We’ve become accustomed to constant improvements in the high-tech world. Computing power doubles every 18 month, new software upgrades become available by the week, and no sooner have you learned version 1.0 of something than version 2.0 is released. It’s enough to make a sane person want to take a long walk amidst the peace and quiet of the natural world.
Except that the high-tech revolution is underway outside, too. Version C4 of photosynthesis has recently been released. C4 is what the cool, new plants are all using, and it’s been grabbing market share from version C3, the garden-variety photosynthetic operating system.
A quick note of clarification: “recently” in this context means “within the past 30 million years.” Lest you think that mother nature is even slower with upgrades than Microsoft, keep in mind that C3 photosynthesis has been in use for nearly a billion years, since green plants first emerged. The emergence of C4 is still very much front-page news.
Photosynthesis is the process by which green plants use the sun’s energy to combine water and carbon dioxide to make sugar. Without getting too far into the details, normal photosynthesis is called C3 because a key molecule in the process contains 3 carbon atoms. In the new and improved C4 system, the key molecule has 4 carbon atoms.
Why the upgrade? As in much of the high tech world, to achieve greater efficiency. In C3 photosynthesis, the 3-carbon molecule sometimes accidentally combines water with oxygen, instead of with carbon dioxide, leading to the formation of hydrogen peroxide instead of sugar. Essentially, the plant ends up wasting water as it creates sugar.
Enter C4 photosynthesis, which evolved in plants highly specialized to environments where water can’t be wasted: the desert. C4 plants make more sugar out of less water than their conventional counterparts, wasting only about a third as much water as C3 plants.
But this advance has come at a cost: the new and improved photosynthesis, just like many high-tech advances in the electronics world, requires more energy to get the job done. This extra energy is readily available in a sunny desert environment and justifies the tradeoff of more energy for less water. But where water isn’t a limiting factor for plant growth, the tradeoff usually isn’t worth it. Despite C4’s advantages, which also include being a more efficient user of nitrogen, ninety nine percent of all the plant species on Earth still use good-old C3. But that isn’t to say that the C4 revolution is confined to desert outposts these days. Far from it.
What would you have if you took an extra-efficient plant designed to work on limited nitrogen and water, gave it all the nitrogen and water it could ever want, and then made sure that no pesky C3 plants got in its way and stole its sunshine? You’d have agriculture.
Corn, one of the most abundant agricultural crops on the face of the earth, is a C4 plant. Corn is a grass, nearly half of all the grass species use C4 photosynthesis, and grass and grain are the underpinnings of meat production. Other important grasses – millet, sorghum, and sugarcane – are also C4 plants.
Amaranth and quinoa, the “super grains” that contain all eight amino acids required by the human body, use C4. Same with beets, spinach, and all members of the broccoli family, like kale and cabbage and collards. The major C3 holdouts among the common vegetable crops are the squashes and nightshades (tomatoes, potatoes, peppers, and eggplant).
What about rice, the staple that nourishes more of the human species than any other grain? Rice is a wetland plant that uses C3 photosynthesis, but perhaps not for much longer. With the globe’s population projected to reach 10 billion people later this century, there are efforts underway to increase rice yields. One line of inquiry: splice C4 genes into rice using genetic engineering. Sort of an operating system upgrade.
C4 plants have captured the attention of researchers for another reason, too. Though they make up only one percent of the world’s plants, C4 plants account for five percent of the globe’s biomass, and because they are so efficient, 30 percent of all the carbon that plants remove from the atmosphere. Climate change mitigation strategy, anyone? Doubling C4’s market share to 10 percent of the earth’s biomass could make a significant dent in the excess atmospheric carbon that we’re emitting from burning fossil fuel, assuming the gains aren’t offset by carbon released by synthetic fertilizer.
As with anything else high tech, the product may not live up to the hype. Be sure to keep your receipts. And back up your files before proceeding.
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