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Science Politely: Plants don’t breathe easy

Plants have quite a different perspective on life than we do. When I’m thirsty, I head over to the tap and fill up a glass of delicious water. When a hiker is being chased by a bear, he runs to safety. As winter and snow approach, we will pull out our sweater and heavy coats from dusty closets and shake them out for a new season of harsh weather. Plants, due to their sedentary nature, find the world a bit more challenging to survive in. For example, the drought we experienced this year caused an unusually low crop for Curtis Orchard, leaving only a two-day season for apple picking. When a clover is looking particularly delicious to a rabbit, well, let’s just say it doesn’t end well for the clover. And as the levels of ozone, carbon dioxide, and methane rise as a result of human-driven climate change, plants also take notice and react.

Imagine you are walking along Meadowbrook’s prairie. Goldenrod and asters dance in the gentle breeze. You take a deep breath of fresh, crisp fall air. Have you ever stopped to think how the air we breathe is recycled? We’ve all learned that we give off carbon dioxide and plants give off oxygen, but did you know that forty percent of carbon dioxide in the atmosphere passes through a plant each year? That’s a lot of carbon dioxide, and plants are very sensitive to both how much they are taking up and how much is in the air around them.

Just as we breathe in and out, so do plants. Instead of one mouth, they have millions of small pores scattered across the leaves. The pore is surrounded by two small cells that swell and shrink to change the size of the pore. These two small cells are called “guard cells,” because they quite literally guard the entrance to the inner plant. This entire complex, the pore and the set of guard cells, is called a stoma. Stomata (plural) sense the environment, and, in response, open and close the pore to let air in, specifically carbon dioxide, while oxygen and water escape.

Stomata are incredibly sensitive to the environment and are one of the few ways that plants can tell what is happening on the outside. Many factors, such as humidity and light availability, determine how the plant opens its pores or how it makes stomata (i.e. how many, how large, etc.). This, in turn, regulates how much water and oxygen is lost from a plant, and as a result, how much water is taken up from the soil environment around the roots. The number and size of stomata also regulate how much carbon dioxide is taken up by the plant. This carbon dioxide is, in turn, used as a building block to make sugars. Plants use the energy in sunlight to combine six carbon dioxide molecules together to make one single sugar molecule. Yup — the air you are breathing out right now, as you are reading this, contains carbon dioxide that was at one point a sugar molecule, probably from sweetening your coffee this morning or that side of fries you ordered at dinner last night. And before that, it had to pass through stomata on a plant leaf somewhere. So, stomata are pretty important. They regulate how much sugar a plant makes, how much water the surrounding soil loses, and how much oxygen is given off into the environment.

Changes in carbon dioxide concentrations do have quite the effect on plants. Plants grown in higher carbon dioxide concentration have fewer stomata than plants grown at current levels of carbon dioxide. If there is more carbon dioxide in the air, then the plant can take in more carbon dioxide without losing as much water (and also without giving off as much oxygen). So why make more stomata if you don’t need them? Leaves do not always make fewer stomata, though. Some plants actually increase the number of stomata, and other plants don’t even appear to recognize the changing carbon dioxide levels in our atmosphere. Unfortunately, researchers have not been able to figure out what signals a plant to alter the number of stomata in response to environmental conditions, but my research aims to answer that very question, specifically in reference to carbon dioxide concentration.

So, why should you care about some dinky little pores on plants? The main reason takes us back to climate change. Regardless of whether or not you “believe” that humans caused climate change, the climate is changing — and pretty quickly. The changing rainfall patterns and increased temperature associated with climate change will affect crop production worldwide. According to the Food and Agriculture Organization of the United Nations, in order to feed the current population, farmers and researchers need to increase crop yield by seventy percent before the year 2050. We are currently on a path that will only increase yields by maximum of forty percent. This doesn’t include any detrimental effects of greenhouse gases (i.e., increased ozone, increased temperature, less rainfall in some regions, etc.). According to a recent study published by the American Society of Agronomy, only a one and a half degree increase in temperature will cause a small decrease in soybean yield in the southern United States.

Don’t get me wrong — it’s not all doom and gloom. The same temperature increase will improve soybean yield in the Midwest about the same amount as the loss in the South. In fact, climate change will alter crop productivity all over the world, increasing yield in some areas and decreasing in others. The catch is that we will have a combined global net decrease in crop yield. Coupling this uncertainty with an increasing population puts even more pressure on our food supply. An emerging field in plant biology and crop science researches how to keep our crops healthy and productive as the climate changes. This field incorporates stomatal development as a key process in helping to keep our crops healthy and our yields high.

My research aims to understand how plants sense and respond to global climate change, but it’s a big job. Understanding how over 300,000 organisms will react to a complex global event requires more than just a single lab of expertise. Stomata development is just a piece of the puzzle for adaptation to climate change. Later on, other researchers will use this knowledge and other plant research on climate change to understand how plants will acclimate themselves on the whole. Because plants are so important to our everyday lives in providing us energy, fuel, and shelter, it’s vitally important that we use our knowledge collectively to keep plants healthy and happy for future generations.

Written by Miranda Jean Haus, PhD candidate in Plant Biology.



Smile Politely is proud to introduce a new running series we are calling “Science Politely” that will feature the work of graduate students at the University of Illinois throughout November and December. Working in collaboration with the students in a graduate course in Integrative Biology, Science Politely is a collaboration aimed at bridging the gap between town and university, between scientist and citizen, and between research and culture.

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