Carbon isotope discrimination in leaf juice of Acacia mangium and its relationship to water-use efficiency

Abstract

Using the PMS pressure chamber and isotope mass spectrometer (MAT-252), the leaf juice of Acacia mangium was obtained, and the carbon isotope discrimination (D) representing the most recently fixed carbon in the juice was determined. At the same time, the water-use efficiency of A. mangium was estimated. The results indicated that the carbon isotope ratio in the air of forest canopy (d_a), 10 m high above ground averaged -7.57±1.41‰ in cloudy days, and -8.54±0.67‰ in sunny days, respectively. The diurnal change of the carbon isotope ratio in the photosynthetic products of the leaf juice (d_p) was of saddle type in cloudy days, but dropped down from morning to later afternoon in sunny days. A strong negative correlation between d_p and leaf-to-air vapor pressure deficit (D) was observed in sunny days, but a slight change in d_p was found in cloudy days. The d_p also decreased with decreasing leaf water potential (Ψ), reflecting that water stress could cause the decrease of d_p. The carbon isotope discrimination of the leaf juice was positively correlated with the ratio between intercellular (P_i) and atmospheric (P_a) partial pressure of CO₂. For A. mangium, the isotope effect on diffusion of atmospheric CO₂ via stomata was denoted by a = 4.6‰, and that in net C₃ diffusion with respect to P_i was indicated by b = 28.2‰. The results were in reasonable accord with the theoretically diffusive and biochemical fractionation of carbon isotope. It was defined that carbon isotope discrimination of photosynthetic products in A. mangium leaf juice was in proportion to that from photosynthetic products in dry material. The water-use efficiency estimated by the carbon isotope discrimination in leaf juice, fit well with that measured by gas exchange system (R² = 0.86, p< 0.0001). The application of leaf juice in measuring the stable carbon isotope discrimination would reduce the effects of fluctuating environmental factors during the synthesis of dry matter, and improve the eco-physiological studies on carbon and water balance when scaling from the plant to canopy in the fields.

Keywords

carbon isotope discrimination / water-use efficiency / photosynthetic products in leaf juice

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Acknowledgements

This study was supported by the National Natural Science Foundation of China (Grant No. 30428022, 30770328, 30871998) and Provincial Nature Science Foundation of Guangdong (No. 07006917).

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg