Kevin Cope, Utah State University
Plants, Soils, and Climate
Photosynthesis is driven primarily by radiation between 400 and 700 nm; however, not all wavelengths are equally efficient. Red light (600 to 700 nm) is 25 to 35% more efficient than blue light (400 to 500 nm) and 5 to 30% more efficient than green light (500 to 600 nm). Although blue light is less efficient than red light, it has been shown to be necessary for normal plant development in all tested crop species. The mixture of pigments in plant leaves allows them to absorb all colors of light. Both red and blue light are absorbed primarily in the upper leaf. Green light penetrates deep into the lower leaf and transmits to leaf layers below the upper leaf canopy. Accordingly, once the upper canopy is saturated with red and blue light, supplemental green light is beneficial in increasing whole plant photosynthesis. Although the effect of spectral quality on single leaves is well characterized, the effect on whole plant growth and development is poorly understood. The narrow spectral output of LEDs makes them particularly effective for photobiological studies. From our initial studies with radish, soybean, and wheat, we determined that blue light levels can be used to better predict plant development than red:far-red light ratios. We also found that plants require at least 80 μmol of blue photons m-2 s-1 in order to develop normally. Further studies are currently being conducted to determine the optimal ratio of red and green light for maximizing whole plant photosynthesis in lettuce and radish.