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Title: LEAF PHOTOSYNTHESIS AND WATER RELATIONS OF GRAIN SORGHUM GROWN IN FREE-AIR CO2 ENRICHMENT (FACE) AND WATER STRESS.

Author
item Wall, Gerard - Gary
item BROOKS, TALBOT - UNIV OF ARIZONA
item Adam, Neal
item COUSINS, A - ARIZONA STATE UNIV
item Kimball, Bruce
item Pinter Jr, Paul
item LAMORTE, R - USDA-ARS, USWCL PHOENIX
item TRIGGS, J - USDA-ARS, USWCL
item OTTMAN, M - UNIV OF ARIZONA
item LEAVITT, S - UNIV OF ARIZONA

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/4/2001
Publication Date: 9/15/2001
Citation: Wall, G.W., Brooks, T.J., Adam, N.R., Cousins, A.B., Kimball, B.A., Pinter Jr, P.J., Lamorte, R.L., Triggs, J., Ottman, M.J., Leavitt, S.W. 2001. Leaf photosynthesis and water relations of grain sorghum grown in free-air co2 enrichment (face) and water stress.. New Phytologist. 152:231-248.

Interpretive Summary: The carbon dioxide (CO2) concentration of the atmosphere is rising. A rise in atmospheric CO2 can affect global climate including future precipitation patterns and soil-water supply. Although an increase in atmospheric CO2 is known to increase primary production in some grain crops, very little is known about its effects on sorghum production. Our results were obtained from a CO2 enrichment study conducted in an open field on sorghum grown with ample and reduced water supply. We determined that when water was limited, the stimulatory effect of a rise in atmospheric CO2 concentration on primary production increased. Consequently, on a relative basis, the beneficial effect of a rise in atmospheric CO2 concentration on primary production will be somewhat greater for water-stressed than well-watered sorghum. More efficient use of water by sorghum plants in a future high CO2-world 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 (Ca) was determined in a Free-air CO2 Enrichment (FACE) experiment consisting of two Ca levels [ambient (370 umol/mol), ambient +200 umol/mol] in combination with two irrigation regimes (Dry, post-plant, and mid-season irrigations; Wet, 100% replacement tof evapotranspiration). Compared with Control, FACE reduced stomatal conductance (gs) by 32% and 37%, but increased net assimilation rate (A) by 23% and 9% in Dry and Wet, respectively. Regardless of Ca level, the intrinsic water use efficiency (A/gs) was increased by 57%. Reductions in gs reduced transpiration rate by 13% and 18%, which increased leaf temperature by 0.96 oC and 1.45 oC for Dry and Wet, respectively. Compared with Control, FACE increased the relative water content by 1 and 2%, whereas total leaf water potential was 9% and 3% less negative for Dry yand Wet, respectively. Soil volumetric water content was not affected by FACE under Dry, but it was increased by 5% under Wet. Compared with Control, FACE had only a nominal effect on evapotranspiration (ET) per day, but FACE caused a modest decrease in season-long cumulative ET under Wet. Compared with Control, in Dry, FACE increased the average LAI by 13%, final shoot biomass by 15%, and marketable yield by 20%. No growth response occurred under Wet. Hence, devoid of any concomitant rise in global temperatures, an increase in Ca will improve water relations and net primary production of a warm-season C4 grass, sorghum, particularly during a drought year.