We live in a time characterized by skyrocketing amounts of carbon dioxide in our atmosphere. But imagine if you could push a "reverse" button and cut carbon dioxide to lower levels not seen for thousands of years.
Supported by an $869,000 CAREER Award from the National Science Foundation, one University of Kansas researcher is doing just that -- with ice age trees.
Joy Ward, assistant professor of ecology and evolutionary biology, studies plants that grew during the last ice age, about 18,000 years to 20,000 years ago, when low carbon dioxide levels were "highly limiting" for plant life.
Through awareness of this ancient past, Ward hopes to show how plants might fare in a future of much higher carbon dioxide concentrations.
"Plants are amazing," Ward said. "They can actually take carbon right out of the atmosphere and use it as their food source, whereas we as humans have to eat vegetables and meat in order to get carbon sources in our diet. But the availability of carbon dioxide has changed over geological time."
According to Ward, ancient air bubbles trapped inside ice cores show that there was about half as much carbon dioxide in the atmosphere during the last ice age compared with present times.
In her lab at KU, Ward has found that today's plants have severe difficulty thriving under such conditions.
"We can scrub carbon dioxide out of the atmosphere at very controlled levels to simulate the past," said Ward. "We have found that the average reduction in growth is about 50 percent for plants grown at these ice age carbon dioxide levels compared with the modern value. For some species, the reduction in growth can be as high as 90 percent and some species completely fail to reproduce."
So how did ancient plants cope with such low carbon dioxide concentrations? To find out, Ward studies leaves and wood found in the Rancho La Brea tar pits in Los Angeles, the famous treasure trove of fossilized ice age plants and animals.
"Those wood specimens are so well-preserved in tar that we can still see tree rings," said Ward. "We can measure those tree rings to figure out how much growth these plants were conducting. We can also use a technique known as 'stable carbon isotope analysis' where we can actually understand something about the physiology of that plant, even though we're only looking at dead wood that's 20,000 to 60,000 years old."
As a strategy to survive in a low carbon dioxide environment, Ward said that some ice age plants may keep their stomata more open. These stomata are tiny, mouth-shaped pores on leaf surfaces that take in carbon dioxide while allowing water to escape.
"However, the cost of doing that is more water may be lost to the environment, which would be detrimental to the plants," said the KU researcher.
Looking to the future, Ward's investigations show that most plants would benefit from the ongoing boost in atmospheric carbon dioxide levels related to climate change. But other indirect consequences of elevated carbon dioxide could prove harmful to plants.
"The majority of plants use the C3 photosynthetic pathway," Ward said. "We know those plants in many cases will be positively benefited by increases in carbon dioxide -- if other factors like water and nutrients are very plentiful. If they are not plentiful the positive effects of carbon dioxide are diminished. They may also be diminished in the light of rising temperatures."
For other plants using the C4 pathway, such as corn, sugarcane and sorghum, the news is not quite as good: Though these plants also will benefit from more atmospheric carbon dioxide, they don't profit as much as C3 plants. In the fields of the future, crops of C4 plants may be "out-competed" by weeds using C3 carbon fixation.
For farmers, the jump in carbon dioxide levels may bring other changes.
"Carbon dioxide can directly alter the time that it takes for a plant to flower," Ward said, based on her new study released this week in the journal New Phytologist. "Some flower earlier under increasing carbon dioxide levels, and some flower later. If I were working in the agricultural sector, I would not want to be surprised to find in the future that my plants were flowering at a different time and not understand why."
--Brendan M. Lynch
The University of Kansas is a major comprehensive research and teaching university. University Relations is the central public relations office for KU's Lawrence campus.
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