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Title: ACCLIMATION RESPONSE OF SPRING WHEAT IN A FREE-AIR CO2 ENRICHMENT (FACE) ATMOSPHERE WITH VARIABLE SOIL NITROGEN REGIMES. NET ASSIMILATION AND STOMATAL CONDUCTANCE OF LEAVES

Author
item Wall, Gerard - Gary
item Adam, Neal
item BROOKS, T - UNIV OF AZ
item Kimball, Bruce
item Pinter Jr, Paul
item La Morte, Robert
item Adamsen, Floyd
item Hunsaker, Douglas - Doug
item WECHSUNG, G - HUMBOLDT UNIV GERMANY
item WECHSUNG, F - POTSDAM-INST GERMANY

Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2000
Publication Date: 11/15/2000
Citation: Wall, G.W., Adam, N.R., Brooks, T.J., Kimball, B.A., Pinter Jr, P.J., La Morte, R.L., Adamsen, F.J., Hunsaker, D.J., Wechsung, G., Wechsung, F. 2000. Acclimation response of spring wheat in a free-air co2 enrichment (face) atmosphere with variable soil nitrogen regimes. net assimilation and stomatal conductance of leaves. Photosynthesis Research. 66:79-95.

Interpretive Summary: The CO2 concentration of the atmosphere is rising. An increase in atmospheric CO2 is known to increase primary production in wheat -- the world's foremost grain source. In more marginal areas of wheat producing regions, however, nutrient deficiencies can limit the beneficial effect of a rise in atmospheric CO2. Our results were obtained from a CO2 enrichment study conducted in an open field on wheat grown with ample and reduced nitrogen supply. We determined that when nutrients such as nitrogen were limited, a decrease in carbon uptake potential occurred in wheat. Consequently, under limited nitrogen supply the beneficial effect of a rise in atmospheric CO2 concentration on primary production will be somewhat less than that observed for wheat grown with ample nitrogen supply. Nevertheless, we believe that an increase in nitrogen use efficiency will enable nitrogen deficient wheat plants to take advantage of the increase in atmospheric CO2. The net result will be an increase in primary production, even in more marginal areas of wheat producing regions where nutrients are lacking. More efficient use of nitrogen by wheat plants in a future high CO2-world will be beneficial to both producers and consumers

Technical Abstract: Since atmospheric CO2 concentrations (Ca) continue to rise, we need to determine if any acclimation (down-regulation) will occur in the photosynthetic apparatus of uppermost expanded sunlit wheat (Triticum aestivum) leaves. Yecora Rojo was grown in an open field exposed to the Ca of ambient (370 æmol mol-1) air (Control) and air enriched to ~200 æmol mol-1 above ambient using a Free-Air CO2 Enrichment (FACE) apparatus (main plot). A high (35 g m-2) and low (7 and 1.5 g m-2 for 1996 and 1997, respectively) level of N was applied to each half of the main CO2 treatments (split-plot). Across seasons and growth stage FACE reduced stomatal conductance (gs) by 30, 39 and 28% compared with Control at mid-morning (MM: 2 hr prior to solar noon), midday (MD: solar noon), and mid-afternoon (MA: 2.5 hr after solar noon). Low-N reduced gs by 16,31, and 32% compared with high-N at MM, MD, and MA, respectively. Despite reductions in gs, daily accumulation of carbon (A ) was 27% greater in FACE compared with Control. Overall high-N increased A by 18% compared with low-N. Since a 7% reduction in the stimulatory effect of elevated CO2 on A occurred under low- compared with high-N, we believe that this reduction constitutes an acclimation. Hence, as Ca continues to rise and N-stress is severe enough, a reduction in carboxylation capacity will occur in the uppermost expanded sunlit leaf of wheat.