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Interviewee: Evan DeLucia, University of Illinois
CO2: A Necessity and a Hazard
By Heather Mayer
Plants need CO2 to breathe, and higher levels of the greenhouse gas make them grow faster. But we may not be able to count on those increased yields. Biologists at the University of Illinois at Urbana Champaign discovered that too much CO2 can make them more susceptible to damage from pests.
“As carbon dioxide in the atmosphere goes up, we might see a small increase in crop productivity, but what’s startling, and a little unnerving, is those increases in productivity might be completely canceled out by greater insect attack,” explains Evan DeLucia, who led the research.
These elevated CO2 levels, which are a result of fossil fuel combustion, make soybean plants less able to fight back against pests, in particular, the invasive Japanese beetle.
DeLucia and his team have been farming soybean fields in an experiment called SoyFACE (Soybean Free Air Concentration Enrichment), which studies how agricultural ecosystems will respond to global change.
DeLucia explains that CO2 levels have been increasing at a rapid rate. “When I was a graduate student in the 1980s it was about 340-350 ppm (parts per million),” he says. “Now it’s about 380 ppm, and it’s expected to go up to 550 ppm by the year 2050.”
SoyFACE’s Unique Design
SoyFACE scientists are using a unique experimental design to simulate the types of conditions the planet will face in years to come, focusing largely on CO2 levels. SoyFACE is a series of plots in a soybean field where there is a ring of pipes around a crop. These pipes inject carbon dioxide upwind, bringing all of the crops to a certain CO2 level, which imitates future conditions, DeLucia explains. In this experiment in particular, the scientists predict the level to be about 200 ppm higher than it is today.
The unique part of this experiment is its divergence from studies conducted indoors or in greenhouses. The crops are exposed to all the natural elements such as wind, rain, temperature, and most importantly, insects.
“It’s actually doing this experiment in a natural setting that led us to these startling discoveries,” DeLucia says.
Beetles Feast and Flourish
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“We notice some things somewhat positive, and something perhaps frighteningly negative,” DeLucia says.
With the higher levels of CO2, the plants grow more rapidly because the gas stimulates the rate of photosynthesis, DeLucia explains. This means soybean yields have marginally increased. But insects, including Japanese beetles, go toward the high CO2 areas for nourishment. Not only is the number of insects at these plots greater, but the scientists also discovered that the insects eat more of the leaves grown under higher CO2 leves than leaves under current levels.
“Damage to soybeans from insects may increase dramatically in the future,” says DeLucia.
To test whether Japanese beetles are actually drawn to the higher CO2 leaves. DeLucia and his team gave beetles the option of either a leaf grown under high CO2 or one under normal levels. The beetles not only chose those with higher levels, but they also ate more of the leaves.
Plants Fight Back
Under normal conditions, plants have defense mechanisms to prevent insects, like these invasive beetles, from destroying them. They produce chemicals to deter insects from eating them. DeLucia’s team of scientists researched in greater detail how soybean plants defend themselves from Japanese beetles. Soybean plants produce a chemical called a protease inhibitor, which slows enzymes called proteases that the beetles use to break down proteins in the plant material. This prevents the beetles from eating too much of the soybean plant and from digesting all of their meal — sometimes resulting in death.
But SoyFACE revealed that soybean plants under elevated carbon dioxide levels are not able to create as much of a chemical defense against Japanese beetles. Under these CO2 conditions, the beetles eat more of the highly nutritious soybean plants. This, scientists found, allows the beetles to live longer and reproduce more.
DeLucia notes that the Japanese beetle is an invasive species, which “are really good at taking advantage of disturbed environments,” says DeLucia.
“A Solvable Problem”
As carbon dioxide levels continue to increase, the effects on the soybean and Japanese beetle populations aren’t the only things to be concerned about, DeLucia says. In order to protect their soybean plants, farmers might spray crops with more pesticides, which would have other negative ecological consequences, DeLucia says. Not only that, but costs for crops will increase because farmers are paying more to protect their plants.
“Farmers will be taking care of those crops by spraying more insecticides, which increases the farmer’s costs, and of course, he’s going to pass those costs onto us,” DeLucia explains. “So one of the fears is that will be another thing that increases food prices in the future.”
With CO2 levels climbing, global temperatures increase, which could result in more frequent, more severe droughts. DeLucia and his scientists plan to study the effects of those factors on plants and insects in their next experiments.
But the planet isn’t doomed to these negative consequences. At least not yet. Global change, which really is at the base of these problems, is caused by human activities, DeLucia points out.
“Elevated carbon dioxide is a global disturbance that we’re imposing on the planet through our industrial practices,” he says. Changing those practices can slow and reverse the rise in carbon dioxide levels.
“This is something we very much need to look at right now so the future generations don’t have to suffer the consequences of our very, very extravagant uses of fossil fuels today,” says DeLucia.
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