Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2002
Publication Date: 11/1/2002
Citation: Heagle, A.S., Miller, J.E., Burkey, K.O., Eason, G., Pursley, W.A. 2002. Growth and yield responses of Phaseolus vulgaris to mixtures of carbon dioxide and ozone. Environmental Quality. 31(6):2008-2014. Interpretive Summary: Elevated carbon dioxide concentrations expected in the 21st century can stimulate plant growth and yield, whereas ground-level ozone concentrations are high enough to suppress plant growth and yield in many areas of the world. Both of these gases exist together in the air so an understanding of how mixtures of ozone and carbon dioxide affect crop yield is needed to improve estimates of future food supply. Recent experiments show that elevated carbon dioxide often protects plants from suppressive effects of ozone, but this has not been tested for many important crop species such as snap bean. We performed a field experiment to determine if elevated carbon dioxide can protect snap bean from ozone. Two bean lines were tested. One is very tolerant to ozone, whereas one is very sensitive. Bean plants were exposed from emergence to maturity to mixtures of ozone and carbon dioxide in open-top field chambers. As expected, elevated carbon dioxide stimulated dbiomas of both bean lines by approximately 50%. On the other hand, elevate ozone suppressed biomass of the ozone-sensitive line by more than 50%, but it did not significantly suppress biomass of the tolerant line. Unlike most crops tested so far, elevated carbon dioxide afforded little protection of the sensitive line from ozone. This extreme sensitivity to ozone may have overwhelmed what protection elevated carbon dioxide might have provided to less ozone sensitive plants. The results show that it will be difficult to generalize the effects of ozone-carbon dioxide mixtures across a range of crops or even across cultivars of a crop species. Accurate prediction of the effects of ozone-carbon dioxide mixtures on agricultural production will require knowledge of effects on individual crops that vary in ozone sensitivity.
Technical Abstract: Elevated carbon dioxide concentrations expected in the 21st century can stimulate plant growth and yield, whereas tropospheric ozone suppresses plant growth and yield in many areas of the world. Recent experiments show that elevated carbon dioxide often protects plants from ozone stress, but this has not been tested for many important crop species including snap bean (Phaseolus vulgaris L.). Our objective was to measure effects of elevated carbon dioxide on snap bean growth and pod weight and determine if elevated carbon dioxide protects snap bean from effects of ozone. An ozone- tolerant cultivar (Tenderette) and an ozone-sensitive selection (S156) were exposed from emergence to maturity to mixtures of carbon dioxide and ozone in open-top field chambers. The two carbon dioxide treatments were ambient and ambient with carbon dioxide added for 24h d-1 resulting in seasonal 12h d-1 (0800-2000 hour EST) mean concentrations of 366 and 697 uLL-1. The two ozone treatments were charcoal-filtered air and nonfiltered air with ozone added for 12h d-1 to acheive seasonal 12h d-1 (0800-2000 hour EST) mean concentrations of 21 and 65 nLL-1, respectively. Elevated carbondioxide significantly stimulated growth and pod weight of Tenderette and S156, whereas elevated ozone signicantly suppressed growth and pod weight of S156 but not of Tenderette. The suppressive effect of elevated ozone on pod dry weight of S156 was approximately 75% at ambient carbon dioxide and approximately 60% at elevated carbon dioxide (harvests combined). This amount of protection from ozone stress afforded by elevated carbon dioxide was much less than reported for other crop species. Species difference in stomatal response to elevated carbon dioxide is suggested as one reason for different levels of carbon dioxide protection from ozone stress.