The Emerson effect describes how plants convert light into energy more efficiently. This phenomenon shows that photosynthesis significantly increases when plants are exposed to specific combinations of light wavelengths, moving beyond a simple additive response. It provides insight into the complex interplay of light and plant energy production.
The Discovery
American scientist Robert Emerson described the Emerson effect in the 1950s. His experiments challenged the idea that a single wavelength of light produced a predictable photosynthetic response. Emerson observed that when plants were exposed to light wavelengths greater than 680 nanometers (nm), photosynthesis efficiency dropped abruptly, a phenomenon known as the “red drop effect.” This was unexpected because chlorophyll still absorbs light effectively in this range.
Emerson then exposed plants to both short-wavelength (less than 660 nm) and long-wavelength (greater than 680 nm) light simultaneously. He found that photosynthesis efficiency increased significantly, exceeding the sum of efficiencies observed when each wavelength was applied individually. This enhancement showed that two different photosystems were involved in photosynthesis. His findings laid the groundwork for identifying the dual photosystem mechanism in plants.
How Different Light Wavelengths Work Together
The Emerson effect reveals the cooperative action of two distinct photosystems within plant chloroplasts: Photosystem I (PSI) and Photosystem II (PSII). Photosystem II primarily absorbs red light, around 680 nm, initiating the electron transport chain by splitting water molecules and releasing electrons. These excited electrons then travel through a series of carriers.
Photosystem I, on the other hand, absorbs far-red light, generally in the range of 700 to 730 nm. When these less energetic electrons reach PSI, far-red light re-excites them to a higher energy state. This re-energizing allows them to complete the electron transport chain, leading to the production of NADPH and ATP, the energy-carrying molecules needed for carbohydrate synthesis.
For photosynthesis to operate at its highest efficiency, both photosystems must be adequately energized and balanced. Red light alone can over-excite PSII, while far-red light alone minimally increases photosynthesis because it primarily excites PSI and does not initiate the process effectively. The combined application of red and far-red light ensures that both PSII and PSI are efficiently supplied with energy, allowing for a synergistic increase in photosynthesis. This cooperative action, where far-red light acts like a “booster pump” for PSI, ensures a smoother and more efficient flow of electrons.
The Importance of the Emerson Effect
Understanding the Emerson effect has significantly influenced modern plant physiology and agricultural practices, especially in controlled environments. This knowledge is important for optimizing lighting conditions in settings like greenhouses and vertical farms. By providing plants with a spectrum that includes both red and far-red light, growers can significantly enhance photosynthetic rates, leading to increased crop yield and improved quality.
For example, LED grow lights, which offer precise control over light spectra, can be tailored to leverage the Emerson effect by incorporating specific ratios of red and far-red wavelengths. This targeted light delivery maximizes the conversion of light energy into chemical energy, promoting faster growth, earlier maturity, and greater resilience to environmental stressors. The Emerson effect also contributes to ongoing research in plant bioengineering and the development of more efficient artificial lighting technologies.