Understanding how plants harness light in shady conditions raises questions about the efficiency of photosynthesis and methods to improve agricultural yields. Recent research highlights new aspects of this interaction between plants and light, offering new avenues for greenhouse horticulture.
Plants living in the shade of other plants receive more light than scientists initially estimated. A team of researchers from the Universities of Utrecht and Wageningen described how this light is used in a recent article published in the scientific journal Plant Cell & Environment. Their findings not only advance knowledge of how photosynthesis works in shaded conditions, but they may also be beneficial for greenhouse horticulture.
« When we better understand how different colors of light influence photosynthesis and plant growth, we can help growers develop intelligent methods to supplement natural light with colored light. »
Photosynthesis, green and infrared light
« The effect occurs in plants shaded by other plants “, explained Hugo de Boer, an environmental scientist at Utrecht University, who initiated the study.
This is because plants only capture part of sunlight for photosynthesis, the process by which they convert light and CO₂ into glucose. Some light passes through their leaves, mostly in the form of green light. We can observe this phenomenon by looking up into a forest canopy: the leaves look like green filters above us. A similar effect occurs with light beyond the visible part of the red spectrum, in the frequency range of 700 to 750 nm, called ‘far red’.
« Plants growing in the shade of other plants receive a greater proportion of green and far-red light than those exposed to full sun. Our research shows that plants have a specific way of using the far-red part of the light spectrum for photosynthesis. »
« Until now, researchers have rarely considered the possibility that plants use far-red light for photosynthesis ”, added Tinko Jans, doctoral student at WUR. This is because previous experiments with monochromatic lights demonstrated that plants primarily use light at visible wavelengths (400 to 700 nm) for photosynthesis, and that light at shorter or longer wavelengths long contributes little to the process.
-« But by combining far-red light with a small amount of visible light, it actually contributes significantly to photosynthesis. Thus, we developed a new method to measure and model how additional far-red light contributes to photosynthesis. »
A shadow avoidance response
Scientists and horticulturists have known for some time that plants can use the far-red part of the light spectrum to identify neighboring plants from the shadows they cast. Tinko Jans noted: “ Many plants respond to a relative increase in far-red light by growing upwards, to win the competition for light. This shade-avoidance response also helps horticulturists, because it allows them to grow more plants close together. Recent developments in LED technology have given great impetus to research into plant response to shade and the use of far-red light in horticulture. »
« In previous experiments, we also studied the shadow avoidance response », added Hugo De Boer. “In addition to showing morphological changes, our shaded plants started growing much faster when we tried to trick them by installing LED lights to supplement the far-red light. To our amazement, our plants were perfectly capable of using this extra light for photosynthesis. »
The researchers carried out a large number of photosynthesis measurements using different colors and intensities of light. Hugo De Boer concluded: “ But quantifying the effect of colors on photosynthesis has proven much more difficult, because the available mathematical models and measurement methods were based on the assumption that plants only use light in the visible spectrum. Thus, we adapted a commonly used photosynthesis model to quantify the effect of colors by combining measurements of photosynthesis and the full light spectrum that reaches the leaf. »
Illustration caption: Researcher Dr. Hugo de Boer places an experimental plant (Bittersweet) in experimental lighting conditions with reduced red and far-red light. Credit: Utrecht University
Article : ‘PCE Coupling Modelling and Experiments to Analyse Leaf Photosynthesis under Far-Red Light’ / ( 10.1111/pce.15340 ) – Utrecht University – Publication dans la revue Plant Cell & Environment
