Air Date: Week of April 10, 1998

The release of carbon dioxide into the atmosphere does more than affect the temperature of the planet. It's also an important nutrient for plants. Produce growers have known for decades that hothouse crops do better at enhanced CO2 levels. But scientists are still trying to learn how plants will react to increased CO2 in the atmosphere. And as Minnesota Public Radio's Mary Losure reports, their research could also shed new light on how the entire planet might respond to climate changes in the future.

Transcript

CURWOOD: The release of carbon dioxide into the atmosphere does more than affect the temperature of the planet. It's also an important nutrient for plants. Produce growers have known for decades that hothouse crops do better at enhanced CO2 levels. But scientists are still trying to learn how plants will react to increased CO2 in the atmosphere. Their research could also shed new light on how the entire planet will respond to climate changes in the future. Minnesota Public Radio's Mary Losure has our report.

LOSURE: The greenhouses at Len Bush Roses in Plymouth, Minnesota, produce 5 and a half million roses every year, near-perfect flowers cut each morning and evening. At intervals throughout the 7 acres of greenhouses, hoses blow pure carbon dioxide into the warm air.

EDSEL: This is the actual injection tube, and you can hear it's injecting right now.

LOSURE: CO2 levels inside this greenhouse are boosted to as high as 1,000 parts per million, nearly 3 times what's found in the air outside. Greenhouse manager Pat Etzel says the effect on the roses is clear.

ETZEL: We can see enhancements anywhere from 10 to 40 to 50% increase in overall growth. And that's translated into longer stems, thicker diameter stems, larger leaves, larger flowers.

LOSURE: This is no surprise. Scientists have known for a long time that carbon dioxide, like water, is essential to plant growth. And when they get more of it, many plants grow better. But researchers are uncertain how plants outside greenhouses and laboratories respond when CO2 levels increase. It's an important question, because atmospheric CO2 levels have climbed 25% since the beginning of the Industrial Revolution. Scientists expect that level to double some time in the next century. Researchers are getting some answers by growing plants with extra CO2 at open air sites around the country. George Hendrey of the Brookhaven National Laboratory is the coordinator of the studies.

HENDREY: We've worked with cotton, with wheat, with pine trees. We're now doing sorghum in large agricultural experiments out in Arizona. And all of these plants that we expose to elevated carbon dioxide show a very dramatic response to elevated carbon dioxide.

LOSURE: George Hendrey says the experiments prove photosynthesis, the process by which plants convert carbon dioxide to food, can increase dramatically under high CO2 conditions, and crop yields can be boosted as much as 30%. And he says those aren't the only benefits.

HENDRY: We see photosynthesis increasing without an equivalent increase in the amount of water use. You get a greater amount of crop production for equal amounts of water used.

LOSURE: Results such as these are often cited by those opposed to curbing fossil fuel use: the largest human source of carbon dioxide. A newsletter funded by the Western Fuels Association, a group of electric utilities, calls CO2 "the best plant food since Miracle Gro." The Western Fuels Association is one of the nation's largest coal customers. But others are more cautious. Harvard Biologist Fakhri Bazazz has been studying the effects of high CO2 since the 1970s.

BAZAZZ: Some plants, agricultural crops in developed countries, will probably do well. But there's the rest of the world.

LOSURE: Professor Bazazz says while increased CO2 may benefit well-fertilized, evenly-spaced crops in the industrialized world, it may not be good news for crops grown in developing countries where farmers can't afford lots of fertilizer and herbicides. And he says no one knows exactly how tropical forests, grasslands, and other ecosystems will fare. For example, higher CO2 levels may change the flowering and fruiting time of plants.

BAZAZZ: If that is changed by high CO2 environments such that you decouple the insects from their food, from their flowers, then the plants will fail completely because they, in a tropical forest particularly, depend solely on these very specific insects.

LOSURE: In natural ecosystems, where many kinds of plants compete with one another, Professor Bazazz says higher CO2 could upset the balance of species. Because some plants are able to take advantage of high CO2 better than others, some species may thrive and others may suffer.

BAZAZZ: And I think if we put all of these things together, I really don't think that the picture is as rosy as some of the initial arguments.

LOSURE: Just how ecosystems respond as CO2 levels continue climbing could also have important implications for climate change. George Hendrey of the Brookhaven National Lab says scientific predictions of global climate change are based on the idea that researchers understand where CO2 is going in the atmosphere.

HENDREY: But what we don't have a good idea is how the natural system will behave in the future, decades to a century or 2 centuries in the future. Will natural systems be able to withdraw more CO2 from the atmosphere?

LOSURE: If natural systems like grasslands or forests are revved up by higher CO2 levels and absorb more of the gas, that could slow global climate change. That's why Hendry says it's critical to figure out how ecosystems respond to changes in the composition of the atmosphere. So far, the open air CO2 experiments have been done mainly in managed plots such as crop lands and a pine plantation in North Carolina. But researchers are starting to do the experiments in natural settings, such as a pinion pine juniper grassland in Arizona. And they're making plans to set up a network of carbon dioxide experiments in other ecosystems around the world. For Living on Earth, I'm Mary Losure.