Atmospheric CO
2 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 (CO
2) mol
−1; E:
Enriched with free-air CO
2 enrichment (FACE) at ∼550 μmol (CO
2) 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 (DW
S; crown, shoots) by 14% (
P = 0.02), whereas deficit irrigation reduced DW
S 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.
相似文献