Characteristics of CO2 exchange between peach stems and the atmosphere
Giorgio A. Alessio A , Fabrizio Pietrini A , Federico Brilli A and Francesco Loreto A BA CNR — Istituto di Biologia Agroambientale e Forestale Via Salaria Km. 29 300–00016 Monterotondo Scalo (Roma), Italy.
B Corresponding author. Email: francesco.loreto@ibaf.cnr.it
Functional Plant Biology 32(9) 787-795 https://doi.org/10.1071/FP05070
Submitted: 10 March 2005 Accepted: 18 May 2005 Published: 26 August 2005
Abstract
Gas exchange by stems is dominated by respiratory CO2 emission, but photosynthetic CO2 uptake might also occur in stem bark. We show that light-dependent CO2 uptake was present and often exceeded CO2 release by respiration in illuminated current-year peach (Prunus persica L.) stems. Respiration of peach stems, as detected by 12CO2 release into air in which the natural concentration of 12CO2 was replaced with 13CO2, was lower in the light than in the dark, but this accounted for only a fraction of the observed total CO2 uptake by illuminated stems. Stem photosynthesis was saturated at low light and was negatively affected by elevated assay temperatures (30°C), especially when combined with light intensities above saturation. An inefficient mechanism of heat dissipation by transpiration in stomata-free stems might help explain this effect. Photosynthesis was rapidly stimulated and the electron transport rate was reduced when photorespiration was suppressed by exposure to low (2 kPa) oxygen. The time-course of these changes was closely associated with a transient burst of CO2 uptake concurrent with a reduced inhibition of fluorescence yield. Photosynthesis was also stimulated by exposure to elevated (twice ambient) CO2 concentration. These combined measurements of gas exchange and fluorescence suggested that (a) photorespiration may also be active in the bark of peach stems, (b) O2 and CO2 concentrations in the bark of peach stems may be similar to ambient concentrations, (c) a large amount of electron transport unrelated to photosynthesis and photorespiration may also be present in peach stems, and (d) stem photosynthesis may be enhanced under future atmospheric conditions.
Keywords: chlorophyll fluorescence, global change factors, mitochondrial respiration, photorespiration, Prunus persica L., stem photosynthesis.
Acknowledgments
We thank Professor Hardy Pfanz and Christiane Wittmann for the discussions that made us aware of the importance of stem photosynthesis. Plants were provided by Donato Giannino and Chiara Nicolodi. Federico Brilli was supported by the European Science Foundation scientific program ‘Volatile Organic Compounds in the Biosphere–Atmosphere System’ (VOCBAS).
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