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Global warming and really big tomatoes

Could a dramatic increase in atmospheric CO2 fuel tremendous increases in agricultural productivity and fight hunger?

The general consensus among scientists holds that global warming and higher levels of atmospheric carbon dioxide (CO2) will hurt poor nations the most. Hotter temperatures, rising seas, and more extreme weather patterns will impact countries in the tropical and sub-tropical regions where poverty is most concentrated. There may be a silver lining. An emergent thread of research implies that in conditions of dramatically elevated CO2 farmers may be able to coax two to three times more edible mass from widely cultivated root crops.

This would be dependent on sufficient additions of water and fertilizer, both of which are expensive and may be in short supply in poorer nations. Regardless, the greater efficiency of root crop cultivation could allow these nations to feed themselves with less water and less fertilizer on a lower total acreage.

If validated, this finding would defy the conventional wisdom about biological responses and could provide a roadmap to more effective farming practices in a carbon-saturated future.

jahren_website-38On campus of the University of Hawai‘i at Mānoa (UHM), Hope Jahren is building four super-greenhouses from materials purchased at local hardware stores to answer this critical question and provide the most definitive answer yet about how plants behave when there is three to five times as much CO2 in ambient air. A professor at UHM’s School of Ocean and Earth Science and Technology (SOEST), Jahren is an eclectic and widely published researcher. Her work ranges from profiling the chemical signatures of explosives to characterizing the dietary isotope footprint of fast food to studying the impact of climate change on biological organisms.

jahren_website-83Inside a greenhouse as big as a basketball court, Jahren and her team are constructing four high-tech 8’x8’ greenhouses where the team will grow sweet potatoes in controlled environments with CO2 levels ranging from the current atmospheric concentration of 384 parts per billion (ppb) to concentrations 200% to 500% greater – levels projected for hundreds of years from now. While other researchers have studied the impact of moderate elevation of atmospheric CO2 concentration on plants, to date scientists have not performed experiments examining how plants behave under very high concentrations. “They have definitely thought about this question but the tragedy is they just didn’t go high enough,” says Jahren. “They used CO2 levels that everybody hoped would be the maximum but which we will exceed very soon in the Earth’s atmosphere.”

Jahren and SOEST assistant researcher Brian Schubert grew radishes in smaller indoor greenhouses under conditions simulating atmospheric CO2 from 384 ppb to conditions extrapolated 300 years out into the future with about five times as much CO2 in the air. To their great surprise the radishes grew like gangbusters. In the greenhouse with the highest concentrations of CO2, roots of radishes grew 279% larger than roots of radishes grown at present-day conditions.

In fact, plants may be capable of radical feats that don’t jibe at all with conventional assumptions. For example, Jahren points out, that in the fossil records scientists have found evidence of vast forests growing North of the Arctic Circle. This defies logic that the Far North cannot support high levels of plant activity. “For sustained periods – tens of millions of years – forests could live through three months of total darkness,” notes Jahren. “That’s something fundamentally different which we don’t see today.” While plants don’t use that capability any more, whether they could retain it or regain it is not well understood.

In a similar vein, scientists have assumed that the response curve of plants to far greater levels of atmospheric CO2 would follow a hyperbolic curve that is commonplace in biological organisms. In other words, plants would initially gain benefit from the higher CO2 levels in the form of faster growth and larger average plant size. But those benefits would level off as the CO2 levels continue to climb.

Even more intriguing, the bulk of the radish growth came below the surface in the rootstock. The likely reason for this is that radishes under conditions of high ambient CO2 can more easily produce sugar. Like people plants use sugar for energy and seek to store it in their body. Unlike humans, plants store sugar as starches. So in response to conditions that facilitated far greater sugar production, radishes poured these resources into their bulbs.

Jahren wants to test her findings further on crops that could truly impact global hunger and encourage humanity to rethink best practices in global agriculture. In the upcoming experiment Jahren’s team will grow sweet potatoes, a common food crop that is loaded with vitamin A, a nutrient critical for fighting blindness in the developing world. Using off-the-shelf components such as wood, fans and PVC pipe, Jahren and her team are constructing the 8’x8’ greenhouses to maintain positive pressure and accept bleeder feeds of CO2. A sensitive gas concentration gauge monitored by researchers will allow the team to maintain consistent CO2 levels inside the greenhouse chambers for extended periods spanning months of time.

jahren_website-93As plants grow in these conditions Jahren and her team will closely monitor progress and then measure the mass of the potatoes. Should the sweet potatoes grow as quickly and add mass as prominently as the radishes, then Jahren’s findings could lead to a massive shift in the way the world grows food and uses water.

Root crops can be less water intensive than surface crops such as rice. In many countries, such as China
and India, where rice is the preferred grain, massive water shortages are looming. “A wholesale or even incremental shift to root crops could save enormous quantities of water,” says Jahren. Root crops also require significantly less pesticide application. This translates into reduced use of petrochemicals, diminished release of toxins into the environment, and lower production costs for farmers. Equally important, root crops on the whole are more resistant to diseases than rice, wheat or corn.

As a kicker, root crops are nutritionally far denser than most surface crops and can feed more people per acre of cultivation while providing, in most instances, higher levels of critical amino acids and other nutrients. “I do believe that global warming is something to be concerned about,” says Jahren. “But this could be one bright spot in an otherwise very dark room that we can exploit in order to feed an ever increasing population.”

About the Researcher
Hope Jahren is a professor in the Department of Geology and Geophysics, which is part of SOEST at UHM. She has published dozens of papers focused on geochemistry and stable isotopes and has won numerous awards including a Leopold Fellowship, three Fullbright Fellowships and the James B. Macelwane Medal from the American Geophyiscal Union as well as the Donath Medal from the Geological Society of America, both awarded to promising young researchers. In 2005, she was named by Popular Science magazine as one of the “Brilliant 10” researchers in the world.

This article originally appeared in the Spring 2012 print edition of Kaunānā.

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