Institution: | a U.S. Arid-Land Agricultural Research Center, USDA-ARS, 21881 North Cardon Lane, Maricopa, AZ 85238, USA b LI-COR BioScience Inc., P.O. Box 4425, Lincoln, NE 68504, USA c Potsdam-Institute for Climate Impact Research, P.O. Box 601203, D-14412 Potsdam, Germany |
Abstract: | Atmospheric CO2 concentration (Ca) is rising, predicted to cause global warming, and alter precipitation patterns. During 1994, spring barley (Hordeum vulgare L. cv. Alexis) was grown in a strip-split-plot experimental design to determine the effects that the main plot Ca treatments A: Ambient at 370 μmol (CO2) mol−1; E: Enriched with free-air CO2 enrichment (FACE) at ∼550 μmol (CO2) mol−1] had on several gas exchange properties of fully expanded sunlit primary leaves. The interacting strip-split-plot irrigation treatments were Dry or Wet 50% (D) or 100% (W) replacement of potential evapotranspiration] at ample nitrogen (261 kg N ha−1) and phosphorous (29 kg P ha−1) fertility. Elevated Ca facilitated drought avoidance by reducing stomatal conductance (gs) by 34% that conserved water and enabled stomata to remain open for a longer period into a drought. This resulted in a 28% reduction in drought-induced midafternoon depression in net assimilation rate (A). Elevated Ca increased A by 37% under Dry and 23% under Wet. Any reduction in A under Wet conditions occurred because of nonstomatal limitations, whereas under Dry it occurred because of stomatal limitations. Elevated Ca increased the diurnal integral of A (A′) that resulted in an increase in the seasonal-long integral of A′ (A″) for barley leaves by 12% (P = 0.14) under both Dry and Wet - 650, 730, 905 and 1020 ± 65 g (C) m−2 y−1 for AD, ED, AW and EW treatments, respectively. Elevated Ca increased season-long average dry weight (DWS; crown, shoots) by 14% (P = 0.02), whereas deficit irrigation reduced DWS by 7% (P = 0.06), although these values may have been affected by a short but severe pea aphid Acyrthosiphon pisum (Harris)] infestation. Hence, an elevated-Ca-based improvement in gas exchange properties enhanced growth of a barley crop. |