Why is grass green? From lawns to lily pads, and moss to mahogany: plants are invariably an emerald hue. But why green, and what can we learn from this fact? We asked biochemist Tobias Erb. Climate Change and Environment © Tatevosian Yana, Shutterstock The colour green is so synonymous with nature and the environment that the words can be used interchangeably. We often describe ourselves as ‘thinking green’, ‘buying green’ or being ‘surrounded by greenery’. But why exactly is our natural world so green … and why is this a question worth asking? “Sunlight is a source of energy,” explains Erb, professor of biochemistry and director at the Max Planck Institute for Terrestrial Microbiology in Germany. “This light comes in different flavours, which you can see in a rainbow.” When plants absorb sunlight, they mainly use the blue and red flavours of sunlight as energy to fix carbon dioxide, the process called photosynthesis. What is left is the green wavelength – and this is what we see. “Blue light is more energy-intensive and penetrates deeper in water, so it would have made sense for early algae and plants to focus on absorbing this light quality,” says Erb. At some point – maybe before, maybe after – algae and plants gained the ability to also absorb lower-energy red light, using a different pigment. So why was green ignored? Because evolution builds on what already exists – and what works. Once the first photosynthetic organisms evolved the ability to absorb blue and red light, and prospered, subsequent plants would have seen little benefit in adding a green pigment. More energy-efficient plants This understanding of why our world is green could have important ramifications for our future. In the transition towards more sustainable energy sources, improving on photosynthesis could play a critical role. “My main motivation as a scientist is to better understand photosynthesis – the biggest, most sustainable energy process of all,” adds Erb. “For over 3 billion years, algae and plants have used sunlight to fix CO2.” Evolution, Erb notes, is a slow process. Human creativity and ingenuity could yet help us to find rapid solutions to some of the most pressing environmental problems – such as redesigning photosynthesis to harvest more energy from the sun. This is an ongoing collaborative scientific effort, exemplified by Erb’s groundbreaking work through the EU-funded SYBORG project. “So, we know that grass is green because it ‘kicks out’ that spectrum of light,” he explains. “This means that plants only make use of some of the light. What if we were to engineer a mechanism whereby the whole spectrum of light is captured, which would allow us to power photosynthesis even at low light intensities?” Clues to how this might be possible have been found in the unlikeliest of places. Aquatic bacteria found at depths of over 100 m have developed elaborate pigments and mechanisms to photosynthesise fragments of light in the inky cold blackness of the deep sea. “There are solutions, and we can learn them from the diversity of nature, to rebuild a more efficient photosynthesis in the lab” says Erb. Click here to find out more about Erb’s research: Green machine: how synthetic biology could build a better leaf Keywords SYBORG, photosynthesis, sunlight, plants, energy, biology, wavelength, biochemistry, nature
