Enhanced water use efficiency in dry loess grassland species grown at elevated air CO2 concentration

Net CO2 assimilation rate (P-N), Stomatal conductance (g(s)), transpiration rate (E), and water use efficiency (WUE) in four perennial C-3 species (gr asses: Dactylis glomerata, Festuca rupicola, dicots: Filipendula vulgaris, Salvia nemorosa) grown for 231 d in open-top chambers at ambient (CA, 350 m u mol mol(-1)) or elevated (CE, 700 mu mol mol(-1)) CO2 concentrations were compared. When measured at CE, PN was significantly higher in CE plants of all four species than in the CA ones. The increase in P-N was less promine nt in the two grasses than in the two dicots. The E was significantly highe r in the CE-grass F. rupicola and CE-dicot F. vulgaris than in the CA plant s. There was no change in E owing to CE in the other grass and dicot. The g (s) in F. vulgaris and F. rupicola increased, while there was a decrease in D. glomerata and no change in S. nemorosa. WUE increased in all species gr own in CE: four- to five-fold in the dicots and less than two-fold in the g rasses. The increase in WUE was primarily due to an increase in P-N and not to a decrease in E.