Far-red light is needed for efficient photochemistry and photosynthesis

Area of Science:

• Plant Physiology
• Photosynthesis Research
• Horticultural Lighting

Background:

• Photosynthetic efficiency declines at light wavelengths over 685nm.
• The Emerson enhancement effect describes improved efficiency with shorter wavelengths added to longer ones.
• The converse effect, where longer wavelengths enhance shorter ones, is less understood.

Purpose of the Study:

• To quantify the impact of far-red light on photosynthetic efficiency in lettuce.
• To investigate the Emerson enhancement effect in reverse.
• To determine the effects of far-red light on quantum yield and photosynthesis.

Main Methods:

• Lettuce (Lactuca sativa) was exposed to red/blue or warm-white light supplemented with far-red light (peak at 735nm).
• Measurements included quantum yield of photosystem II (ΦPSII) and non-photochemical quenching (NPQ).
• Net photosynthesis (Pn) was assessed under varying far-red light intensities.

Main Results:

• Far-red light immediately boosted lettuce ΦPSII by 6.5% (red/blue) and 3.6% (warm-white).
• Prolonged exposure increased ΦPSII and reduced NPQ, indicating less heat dissipation.
• Increased ΦPSII correlated with higher net photosynthesis, showing a dose-dependent response to far-red light.

Conclusions:

• Far-red light significantly enhances the photosynthetic efficiency of shorter wavelength light that over-excites photosystem II.
• This enhancement is linked to improved photosystem I and II function and reduced energy dissipation.
• The findings suggest optimizing light spectra in horticulture can improve crop yields.