Insects take a bigger bite out of plants in a higher...( Atmospheric carbon dioxide levels ar...)

Atmospheric carbon dioxide levels are rising at an alarming rate, and new research indicates that soybean plant defenses go down as CO2 goes up. Elevated CO2 impairs a key component of the plants defenses against leaf-eating insects, according to the report.

The University of Illinois study appears this week online in the Proceedings of the National Academy of Sciences.

Deforestation and the burning of fossil fuels have significantly increased carbon dioxide levels since the late 18th century, said plant biology professor and department head Evan DeLucia, an author of the study.

Currently, CO2 in the atmosphere is about 380 parts per million, DeLucia said. At the beginning of the Industrial Revolution it was 280 parts per million, and it had been there for at least 600,000 years probably several million years before that.

Current predictions are that atmospheric carbon dioxide will reach 550 parts per million by the year 2050, DeLucia said, and the rapid industrialization of India and China may even accelerate that timetable.

The new study, led by entomology professor and department head May Berenbaum, used the Soybean Free Air Concentration Enrichment (Soy FACE) facility at Illinois. This open-air research lab can expose the plants in a soybean field to a variety of atmospheric CO2 and ozone levels without isolating the plants from other environmental influences, such as rainfall, sunlight and insects.

High atmospheric carbon dioxide is known to accelerate the rate of photosynthesis. It also increases the proportion of carbohydrates relative to nitrogen in plant leaves.

The researchers wanted to know how this altered carbon-to-nitrogen ratio affected the insects that fed on the plants. They predicted the insects would eat more leaves to meet their nitrogen needs.

When they exposed the soybean field to elevated carbon dioxide levels, the researchers saw the
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