Respiratory Effects on the Carbon IsotopeDiscrimination Near the Compensation Point
Date
2017
Authors
Barbour, Margaret M
Ryazanova, Svetlana
Tcherkez, Guillaume
Journal Title
Journal ISSN
Volume Title
Publisher
Springer International Publishing AG
Abstract
The carbon isotope discrimination associated with net photosynthesis (Δobs) when photosynthetic rates are low, such as approaching the light and CO2 compensation points, has rarely been measured but may contain useful information on day respiration (Rd). In fact, at low assimilation rates, the relative importance of respiratory CO2 release is larger and its isotopic signal can be captured. In this chapter, we describe the measurement of Δobs in cocklebur, spinach and magnolia leaves at very low irradiance and CO2 concentration. The carbon isotope fractionation associated with day respiration appears to be similar when approaching the light and CO2 compensation points, and not strongly affected by oxygen concentration. Under the experimental conditions imposed, the apparent fractionation associated with day respiration was found to be −100‰ for cocklebur and spinach, and −62‰ for magnolia. These strongly negative values were due to the use of 13C-depleted CO2 during gas exchange measurements and the use of respiratory carbon fixed prior to gas exchange measurements. Theoretical considerations allowed estimation of the proportion of newly-fixed carbon as a respiratory substrate, which was found to be zero for all species when a single respiratory source is assumed. When two respiratory sources are assumed (with a respiratory pool in photosynthesizing cells and a photosynthetically disconnected pool in heterotrophic, non-photosynthesizing cells), the heterotrophic component dominated day respiration in cocklebur and magnolia leaves, with newly-fixed carbon contributing little to total efflux in magnolia, but representing about one half in cocklebur. In contrast, respiration from photosynthesizing cells dominated Rd in spinach leaves, but newly-fixed carbon formed just 11% of the respiratory substrate. Therefore, day respiration appears to be mostly fed by “old” carbon sources, and this can lead to a considerable isotopic difference between net fixed CO2 and CO2 liberated by day respiration at the same moment.
Description
Keywords
Citation
Collections
Source
Type
Book chapter
Book Title
Plant Respiration: Metabolic Fluxes and Carbon Balance
Entity type
Access Statement
License Rights
Restricted until
2037-12-31
Downloads
File
Description