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Title: A GLOBAL PERSPECTIVE OF IN SITU "AMBIENT" CARBON DIOXIDE FOR ASSESSING THE RESPONSE OF PLANTS TO ATMOSPHERIC CO2

Author
item Ziska, Lewis
item Bunce, James
item GHANNOUM, OULA - HAWKESBURY UNIV.,NSW AUST
item CONROY, JANN - HAWKESBURY UNIV.,NSW AUST
item Baker, Jeffrey
item KOGAYASHI, KAZUHIKO - TSUKUBA UNIV.,TOKYO, JA

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Since the late 1950s, data obtained from the Mauna Loa observatory in Hawaii has shown that the atmospheric concentration of carbon dioxide (CO2)is increasing rapidly. Carbon dioxide is the sole source of carbon for 99 percent of all known life forms; consequently, an intense global effort has gone into predicting the impact on plant growth as atmospheric CO2 increases. In these studies, the baseline CO2 concentration has always been assumed to be observed at Mauna Loa, about 360 parts per million (ppm). However, Mauna Loa samples large undisturbed air masses at 10,000 feet, and it is unclear if ground-level carbon dioxide, C02 that most plants experience, is at the same concentration. In this experiment we tabulated ground level carbon dioxide data from research sites around the world and found that actual carbon dioxide concentration can vary from 500 ppm at night to 350 ppm during the day, with average values in most locales exceeding 400 ppm. This is much higher than the Mauna Loa standard. A comparison of the ground-level CO2 concentration with the presumed Mauna Loa standard revealed significant errors in how plants respond to projected CO2 levels. Consequently, these data indicate that many of the previous studies which have characterized plant growth to carbon dioxide are probably in error. Overall, the data will be of use and benefit scientists who are seeking to project the impact of rising atmospheric CO2 on crop productivity.

Technical Abstract: Studies which determine the response of plants to future atmospheric carbon dioxide assume an ambient concentration of 360-370 ppm, based on long-term data obtained from the Mauna Loa observatory. However, it is unclear if ground level carbon dioxide values are similar to those obtained at Mauna Loa. In the current study, ground level carbon dioxide values were obtained from global agricultural field sites (Australia, Japan and the U.S.). These values indicated that the actual carbon dioxide concentration can vary from 500 ppm at night to 350 ppm during the day, with average 24-h values ranging from 390 to 465 ppm. Responses of plant growth to these in situ carbon dioxide values were compared to growth at constant carbon dioxide concentration using controlled environment chambers and three plant species, soybean (Glycine max, L (Merr.), velvetleaf (Albutilon theophrasti L.) and tomato (Lycopersicon esculentum L.). Significant increases in net assimilation rate at actual relative to constant ambient carbon dioxide were observed for all three species, as well as significant increases in leaf area, growth and total biomass for two of the three species tested (velvetleaf and soybean). Data from these experiments suggest that previous evaluations of plant response to atmospheric carbon dioxide which utilized a constant CO2 value (about 90% of all studies) may not accurately reflect in situ conditions.