Responses of CO 2 Assimilation, Transpiration and Water Use Efficiency to Long-Term Elevated CO 2 in Perennial C 3 Xeric Loess Steppe Species

Abstract

Summary CO 2 assimilation (A), transpiration (E), water use efficiency (WUE), leaf-nitrogen and carbohydrate responses to 11 months elevated (700 μmol mol -1 ) CO 2 exposure in four perennial C 3 species ( Festuca rupicola, Dactylis glomerata, Filipendula vulgaris, Salvia nemorosa ) from a xeric temperate loess steppe are reported. The responses in the species varied greatly owing to their differing acclimation. The acclimation of photosynthesis was somewhat downward in F. rupicola , fully downward in D. glomerata , and upward in S. nemorosa and F. vulgaris . The reduction in the initial slope of the A/q response curve in F. rupicola and D. glomerata suggested a decrease in Rubisco capacity. Net CO 2 assimilation at 700 μmol mol -1 CO 2 c a in the high CO 2 F. rupicola was higher than in those grown at present (350 μmol mol -1 ) CO 2 ; there was no difference in D. glomerata . The initial slope of the A/c i curve indicated an increased Rubisco capacity in high CO 2 F. vulgaris and S. nemorosa . Their net CO 2 assimilation was higher in the plants grown in the high CO 2 treatment at c i 's ovet 200 μmol mol -1 than that in the plants grown at present CO 2 . The A/c i response curves, which were saturated in all species grown at present CO 2 , did not reach saturation in the plants grown at elevated CO 2 , reflecting that the Pi limitation of CO 2 assimilation was alleviated in the plants grown at high CO 2 . Transpiration decreased with an increase in q in both the present and elevated CO 2 F. rupicola and D. glomerata . In F. vulgaris , an increase in q caused a reduction in transpiration in the plants grown at high CO 2 only. Transpiration rate in both the present and elevated CO 2 S. nemorosa was not affected by any change in c i . It is suggested then that long-term exposure to high CO 2 causes a similar acclimation of stomatal regulation and transpiration to that of photosynthesis. High CO 2 caused a significant decrease in protein-nitrogen content only in D. glomerata . Starch increased in F. rupicola and D. glomerata and soluble sugar content was higher in all species grown at high CO 2 than at ambient. Instantaneous WUE significantly increased in all species grown at elevated CO 2 .