small and medium-sized growers in the southeastern United States. When produced in adverse environmental conditions, lettuce is vulnerable to yield losses and deterioration of quality. Previous research has indicated that elevated levels of potassium (K) positively affects the quality of several fruits and vegetables, including strawberry, melon, pepper, and tomato. However, research concerning the impact of elevated K levels on leafy vegetables, such as lettuce, is lacking. Therefore, seeds of dark-red ‘Lollo’ lettuce were sown in a soilless medium and germinated under greenhouse conditions at 25/20 °C (day/night). Upon emergence of the first true leaf, plantlets were transferred into 11-L Rubbermaid© plastic containers and placed into growth chambers at 25 and 33 °C. Plants were produced with increasing K treatments of 117.3 (control), 234.6 (2x), 469.2 (4x), and 4) 938.4 (8x) mg·L-1. Plants were harvested 30 days after seeding. Increasing K treatments resulted in a negative quadratic response on lettuce dry mass and generated 14% more leaf calcium at 234.6 mg·L-1 compared to the control treatment. Increasing temperature from 25 to 33 °C resulted in the increased leaf dry matter and biomass by 40% and 43%, respectively. Conversely, leaf water content increased by 3% from 25 to 33 °C. Increasing nutrient solution K alone did not affect lettuce quality (phenolics and mineral content). However, plants produced at 33 °C showed a greater accumulation of quercetin glycosides compared to plants produced at 25 °C. Additionally, interactions between temperature and K treatment influenced leaf concentrations of phosphorous, sulfur, and copper. The results from this study suggest that temperature is a stronger regulatory factor than increasing K in the determination of lettuce yield and quality; however, increasing K concentration to 234.6 mg·L-1 results in greater concentrations of leaf mineral content without compromising plant yield.