Leaf Stable Carbon Isotope Composition Records Increased Water-Use Efficiency of C 3 Plants in Response to Atmospheric CO 2 Enrichment

A total of 17 temperate C 3 grass and herb species were grown for 5 weeks at three mole fraction treatments of atmospheric CO 2 (350, 525 and 700 μmol mol -1 ). Leaf stable carbon isotope compositions (δ 13 C) were determined to record long-term exchange responses together with instantaneous gas exchange measurements. The isotopic composition of the atmospheric CO 2 (δ 13 C a ) integrated over the course of the CO 2 treatments was recorded biologically using the C 4 species Zea mays. We found that increases in the mole fraction of atmospheric CO 2 above current levels resulted in a sustained increase in instantaneous (photosynthesis, A/conductance, g s ) leaf water-use efficiency (IWUE), as calculated from carbon isotope-derived p i /p a ratios. Grass species showed a marked decline in the magnitude of WUE increase as the CO 2 mole fraction was increased from 525 to 700 μmol mol -1 , a response which was absent in herb species. Isotopic derivation of the ratio of intercellular CO 2 mole fraction (p i ) to that in the surrounding atmosphere (p a ), considered as a set point of leaf metabolism, showed no significant (P = 0.06) changes in response to increases in the mole fraction of CO 2 , for herb and grass species. Measurements of p i /p a determined from measurements of leaf gas exchange differed significantly (P<0.01) from those derived from stable isotope ratios. These differences are attributed to contrasting stomatal behaviour between herb and grass species. Leaf intercellular CO 2 mole fraction and previously reported above-ground biomass responses to CO 2 increases for the same species were positively correlated (P<0.05). This suggests that as atmospheric CO 2 levels continue to rise species showing sustained higher rates of leaf photosynthesis, may be translated into increased productivity depending on soil water and nutrient status.

[1]  Graham D. Farquhar,et al.  On the Relationship Between Carbon Isotope Discrimination and the Intercellular Carbon Dioxide Concentration in Leaves , 1982 .

[2]  D. R. Hoagland,et al.  Lectures on the Inorganic Nutrition of Plants. , 1945 .

[3]  G. Farquhar,et al.  Isotopic Composition of Plant Carbon Correlates With Water-Use Efficiency of Wheat Genotypes , 1984 .

[4]  F. Woodward,et al.  Field Measurements of Photosynthesis, Stomatal Conductance, Leaf Nitrogen and δ 13 C Along Altitudinal Gradients in Scotland , 1989 .

[5]  A. Knapp.  Gas Exchange Dynamics in C^3 and C^4 Grasses: Consequence of Differences in Stomatal Conductance , 1993 .

[6]  R. Hunt,et al.  Response to CO 2 Enrichment in 27 Herbaceous Species , 1991 .

[7]  G. Farquhar,et al.  Characterisation of Non-Uniform Photosynthesis Induced by Abscisic Acid in Leaves Having Different Mesophyll Anatomies , 1988 .

[8]  G. Farquhar,et al.  Growth and carbon economy of wheat seedlings as affected by soil resistance to penetration and ambient partial pressure of CO2 , 1990 .

[9]  W. Arp.  Effects of source‐sink relations on photosynthetic acclimation to elevated CO2 , 1991 .

[10]  G. Farquhar,et al.  On the Nature of Carbon Isotope Discrimination in C4 Species , 1983 .

[11]  Roderick Hunt,et al.  Further responses to CO2 enrichment in British herbaceous species. , 1993 .

[12]  G. Farquhar,et al.  Correlation between the Carbon Isotope Discrimination in Leaf Starch and Sugars of C(3) Plants and the Ratio of Intercellular and Atmospheric Partial Pressures of Carbon Dioxide. , 1988, Plant physiology.

[13]  H. Policy,et al.  Increase in C3 plant water-use efficiency and biomass over Glacial to present C02 concentrations , 1993, Nature.

[14]  John R. Evans,et al.  Determination of the Average Partial Pressure of CO2 in Chloroplasts From Leaves of Several C3 Plants , 1991 .

[15]  I. R. Cowan,et al.  Stomatal conductance correlates with photosynthetic capacity , 1979, Nature.

[16]  G. Farquhar,et al.  Low conductances for CO2 diffusion from stomata to the sites of carboxylation in leaves of woody species , 1992 .

[17]  J. Ehleringer,et al.  Carbon Isotope Discrimination and Photosynthesis , 1989 .

[18]  James R. Ehleringer,et al.  Carbon and Water Relations in Desert Plants: An Isotopic Perspective , 1993 .

[19]  M. O'Leary.  Biochemical Basis of Carbon Isotope Fractionation , 1993 .

[20]  B. Strain,et al.  Root restriction as a factor in photosynthetic acclimation of cotton seedlings grown in elevated carbon dioxide. , 1991, Plant physiology.