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Bazzaz and Fajer - SCIENTIFIC AMERICAN REPRINTED WITH...

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SCIENTIFIC AMERICAN REPRINTED WITH PERMISSION: Plant Life in a CO7-Rich World Even without considerations ofglobal warming, increasing atmospheric levels of carbon dioxide may greatly alter the structure and function of ecosystems. These changes will not necessarily benefit plants by Fakhri A. Bazzaz and Eric D. Fajer P iants are the green cornerstone of terrestrial life. The abundance and productivity of trees and @-as=, herbs, shaobs, mow and weeds shape how ecosystems cirrulate gases and nutrients, deanse waterW?mild soils and provide sustenance for a variety of other lifeforms Any significant varih tion in the productivity and compo- sition of plant life would precipitate a cascade of dxmges affecting herbi- vores, carnivores and omnivores alike. One such change may be mder way. Fuel combustion and deforestation are rapidly dtering the nature of the earrh's atmosphere. Perhaps the most impor- tant atmospheric campmm affmed by human activity is cabon dioxide (CO,). Since. the dam of the industrial age, the concentrations of this gas have increased from 280 ro J s ~ parts per miUion-the hghest level h the past 160,000 years for which a CO, record i FAKHRJ A B A Z W and ERE D. F m have studid veTious aqxtsoftheco~lp plex role of atmospheric carbon dioxide inecosy-BaazazfstBeKHfim- ken Professor of S c i e at Harvard Uni- versity and for the past two decades has reseat&& how rlsfng CO, levels will al- ter plant life. He rrceived hij PILD. from the uniwmity of llllmJis in 1963. [email protected] recently completed Ms PhD. at Harm4 where he examiwd the Bnpact of high C& levels on plants and hbiwrous in- sects: He is a postdoctoral marcher at the Center for Scieace and International Affairs at the john F. Kermedy School of GovemmeM. The awhors gratefully ac- knowledge the support of the U.S. De- m e n t of Energy. ELprinied with jzt'missi(m. Copyright can be found in ice core samples. Mea- swements at the Mauna Loa observa- tory in Hawaii have documented about a 20 percent increase in CO, lwels be- tween 1957 and the present. Although estimates vary, experts anticipate that global mnceno-aions of CO, will dou- ble by the middle to the end of the 2 1 st century. At first glance, elevated carbon diox- ide lwels might s&m an agricultural blessing. Initial studies suggested that a high CO, environment would enhance plant growth. This CO, fenilkation ef- fect, as it is called, is w e d to be particularly pronounced if plants have plentiful supplies of nutrients, light and water. The CO, fertikation effect also prom- ises to provide a buffer for concerns about g l W warming. Plants growing larger in such an environment could be counted on to draw more CO, from the atmosphere. Tbus, the lwd of this g m n b w e gas-which mps energy from the sun that is reradiated as heat from the earth's surface-would be lower than expected. Indeed, the f e d - zation effect has been considered in.
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