Ghashghaie et al. (2003)
Carbon isotope discrimination during photosynthetic CO2 assimilation
has been extensively studied and rigorous models have been developed,
while the fractionations during photorespiratory and dark respiratory
processes have been less well investigated. Whilst models of
discrimination have included specific factors for fractionation during
respiration (e) and photorespiration (f), these effects have been
considered to be very small, i.e. not significantly modifying the net
discrimination expressed in organic material. On this paper we consider
the fractionation effects associated with specific reactions, set
against the overall discrimination which occurs during source-product
transformations. We review the studies which have recently shown that
discrimination occurs during respiration at night in intact C3 leaves,
leading to the production of CO2 enriched in 13C (i.e. e = -6 ‰), and
modifying the signature of the remaining plant material. Under
photorespiratory conditions (i.e. increased oxygen concentration and
high temperature), the photorespiratory fractionation factor may be
high (with f around +10 ‰), and significantly alters the observed net
photosynthetic discrimination measured during gas exchange.
Fractionation factors for both respiration and photorespiration have
been shown to be variable among species and with environmental
conditions, and we suggest that the term “apparent fractionation” be
used to describe the net effect for each process. In this paper we
review the fractionations during photorespiration and dark respiration
and the metabolic origin of the CO2 released during these processes,
and we discuss the ecological implications of such fractionations.
Key words: Carbon isotope, C3 plants, discrimination, fractionation, isotope effect, photorespiration, respiration
Key words: Carbon isotope, C3 plants, discrimination, fractionation, isotope effect, photorespiration, respiration
