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Title: CARBON ISOTOPE DISCRIMINATION IN A C4 GRASS (SORGHUM BICOLOR) EXPOSED TO FREE-AIR CO2 ENRICHMENT (FACE) AND DROUGHT

Author
item WILLIAMS, D - UNIV OF ARIZONA
item GEMPKO, V - UNIV OF ARIZONA
item FRAVOLINI, A - UNIV OF ARIZONA
item LEAVITT, S - UNIV OF ARIZONA
item Wall, Gerard - Gary
item Kimball, Bruce
item Pinter Jr, Paul

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2001
Publication Date: 9/15/2001
Citation: Williams, D.G., Gempko, V., Fravolini, A., Leavitt, S.W., Wall, G.W., Kimball, B.A., Pinter Jr, P.J. 2001. Carbon isotope discrimination in a c4 grass (sorghum bicolor) exposed to free-air co2 enrichment (face) and drought. New Phytologist. 150(2):285-293.

Interpretive Summary: The carbon dioxide concentration of the atmosphere is rising. A rise in atmospheric carbon dioxide can affect global climate, including future precipitation patterns and soil-water supply. Although an increase in atmospheric carbon dioxide is known to increase primary production in some grain crops, little is known about its effects on sorghum production. Our results were obtained from a carbon dioxide enrichment study conducted in an open field on sorghum grown with ample and reduced water supply. We determined that elevated carbon dioxide reduced the harmful effects of drought stress. This enabled sorghum plants grown in elevated atmospheric carbon dioxide to maintain carbon gain for a longer period into a drought. An increase in carbon gain will increase net primary productivity of sorghum. This will be beneficial to both producers and consumers, particularly during a drought year.

Technical Abstract: The physiological response of grain sorghum [Sorghum bicolor (L.) Moench] to future high levels of atmospheric CO2 was determined in a Free-air CO2 Enrichment (FACE) experiment consisting of two atmospheric CO2 levels [ambient (370 æmol/mol), ambient +200 æmol/mol] in combination with two irrigation regimes (Dry, post- plant and mid-season irrigations; Wet, 100% replacement of evapotranspiration). Irrigation treatments strongly affected midday leaf water potential, the ratio of internal (pi) to atmospheric (pa) CO2 concentration (pi/pa), carbon isotope discrimination, and bundle sheath leakiness. Differences in carbon isotope discrimination between Wet and Dry treatments resulted from changes in leakiness and to stomatal influence on pi/pa. During peak drought stress, just prior to the second irrigation of the Dry-treatment plots, carbon isotope discrimination was positively correlated with leaf water potential and leakiness, and negatively correlated with pi/pa. FACE had very little effect on leaf water potential, carbon isotope discrimination and leakiness. However, leakiness and carbon isotope discrimination in Dry plots was slightly higher in Control than FACE. FACE lessened the impact of drought on leakiness and carbon isotope discrimination by ameliorating leaf and soil water status. Improved water status because of elevated CO2 enabled sorghum leaves to maintain higher carbon gain for a longer period into a drought. Hence, elevated CO2 increase net primary production of sorghum, but only under drought conditions.