Throughout my studies in school, there were a handful of “a-ha” moments. For me, that was when I learned that plants have a budget. Instead of cash and bitcoins, theirs was measured (mostly) in water and energy. With this historic year of drought, a plant should make smart gambles, or its budget—and life—will shrivel.
Using what senses they have, plants make educated “guesses” about the situation. Unlike animals, a plant cannot walk to Lake Tetonka to take a drink. During this unprecedented drought, a plant must increase its odds where it is sown.
Often there is plenty of sun during drought. If left unchecked, photosynthesis can get out of control, using all the water the plant is trying to squirrel away. Just like us humans, plants need water for other things. So, one goal of many plants is to slow photosynthesis down, often by closing stomata. These stomata allow gases needed to make energy move in and out of the plant. When stomata close, water vapor also stops flowing out, helping the plant somewhat. A plant may also increase or at least maintain its root system—usually at the expense of leaves. Obviously, slowing photosynthesis causes issues, such as reduced growth. Yet, depending on the cards the plant is dealt, playing conservative and taking a hit in the future might pay off.
You have probably seen examples of a plant toning down photosynthesis in other ways. Corn was the easiest to spot this summer. When under drought stress, corn leaves seem to curl and stiffen rather than simply wilt. This curling process limits the sunlit area of the leaf, which puts a lid on photosynthesis. Within the curl, the air tends to be more humid too, preventing more water loss by wind.
However, a few species might decide to cash in their chips and sprint to the finish line. Also known as drought escapers, these plants live fast. By accelerating flower growth, drought escapers aim to get at least a few of their seeds in the ground before dying. Many annual flowers in the desert practice this, and even crops such as wheat can be bred to act more like a drought escaper.
Other plants plan for longer periods of dryness and have evolved ways to cope. Common purslane, for example, is living its best life right now. If you notice a rubbery, creeping weed with yellow flowers driving you nuts in your yard, chances are it is purslane. This plant’s fleshy leaves store water for later use, sort of like a cactus. Purslane can also choose between two types of photosynthesis, one better for harsh drought and another perfect for typical summer days. Because of this flexibility, purslane can save water and still grow, giving it a leg up on its wilting neighbors.
Whether a plant holds its cards, goes big, or has an ace up its sleeve, plants can have multiple strategies to survive. We will see who comes out on top this dry year.