Grasses and gases: life in the heat

Many people know that plants make the oxygen that most organisms need to breath, but plants are also sugar manufacturers. Through the process of photosynthesis, plants use light energy from the sun and water from their surroundings to convert carbon dioxide in the atmosphere into sugars they can use for growth. Besides producing oxygen and making their own food (sugars), plants provide the basic energy source for virtually all life on earth. Plants can accomplish this amazing chemical feat in nearly all types of environments; even some that may seem unsuitable. One big problem for plants living in the Great Plains is the scarce availability of water, made worse by increasing drought.

So, how do plants deal with this problem? Graduate student Seton Bachle in the Division of Biology is conducting research to get to the root of the issue. As a plant ecophysiologist, Seton is interested in how the structure of different plants allows them to successfully perform photosynthesis in different environments. Specifically, he looks at the networks of tiny tubes that transport water throughout a plant, along with the specialized tissues and openings that allow gasses to move in and out of a plant. Here in the Great Plains, he is especially interested in the structural differences that arise in populations of grass experiencing different levels of “droughtiness” – a word I learned from Seton to describe the severity of drought or dryness.

Seton hypothesizes that grass populations living in drier environments, like those in western Kansas, should be just as efficient at turning light energy into sugars compared to plants of the same species living in wetter environments; because native grasses should have adaptations that allow them to survive in their local climate.

A photograph of the internal structures of a Big Bluestem leaf taken under a microscope. Seton uses photographs like these to compare structural differences among grass populations. The letters label some of the different structures Seton measures. Photo Credit: Seton Bachle

Seton uses an abundant grass species, Big Bluestem, to test his hypothesis. He collects samples of Big Bluestem from Oklahoma, Kansas, Nebraska, Minnesota, Colorado and South Dakota and looks at thin slices of their leaves under a microscope. Getting this close-up view allows him to compare the structures and tissues of plants from one grass population to those of the others. From these comparisons, Seton can assess which traits are found in grass populations that survive in locations that receive less rainfall. One plant structure Seton is particularly interested in are the stomata: tiny openings on the underside of leaves that can open and close to control gasses coming into and leaving the plant.

“When plants photosynthesize, they need to open their stomata to release oxygen, which also allows the plant to cool and unfortunately causes water to leave the plant”, Seton tells me. “This becomes a problem when a plant lives in a hot and dry environment, like the prairie, where plants need to conserve water”.

To figure out what plants are doing to conserve water but also make the most out of the sunshine, he uses an infrared gas analyzer (as seen in the picture below). This device clamps onto leaves and uses a laser to measure how much carbon dioxide is taken in by the plant and how much oxygen and water are released. Seton says this device can also be used to manipulate the amount of carbon dioxide a plant is exposed to. This neat feature provides the opportunity to test how plants adapted to different conditions could respond to rising levels of atmospheric carbon dioxide associated with climate change.

The infrared gas analyzer in action, using a laser to measure the carbon dioxide taken in as well as the oxygen and water released by the grass leaf it’s attached to.

So far in his research, Seton has figured out that when grasses close their stomata to conserve water during drought they begin to overheat! While plants use their stomata to control gases coming in and out of their tissues, plants also use these structures to release heat that is produced as a by-product of manufacturing sugar. This means that plants experiencing a drought are less efficient at photosynthesis because when they keep their stomata closed to conserve water, they are doing damage to their tissues by trapping heat that would normally escape through open stomata. While Seton’s research did support his original hypothesis, he was also able to detect this unexpected result that plants in droughty places overheat while trying to prevent water loss. Importantly, this means less efficient sugar and oxygen production for plants experiencing drought.

Seton’s research is important because the dominant types of food crops eaten by humans are grasses (things like corn, wheat, and rice). He says, “that understanding how one species of grass is influenced by increasing drought and atmospheric carbon dioxide can tell us a lot about how other grasses will respond, so that we can be better prepared for our future.”

l-gulosus.jpgThis post was written by Garrett Hopper. Garrett is a Ph. D. student interested in the role of aquatic animals in stream ecosystems.

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