12C/13C fractionations in plant primary metabolism

Natural 13C abundance is now an unavoidable tool to study ecosystem and plant carbon economies. A growing number of studies take advantage of isotopic fractionation between carbon pools or 13C abundance in respiratory CO2 to examine the carbon source of respiration, plant biomass production or organic matter sequestration in soils. 12C/13C isotope effects associated with plant metabolism are thus essential to understand natural isotopic signals. However, isotope effects of enzymes do not influence metabolites separately, but combine to yield a 12C/13C isotopologue redistribution orchestrated by metabolic flux patterns. In this review, we summarise key metabolic isotope effects and integrate them into the corpus of plant primary carbon metabolism.